MedWorm.com provides a medical RSS filtering service. Over 6000 RSS medical sources are combined and output via different filters. This feed contains the latest items from the 'Molecular Microbiology' source. Fri, 19 Mar 2010 17:36:41 +0100 http://www.medworm.com/index.php?rid=3353990&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07103.x This study is the first to assess the involvement of individual residues and domains of OspC in its in vivo function. The data support the hypothesis that OspC interacts with a mammalian derived ligand that is critical for survival during early infection. These results shed new light on the structure[ndash]functions relationships of OspC and challenge existing hypotheses regarding OspC function in mammals. (Source: Molecular Microbiology) Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3353990 Thu, 11 Mar 2010 00:00:00 +0100 3353990 http://www.medworm.com/index.php?rid=3353992&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07095.x Specificity of protein[ndash]protein interactions plays a vital role in signal transduction. The chemosensory pathway of Rhodobacter sphaeroides comprises multiple homologues of chemotaxis proteins characterized in organisms such as Escherichia coli. Three CheA homologues are essential for chemotaxis in R. sphaeroides under laboratory conditions. These CheAs are differentially localized to two chemosensory clusters, one at the cell pole and one in the cytoplasm. The polar CheA, CheA2, has the same domain structure as E. coli CheA and can phosphorylate all R. sphaeroides chemotaxis response regulators. CheA3 and CheA4 independently localize to the cytoplasmic cluster; each protein has a subset of the CheA domains, with CheA3 phosphorylating CheA4 together making a functional CheA protein. I... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3353992 Wed, 10 Mar 2010 00:00:00 +0100 3353992 http://www.medworm.com/index.php?rid=3349918&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07097.x FlhA is the largest integral membrane component of the flagellar type III protein export apparatus of Salmonella and is composed of an N-terminal transmembrane domain (FlhATM) and a C-terminal cytoplasmic domain (FlhAC). FlhAC is thought to form a platform of the export gate for the soluble components to bind to for efficient delivery of export substrates to the gate. Here, we report a structure of FlhAC at 2.8 Å resolution. FlhAC consists of four subdomains (ACD1, ACD2, ACD3 and ACD4) and a linker connecting FlhAC to FlhATM. The sites of temperature-sensitive (ts) mutations that impair protein export are distributed to all four domains, with half of them at subdomain interfaces. Analyses of the ts mutations and four suppressor mutations to the G368C ts mutation suggested that FlhAC chang... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3349918 Wed, 10 Mar 2010 00:00:00 +0100 3349918 http://www.medworm.com/index.php?rid=3326580&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07093.x Rho GTPases have multiple, yet poorly defined functions during cytokinesis. By screening a Neurospora crassa knock-out collection for Rho guanine nucleotide exchange factor (GEF) mutants that phenocopy rho-4 defects (i.e. lack of septa, slow growth, abnormal branching and cytoplasmic leakage), we identified two strains defective in homologues of Bud3p and Rgf3 of budding and fission yeast respectively. The function of these proteins as RHO4-specific GEFs was determined by in vitro assays. In vivo microscopy suggested that the two GEFs and their target GTPase act as two independent modules during the selection of the septation site and the actual septation process. Furthermore, we determined that the N. crassa homologue of the anillinrelated protein BUD4 is required for septum initiation an... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3326580 Wed, 03 Mar 2010 00:00:00 +0100 3326580 http://www.medworm.com/index.php?rid=3353993&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07094.x To transit between hosts, intracellular Legionella pneumophila transform into a motile, infectious, transmissive state. Here we exploit the pathogen's life cycle to examine how guanosine tetraphosphate (ppGpp) and DksA cooperate to govern bacterial differentiation. Transcriptional profiling revealed that during transmission alarmone accumulation increases the mRNA for flagellar and Type IV-secretion components, secreted host effectors and regulators, and decreases transcripts for translation, membrane modification and ATP synthesis machinery. DksA is critical for differentiation, since mutants are defective for stationary phase survival, flagellar gene activation, lysosome avoidance and macrophage cytotoxicity. The roles of ppGpp and DksA depend on the context. For macrophage transmission,... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3353993 Sun, 28 Feb 2010 00:00:00 +0100 3353993 http://www.medworm.com/index.php?rid=3353991&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07100.x AtzR is a LysR-type regulator responsible for activation of the cyanuric acid utilization operon atzDEF. AtzR binds the PatzDEF promoter region at a strong recognition element, designated the repressor binding site, and a weaker binding determinant, the activator binding site (ABS). AtzR activates transcription in response to two dissimilar signals, nitrogen limitation and cyanuric acid. In the present work we analyse the structure and function of the cis-acting elements involved in AtzR activation of atzDEF. Hydroxyl radical footprinting assays revealed that the ABS is composed of three functional subsites spaced at one helix-turn intervals. Two modes of interaction with the ABS are detected in vitro: AtzR binds at the ABS-2 and ABS-3 subsites in the absence of inducer, and relocates to i... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3353991 Sun, 28 Feb 2010 00:00:00 +0100 3353991 http://www.medworm.com/index.php?rid=3326581&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07092.x In this study we analysed CARDS toxin gene (annotated mpn372) transcription and identified its promoter. We also compared CARDS toxin mRNA and protein profiles in M. pneumoniae during distinct in vitro growth phases. CARDS toxin mRNA expression was maximal, but at low levels, during early exponential growth and declined sharply during mid-to-late log growth phases, which was in direct contrast to other mycoplasma genes examined. Between 7% and 10% of CARDS toxin was localized to the mycoplasma membrane at mid-exponential growth, which was reinforced by immunogold electron microscopy. No CARDS toxin was released into the medium. Upon M. pneumoniae infection of mammalian cells, increased expression of CARDS toxin mRNA was observed when compared with SP-4 broth-grown cultures. Further, confoc... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3326581 Sun, 28 Feb 2010 00:00:00 +0100 3326581 http://www.medworm.com/index.php?rid=3306354&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07085.x Secretins are a family of large bacterial outer membrane channels that serve as exit ports for folded proteins, filamentous phage and surface structures. Despite the large size of their substrates, secretins do not compromise the barrier function of the outer membrane, implying a gating mechanism. The region in the primary structure that forms the putative gate has not previously been determined for any secretin. To identify residues involved in gating the pIV secretin of filamentous bacteriophage f1, we used random mutagenesis of the gene followed by positive selection for mutants with compromised barrier function ('leaky' mutants). We identified mutations in 34 residues, 30 of which were clustered into two regions located in the centre of the conserved C-terminal secretin family domain: ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3306354 Thu, 25 Feb 2010 00:00:00 +0100 3306354 http://www.medworm.com/index.php?rid=3306359&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07084.x The proteomes expressed at 4°C and 18°C by the psychrophilic Antarctic bacterium Pseudoalteromonas haloplanktis have been compared using two-dimensional differential in-gel electrophoresis, showing that translation, protein folding, membrane integrity and anti-oxidant activities are upregulated at 4°C. This proteomic analysis revealed that the trigger factor is the main upregulated protein at low temperature. The trigger factor is the first molecular chaperone interacting with virtually all newly synthesized polypeptides on the ribosome and also possesses a peptidyl-prolyl cis-trans isomerase activity. This suggests that protein folding at low temperatures is a rate-limiting step for bacterial growth in cold environments. It is proposed that the psychrophilic trigger factor rescues the ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3306359 Wed, 24 Feb 2010 00:00:00 +0100 3306359 http://www.medworm.com/index.php?rid=3306358&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07089.x Attachment to host cells via adhesive surface structures is a prerequisite for the pathogenesis of many bacteria. Uropathogenic Escherichia coli assemble P and type 1 pili for attachment to the host urothelium. Assembly of these pili requires the conserved chaperone/usher pathway, in which a periplasmic chaperone controls the folding of pilus subunits and an outer membrane usher provides a platform for pilus assembly and secretion. The usher has differential affinity for pilus subunits, with highest affinity for the tip-localized adhesin. Here, we identify residues F21 and R652 of the P pilus usher PapC as functioning in the differential affinity of the usher. R652 is important for high-affinity binding to the adhesin whereas F21 is important for limiting affinity for the PapA major rod su... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3306358 Wed, 24 Feb 2010 00:00:00 +0100 3306358 http://www.medworm.com/index.php?rid=3306357&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07052.x Pigments contribute to the pathogenicity of many fungi, mainly by protecting fungal cells from host defence activities. Here, we have dissected the biosynthetic pathway of a tryptophan-derived pigment of the human pathogen Candida glabrata, identified key genes involved in pigment production and have begun to elucidate the possible biological function of the pigment. Using transcriptional analyses and a transposon insertion library, we have identified genes associated with pigment production. Targeted deletion mutants revealed that the pigment is a by-product of the Ehrlich pathway of tryptophan degradation: a mutant lacking a tryptophan-upregulated aromatic aminotransferase (Aro8) displayed significantly reduced pigmentation and a recombinantly expressed version of this protein was suffic... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3306357 Wed, 24 Feb 2010 00:00:00 +0100 3306357 http://www.medworm.com/index.php?rid=3301843&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07090.x While pathways for N-glycosylation in Eukarya and Bacteria have been solved, considerably less is known of this post-translational modification in Archaea. In the halophilic archaeon Haloferax volcanii, proteins encoded by the agl genes are involved in the assembly and attachment of a pentasaccharide to select asparagine residues of the S-layer glycoprotein. AglP, originally identified based on the proximity of its encoding gene to other agl genes whose products were shown to participate in N-glycosylation, was proposed, based on sequence homology, to serve as a methyltransferase. In the present report, gene deletion and mass spectrometry were employed to reveal that AglP is responsible for adding a 14 Da moiety to a hexuronic acid found at position four of the pentasaccharide decorating t... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3301843 Wed, 24 Feb 2010 00:00:00 +0100 3301843 http://www.medworm.com/index.php?rid=3301844&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07077.x The adenylate cyclase toxin-haemolysin of Bordetella (CyaA) targets CD11b+ myeloid phagocytes and translocates across their cytoplasmic membrane an adenylate cyclase (AC) enzyme that catalyses conversion of cytosolic ATP into cAMP. In parallel, CyaA acts as a cytolysin forming cation-selective pores, which permeabilize cell membrane and eventually provoke cell lysis. Using cytolytic activity, potassium efflux and patch-clamp assays, we show that a combination of substitutions within the pore-forming (E570Q) and acylation-bearing domain (K860R) ablates selectively the cell-permeabilizing activity of CyaA. At the same time, however, the capacity of such mutant CyaA to translocate the AC domain across cytoplasmic membrane into cytosol of macrophage cells and to elevate cellular cAMP concentra... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3301844 Tue, 23 Feb 2010 00:00:00 +0100 3301844 http://www.medworm.com/index.php?rid=3297964&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07079.x Regulation of the biosynthesis of the flagellar filament in bacteria containing multiple flagellin genes is not well understood. The major food-borne pathogen Campylobacter jejuni possesses on both poles a flagellum that consists of two different flagellin subunits, FlaA and FlaB. Here we identify the protein Cj1464 as a regulator of C. jejuni flagellin biosynthesis. The protein shares characteristics of the FlgM family of anti-[sigma] factor proteins: it represses transcription of [sigma]28-dependent genes, forms a complex with [sigma] factor FliA, and is secreted through the flagellar filament. However, unlike other FlgM proteins, the interaction of C. jejuni FlgM with FliA is regulated by temperature and the protein does not inhibit FliA activity during the formation of the hook-basal b... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3297964 Tue, 23 Feb 2010 00:00:00 +0100 3297964 http://www.medworm.com/index.php?rid=3287380&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07066.x The serum resistance of the common respiratory pathogen Moraxella catarrhalis is mainly dependent on ubiquitous surface proteins (Usp) A1 and A2 that interact with complement factor 3 (C3) and complement inhibitor C4b binding protein (C4BP) preventing the alternative and classical pathways of the complement system respectively. UspA2 also has the capacity to attract vitronectin that in turn binds C9 and hereby inhibits membrane attack complex (MAC) formation. We found UspA2 as a major vitronectin binding protein and hence the UspA2/vitronectin interaction was studied in detail. The affinity constant (KD) for vitronectin binding to UspA2 was 2.3 × 10[minus]8 M, and the N-terminal region encompassing residues UspA2 30[ndash]170 bound vitronectin with a KD of 7.9 × 10[minus]8 M. Electron mi... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3287380 Fri, 19 Feb 2010 00:00:00 +0100 3287380 http://www.medworm.com/index.php?rid=3287377&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07082.x The ubiquitous glyoxalase system removes methylglyoxal as a harmful by-product of glycolysis. Because malaria parasites have drastically increased glycolytic fluxes, they could be highly susceptible to the inhibition of this detoxification pathway. Here we analysed the intracellular localization, oligomerization and inhibition of the glyoxalases from Plasmodium falciparum. Glyoxalase I (GloI) and one of the two glyoxalases II (cGloII) were located in the cytosol of the blood stages. The second glyoxalase II (tGloII) was detected in the apicoplast pointing to alternative metabolic pathways. Using a variety of methods, cGloII was found to exist in a monomer[ndash]dimer equilibrium that might have been overlooked for homologues from other organisms and that could be of physiological importanc... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3287377 Fri, 19 Feb 2010 00:00:00 +0100 3287377 http://www.medworm.com/index.php?rid=3283229&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07078.x In this report, the Lyme disease spirochete Borrelia burgdorferi was used as a genetic model to investigate the roles of these two fliG homologues. It was found that fliG2 encodes a typical motor switch complex protein that is required for the flagellation and motility of B. burgdorferi. In contrast, the function of fliG1 is quite unique. Disruption of fliG1 did not affect flagellation and the mutant was still motile but failed to translate in highly viscous media. GFP-fusion and motion tracking analyses revealed that FliG1 asymmetrically locates at one end of cells and the loss of fliG1 somehow impacted one bundle of flagella rotation. In addition, animal studies demonstrated that the fliG1[minus] mutant was quickly cleared after inoculation into the murine host, which highlights the impo... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3283229 Thu, 18 Feb 2010 00:00:00 +0100 3283229 http://www.medworm.com/index.php?rid=3283234&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07054.x Major pathogenic clonal complexes (cc) of Neisseria meningitidis differ substantially in their point prevalence among healthy carriers. We show that frequently carried pathogenic cc (e.g. sequence type ST-41/44 cc and ST-32 cc) depend on extracellular DNA (eDNA) to initiate in vitro biofilm formation, whereas biofilm formation of cc with low point prevalence (ST-8 cc and ST-11 cc) was eDNA-independent. For initial biofilm formation, a ST-32 cc type strain, but not a ST-11 type strain, utilized eDNA. The release of eDNA was mediated by lytic transglycosylase and cytoplasmic N-acetylmuramyl-l-alanine amidase genes. In late biofilms, outer membrane phospholipase A-dependent autolysis, which was observed in most cc, but not in ST-8 and ST-11 strains, was required for shear force resistance of ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3283234 Wed, 17 Feb 2010 00:00:00 +0100 3283234 http://www.medworm.com/index.php?rid=3283232&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07071.x A secreted competence-stimulating peptide (CSP), encoded by comC, constitutes, together with the two-component system ComD-ComE, the master switch for competence induction in Streptococcus pneumoniae. Interaction between CSP and its membrane-bound histidine-kinase receptor, ComD, is believed to lead to autophosphorylation of ComD, which then transphosphorylates the ComE response regulator to activate transcription of a limited set of genes, including the comCDE operon. This generates a positive feedback loop, amplifying the signal and co-ordinating competence throughout the population. On the other hand, the promoter(s) and proteins important for basal comCDE expression have not been defined. We now report that CSP-induced and basal comCDE transcription both initiate from the same promoter... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3283232 Wed, 17 Feb 2010 00:00:00 +0100 3283232 http://www.medworm.com/index.php?rid=3283230&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07076.x Enzymatic haem catabolism by haem oxygenases is conserved from bacteria to humans and proceeds through a common mechanism leading to the formation of iron, carbon monoxide and biliverdin. The first members of a novel class of haem oxygenases were recently identified in Staphylococcus aureus (IsdG and IsdI) and were termed the IsdG-family of haem oxygenases. Enzymes of the IsdG-family form tertiary structures distinct from those of the canonical haem oxygenase family, suggesting that IsdG-family members degrade haem via a unique reaction mechanism. Herein we report that the IsdG-family of haem oxygenases degrade haem to the oxo-bilirubin chromophore staphylobilin. We also present the crystal structure of haem-bound IsdI in which haem ruffling and constrained binding of oxygen is consistent ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3283230 Wed, 17 Feb 2010 00:00:00 +0100 3283230 http://www.medworm.com/index.php?rid=3262355&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07070.x We report that IbpA and IbpB, the sHSPs of Escherichia coli, are substrates for the AAA+ Lon protease. This ATP-fueled enzyme degraded purified IbpA substantially more slowly than purified IbpB, and we demonstrate that this disparity is a consequence of differences in maximal Lon degradation rates and not in substrate affinity. Interestingly, however, IbpB stimulated Lon degradation of IbpA both in vitro and in vivo. Furthermore, although the variable N- and C-terminal tails of the Ibps were dispensable for proteolytic recognition, these tails contain critical determinants that control the maximal rate of Lon degradation. Finally, we show that E. coli Lon degrades variants of human [alpha]-crystallin, indicating that Lon recognizes conserved determinants in the folded [alpha]-crystallin do... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3262355 Thu, 11 Feb 2010 00:00:00 +0100 3262355 http://www.medworm.com/index.php?rid=3326582&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07086.x Legionellosis or Legionnaires' disease is an emerging and often-fatal form of pneumonia that is most severe in elderly and immunocompromised people, an ever-increasing risk group for infection. In recent years, the genomics of Legionella spp. has significantly increased our knowledge of the pathogenesis of this disease by providing new insights into the evolution and genetic and physiological basis of Legionella[ndash]host interactions. The seventh international conference on Legionella, Legionella 2009, illustrated many recent conceptual advances in epidemiology, pathogenesis and ecology. Experts in different fields presented new findings on basic mechanisms of pathogen[ndash]host interactions and bacterial evolution, as well as the clinical management and environmental prevalence and per... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3326582 Wed, 10 Feb 2010 00:00:00 +0100 3326582 http://www.medworm.com/index.php?rid=3306363&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07087.x We present a fluorescence recovery after photobleaching-based method for monitoring the progression of septal Z-ring contraction in dividing Escherichia coli cells. In a large number of cells undergoing division, we irreversibly bleached cytosolically expressed Enhanced Green Fluorescent Protein on one side of the septal invagination and followed the fluorescence relaxation on both sides of the septum. Since the relaxation time depends on the cross-sectional area of the septum, it can be used to determine the septal radius r. Assuming that the fraction of the observed cells with r-values in a given interval reflects the duration of that interval in the division process we could derive an approximate time-course for the contraction event, as a population average. By applying the method repe... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3306363 Wed, 10 Feb 2010 00:00:00 +0100 3306363 http://www.medworm.com/index.php?rid=3306362&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07088.x The bacterium Caulobacter crescentus has morphologically and functionally distinct cell poles that undergo sequential changes during the cell cycle. We show that the PopZ oligomeric network forms polar ribosome exclusion zones that change function during cell cycle progression. The parS/ParB chromosomal centromere is tethered to PopZ at one pole prior to the initiation of DNA replication. During polar maturation, the PopZ-centromere tether is broken, and the PopZ zone at that pole then switches function to act as a recruitment factor for the ordered addition of multiple proteins that promote the transformation of the flagellated pole into a stalked pole. Stalked pole assembly, in turn, triggers the initiation of chromosome replication, which signals the formation of a new PopZ zone at the ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3306362 Wed, 10 Feb 2010 00:00:00 +0100 3306362 http://www.medworm.com/index.php?rid=3306361&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07081.x Whereas mammalian cells and most other organisms can synthesize polyamines from basic amino acids, the protozoan parasite Trypanosoma cruzi is incapable of polyamine biosynthesis de novo and therefore obligatorily relies upon putrescine acquisition from the host to meet its nutritional requirements. The cell surface proteins that mediate polyamine transport into T. cruzi, as well as most eukaryotes, however, have by-in-large eluded discovery at the molecular level. Here we report the identification and functional characterization of two polyamine transporters, TcPOT1.1 and TcPOT1.2, encoded by alleles from two T. cruzi haplotypes. Overexpression of the TcPOT1.1 and TcPOT1.2 genes in T. cruzi epimastigotes revealed that TcPOT1.1 and TcPOT1.2 were high-affinity transporters that recognized b... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3306361 Wed, 10 Feb 2010 00:00:00 +0100 3306361 http://www.medworm.com/index.php?rid=3306360&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07083.x Agmatine is the decarboxylation product of arginine and a number of bacteria have devoted enzymatic pathways for its metabolism. Pseudomonas aeruginosa harbours the aguBA operon that metabolizes agmatine to putrescine, which can be subsequently converted into other polyamines or shunted into the TCA cycle for energy production. We discovered an alternate agmatine operon in the P. aeruginosa strain PA14 named agu2ABCA' that contains two genes for agmatine deiminases (agu2A and agu2A'). This operon was found to be present in 25% of clinical P. aeruginosa isolates. Agu2A' contains a twin-arginine translocation signal at its N-terminus and site-directed mutagenesis and cell fractionation experiments confirmed this protein is secreted to the periplasm. Analysis of the agu2ABCA' promoter demonst... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3306360 Wed, 10 Feb 2010 00:00:00 +0100 3306360 http://www.medworm.com/index.php?rid=3287378&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07069.x Sinorhizobium meliloti DctB is a typical transmembrane sensory histidine kinase, which senses C4-dicarboxylic acids (DCA) and regulates the expression of DctA, the DCA transporter. We previously reported the crystal structures of its periplasmic sensory domain (DctBp) in apo and succinate-bound states, and these structures showed dramatic conformational changes at dimeric level. Here we show a ligand-induced dimeric switch in solution and a strong correlation between DctBp's dimerization states and the in vivo activities of DctB. Using site-directed mutagenesis, we identify important determinants for signal perception and transduction. Specifically, we show that the ligand-binding pocket is essential for DCA-induced 'on' activity of DctB. Mutations at different sections of DctBp's dimeriza... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3287378 Wed, 10 Feb 2010 00:00:00 +0100 3287378 http://www.medworm.com/index.php?rid=3262356&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07065.x SpyCEP is a Streptococcus pyogenes protease that cleaves CXCL8/IL-8 and its activity is associated with human invasive disease severity. We investigated the role of SpyCEP in S. pyogenes necrotizing fasciitis and respiratory tract infection in mice using isogenic strains differing only in SpyCEP expression. SpyCEP cleaved human CXCL1, 2, 6 and 8 plus murine CXCL1 and 2 at a structurally conserved site. Mice were infected in thigh muscle with a strain of S. pyogenes that expresses a high level of SpyCEP, or with an isogenic non-SpyCEP expressing strain. SpyCEP expression by S. pyogenes hindered bacterial clearance from muscle, and enhanced bacterial spread, associated with cleavage of murine chemoattractant CXCL1. Mice were then infected with Lactococcus lactis strains that differed only in... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3262356 Wed, 10 Feb 2010 00:00:00 +0100 3262356 http://www.medworm.com/index.php?rid=3254093&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07058.x Carbon dioxide (CO2) and its hydration product bicarbonate (HCO3-) are essential molecules in various physiological processes of all living organisms. The reversible interconversion between CO2 and HCO3- is in equilibrium. This reaction is slow without catalyst, but can be rapidly facilitated by Zn2+-metalloenzymes named carbonic anhydrases (CAs). To gain an insight into the function of multiple clades of fungal CA, we chose to investigate the filamentous fungi Aspergillus fumigatus and A. nidulans. We identified four and two CAs in A. fumigatus and A. nidulans, respectively, named cafA-D and canA-B. The cafA and cafB genes are constitutively, strongly expressed whereas cafC and cafD genes are weakly expressed but CO2-inducible. Heterologous expression of the A. fumigatus cafB, and A. nidu... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3254093 Tue, 09 Feb 2010 00:00:00 +0100 3254093 http://www.medworm.com/index.php?rid=3254095&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07075.x From the perspective of a bacterium, higher eukaryotes are oversexed, unadventurous and reproduce in an inconvenient way. Sex, or recombination following horizontal gene transfer (HGT) events, to be less provocative, is a rare event for a bacterium, but a potentially profound one. Through HGT a bacterium can acquire DNA from distant as well as closely related species and, thereby, instantly obtain genes that encode novel functions or replace its existing genes with better ones. While there is an abundance of retrospective evidence for HGT in bacteria, there has been little consideration of the dynamics of the process. In this issue of Molecular Microbiology Lind et al. explore these dynamics theoretically, and then experimentally by substituting Salmonella Typhimurium ribosomal genes with ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3254095 Mon, 08 Feb 2010 00:00:00 +0100 3254095 http://www.medworm.com/index.php?rid=3254094&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07059.x Mechanisms of hydrogen peroxide generation in Escherichia coli were investigated using a strain lacking scavenging enzymes. Surprisingly, the deletion of many abundant flavoenzymes that are known to autoxidize in vitro did not substantially lessen overall H2O2 formation. However, H2O2 production diminished by 25[ndash]30% when NadB turnover was eliminated. The flavin-dependent desaturating dehydrogenase, NadB uses fumarate as an electron acceptor in anaerobic cells. Experiments showed that aerobic NadB turnover depends upon its oxidation by molecular oxygen, with H2O2 as a product. This reaction appears to be mechanistically adventitious. In contrast, most desaturating dehydrogenases are associated with the respiratory chain and deliver electrons to fumarate anaerobically or oxygen aerobic... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3254094 Mon, 08 Feb 2010 00:00:00 +0100 3254094 http://www.medworm.com/index.php?rid=3243310&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07063.x Fungi are capable of generating diverse cell types through developmental processes that stem from hyphae, acting as pluripotent cells. The formation of mitospores on emergence of hyphae to the air involves the participation of transcription factors, which co-ordinate the genesis of new cell types, eventually leading to spore formation. In this investigation, we show that bZip transcription factor FlbB, which has been attributed to participate in transducing the aerial stimulus signal, activates the expression of c-Myb transcription factor FlbD. Both factors then jointly activate brlA, a C2H2 zinc finger transcription factor, which plays a central role in spore formation. This sequence of regulatory events resembles developmental control mechanisms involving c-Myb and bZip counterparts in m... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3243310 Fri, 05 Feb 2010 00:00:00 +0100 3243310 http://www.medworm.com/index.php?rid=3243314&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07029.x Carbohydrate catabolite repression (CCR) in Streptococcus mutans can be independent of catabolite control protein A (CcpA) and requires specific components of phosphoenolpyruvate-dependent sugar:phosphotransferase system (PTS) permeases. Here, the effects of various ptsH (HPr) and hprK (HPr kinase/phosphatase) mutations on growth and CCR were evaluated. An hprKV265F mutation, which enhanced Ser46 phosphorylation of HPr, inhibited growth on multiple PTS sugars. A ptsHS46A mutation reversed the effects of hprKV265F in most cases. A strain carrying a ptsHS46D mutation, which mimics HPr(Ser-P), presented with more severe growth defects than the hprKV265F mutant. The hprKV265F mutant enhanced CCR of the fruA and levD operons, a phenotype reversible by the ptsHS46A mutation. The effects of the h... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3243314 Thu, 04 Feb 2010 00:00:00 +0100 3243314 http://www.medworm.com/index.php?rid=3243313&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07026.x In this study, we used Illumina-based massively parallel sequencing to gain new insight into the transcriptome (RNA-Seq) of the human malaria parasite, Plasmodium falciparum. Using data collected at seven time points during the intraerythrocytic developmental cycle, we (i) detect novel gene transcripts; (ii) correct hundreds of gene models; (iii) propose alternative splicing events; and (iv) predict 5' and 3' untranslated regions. Approximately 70% of the unique sequencing reads map to previously annotated protein-coding genes. The RNA-Seq results greatly improve existing annotation of the P. falciparum genome with over 10% of gene models modified. Our data confirm 75% of predicted splice sites and identify 202 new splice sites, including 84 previously uncharacterized alternative splicing ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3243313 Thu, 04 Feb 2010 00:00:00 +0100 3243313 http://www.medworm.com/index.php?rid=3243311&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07038.x Candida albicans is a diploid fungal pathogen lacking a defined complete sexual cycle, and thus has been refractory to standard forward genetic analysis. Instead, transcription profiling and reverse genetic strategies based on Saccharomyces cerevisiae have typically been used to link genes to functions. To overcome restrictions inherent in such indirect approaches, we have investigated a forward genetic mutagenesis strategy based on the UAU1 technology. We screened 4700 random insertion mutants for defects in hyphal development and linked two new genes (ARP2 and VPS52) to hyphal growth. Deleting ARP2 abolished hyphal formation, generated round and swollen yeast phase cells, disrupted cortical actin patches and blocked virulence in mice. The mutants also showed a global lack of induction of... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3243311 Thu, 04 Feb 2010 00:00:00 +0100 3243311 http://www.medworm.com/index.php?rid=3239198&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07018.x Phospholipid biosynthetic pathways play crucial roles in the virulence of several pathogens; however, little is known about how phospholipid synthesis affects pathogenesis in fungi such as Candida albicans. A C. albicans phosphatidylserine (PS) synthase mutant, cho1[Delta]/[Delta], lacks PS, has decreased phosphatidylethanolamine (PE), and is avirulent in a mouse model of systemic candidiasis. The cho1[Delta]/[Delta] mutant exhibits defects in cell wall integrity, mitochondrial function, filamentous growth, and is auxotrophic for ethanolamine. PS is a precursor for de novo PE biosynthesis. A psd1[Delta]/[Delta] psd2[Delta]/[Delta] double mutant, which lacks the PS decarboxylase enzymes that convert PS to PE in the de novo pathway, has diminished PE levels like those of the cho1[Delta]/[Del... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3239198 Thu, 04 Feb 2010 00:00:00 +0100 3239198 http://www.medworm.com/index.php?rid=3239195&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07064.x Although much is known about the structure and biosynthesis of microbial cell envelope constituents, the three-dimensional organization, assembly and interactions of the individual components remain poorly understood. How do cell walls remodel during cell growth or incubation with drugs? What is the supramolecular architecture of proteins in bacterial surface layers, in outer membranes and in intracytoplasmic membranes? What is the spatial arrangement of cell surface receptors, clustered or homogeneous? What are the adhesive and mechanical properties of cell surface proteins and how are they related to function? Traditionally, these questions have been difficult [ndash] or impossible [ndash] to address owing to the lack of high-resolution single-cell and single-molecule probing techniques.... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3239195 Thu, 04 Feb 2010 00:00:00 +0100 3239195 http://www.medworm.com/index.php?rid=3239199&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07057.x Mutations in the fmt gene (encoding formyl methionine transferase) that eliminate formylation of initiator tRNA (Met-tRNAi) confer resistance to the novel antibiotic class of peptide deformylase inhibitors (PDFIs) while concomitantly reducing bacterial fitness. Here we show in Salmonella typhimurium that novel mutations in initiation factor 2 (IF2) located outside the initiator tRNA binding domain can partly restore fitness of fmt mutants without loss of antibiotic resistance. Analysis of initiation of protein synthesis in vitro showed that with non-formylated Met-tRNAi IF2 mutants initiated much faster than wild-type IF2, whereas with formylated fMet-tRNAi the initiation rates were similar. Moreover, the increase in initiation rates with Met-tRNAi conferred by IF2 mutations in vitro corre... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3239199 Wed, 03 Feb 2010 00:00:00 +0100 3239199 http://www.medworm.com/index.php?rid=3235483&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07020.x The availability of nutrients is a major determinant for the timing of morphogenesis and antibiotic production in the soil-dwelling bacterium Streptomyces coelicolor. Here we show that N-acetylglucosamine transport, the first step of an important nutrient signalling cascade, is mediated by the NagE2 permease of the phosphotransferase system, and that the activity of this permease is linked to nutritional control of development and antibiotic production. The permease serves as a high-affinity transporter for N-acetylglucosamine (Km of 2.6 µM). The permease complex was reconstituted with individually purified components. This showed that uptake of N-acetylglucosamine requires a phosphoryl group transfer from phosphoenolpyruvate via the phosphotransferases EI, HPr and IIACrr to NagF, which i... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3235483 Wed, 03 Feb 2010 00:00:00 +0100 3235483 http://www.medworm.com/index.php?rid=3231087&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07032.x During chemotactic signalling by Escherichia coli, the small cytoplasmic CheW protein couples the histidine kinase CheA to chemoreceptor control. Although essential for assembly and operation of receptor signalling complexes, CheW in stoichiometric excess disrupts chemotactic behaviour. To explore the mechanism of the CheW excess effect, we measured the physiological consequences of high cellular levels of wild-type CheW and of several CheW variants with reduced or enhanced binding affinities for receptor molecules. We found that high levels of CheW interfered with trimer assembly, prevented CheA activation, blocked cluster formation, disrupted chemotactic ability and elevated receptor methylation levels. The severity of these effects paralleled the receptor-binding affinities of the CheW ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3231087 Tue, 02 Feb 2010 00:00:00 +0100 3231087 http://www.medworm.com/index.php?rid=3306356&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07062.x In this study we explored the effect of HDAC inhibition on the life cycle of the human pathogen Giardia lamblia, a highly reduced parasitic protozoan characterized by minimized cellular processes. We found that the HDAC inhibitor FR235222 increased the level of histone acetylation and induced transcriptional regulation of [sim]2% of genes in proliferating and encysting parasites. In addition, our analyses showed that the levels of histone acetylation decreased during differentiation into cysts, the infective stage of the parasite. Importantly, FR235222 treatment during encystation reversed this histone hypo-acetylation and potently blocked the formation of cysts. These results provide the first direct evidence for epigenetic regulation of gene expression in this simple eukaryote. This sugg... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3306356 Mon, 01 Feb 2010 00:00:00 +0100 3306356 http://www.medworm.com/index.php?rid=3306355&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07080.x Lambdoid phage 21 has the prototype pinholin-SAR endolysin lysis system, which is widely distributed among phages. Its prototype pinholin, S2168, triggers at an allele-specific time to form small, heptameric lesions, or pinholes, in the cytoplasmic membrane, thus initiating lysis. S2168 has two transmembrane domains, TMD1 and TMD2. Only TMD2 is required for the formation of pinholes, whereas TMD1 acts as an inhibitor of TMD2 and must be externalized to the periplasm in the lytic pathway. Previously we provided evidence that S2168 first accumulates as inactive dimers with both transmembrane domains embedded in the bilayer. Here we analyse an extensive collection of S21 mutants to identify residues and domains critical to the function and regulation of the pinholin. Evidence is presented ind... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3306355 Mon, 01 Feb 2010 00:00:00 +0100 3306355 http://www.medworm.com/index.php?rid=3301846&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07061.x The unique mitochondrial DNA of trypanosomes is a catenated network of minicircles and maxicircles called kinetoplast DNA (kDNA). The network is essential for survival, and requires an elaborate topoisomerase-mediated release and reattachment mechanism for minicircle theta structure replication. At least seven DNA polymerases (pols) are involved in kDNA transactions, including three essential proteins related to bacterial DNA pol I (POLIB, POLIC and POLID). How Trypanosoma brucei utilizes multiple DNA pols to complete the topologically complex task of kDNA replication is unknown. To fill this gap in knowledge we investigated the cellular role of POLIB using RNA interference (RNAi). POLIB silencing resulted in growth inhibition and progressive loss of kDNA networks. Additionally, unreplicat... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3301846 Mon, 01 Feb 2010 00:00:00 +0100 3301846 http://www.medworm.com/index.php?rid=3301845&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07072.x Thymine starvation results in a terminal cellular condition known as thymineless death (TLD), which is the basis of action for several common antibiotics and anticancer drugs. We characterized the onset and progression of TLD in Escherichia coli and found that DNA damage is the only salient property that distinguishes cells irreversibly senesced under thymine starvation from cells reversibly arrested by the nucleotide limitation. The damage is manifested as the relative loss of genetic material spreading outward from the replication origin: the extent of TLD correlates with the progression of damage. The reduced lethality in mutants deficient in the RecFOR/JQ repair pathway also correlates with the extent of damage, which explains most of the observed variance in cell killing. We propose t... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3301845 Mon, 01 Feb 2010 00:00:00 +0100 3301845 http://www.medworm.com/index.php?rid=3287379&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07068.x In Escherichia coli, the TolC[ndash]AcrAB complex forms a major antibiotic efflux system with broad substrate specificity. During the complex assembly, the periplasmic helices and bottom turns of TolC are thought to interact with a hairpin helix of AcrA and hairpin loops of AcrB respectively. In the present study we show that a four-residue substitution in TolC's turn 1, which connects outer helices 3 and 4 proximal to TolC's periplasmic aperture, confers antibiotic hypersensitivity, without affecting TolC-mediated phage or colicin infection. However, despite the null-like drug sensitivity phenotype, chemical cross-linking analysis revealed no apparent defects in the ability of the mutant TolC protein to physically interact with AcrA and AcrB. A role for TolC turn 1 residues in the functio... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3287379 Mon, 01 Feb 2010 00:00:00 +0100 3287379 http://www.medworm.com/index.php?rid=3283233&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07067.x Translation elongation factor G (EF-G) in bacteria plays two distinct roles in different phases of the translation system. EF-G catalyses the translocation of tRNAs on the ribosome in the elongation step, as well as the dissociation of the post-termination state ribosome into two subunits in the recycling step. In contrast to this conventional view, it has very recently been demonstrated that the dual functions of bacterial EF-G are distributed over two different EF-G paralogues in human mitochondria. In the present study, we show that the same division of roles of EF-G is also found in bacteria. Two EF-G paralogues are found in the spirochaete Borrelia burgdorferi, EF-G1 and EF-G2. We demonstrate that EF-G1 is a translocase, while EF-G2 is an exclusive recycling factor. We further demonst... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3283233 Mon, 01 Feb 2010 00:00:00 +0100 3283233 http://www.medworm.com/index.php?rid=3283231&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07073.x Inheritable bacterial defence systems against phage infection and foreign DNA, termed CRISPR (clustered regularly interspaced short palindromic repeats), consist of cas protein genes and repeat arrays interspaced with sequences originating from invaders. The Cas proteins together with processed small spacer-repeat transcripts (crRNAs) cause degradation of penetrated foreign DNA by unknown mechanisms. Here, we have characterized previously unidentified promoters of the Escherichia coli CRISPR arrays and cas protein genes. Transcription of precursor crRNA is directed by a promoter located within the CRISPR leader. A second promoter, directing cas gene transcription, is located upstream of the genes encoding proteins of the Cascade complex. Furthermore, we demonstrate that the DNA-binding pro... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3283231 Mon, 01 Feb 2010 00:00:00 +0100 3283231 http://www.medworm.com/index.php?rid=3239197&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07050.x A molecular ruler, FliK, controls the length of the flagellar hook. FliK measures hook length and catalyses the secretion-substrate specificity switch from rod-hook substrate specificity to late substrate secretion, which includes the filament subunits. Here, we show normal hook-length control and filament assembly in the complete absence of the C-ring thus refuting the previous 'cup' model for hook-length control. Mutants of C-ring components, which are reported to produce short hooks, show a reduced rate of hook[ndash]basal body assembly thereby allowing for a premature secretion-substrate specificity switch. Unlike fliK null mutants, hook-length control in an autocleavage-defective mutant of flhB, the protein responsible for the switch to late substrate secretion, is completely abolishe... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3239197 Mon, 01 Feb 2010 00:00:00 +0100 3239197 http://www.medworm.com/index.php?rid=3239196&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07060.x A Plasmodium falciparum hexose transporter (PfHT) has previously been shown to be a facilitative glucose and fructose transporter. Its expression in Xenopus laevis oocytes and the use of a glucose analogue inhibitor permitted chemical validation of PfHT as a novel drug target. Following recent re-annotations of the P. falciparum genome, other putative sugar transporters have been identified. To investigate further if PfHT is the key supplier of hexose to P. falciparum and to extend studies to different stages of Plasmodium spp., we functionally analysed the hexose transporters of both the human parasite P. falciparum and the rodent parasite Plasmodium berghei using gene targeting strategies. We show here the essential function of pfht for the erythrocytic parasite growth as it was not poss... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3239196 Mon, 01 Feb 2010 00:00:00 +0100 3239196 http://www.medworm.com/index.php?rid=3231092&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07031.x Anabaena sp. strain PCC 7120 is a filamentous cyanobacterium that can fix N2 in differentiated cells called heterocysts, which exchange nutritional and regulatory compounds with the neighbouring photosynthetic vegetative cells. The cells in the filament appear to be joined by some protein structures, of which SepJ (FraG) that is located at the cell poles in the intercellular septa and is needed for filament integrity seems to be a component. Other known proteins required for filament integrity include FraC and FraH. Whereas fraC (alr2392) was constitutively expressed as an operon together with two downstream genes, alr2393 (fraD) and alr2394 (fraE), fraH (alr1603) was induced under nitrogen deprivation. Single mutants of these genes showed filament fragmentation under nitrogen deprivation ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3231092 Mon, 01 Feb 2010 00:00:00 +0100 3231092 http://www.medworm.com/index.php?rid=3231091&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07051.x Fungal secondary metabolites are important bioactive compounds but the conditions leading to expression of most of the putative secondary metabolism (SM) genes predicted by fungal genomics are unknown. Here we describe a novel mechanism involved in SM-gene regulation based on the finding that, in Aspergillus nidulans, mutants lacking components involved in heterochromatin formation show de-repression of genes involved in biosynthesis of sterigmatocystin (ST), penicillin and terrequinone A. During the active growth phase, the silent ST gene cluster is marked by histone H3 lysine 9 trimethylation and contains high levels of the heterochromatin protein-1 (HepA). Upon growth arrest and activation of SM, HepA and trimethylated H3K9 levels decrease concomitantly with increasing levels of acetyla... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3231091 Mon, 01 Feb 2010 00:00:00 +0100 3231091 http://www.medworm.com/index.php?rid=3231090&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07053.x Phosducin-like proteins are conserved regulatory components of G-protein signalling pathways, which mediate many physiological processes. Identified throughout eukaryotic genomes, they are thought to serve as regulators of G[beta][gamma] assembly. Cryphonectria parasitica, a plant pathogen and causative agent of chestnut blight, contains three G[alpha], one G[beta], one G[gamma] subunits and phosducin-like protein BDM-1 that have important roles in pigmentation, sporulation and virulence. Deletion of either G[beta] subunit or BDM-1 produces identical phenotypes. Additionally, we report that the G[beta] subunit is not detectable in absence of BDM-1. Given that the regulatory role of phosducin-like proteins may be influenced by protein kinase 2 (CK2), we confirmed that BDM-1 is a phosphoprot... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3231090 Mon, 01 Feb 2010 00:00:00 +0100 3231090 http://www.medworm.com/index.php?rid=3231089&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07055.x In Escherichia coli the Min system prevents Z ring assembly at cell poles by topologically regulating the division inhibitor MinC. The MinC protein has two domains of equal size and both domains can target FtsZ and block cell division in the proper context. Recently, we have shown that, along with MinD, the C-terminal domain of MinC (MinCC) competes with FtsA, and to a lesser extent with ZipA, for interaction with the C-terminal tail of FtsZ to block division. Here we explored the interaction between the N-terminal domain of MinC (MinCN) and FtsZ. A search for mutations in ftsZ that confer resistance to MinCN identified an [alpha]-helix at the interface of FtsZ subunits as being critical for the activity of MinCN. Focusing on one such mutant FtsZ[ndash]N280D, we showed that it greatly redu... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3231089 Mon, 01 Feb 2010 00:00:00 +0100 3231089 http://www.medworm.com/index.php?rid=3231088&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07056.x RfaH is a bacterial elongation factor that increases expression of distal genes in several long, horizontally acquired operons. RfaH is recruited to the transcription complex during RNA chain elongation through specific interactions with a DNA element called ops. Following recruitment, RfaH remains bound to RNA polymerase (RNAP) and acts as an antiterminator by reducing RNAP pausing and termination at some factor-independent and Rho-dependent signals. RfaH consists of two domains connected by a flexible linker. The N-terminal RfaH domain (RfaHN) recognizes the ops element, binds to the RNAP and reduces pausing and termination in vitro. Functional analysis of single substitutions in this domain reported here suggests that three separate RfaHN regions mediate these functions. We propose that... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3231088 Mon, 01 Feb 2010 00:00:00 +0100 3231088 http://www.medworm.com/index.php?rid=3211916&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07027.x Pseudomonas aeruginosa uses a type III secretion system to inject protein effectors into a targeted host cell. Effector secretion is triggered by host cell contact. How effector secretion is prevented prior to cell contact is not well understood. In all secretion systems studied to date, the needle tip protein is required for controlling effector secretion, but the mechanism by which needle tip proteins control effector secretion is unclear. Here we present data that the P. aeruginosa needle tip protein, PcrV, controls effector secretion by assembling into a functional needle tip complex. PcrV likely does not simply obstruct the secretion channel because the pore-forming translocator proteins can still be secreted while effector secretion is repressed. This finding suggests that PcrV contr... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3211916 Wed, 27 Jan 2010 00:00:00 +0100 3211916 http://www.medworm.com/index.php?rid=3211913&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07047.x The response regulator DegU and its cognate kinase DegS constitute a two-component system in Bacillus subtilis that regulates many cellular processes, including exoprotease production and competence development. Using DNA footprint assay, gel shift assay and mutational analyses of P3degU-lacZ fusions, we showed that phosphorylated DegU (DegU-P) binds to two direct repeats (DR1 and DR2) of the consensus DegU-binding sequence in the P3degU promoter. The alteration of chromosomal DR2 severely decreased degU expression, demonstrating its importance in positive autoregulation of degU. Observation of DegU protein levels suggested that DegU is degraded. Western blot analysis of DegU in disruption mutants of genes encoding various ATP-dependent proteases strongly suggested that ClpCP degrades DegU... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3211913 Wed, 27 Jan 2010 00:00:00 +0100 3211913 http://www.medworm.com/index.php?rid=3208015&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07007.x Staphylococcal cell separation depends largely on the bifunctional autolysin Atl that is processed to amidase-R1,2 and R3-glucosaminidase. These murein hydrolases are targeted via repeat domains (R) to the septal region of the cell surface, thereby allowing localized peptidoglycan hydrolysis and separation of the dividing cells. Here we show that targeting of the amidase repeats is based on an exclusion strategy mediated by wall teichoic acid (WTA). In Staphylococcus aureus wild-type, externally applied repeats (R1,2) or endogenously expressed amidase were localized exclusively at the cross-wall region, while in [Delta]tagO mutant that lacks WTA binding was evenly distributed on the cell surface, which explains the increased fragility and autolysis susceptibility of the mutant. WTA prevent... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3208015 Tue, 26 Jan 2010 00:00:00 +0100 3208015 http://www.medworm.com/index.php?rid=3197351&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07034.x In this study, using a rodent malaria model, we show that the PDH E1[alpha] and E3 subunits colocalize with the FAS II enzyme FabI in the apicoplast of liver stages but are not significantly expressed in blood stages. Deletion of the E1[alpha] or E3 subunit genes of Plasmodium yoelii PDH caused no defect in blood stage development, mosquito stage development or early liver stage development. However, the gene deletions completely blocked the ability of the e1[alpha]- and e3- parasites to form exo-erythrocytic merozoites during late liver stage development, thus preventing the initiation of a blood stage infection. This phenotype is similar to that observed for deletions of genes involved in FAS II elongation. The data strongly support the hypothesis that the sole role of PDH is to provide ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3197351 Fri, 22 Jan 2010 00:00:00 +0100 3197351 http://www.medworm.com/index.php?rid=3197348&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07046.x Here, we report that the model Gram-positive organism, Bacillus subtilis, expresses and secretes a muralytic enzyme, YocH, in response to cell wall-derived muropeptides derived from growing cells but not lysed cells. This induction is dependent on PrkC, a membrane Ser/Thr kinase that binds to peptidoglycan and that belongs to a broadly conserved family including the essential PknB kinase of M. tuberculosis. YocH stimulates its own expression in a PrkC-dependent manner demonstrating the presence of an autoregulatory loop during growth. Cells lacking YocH display a survival defect in stationary phase but enzymes secreted by other cells in the culture rescue this defect. The essential translation factor EF-G is an in vivo substrate of PrkC and this phosphorylation occurs in response to murope... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3197348 Fri, 22 Jan 2010 00:00:00 +0100 3197348 http://www.medworm.com/index.php?rid=3181896&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07030.x Genes introduced by gene replacements and other types of horizontal gene transfer (HGT) represent a significant presence in many archaeal and eubacterial genomes. Most alien genes are likely to be neutral or deleterious upon arrival and their long-term persistence may require a mechanism that improves their selective contribution. To examine the fate of inter-species gene replacements, we exchanged three native S. typhimurium genes encoding ribosomal proteins with orthologues from various other microbes. The results show that replacement of each of these three genes reduces fitness to such an extent that it would provide an effective barrier against inter-species gene replacements in eubacterial populations. However, these fitness defects could be partially ameliorated by gene amplificatio... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3181896 Mon, 18 Jan 2010 00:00:00 +0100 3181896 http://www.medworm.com/index.php?rid=3181895&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07041.x Mycobacterium tuberculosis (M. tb) has a complex lifestyle in different environments and involving several developmental stages. The success of M. tb results from its remarkable capacity to survive within the infected host, where it can persist in a non-replicating state for several decades. The survival strategies developed by M. tb are linked to the presence of an unusual cell envelope. However, little is known regarding its capacity to modulate and adapt production of cell wall components in response to environmental conditions or to changes in cell shape and cell division. Signal sensing leading to cellular responses must be tightly regulated to allow survival under variable conditions. Although prokaryotes generally control their signal transduction processes through two-component sys... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3181895 Mon, 18 Jan 2010 00:00:00 +0100 3181895 http://www.medworm.com/index.php?rid=3181894&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07042.x In this study we revealed the importance of the Cpx regulon in the event of [beta]-barrel OMP mis-assembly, by utilizing mutants expressing either a defective [beta]-barrel OMP assembly machinery (Bam) or assembly defective [beta]-barrel OMPs. Analysis of specific mRNAs showed that [Delta]cpxR bam double mutants failed to induce degP expression beyond the wild type level, despite activation of the [sigma]E pathway. The synthetic conditional lethal phenotype of [Delta]cpxR in mutant Bam or [beta]-barrel OMP backgrounds was reversed by wild type DegP expressed from a heterologous plasmid promoter. Consistent with the involvement of the Cpx regulon in the event of aberrant [beta]-barrel OMP assembly, the expression of cpxP, the archetypal member of the cpx regulon, was upregulated in defectiv... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3181894 Mon, 18 Jan 2010 00:00:00 +0100 3181894 http://www.medworm.com/index.php?rid=3181893&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07037.x Purple non-sulphur phototrophic bacteria (PNSB) are excellent models for analysing the co-ordination of major metabolisms, including oxidative phosphorylation, photophosphorylation, carbon dioxide fixation and nitrogen fixation. In species studied to date, a two-component system called RegBA controls these functions and it has been thought that this redox sensing regulatory system is essential for co-ordinating electron flow and cannot be easily replaced. Here we show that this is not the case for all PNSB and that the oxygen-sensing FixLJ-K system, initially described in rhizobia, controls microaerobic respiration, photophosphorylation and other major metabolic traits in Rhodopseudomonas palustris. A R. palustris fixK mutant grew normally aerobically but was impaired in microaerobic growt... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3181893 Mon, 18 Jan 2010 00:00:00 +0100 3181893 http://www.medworm.com/index.php?rid=3181901&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06991.x Pseudomonas aeruginosa, the principal pathogen of cystic fibrosis patients, forms antibiotic-resistant biofilms promoting chronic colonization of the airways. The extracellular (EPS) matrix is a crucial component of biofilms that provides the community multiple benefits. Recent work suggests that the secondary messenger, cyclic-di-GMP, promotes biofilm formation. An analysis of factors specifically expressed in P. aeruginosa under conditions of elevated c-di-GMP, revealed functions involved in the production and maintenance of the biofilm extracellular matrix. We have characterized one of these components, encoded by the PA4625 gene, as a putative adhesin and designated it cdrA. CdrA shares structural similarities to extracellular adhesins that belong to two-partner secretion systems. The ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3181901 Sun, 17 Jan 2010 00:00:00 +0100 3181901 http://www.medworm.com/index.php?rid=3181900&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07025.x Iron acquisition mechanisms play an important role in the pathogenesis of many infectious microbes. In Bacillus anthracis, the siderophore petrobactin is required for both growth in iron-depleted conditions and for full virulence of the bacterium. Here we demonstrate the roles of two putative petrobactin binding proteins FatB and FpuA (encoded by GBAA5330 and GBAA4766 respectively) in B. anthracis iron acquisition and pathogenesis. Markerless deletion mutants were created using allelic exchange. The [Delta]fatB strain was capable of wild-type levels of growth in iron-depleted conditions, indicating that FatB does not play an essential role in petrobactin uptake. In contrast, [Delta]fpuA bacteria exhibited a significant decrease in growth under low-iron conditions when compared with wild-ty... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3181900 Sun, 17 Jan 2010 00:00:00 +0100 3181900 http://www.medworm.com/index.php?rid=3181899&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07035.x Mitochondria are critical for supplying energy to the cell, but during catabolism this organelle also produces reactive oxygen species that can cause oxidative damage. Accordingly, quality control of mitochondria is important to maintain cellular homeostasis. It has been assumed that autophagy is the pathway for mitochondrial recycling, and that the selective degradation of mitochondria via autophagy (mitophagy) is the primary mechanism for mitochondrial quality control, although there is little experimental evidence to support this idea. Recent studies in yeast identified several mitophagy-related genes and have uncovered components involved in the molecular mechanism and regulation of mitophagy. Similarly, studies of Parkinson disease and reticulocyte maturation reveal that Parkin and Ni... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3181899 Sun, 17 Jan 2010 00:00:00 +0100 3181899 http://www.medworm.com/index.php?rid=3181898&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07040.x The pathogenesis of Plasmodium falciparum depends on efficient invasion into host erythrocytes. Parasite ligands encoded by multi-gene families interact with erythrocyte receptors. P. falciparum reticulocyte binding protein homologues (PfRhs) are expressed at the apical surface of invasive merozoites and have divergent ectodomains that are postulated to bind different erythrocyte receptors. Variant expression of these paralogues results in the use of alternative invasion pathways. Two PfRh proteins, PfRh2a and PfRh2b, are identical for 2700 N-terminal amino acids and differ only in a C-terminal 500 amino acid region, which includes a unique ectodomain, transmembrane domain and cytoplasmic domain. Despite their similarity, PfRh2b is required for a well-defined invasion pathway while PfRh2a ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3181898 Sun, 17 Jan 2010 00:00:00 +0100 3181898 http://www.medworm.com/index.php?rid=3181897&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07045.x Like Eukarya and Bacteria, Archaea are also capable of performing N-glycosylation. In the halophilic archaeon Haloferax volcanii, N-glycosylation is mediated by the products of the agl gene cluster. In the present report, this gene cluster was expanded to include an additional sequence, aglM, shown to participate in the biosynthesis of hexuronic acids contained within a pentasaccharide decorating the S-layer glycoprotein, a reporter H. volcanii glycoprotein. In response to different growth conditions, changes in the transcription profile of aglM mirrored changes in the transcription profiles of aglF, aglG and aglI, genes encoding confirmed participants in the H. volcanii N-glycosylation pathway, thus offering support to the hypothesis that in H. volcanii, N-glycosylation serves an adaptive... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3181897 Sun, 17 Jan 2010 00:00:00 +0100 3181897 http://www.medworm.com/index.php?rid=3175452&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07039.x The antifungal mode of action of chitosan has been studied for the last 30 years, but is still little understood. We have found that the plasma membrane forms a barrier to chitosan in chitosan-resistant but not chitosan-sensitive fungi. The plasma membranes of chitosan-sensitive fungi were shown to have more polyunsaturated fatty acids than chitosan-resistant fungi, suggesting that their permeabilization by chitosan may be dependent on membrane fluidity. A fatty acid desaturase mutant of Neurospora crassa with reduced plasma membrane fluidity exhibited increased resistance to chitosan. Steady-state fluorescence anisotropy measurements on artificial membranes showed that chitosan binds to negatively charged phospholipids that alter plasma membrane fluidity and induces membrane permeabilizat... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3175452 Fri, 15 Jan 2010 00:00:00 +0100 3175452 http://www.medworm.com/index.php?rid=3175455&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07024.x Reactive oxidant species produced by phagocytes have been reported as being involved in the killing of Aspergillus fumigatus. Fungal superoxide dismutases (SODs) that detoxify superoxide anions could be putative virulence factors for this opportunistic pathogen. Four genes encoding putative Sods have been identified in the A. fumigatus genome: a cytoplasmic Cu/ZnSOD (AfSod1p), a mitochondrial MnSOD (AfSod2p), a cytoplasmic MnSOD (AfSod3p) and AfSod4 displaying a MnSOD C-terminal domain. During growth, AfSOD1 and AfSOD2 were highly expressed in conidia whereas AfSOD3 was only strongly expressed in mycelium. AfSOD4 was weakly expressed compared with other SODs. The deletion of AfSOD4 was lethal. [Delta]sod1 and [Delta]sod2 mutants showed a growth inhibition at high temperature and a hypersen... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3175455 Thu, 14 Jan 2010 00:00:00 +0100 3175455 http://www.medworm.com/index.php?rid=3175454&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07028.x Type VI secretion systems (T6SS) are multi-component machines encoded within the genomes of most Gram-negative bacteria that associate with plant, animal and/or human cells, and therefore are considered as potential virulence factors. We recently launched a study on the Sci-1 T6SS of enteroaggregative Escherichia coli (EAEC). The Sci-1 T6SS is composed of all or a subset of the 21 gene products encoded within the cluster, 13 of which are shared by all T6SS identified so far. In the present work, we focussed our attention on the SciZ protein. We first showed that SciZ is required for the release of the Hcp protein in the culture supernatant and for efficient biofilm formation, demonstrating that SciZ is necessary for EAEC T6SS function. Indeed, SciZ forms a complex with SciP, SciS and SciN,... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3175454 Thu, 14 Jan 2010 00:00:00 +0100 3175454 http://www.medworm.com/index.php?rid=3175453&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07036.x In Bacillus subtilis, the WalRK (YycFG) two-component system controls peptidoglycan metabolism in exponentially growing cells while PhoPR controls the response to phosphate limitation. Here we examine the roles of WalRK and PhoPR in peptidoglycan metabolism in phosphate-limited cells. We show that B. subtilis cells remain viable in a phosphate-limited state for an extended period and resume growth rapidly upon phosphate addition, even in the absence of a PhoPR-mediated response. Peptidoglycan synthesis occurs in phosphate-limited wild-type cells at [sim]27% the rate of exponentially growing cells, and at [sim]18% the rate of exponentially growing cells in the absence of PhoPR. In phosphate-limited cells, the WalRK regulon genes yocH, cwlO(yvcE), lytE and ydjM are expressed in a manner that... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3175453 Thu, 14 Jan 2010 00:00:00 +0100 3175453 http://www.medworm.com/index.php?rid=3171474&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07033.x The apicoplast of Plasmodium falciparum carries a 35 kb circular genome (plDNA) that replicates at the late trophozoite stage of the parasite intraerythocytic cycle. plDNA replication proceeds predominantly via a d-loop/bi-directional ori mechanism with replication ori localized within inverted repeat region. Although replication of the apicoplast genome is a validated drug target, the proteins involved in the replication process are only partially characterized. We analysed DNA[ndash]protein interactions at a plDNA replication ori region and report the identification of a nuclear-encoded DnaJ homologue that binds directly to ori elements of the plDNA molecule. PfDnaJA interacted with the minor groove of the DNA double-helix and recognized a 13 bp sequence within the ori. Inhibition of bin... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3171474 Thu, 14 Jan 2010 00:00:00 +0100 3171474 http://www.medworm.com/index.php?rid=3166745&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07021.x The bacterial RNA polymeras holoenzyme consists of a catalytic core enzyme in complex with a [sigma] factor that is required for promoter-specific transcription initiation. During initiation, members of the [sigma]70 family of [sigma] factors contact two conserved promoter elements, the [minus]10 and [minus]35 elements, which are separated by [sim]17 base pairs (bp). [sigma]70 family members contain four flexibly linked domains. Two of these domains, [sigma]2 and [sigma]4, contain determinants for interactions with the promoter [minus]10 and [minus]35 elements respectively. [sigma]2 and [sigma]4 also contain core-binding determinants. When bound to core the inter-domain distance between [sigma]2 and [sigma]4 matches the distance between promoter elements separated by [sim]17 bp. Prior work... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3166745 Wed, 13 Jan 2010 00:00:00 +0100 3166745 http://www.medworm.com/index.php?rid=3211914&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07044.x Small RNAs (sRNAs) that act by base pairing with trans-encoded mRNAs modulate metabolism in response to a variety of environmental stimuli. Here, we describe an Hfq-binding sRNA (FnrS) whose expression is induced upon a shift from aerobic to anaerobic conditions and which acts to downregulate the levels of a variety of mRNAs encoding metabolic enzymes. Anaerobic induction in minimal medium depends strongly on FNR but is also affected by the ArcA and CRP transcription regulators. Whole genome expression analysis showed that the levels of at least 32 mRNAs are downregulated upon FnrS overexpression, 15 of which are predicted to base pair with FnrS by TargetRNA. The sRNA is highly conserved across its entire length in numerous Enterobacteria, and mutational analysis revealed that two separate... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3211914 Tue, 12 Jan 2010 00:00:00 +0100 3211914 http://www.medworm.com/index.php?rid=3197350&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07048.x Iron is an important element for many essential processes in living organisms. To acquire iron, the basidiomycete Ustilago maydis synthesizes the iron-chelating siderophores ferrichrome and ferrichrome A. The chemical structures of these siderophores have been elucidated long time ago but so far only two enzymes involved in their biosynthesis have been described. Sid1, an ornithine monoxygenase, is needed for the biosynthesis of both siderophores, and Sid2, a non-ribosomal peptide synthetase (NRPS), is involved in ferrichrome generation. In this work we identified four novel enzymes, Fer3, Fer4, Fer5 and Hcs1, involved in ferrichrome A biosynthesis in U. maydis. By HPLC-MS analysis of siderophore accumulation in culture supernatants of deletion strains, we show that Fer3, an NRPS, Fer4, an... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3197350 Tue, 12 Jan 2010 00:00:00 +0100 3197350 http://www.medworm.com/index.php?rid=3243312&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2010.07043.x LysR-type transcriptional regulators (LTTRs) constitute the largest family of regulators in prokaryotes. The full-length structures of the LTTR TsaR from Comamonas testosteroni T-2 and its complex with the natural inducer para-toluensulfonate have been characterized by X-ray diffraction. Both ligand-free and complexed forms reveal a dramatically different quaternary structure from that of CbnR from Ralstonia eutropha, or a putative LysR-type regulator from Pseudomonas aeruginosa, the only other determined full-length structures of tetrameric LTTRs. Although all three show a head-to-head tetrameric ring, TsaR displays an open conformation, whereas CbnR and PA01-PR present additional contacts in opposing C-terminal domains that close the ring. Such large differences may be due to a broader s... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3243312 Tue, 05 Jan 2010 00:00:00 +0100 3243312 http://www.medworm.com/index.php?rid=3142139&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07000.x The melanogenic marine bacterium Marinomonas mediterranea synthesizes a novel antimicrobial protein (LodA) with lysine-epsilon oxidase activity (EC 1.4.3.20). Homologues to LodA have been detected in several Gram-negative bacteria, where they are involved in biofilm development. Adjacent to lodA is located a second gene, lodB, of unknown function. This genomic organization is maintained in all the microorganisms containing homologues to these genes. In this work we show that lodA and lodB constitute an operon. Western blot analysis and enzymatic determinations revealed that LodA is secreted to the external medium when the culture reaches the stationary phase. LodB, on the other hand, has only been detected inside cells, but it is not secreted. The expression of the lysine-epsilon oxidase (... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3142139 Tue, 05 Jan 2010 00:00:00 +0100 3142139 http://www.medworm.com/index.php?rid=3138832&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07023.x We report here that regulation of differentiation-related mRNAs by the S. coelicolor AbsB/RNase III enzyme occurs largely by ribonucleolytic cleavage of transcripts encoding the pleiotropic transcription factor, AdpA, and that AdpA and AbsB participate in a novel feedback-control loop that reciprocally regulates the cellular levels of both proteins. Our results reveal a previously unsuspected mechanism for global ribonuclease-mediated control of gene expression in streptomycetes. (Source: Molecular Microbiology) Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3138832 Mon, 04 Jan 2010 00:00:00 +0100 3138832 http://www.medworm.com/index.php?rid=3118585&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07015.x The outer membrane (OM) of the pathogenic diderm spirochete, Borrelia burgdorferi, contains integral [beta]-barrel outer membrane proteins (OMPs) in addition to its numerous outer surface lipoproteins. Very few OMPs have been identified in B. burgdorferi, and the protein machinery required for OMP assembly and OM localization is currently unknown. Essential OM BamA proteins have recently been characterized in Gram-negative bacteria that are central components of an OM [beta]-barrel assembly machine and are required for proper localization and insertion of bacterial OMPs. In the present study, we characterized a putative B. burgdorferi BamA orthologue encoded by open reading frame bb0795. Structural model predictions and cellular localization data indicate that the B. burgdorferi BB0795 pro... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3118585 Thu, 24 Dec 2009 00:00:00 +0100 3118585 http://www.medworm.com/index.php?rid=3114719&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06967.x The ability of Escherichia coli to kill other E. coli using protein antibiotics known as colicins has been known for many years, but the mechanisms involved poorly understood. Recent progress has been rapid, however, particularly concerning events on either side of the outer membrane (OM). Structures of colicins bound to OM receptors have been determined and we have detailed mechanistic information on how colicins subvert the periplasmic complexes of TolQRAB/Pal or TonB/ExbB/ExbD to trigger cell entry. In this issue of Molecular Microbiology, Jakes and Finkelstein answer a long-standing problem concerning the uptake mechanism of the pore-forming colicin ColIa: How does the TonB box of the colicin cross the OM following high-affinity binding of ColIa to its primary receptor, the siderophore... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3114719 Wed, 23 Dec 2009 00:00:00 +0100 3114719 http://www.medworm.com/index.php?rid=3114715&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07004.x Ribonucleases J1 and J2 are recently discovered enzymes with dual 5'-to-3' exoribonucleolytic/endoribonucleolytic activity that plays a key role in the maturation and degradation of Bacillus subtilis RNAs. RNase J1 is essential, while its paralogue RNase J2 is not. Up to now, it had generally been assumed that the two enzymes functioned independently. Here we present evidence that RNases J1 and J2 form a complex that is likely to be the predominant form of these enzymes in wild-type cells. While both RNase J1 and the RNase J1/J2 complex have robust 5'-to-3' exoribonuclease activity in vitro, RNase J2 has at least two orders of magnitude weaker exonuclease activity, providing a possible explanation for why RNase J1 is essential. The association of the two proteins also has an effect on the ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3114715 Wed, 23 Dec 2009 00:00:00 +0100 3114715 http://www.medworm.com/index.php?rid=3211915&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07005.x The malarial sporozoite is the stage that infects the liver, and genes expressed in this stage are potential targets for vaccine development. Here, we demonstrate that specific gene expression in this stage is regulated by an AP2-related transcription factor, designated AP2-Sp (APETALA2 in sporozoites), that is expressed from the late oocyst to the salivary gland sporozoite. Disruption of the AP2-Sp gene did not affect parasite replication in the erythrocyte but resulted in loss of sporozoite formation. The electrophoretic mobility-shift assay showed that the DNA-binding domain of AP2-Sp recognizes specific eight-base sequences, beginning with TGCATG, which are present in the proximal promoter region of all known sporozoite-specific genes. Promoter assays demonstrated that these sequences ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3211915 Wed, 16 Dec 2009 00:00:00 +0100 3211915 http://www.medworm.com/index.php?rid=3197349&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07014.x Bypass of the penicillin-binding proteins by an l,d-transpeptidase (Ldtfm) confers cross-resistance to [beta]-lactam and glycopeptide antibiotics in mutants of Enterococcus faecium selected in vitro. Ldtfm is produced by the parental strain D344S although it insignificantly contributes to peptidoglycan cross-linking as pentapeptide stems cannot be used as acyl donors by this enzyme. Here we show that production of the tetrapeptide substrate of Ldtfm is controlled by a two-component regulatory system (DdcRS) and a metallo-d,d-carboxypeptidase (DdcY). The locus was silent in D344S and its activation was due to amino acid substitutions in DdcS or DdcR that led to production of DdcY and hydrolysis of the C-terminal d-Ala residue of the cytoplasmic peptidoglycan precursor UDP-MurNAc-pentapeptid... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3197349 Wed, 16 Dec 2009 00:00:00 +0100 3197349 http://www.medworm.com/index.php?rid=3171476&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07010.x We describe the characterization of the role and specificity of the Tlp1 chemoreceptor (Cj1506c). In vitro and in vivo models were used to determine if Tlp1 had a role in host colonization. The tlp1- isogenic mutant was more adherent in cell culture, however, showed reduced colonization ability in chickens. Specific interactions between the purified sensory domain of Tlp1 and l-aspartate were identified using an amino acid array and saturation transfer difference nuclear magnetic resonance spectroscopy. Chemotaxis assays showed differences between migration of wild-type C. jejuni cells and that of a tlp1- isogenic mutant, specifically towards aspartate. Furthermore, using yeast two-hybrid and three-hybrid systems for analysis of protein[ndash]protein interactions, the cytoplasmic signallin... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3171476 Wed, 16 Dec 2009 00:00:00 +0100 3171476 http://www.medworm.com/index.php?rid=3171475&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07022.x In promoter DNA, the preferred distance of the [minus]10 and [minus]35 elements for interacting with RNA polymerase-bound [sigma]70 is 17 bp. However, the Devi et al. paper in this issue of Molecular Microbiology demonstrates that when the C-terminal domain of [sigma]70, including the 3.2 linker, is not attached to the core enzyme, distances between 0 and 3 bp can be accommodated. This attests to the great flexibility of the 3.2 linker. The particularly stable complex with the 2 bp separation may lend itself to structural studies of an early elongation complex containing [sigma]70. (Source: Molecular Microbiology) Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3171475 Wed, 16 Dec 2009 00:00:00 +0100 3171475 http://www.medworm.com/index.php?rid=3166750&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07019.x The precise regulation of morphogenesis is a key mechanism by which cells respond to a variety of stresses, including those encountered by microbial pathogens in the host. The polarity protein Cdc42 regulates cellular morphogenesis throughout eukaryotes, and we explore the role of Cdc42 proteins in the host survival of the human fungal pathogen Cryptococcus neoformans. Uniquely, C. neoformans has two functional Cdc42 paralogues, Cdc42 and Cdc420. Here we investigate the contribution of each paralogue to resistance to host stress. In contrast to non-pathogenic model organisms, C. neoformans Cdc42 proteins are not required for viability under non-stress conditions but are required for resistance to high temperature. The paralogues play differential roles in actin and septin organization and ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3166750 Wed, 16 Dec 2009 00:00:00 +0100 3166750 http://www.medworm.com/index.php?rid=3166749&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07017.x Cells invest a significant amount of their energy synthesizing proteins, and a large portion of the energy expenditure goes into making ribosomes, the RNA-protein machines at the centre of translation. When ribosomes are damaged in a cell, i.e. during stressful conditions, cells must first recognize the damage and then mount a response. Remme et al. show that instead of having to rebuild ribosomes from scratch, bacteria can repair ribosomes by replacing damaged proteins in situ, thereby saving significant time and energy. Given the central role of translation, such repair mechanisms might be widespread in nature. (Source: Molecular Microbiology) Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3166749 Wed, 16 Dec 2009 00:00:00 +0100 3166749 http://www.medworm.com/index.php?rid=3166748&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07008.x Central to the response of Mycobacterium tuberculosis to environmental stress is the regulation of genes under the control of alternative sigma factors. Sigma E of M. tuberculosis plays an important role in the intracellular life of the bacterium and regulates several genes which are important for maintaining the integrity of the cell envelope stress. This makes it important to understand how SigE is activated under stress. Here we elucidate the mechanisms regulating interaction of SigE with its cognate anti-sigma factor RseA. Cysteines 70 and 73 are required for redox-dependent interaction of RseA with SigE. Under surface stress, PknB-dependent phosphorylation of RseA on T39 is required for its cleavage by ClpC1P2 thereby activating the SigE regulon. Rv2745c (MSMEG_2694), a transcriptiona... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3166748 Wed, 16 Dec 2009 00:00:00 +0100 3166748 http://www.medworm.com/index.php?rid=3166747&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07013.x Proteasome-bearing bacteria make use of a ubiquitin-like modification pathway to target proteins for proteasomal turnover. In a process termed pupylation, proteasomal substrates are covalently modified with the small protein Pup that serves as a degradation signal. Pup is attached to substrate proteins by action of PafA. Prior to its attachment, Pup needs to undergo deamidation at its C-terminal residue, converting glutamine to glutamate. This step is catalysed in vitro by Dop. In order to characterize Dop activity in vivo, we generated a dop deletion mutant in Mycobacterium smegmatis. In the [Delta]dop strain, pupylation is severely impaired and the steady-state levels of two known proteasomal substrates are drastically increased. Pupylation can be re-established by complementing the muta... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3166747 Wed, 16 Dec 2009 00:00:00 +0100 3166747 http://www.medworm.com/index.php?rid=3166746&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07016.x The euryarchaeal transcriptional repressor NrpR regulates a variety of nitrogen assimilation genes by 2-oxoglutarate-reversible binding to conserved palindromic operators. The number and positioning of these operators varies among promoter regions of regulated genes, suggesting NrpR can bind in different patterns. Particularly intriguing is the contrast between the nif and glnK1 promoter regions of Methanococcus maripaludis, where two operators are present but with different configurations. Here we study NrpR binding and regulation at the glnK1 promoter, where the two operator sequences overlap and occur on opposite faces of the double helix. We find that both operators function in binding, with a dimer of NrpR binding simultaneously to each overlapping operator. We show in vivo that the f... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3166746 Wed, 16 Dec 2009 00:00:00 +0100 3166746 http://www.medworm.com/index.php?rid=3118591&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07006.x Dynamic oscillation of the Min system in Escherichia coli determines the placement of the division plane at the midcell. In addition to stimulating MinD ATPase activity, we report here that MinE can directly interact with the membrane and this interaction contributes to the proper MinDE localization and dynamics. The N-terminal domain of MinE is involved in direct contact between MinE and the membranes that may subsequently be stabilized by the C-terminal domain of MinE. In an in vitro system, MinE caused liposome deformation into membrane tubules, a property similar to that previously reported for MinD. We isolated a mutant MinE containing residue substitutions in R10, K11 and K12 that was fully capable of stimulating MinD ATPase activity, but was deficient in membrane binding. Importantl... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3118591 Wed, 16 Dec 2009 00:00:00 +0100 3118591 http://www.medworm.com/index.php?rid=3118588&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07009.x [sigma]E, one of the best characterized mycobacterial extracytoplasmic function sigma factors, is involved in virulence, surface stress response and modulation of the inflammatory response during infection. The regulation of its activity is very complex and involves transcriptional, translational and post-translational control. Post-translational regulation is controlled by RseA, an anti-[sigma] factor belonging to the zinc-associated anti-[sigma] factor family. In this issue of Molecular Microbiology, Barik et al. demonstrate that RseA is a redox-sensing protein that is able to bind [sigma]E only in reducing environment. Importantly, they describe a novel positive feedback loop responsible for [sigma]E release and activation following surface stress, due to ClpC1P2-dependent proteolytic d... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3118588 Wed, 16 Dec 2009 00:00:00 +0100 3118588 http://www.medworm.com/index.php?rid=3118587&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07011.x Autoregulatory gene circuits can be physically encoded within the genome in a number of different configurations. By physical encoding, we mean the orientation and relative proximity of the genes within the circuit. In this work, we quantified the behaviour of an inducible, negatively autoregulated gene circuit arranged in different transcriptional configurations using the tetRA circuit from Tn10 as our basis. Mathematical modelling predicted that circuits arranged in configurations where the expression of the transcription factor is decoupled from its target genes afforded more flexibility relative to configurations where expression is coupled. We found that these decoupled configurations reduced the concentration of transcription factor needed to regulate inducible expression from the ci... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3118587 Wed, 16 Dec 2009 00:00:00 +0100 3118587 http://www.medworm.com/index.php?rid=3118586&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07012.x We report that RNases J1 and J2 affect the rate of decay of Class I messages and the length of the first phase in decay of Class II messages. (Source: Molecular Microbiology) Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3118586 Wed, 16 Dec 2009 00:00:00 +0100 3118586 http://www.medworm.com/index.php?rid=3114716&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07001.x The Oxa1/YidC/Alb3 family plays a key role in the biogenesis of the respiratory and photosynthetic complexes in bacteria and organelles. In Saccharomyces cerevisiae, Oxa1 mediates the co-translational insertion of mitochondrially encoded subunits of the three respiratory complexes III, IV and V within the inner membrane and also controls a late step in complex V assembly. No crystal structure of YidC or Oxa1 is available and little is known about the respective role of each transmembrane segment (TM) and hydrophilic loop of this polytopic protein on the biogenesis of the three complexes. Here, we have generated a collection of random point mutations located in the hydrophobic and hydrophilic domains of the protein and characterized their effects on the assembly of the three respiratory com... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3114716 Wed, 16 Dec 2009 00:00:00 +0100 3114716 http://www.medworm.com/index.php?rid=3092404&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06959.x ESAT6 has recently been demonstrated to cause haemolysis and macrophage lysis. Our studies demonstrate that ESAT6 causes cytolysis of type 1 and type 2 pneumocytes. Both types of pneumocytes express membrane laminin, and ESAT6 exhibits dose-dependent binding to both cell types and to purified human laminin. While minimal ESAT6 was detected on the surface of Mycobacterium tuberculosis grown in vitro, exogenously provided ESAT6 specifically associated with the bacterial cell surface, and the bacterium-associated ESAT6 retained its cytolytic ability. esat6 transcripts were upregulated [sim]4- to [sim]13-fold in bacteria replicating in type 1 cells, and [sim]3- to [sim]5 fold in type 2 cells. In vivo, laminin is primarily concentrated at the basolateral surface of pneumocytes where they rest o... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3092404 Wed, 16 Dec 2009 00:00:00 +0100 3092404 http://www.medworm.com/index.php?rid=3088930&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06999.x The essential proteins DnaB, DnaD and DnaI of Bacillus subtilis are required for initiation, but not elongation, of DNA replication, and for replication restart at stalled forks. The interactions and functions of these proteins have largely been determined in vitro based on their roles in replication restart. During replication initiation in vivo, it is not known if these proteins, and the replication initiator DnaA, associate with oriC independently of each other by virtue of their DNA binding activities, as a (sub)complex like other loader proteins, or in a particular dependent order. We used temperature-sensitive mutants or a conditional degradation system to inactivate each protein and test for association of the other proteins with oriC in vivo. We found that there was a clear order o... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3088930 Tue, 15 Dec 2009 00:00:00 +0100 3088930 http://www.medworm.com/index.php?rid=3082187&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06997.x In this work we unmask a novel downregulation mechanism of the uric acid/xanthine transporter UapA, the prototype member of the ubiquitous Nucleobase-Ascorbate Transporter family, directly related to its function. In the presence of substrates, UapA is endocytosed, sorted into the multivesicular body pathway and degraded in vacuoles. Substrate-induced endocytosis, unlike ammonium-induced turnover, is absolutely dependent on UapA activity and several lines of evidence showed that the signal for increased endocytosis is the actual translocation of substrates through the UapA protein. The use of several UapA functional mutants with altered kinetics and specificity has further shown that transport-dependent UapA endocytosis occurs through a mechanism, which senses subtle conformational changes... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3082187 Sat, 12 Dec 2009 00:00:00 +0100 3082187 http://www.medworm.com/index.php?rid=3078913&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06995.x The nucleoid-associated protein H-NS is important for gene regulation in Escherichia coli. We have studied H-NS interaction with StpA and an uncharacterized H-NS-like protein, Hfp, in the uropathogenic E. coli isolate 536 that expresses all three nucleoid-associated proteins. We found distinct interactions of the three proteins at the protein level, resulting in the formation of heteromers, as well as differences in their gene expression at the transcriptional level. Mutants lacking either StpA or Hfp alone did not exhibit a phenotype at 37°C, which is consistent with a low level of expression at that temperature. Expression of the hfp and stpA genes was found to be induced by apparently diametrical conditions, and StpA and Hfp levels could be correlated to modulatory effects on the expre... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3078913 Fri, 11 Dec 2009 00:00:00 +0100 3078913 http://www.medworm.com/index.php?rid=3078916&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06979.x Candida albicans is an opportunistic fungal pathogen of humans. The ability of the fungus to grow as both yeast and filamentous forms is essential for its pathogenicity. Morphogenesis of C. albicans is largely regulated through the secondary messenger cAMP, produced by the soluble adenylyl cyclase, Cyr1p. Recent evidence suggests that Cyr1p can be directly stimulated by environmental cues to increase cytoplasmic cAMP levels and thus promote hyphal development. In this issue of Molecular Microbiology, Zou et al. demonstrate that, in response to some environmental cues, Cyr1p functions as part of a tripartite complex additionally involving Cap1p and G-actin. All three proteins in the complex are required to raise cytosolic cAMP levels after stimulation with serum and bacterial peptidoglycan.... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3078916 Thu, 10 Dec 2009 00:00:00 +0100 3078916 http://www.medworm.com/index.php?rid=3075097&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06996.x H-NS is one of the most intensively studied members of the family of bacterial nucleoid-associated proteins. It is a DNA-binding protein with a preference for A+T-rich DNA sequences, and it represses the transcription of hundreds of genes in Gram-negative bacteria, including pathogens. In most cases where the issue has been investigated, the repressive activity of H-NS is opposed by the intervention of an antagonistically acting DNA-binding protein, a remodelling of local DNA structure, or a combination of these two. H-NS activity can also be modulated by protein[ndash]protein interaction with members of the Hha/YdgT protein family, molecules that share partial amino acid sequence similarity to the oligomerization domain of H-NS. Of particular interest is the ability of H-NS to interact wi... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3075097 Thu, 10 Dec 2009 00:00:00 +0100 3075097 http://www.medworm.com/index.php?rid=3075101&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06977.x FtnA is the major iron-storage protein of Escherichia coli accounting for [le]50% of total cellular iron. The FtnA gene (ftnA) is induced by iron in an Fe2+[ndash]Fur-dependent fashion. This effect is reportedly mediated by RyhB, the Fe2+[ndash]Fur-repressed, small, regulatory RNA. However, results presented here show that ftnA iron induction is independent of RyhB and instead involves direct interaction of Fe2+[ndash]Fur with an 'extended' Fur binding site (containing five tandem Fur boxes) located upstream ([minus]83) of the ftnA promoter. In addition, H-NS acts as a direct repressor of ftnA transcription by binding at multiple sites (I[ndash]VI) within, and upstream of, the ftnA promoter. Fur directly competes with H-NS binding at upstream sites (II[ndash]IV) and consequently displaces ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3075101 Wed, 09 Dec 2009 00:00:00 +0100 3075101 http://www.medworm.com/index.php?rid=3066644&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06988.x A hallmark of Yersinia type III machines is the presence of needles extending from the bacterial surface. Needles perform two functions, serving as the conduits for the transport of effectors into immune cells but also acting as a sensor. The polymerized needle protein, YscF, is thought to perceive threshold levels of environmental calcium ions to trigger secretion. yopR (yscH) is a gene downstream of yscEFG, encoding the chaperones and principal building blocks of the needle. Here we investigated the contribution of YopR towards type III secretion and pathogenesis. Yersinia pestis KIM D27 mutants lacking yopR were defective for virulence in a mouse model of septicemic plague. yopR variants of Yersinia enterocolitica W22703 displayed a reduced ability to inject effectors into macrophages a... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3066644 Tue, 08 Dec 2009 00:00:00 +0100 3066644 http://www.medworm.com/index.php?rid=3118592&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07003.x The major fungal pathogen Candida albicans has the metabolic flexibility to assimilate a wide range of nutrients in its human host. Previous studies have suggested that C. albicans can encounter glucose-poor microenvironments during infection and that the ability to use alternative non-fermentable carbon sources contributes to its virulence. JEN1 encodes a monocarboxylate transporter in C. albicans and we show that its paralogue, JEN2, encodes a novel dicarboxylate plasma membrane transporter, subjected to glucose repression. A strain deleted in both genes lost the ability to transport lactic, malic and succinic acids by a mediated mechanism and it displayed a growth defect on these substrates. Although no significant morphogenetic or virulence defects were found in the double mutant strai... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3118592 Fri, 04 Dec 2009 00:00:00 +0100 3118592 http://www.medworm.com/index.php?rid=3118590&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06998.x We describe here genetic linkage of the Yts1 and Yts2 T2SSs with a transcriptional regulator in the highly pathogenic Y. enterocolitica biotype 1B. While the Yts2-associated PypC regulator activates the Yts2 operon, the PclR regulator does not induce transcription of its cognate Yts1 operon. Instead, Yts1 and pclR are activated by the addition of MgCl2 to the growth medium at 17°C and 26°C, but not at 37°C. We identified three proteins, ChiY, EngY (YE2830) and YE3650, that are secreted depending on a functional Yts1 T2SS in response to MgCl2 at low temperature. While the activation of chiY by MgCl2 depends on pclR, PclR overproduction is not sufficient for chiY transcription in an Escherichia coli background, demonstrating the need for additional Y. enterocolitica-specific factors. As C... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3118590 Fri, 04 Dec 2009 00:00:00 +0100 3118590 http://www.medworm.com/index.php?rid=3118589&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06990.x Biochemical studies have revealed two distinct classes of Coenzyme B-Coenzyme M heterodisulfide (CoB-S-S-CoM) reductase (Hdr), a key enzyme required for anaerobic respiration in methane-producing archaea. A cytoplasmic HdrABC enzyme complex is found in most methanogens, whereas a membrane-bound HdrED complex is found exclusively in members of the order Methanosarcinales. Unexpectedly, genomic data indicate that multiple copies of both Hdr classes are found in all sequenced Methanosarcinales genomes. The Methanosarcina acetivorans hdrED1 operon is constitutively expressed and required for viability under all growth conditions examined, consistent with HdrED being the primary Hdr. HdrABC appears to be specifically involved in methylotrophic methanogenesis, based on reduced growth and methano... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3118589 Fri, 04 Dec 2009 00:00:00 +0100 3118589 http://www.medworm.com/index.php?rid=3114717&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.07002.x Ribosomal functions are vital for all organisms. Bacterial ribosomes are stable 2.4 MDa particles composed of three RNAs and over 50 different proteins. Accumulating damage to ribosomal RNA or proteins can disturb ribosome functioning. Organisms could benefit from degrading or possibly repairing inactive or partially active ribosomes. Reactivation of chemically damaged ribosomes by a process of protein replacement was studied in vitro. Ribosomes were inactivated by chemical modification of Cys residues. Incubation of modified ribosomes with total ribosomal proteins led to reactivation of translational activity. Intriguingly, ribosomal proteins extracted by LiCl are equally active in the restoration of ribosome function. Incubation of 70S ribosomes with isotopically labelled r-proteins foll... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3114717 Fri, 04 Dec 2009 00:00:00 +0100 3114717 http://www.medworm.com/index.php?rid=3082189&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06993.x In Gram-negative bacteria, a variety of high molecular weight 'exoproteins' are translocated across the outer membrane (OM) via the two-partner secretion (TPS) pathway by interacting with a dedicated transporter. It is unclear, however, whether the translocation of exoproteins across the OM is coupled to their translocation across the inner membrane (IM). To address this question, we separated the production of an Escherichia coli O157:H7 exoprotein (OtpA) and its transporter (OtpB) temporally by placing otpA and otpB under the control of distinct regulatable promoters. We found that when both full-length and truncated forms of OtpA were expressed prior to OtpB, a significant fraction of the exoprotein was secreted. The results indicate that OtpA can be translocated into the periplasm and ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3082189 Fri, 04 Dec 2009 00:00:00 +0100 3082189 http://www.medworm.com/index.php?rid=3075098&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06987.x The NarX[ndash]NarL and NarQ[ndash]NarP sensor[ndash]response regulator pairs control Escherichia coli gene expression in response to nitrate and nitrite. Previous analysis suggests that the Nar two-component systems form a cross-regulation network in vivo. Here we report on the kinetics of phosphoryl transfer between different sensor[ndash]regulator combinations in vitro. NarX exhibited a noticeable kinetic preference for NarL over NarP, whereas NarQ exhibited a relatively slight kinetic preference for NarL. These findings were substantiated in reactions containing one sensor and both response regulators, or with two sensors and a single response regulator. We isolated 21 NarX mutants with missense substitutions in the cytoplasmic central and transmitter modules. These confer phenotypes t... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3075098 Fri, 04 Dec 2009 00:00:00 +0100 3075098 http://www.medworm.com/index.php?rid=3051870&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06952.x Current dogma dictates that bacterial proteins with misoxidized disulfide bonds are shuffled into correctly oxidized states by DsbC. There are two proposed mechanisms for DsbC activity. The first involves a DsbC-only model of substrate disulfide rearrangement. The second invokes cycles of reduction and oxidation of substrate disulfide bonds by DsbC and DsbA respectively. Here, we addressed whether the second mechanism is important in vivo by identifying whether a periplasmic reductase could complement DsbC. We screened for naturally occurring periplasmic reductases in Bacteroides fragilis, a bacterium chosen because we predicted it encodes reductases and has a reducing periplasm. We found that the B. fragilis periplasmic protein TrxP has a thioredoxin fold with an extended N-terminal regio... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3051870 Thu, 03 Dec 2009 00:00:00 +0100 3051870 http://www.medworm.com/index.php?rid=3051869&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06975.x Dipicolinic acid (DPA) is a major component of bacterial endospores, comprising 5[ndash]15% of the spore dry weight, and is important for spore stability and resistance properties. The biosynthetic precursor to DPA, dihydro-dipicolinic acid (DHDPA), is produced by DHDPA synthase within the lysine biosynthesis pathway. In Bacillus subtilis, and most other bacilli and clostridia, DHDPA is oxidized to DPA by the products of the spoVF operon. Analysis of the genomes of the clostridia in Cluster I, including the pathogens Clostridium perfringens, Clostridium botulinum and Clostridium tetani, has shown that no spoVF orthologues exist in these organisms. DPA synthase was purified from extracts of sporulating C. perfringens cells. Peptide sequencing identified an electron transfer flavoprotein, Et... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3051869 Thu, 03 Dec 2009 00:00:00 +0100 3051869 http://www.medworm.com/index.php?rid=3051867&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06972.x Nutrient-dependent germination of Bacillus anthracis spores is stimulated when receptors located in the inner membrane detect combinations of amino acid and purine nucleoside germinants. B. anthracis produces five distinct germinant receptors, GerH, GerK, GerL, GerS and GerX. Otherwise isogenic mutant strains expressing only one of these receptors were created and tested for germination and virulence. The GerH receptor was necessary and sufficient for wild-type levels of germination with inosine-containing germinants in the absence of other receptors. GerK and GerL were sufficient for germination in 50 mM L-alanine. When mutants were inoculated intratracheally, any receptor, except for GerX, was sufficient to allow for a fully virulent infection. In contrast, when inoculated subcutaneously... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3051867 Thu, 03 Dec 2009 00:00:00 +0100 3051867 http://www.medworm.com/index.php?rid=3047852&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06954.x Cysteine desulphurases are primary sources of sulphur that can eventually be used for Fe/S biogenesis or thiolation of various cofactors and tRNA. Escherichia coli contains three such enzymes, IscS, SufS and CsdA. The importance of IscS and SufS in Fe/S biogenesis is well established. The physiological role of CsdA in contrast remains uncertain. We provide here additional evidences for a functional redundancy between the three cysteine desulphurases in vivo. In particular, we show that a deficiency in isoprenoid biosynthesis is the unique cause of the lethality of the iscS sufS mutant. Moreover, we show that CsdA is engaged in two separate sulphur transfer pathways. In one pathway, CsdA interacts functionally with SufE[ndash]SufBCD proteins to assist Fe/S biogenesis. In another pathway, Cs... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3047852 Wed, 02 Dec 2009 00:00:00 +0100 3047852 http://www.medworm.com/index.php?rid=3047853&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06947.x Francisella tularensis causes the human disease tularemia. F. tularensis is able to survive and replicate within macrophages, a trait that has been correlated with its high virulence, but it is unclear the exact mechanism(s) this organism uses to escape killing within this hostile environment. F. tularensis virulence is dependent upon the Francisella pathogenicity island (FPI), a cluster of genes that we show here shares homology with type VI secretion gene clusters in Vibrio cholerae and Pseudomonas aeruginosa. We demonstrate that two FPI proteins, VgrG and IglI, are secreted into the cytosol of infected macrophages. VgrG and IglI are required for F. tularensis phagosomal escape, intramacrophage growth, inflammasome activation and virulence in mice. Interestingly, VgrG secretion does not ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3047853 Tue, 01 Dec 2009 00:00:00 +0100 3047853 http://www.medworm.com/index.php?rid=3171477&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06983.x Septins are conserved, cytoskeletal GTPases that contribute to cytokinesis, exocytosis, cell surface organization and vesicle fusion by mechanisms that are poorly understood. Roles of septins in morphogenesis and virulence of a human pathogen and basidiomycetous yeast Cryptococcus neoformans were investigated. In contrast to a well-established paradigm in S. cerevisiae, Cdc3 and Cdc12 septin homologues are dispensable for growth in C. neoformans yeast cells at 24°C but are essential at 37°C. In a bilateral cross between septin mutants, cells fuse but the resulting hyphae exhibit morphological abnormalities, including lack of properly fused specialized clamp cells and failure to produce spores. Interestingly, post-mating hyphae of the septin mutants have a defect in nuclear distribution. ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3171477 Wed, 25 Nov 2009 00:00:00 +0100 3171477 http://www.medworm.com/index.php?rid=3118594&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06980.x A key virulence trait of Candida albicans is its ability to undergo the yeast-to-hyphal growth transition in response to environmental signals. This transition critically requires a rapid activation of the adenylyl cyclase Cyr1 to generate a cAMP spike. However, the identity of the signal sensors and mechanisms of signal processing and integration remain largely unclear. Recent evidence suggests that some sensors are embedded in Cyr1 itself. To test this hypothesis, we asked whether purified Cyr1 can respond to hyphal induction. Here, we report that Cyr1 co-purifies with Cap1 and G-actin as a tripartite complex which can increase cAMP synthesis in response to hyphal inducing signals in an actin-dependent manner. Cap1 binds Cyr1 and G-actin through its N- and C-terminus respectively. Deleti... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3118594 Wed, 25 Nov 2009 00:00:00 +0100 3118594 http://www.medworm.com/index.php?rid=3118593&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06982.x Two-component signal transduction (TCST) is the most prevalent mechanism employed by microbes to sense and respond to environmental changes. It is characterized by the signal-induced transfer of phosphate from a sensor histidine kinase (HK) to a response regulator (RR), resulting in a cellular response. An emerging theme in the field of TCST signalling is the discovery of auxiliary factors, distinct from the HK and RR, which are capable of influencing phosphotransfer. One group of TCST auxiliary proteins accomplishes this task by acting on HKs. Auxiliary regulators of HKs are widespread and have been identified in all cellular compartments, where they can influence HK activity through interactions with the sensing, transmembrane or enzymatic domains of the HK. The effects of an auxiliary r... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3118593 Wed, 25 Nov 2009 00:00:00 +0100 3118593 http://www.medworm.com/index.php?rid=3088932&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06976.x This report describes several key aspects of a novel form of RecA-independent homologous recombination. We found that synthetic single-stranded DNA oligonucleotides (oligos) introduced into bacteria by transformation can site-specifically recombine with bacterial chromosomes in the absence of any additional phage-encoded functions. Oligo recombination was tested in four genera of Gram-negative bacteria and in all cases evidence for recombination was apparent. The experiments presented here were designed with an eye towards learning to use oligo recombination in order to bootstrap identification and development of phage-encoded recombination systems for recombineering in a wide range of bacteria. The results show that oligo concentration and sequence have the greatest influence on recombina... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3088932 Wed, 25 Nov 2009 00:00:00 +0100 3088932 http://www.medworm.com/index.php?rid=3088931&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06984.x Sexual development in fungi is controlled by mating type loci that prevent self-fertilization. In the phytopathogenic fungus Ustilago maydis, the b mating type locus encodes two homeodomain proteins, termed bE and bW. After cell fusion, a heterodimeric bE/bW complex is formed if the proteins are derived from different alleles. The bE/bW complex is required and sufficient to initiate pathogenic development and sexual reproduction; for the stages of pathogenic development succeeding plant penetration, however, its role was unclear. To analyse b function during in planta development, we generated a temperature-sensitive bEts protein by exchange of a single amino acid. bEts strains are stalled in pathogenic development at restrictive temperature in planta, and hyphae develop enlarged, bulbous ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3088931 Wed, 25 Nov 2009 00:00:00 +0100 3088931 http://www.medworm.com/index.php?rid=3082190&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06989.x The ability of some microbial species to oxidize monomethylamine via glutamate-mediated pathways was proposed in the 1960s; however, genetic determinants of the pathways have never been described. In the present study we describe a gene cluster essential for operation of the N-methylglutamate pathway in the methylotrophic beta-proteobacterium Methyloversatilis universalis FAM5. Four major polypeptides from protein fractions displaying high activities of N-methylglutamate synthetase, N-methylglutamate dehydrogenase and [gamma]-glutamylmethylamide synthetase were selected for mass spectrometry-based identification. The activities of enzymes were associated with the presence of peptides identified as ferredoxin-dependent glutamate synthase (GltB2), large subunit of putative heterotetrameric s... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3082190 Wed, 25 Nov 2009 00:00:00 +0100 3082190 http://www.medworm.com/index.php?rid=3082188&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06994.x RdgB is a bacterial dNTPase with a strong in vitro preference for non-canonical DNA precursors dHapTP, dXTP and dITP that contain deaminated or aminogroup-modified purines. Utilization of these nucleotides by replisomes in rdgB mutants of Escherichia coli produces modified DNA, on which EndoV nicking near the base analogues initiates excision repair. Some EndoV-initiated excision events cause chromosomal fragmentation, which becomes inhibitory if recombinational repair is also inactivated (the rdgB recA co-inhibition). To reveal the sources and the identities of the non-canonical DNA precursors, intercepted by RdgB in E. coli, we characterized 17 suppressors of the rdgB recA co-inhibition. Ten suppressors affect genes of the RNA/DNA precursor metabolism, identifying the source of non-canon... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3082188 Wed, 25 Nov 2009 00:00:00 +0100 3082188 http://www.medworm.com/index.php?rid=3078917&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06974.x The scpAB and sspABC operons of Staphylococcus aureus encode Staphopain cysteine proteases ScpA and SspB, and their respective Staphostatins ScpB and SspC, which are thought to protect against premature activation of Staphopain precursors during protein export. However, we found that the proSspB precursor was secreted and activated without detriment to S. aureus in the absence of SspC function. Our data indicate that this is feasible due to a restricted substrate specificity of mature SspB, a stable precursor structure and slow secretion kinetics. In contrast, mature ScpA had a broad substrate specificity, such that it was prone to autolytic degradation, but also was uniquely able to degrade elastin fibres. Modelling of proScpA relative to the proSspB structure identified several differenc... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3078917 Wed, 25 Nov 2009 00:00:00 +0100 3078917 http://www.medworm.com/index.php?rid=3078915&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06986.x During the course of experiments aimed at identifying genes with ribonuclease III (RNase III)-dependent expression in Escherichia coli, we found that steady state levels of bdm mRNA were dependent on cellular concentrations of RNase III. The half-lives of adventitiously overexpressed bdm mRNA and the activities of a transcriptional bdm'[ndash]'cat fusion were observed to be dependent on cellular concentrations of RNase III, indicating the existence of cis-acting elements in bdm mRNA responsive to RNase III. In vitro and in vivo cleavage analyses of bdm mRNA identified two RNase III cleavage motifs, one in the 5'-untranslated region and the other in the coding region of bdm mRNA, and indicated that RNase III cleavages in the coding region constitute a rate-determining step for bdm mRNA degr... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3078915 Wed, 25 Nov 2009 00:00:00 +0100 3078915 http://www.medworm.com/index.php?rid=3078914&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06985.x Integrative and conjugative elements (ICEs), a.k.a. conjugative transposons, are mobile genetic elements involved in many biological processes, including pathogenesis, symbiosis and the spread of antibiotic resistance. Unlike conjugative plasmids that are extra-chromosomal and replicate autonomously, ICEs are integrated in the chromosome and replicate passively during chromosomal replication. It is generally thought that ICEs do not replicate autonomously. We found that when induced, Bacillus subtilis ICEBs1 undergoes autonomous plasmid-like replication. Replication was unidirectional, initiated from the ICEBs1 origin of transfer, oriT, and required the ICEBs1-encoded relaxase NicK. Replication also required several host proteins needed for chromosomal replication, but did not require the ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3078914 Wed, 25 Nov 2009 00:00:00 +0100 3078914 http://www.medworm.com/index.php?rid=3075100&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06978.x Integrative conjugative elements (ICEs) occur frequently in Gram-positive and Gram-negative bacteria. In contrast to plasmids, they are stably integrated in the bacterial genome, often inserted in a tRNA gene. They are excised from the host chromosome upon induction in order to be transferred to a recipient cell. When conjugative transfer is completed, they stably reintegrate in the chromosome. It is generally thought that ICEs are incapable of autonomous replication, instead relying on replication and segregation along with the host chromosome. In this issue of Molecular Microbiology Lee and co-workers demonstrate that ICEBs1 from Bacillus subtilis is capable of autonomous plasmid-like replication in its circular form after excision. The authors show that ICEBs1 replication is unidirectio... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3075100 Wed, 25 Nov 2009 00:00:00 +0100 3075100 http://www.medworm.com/index.php?rid=3075099&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06981.x Virulence of nosocomial pathogen Staphylococcus epidermidis is essentially related to formation of adherent biofilms, assembled by bacterial attachment to an artificial surface and subsequent production of a matrix that mediates interbacterial adhesion. Growing evidence supports the idea that proteins are functionally involved in S. epidermidis biofilm accumulation. We found that in S. epidermidis 1585v overexpression of a 460 kDa truncated isoform of the extracellular matrix-binding protein (Embp) is necessary for biofilm formation. Embp is a giant fibronectin-binding protein harbouring 59 Found In Various Architectures (FIVAR) and 38 protein G-related albumin-binding (GA) domains. Studies using defined Embp-positive and -negative S. epidermidis strains proved that Embp is sufficient and ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3075099 Wed, 25 Nov 2009 00:00:00 +0100 3075099 http://www.medworm.com/index.php?rid=3051868&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06969.x Prokaryotic toxin [ndash] antitoxin (TA) loci encode mRNA interferases that inhibit translation, either by cleaving mRNA codons at the ribosomal A site or by cleaving any RNA site-specifically. So far, seven mRNA interferases of Escherichia coli have been identified, four of which cleave mRNA by a translation-dependent mechanism. Here, we experimentally confirmed the presence of three novel TA loci in E. coli. We found that the yafNO, higBA (ygjNM) and ygiUT loci encode mRNA interferases related to RelE. YafO and HigB cleaved translated mRNA only, while YgiU cleaved RNA site-specifically at GC[A/U], independently of translation. Thus, YgiU is the first RelE-related mRNA interferase that cleaves mRNA independently of translation, in vivo. All three loci were induced by amino acid starvation... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3051868 Wed, 25 Nov 2009 00:00:00 +0100 3051868 http://www.medworm.com/index.php?rid=3026365&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06955.x Oxidative stress is one of the main challenges bacteria must cope with during infection. Here, we identify a new oxidative stress sensing and response ospR (oxidative stress response and pigment production Regulator) gene in Pseudomonas aeruginosa. Deletion of ospR leads to a significant induction in H2O2 resistance. This effect is mediated by de-repression of PA2826, which lies immediately upstream of ospR and encodes a glutathione peroxidase. Constitutive expression of ospR alters pigment production and [beta]-lactam resistance in P. aeruginosa via a PA2826-independent manner. We further discovered that OspR regulates additional genes involved in quorum sensing and tyrosine metabolism. These regulatory effects are redox-mediated as addition of H2O2 or cumene hydroperoxide leads to the di... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3026365 Wed, 25 Nov 2009 00:00:00 +0100 3026365 http://www.medworm.com/index.php?rid=3026356&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06971.x Borrelia burgdorferi encodes a novel DNA-binding protein in the Fur/PerR family of transcriptional regulators termed BosR (BB0647). This issue of Molecular Microbiology contains two molecular genetic studies that help to clarify the function of BB0647 and resolve longstanding controversies. Loss of BB0647 appears to have a pronounced effect on borrelial gene expression and, in one study, caused significant in vitro growth defects. BB0647 was also found to be essential for infection of the mammalian host but not the tick vector. Both Ouyang et al. and Hyde et al. also demonstrate, quite unexpectedly, that BB0647 is required for induction of RpoS, an alternative sigma factor that controls a cadre of B. burgdorferi genes, most notably ospC, which enable the spirochetes to establish mammalian ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3026356 Wed, 25 Nov 2009 00:00:00 +0100 3026356 http://www.medworm.com/index.php?rid=3022647&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06953.x The disulphide bond-introducing enzyme of bacteria, DsbA, sometimes oxidizes non-native cysteine pairs. DsbC should rearrange the resulting incorrect disulphide bonds into those with correct connectivity. DsbA and DsbC receive oxidizing and reducing equivalents, respectively, from respective redox components (quinones and NADPH) of the cell. Two mechanisms of disulphide bond rearrangement have been proposed. In the redox-neutral 'shuffling' mechanism, the nucleophilic cysteine in the DsbC active site forms a mixed disulphide with a substrate and induces disulphide shuffling within the substrate part of the enzyme[ndash]substrate complex, followed by resolution into a reduced enzyme and a disulphide-rearranged substrate. In the 'reduction[ndash]oxidation' mechanism, DsbC reduces those subst... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3022647 Tue, 24 Nov 2009 00:00:00 +0100 3022647 http://www.medworm.com/index.php?rid=3011977&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06950.x In vivo and in vitro analyses indicate that transcription of the argO gene coding for an arginine exporter is regulated by the global transcriptional regulator Lrp, an effect that went by unnoticed in previous genome-scale screenings of the Lrp regulatory network in Escherichia coli. Lrp activates the argO promoter fourfold; exogenous leucine antagonizes, but does not completely eliminate this effect. Activation by Lrp interferes with the previously demonstrated activation of the argO promoter by ArgP. This interference results from the mutual inhibitory binding of the two activators to overlapping targets. As a consequence, each regulator acts more potently in the absence of the other. Dimeric Lrp binds cooperatively to at least three regularly spaced semi-palindromic binding sites. Leuci... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3011977 Fri, 20 Nov 2009 00:00:00 +0100 3011977 http://www.medworm.com/index.php?rid=3007695&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06935.x The best characterized pathway for the initiation of mRNA degradation in Escherichia coli involves the removal of the 5'-terminal pyrophosphate to generate a monophosphate group that stimulates endonucleolytic cleavage by RNase E. We show here however, using well-characterized oligonucleotide substrates and mRNA transcripts, that RNase E can cleave certain RNAs rapidly without requiring a 5'-monophosphorylated end. Moreover, the minimum substrate requirement for this mode of cleavage, which can be categorized as 'direct' or 'internal' entry, appears to be multiple single-stranded segments in a conformational context that allows their simultaneous interaction with RNase E. While previous work has alluded to the existence of a 5' end-independent mechanism of mRNA degradation, the relative si... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3007695 Thu, 19 Nov 2009 00:00:00 +0100 3007695 http://www.medworm.com/index.php?rid=3114718&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06968.x polY, a transcriptional regulatory gene in the polyoxin biosynthetic cluster of Streptomyces cacaoi, was analysed, and its deduced product (PolY) showed amino acid sequence homology to AfsR from Streptomyces coelicolor A3(2). PolY contains an OmpR-like DNA binding domain at its N-terminal and an ATPase domain in the middle of the protein. Disruption of polY abolished polyoxin biosynthesis, which could be restored by the integration of a single copy of polY into the chromosome of the disruption mutant. Transcription of polR, a pathway-specific regulatory gene of polyoxin biosynthesis, was controlled by polY. Electrophoretic mobility shift assay and DNase I protection experiments indicated that PolY bound to the promoter region of polR, and the binding site contained a direct nucleotide repe... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3114718 Tue, 17 Nov 2009 00:00:00 +0100 3114718 http://www.medworm.com/index.php?rid=3078918&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06973.x The cytoplasmic C-ring of the flagellum consists of FliG, FliM and FliN and acts as an affinity cup to localize secretion substrates for protein translocation via the flagellar-specific type III secretion system. Random T-POP transposon mutagenesis was employed to screen for insertion mutants that allowed flagellar type III secretion in the absence of the C-ring using the flagellar type III secretion system-specific hook[ndash][beta]-lactamase reporter (Lee and Hughes, 2006). Any condition resulting in at least a twofold increase in flhDC expression was sufficient to overcome the requirement for the C-ring and the ATPase complex FliHIJ in flagellar type III secretion. Insertions in known and unknown flagellar regulatory loci were isolated as well as chromosomal duplications of the flhDC re... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3078918 Tue, 17 Nov 2009 00:00:00 +0100 3078918 http://www.medworm.com/index.php?rid=3051873&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06962.x We identified a choline, betaine and carnitine transporter, designated Cbc, from Pseudomonas syringae and Pseudomonas aeruginosa that is unusual among members of the ATP-binding cassette (ABC) transporter family in its use of multiple periplasmic substrate-binding proteins (SBPs) that are highly specific for their substrates. The SBP encoded by the cbcXWV operon, CbcX, binds choline with a high affinity (Km, 2.6 [mu]M) and, although it also binds betaine (Km, 24.2 [mu]M), CbcXWV-mediated betaine uptake did not occur in the presence of choline. The CbcX orthologue ChoX from Sinorhizobium meliloti was similar to CbcX in these binding properties. The core transporter CbcWV also interacts with the carnitine-specific SBP CaiX (Km, 24 [mu]M) and the betaine-specific SBP BetX (Km, 0.6 [mu]M). Unl... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3051873 Tue, 17 Nov 2009 00:00:00 +0100 3051873 http://www.medworm.com/index.php?rid=3051872&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06964.x The bacterial endospore is a dormant and heat-resistant form of life. StoA (SpoIVH) in Bacillus subtilis is a membrane-bound thioredoxin-like protein involved in endospore cortex synthesis. It is proposed to reduce disulphide bonds in hitherto unknown proteins in the intermembrane compartment of developing forespores. Starting with a bioinformatic analysis combined with mutant studies we identified the sporulation-specific, high-molecular-weight, class B penicillin-binding protein SpoVD as a putative target for StoA. We then demonstrate that SpoVD is a membrane-bound protein with two exposed redox-active cysteine residues. Structural modelling of SpoVD, based on the well characterized orthologue PBP2x of Streptococcus pneumoniae, confirmed that a disulphide bond can form close to the activ... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3051872 Tue, 17 Nov 2009 00:00:00 +0100 3051872 http://www.medworm.com/index.php?rid=3051871&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06965.x Bacterial c-type cytochrome maturation is dependent on a complex enzymic machinery. The key reaction is catalysed by cytochrome c haem lyase (CCHL) that usually forms two thioether bonds to attach haem b to the cysteine residues of a haem c binding motif (HBM) which is, in most cases, a CX2CH sequence. Here, the HBM specificity of three distinct CCHL isoenzymes (NrfI, CcsA1 and CcsA2) from the Epsilonproteobacterium Wolinella succinogenes was investigated using either W. succinogenes or Escherichia coli as host organism. Several reporter c-type cytochromes were employed including cytochrome c nitrite reductases (NrfA) from E. coli and Campylobacter jejuni that differ in their active-site HBMs (CX2CK or CX2CH). W. succinogenes CcsA2 was found to attach haem to standard CX2CH motifs in vario... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3051871 Tue, 17 Nov 2009 00:00:00 +0100 3051871 http://www.medworm.com/index.php?rid=3026367&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06942.x Staphylococcus aureus produces a wide array of virulence factors and causes a correspondingly diverse array of infections. Production of these virulence factors is under the control of a complex network of global regulatory elements, one of which is sarA. sarA encodes a DNA binding protein that is considered to function as a transcription factor capable of acting as either a repressor or an activator. Using competitive ELISA assays, we demonstrate that SarA is present at approximately 50 000 copies per cell, which is not characteristic of classical transcription factors. We also demonstrate that SarA is present at all stages of growth in vitro and is capable of binding DNA with high affinity but that its binding affinity and pattern of shifted complexes in electrophoretic mobility shift as... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3026367 Tue, 17 Nov 2009 00:00:00 +0100 3026367 http://www.medworm.com/index.php?rid=3026364&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06963.x Thiol-disulphide oxidoreductases catalyse the formation or breakage of disulphide bonds to control the red-ox status of a variety of proteins. Their activity is compartmentalized, as exemplified by the distinct roles these enzymes play in the cytoplasm and periplasm of Gram-negative bacteria. In this issue of Molecular Microbiology, an article from Lars Hederstedt and collaborators at Lund University sheds light on another member of this superfamily of proteins, the thioredoxin-like protein StoA from Bacillus subtilis. Interestingly, StoA function is required in yet another subcellular compartment: the intermembrane space that separates forespores from mother cells in endospore-forming bacteria. Specifically, this study demonstrates that the high-molecular-weight penicillin-binding protein... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3026364 Tue, 17 Nov 2009 00:00:00 +0100 3026364 http://www.medworm.com/index.php?rid=3026363&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06966.x Colicin Ia, a channel-forming bactericidal protein, uses the outer membrane protein, Cir, as its primary receptor. To kill Escherichia coli, it must cross this membrane. The crystal structure of Ia receptor-binding domain bound to Cir, a 22-stranded plugged [beta]-barrel protein, suggests that the plug does not move. Therefore, another pathway is needed for the colicin to cross the outer membrane, but no 'second receptor' has ever been identified for TonB-dependent colicins, such as Ia. We show that if the receptor-binding domain of colicin Ia is replaced by that of colicin E3, this chimera effectively kills cells, provided they have the E3 receptor (BtuB), Cir, and TonB. This is consistent with wild-type Ia using one Cir as its primary receptor (BtuB in the chimera) and a second Cir as th... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3026363 Tue, 17 Nov 2009 00:00:00 +0100 3026363 http://www.medworm.com/index.php?rid=3026361&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06961.x Acquiring nutrients from the environment is essential for all microbes, and the ATP-binding cassette (ABC) transporters are one of the major routes by which bacteria achieve it. In this issue of Molecular Microbiology, Chen et al. describe their characterization of what appeared at first glance a simple ABC transporter for acquisition of quaternary ammonium compounds (QACs) in Pseudomonas sp., but their persistence in fully determining the properties of this system led to the experimental demonstration that QAC uptake utilizes three different substrate-binding proteins (SBPs), two of which are encoded at remote locations on the genome as 'orphan' SBPs that are each able to function with a single core ABC transporter. Building on the unusual nature of this system, in which multiple SBPs wit... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3026361 Tue, 17 Nov 2009 00:00:00 +0100 3026361 http://www.medworm.com/index.php?rid=3026360&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06970.x Biosynthesis of selenocysteine, the 21st proteinogenic amino acid, occurs bound to a dedicated tRNA in all three domains of life, Bacteria, Eukarya and Archaea, but differences exist between the mechanism employed by bacteria and eukaryotes/archaea. The role of selenophosphate and the enzyme providing it, selenophosphate synthetase, in archaeal selenoprotein synthesis was addressed by mutational analysis. Surprisingly, MMP0904, encoding a homologue of eukaryal selenophosphate synthetase in Methanococcus maripaludis S2, could not be deleted unless selD, encoding selenophosphate synthetase of Escherichia coli, was present in trans, demonstrating that the factor is essential for the organism. In contrast, the homologous gene of M. maripaludis JJ could be readily deleted, obviating the strain'... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3026360 Tue, 17 Nov 2009 00:00:00 +0100 3026360 http://www.medworm.com/index.php?rid=2992470&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06933.x Aquaporins mediate rapid and selective water transport across biological membranes. The yeast Saccharomyces cerevisiae possesses two aquaporins, Aqy1 and Aqy2. Here, we show that Aqy2 is involved in controlling cell surface properties and that its expression is controlled by osmoregulatory and morphogenic signalling pathways. Deletion of AQY2 results in diminished fluffy colony morphology while overexpression of AQY2 causes strong agar invasion and adherence to plastic surfaces. Hyper-osmotic stress inhibits morphological developments including the above characteristics as well as AQY2 expression through the osmoregulatory Hog1 mitogen-activated protein kinase. Moreover, two pathways known to control morphological developments are involved in regulation of AQY2 expression: the protein kina... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=2992470 Sat, 14 Nov 2009 00:00:00 +0100 2992470 http://www.medworm.com/index.php?rid=2992475&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06922.x The F-box protein Frp1 is required for pathogenicity of Fusarium oxysporum f. sp. lycopersici towards tomato. The [Delta]frp1 mutant is deficient in expression of genes for cell wall-degrading enzymes (CWDEs) and ICL1, encoding a key enzyme for the assimilation of C2 carbon sources. An explanation for the inability of the [Delta]frp1 mutant to express these genes may be found in constitutive carbon catabolite repression. Cre1 is the transcriptional repressor in filamentous fungi known to repress several CWDE genes and other genes required for assimilation of non-sugar carbon sources. Here, we demonstrate that Frp1 and Cre1 both control the repression/derepression state of such genes. The replacement of CRE1 with GST::CRE1 resulted in a derepressed phenotype in wild-type background, suggest... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=2992475 Fri, 13 Nov 2009 00:00:00 +0100 2992475 http://www.medworm.com/index.php?rid=2992474&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06923.x Messenger RNAs that lack in-frame stop codons promote ribosome stalling and accumulation of aberrant and potentially harmful polypeptides. The SmpB-tmRNA quality control system has evolved to solve problems associated with non-stop mRNAs, by rescuing stalled ribosomes and directing the addition of a peptide tag to the C-termini of the associated proteins, marking them for proteolysis. In Escherichia coli, the ClpXP system is the major contributor to disposal of tmRNA-tagged proteins. We have shown that the AAA+ Lon protease can also degrade tmRNA-tagged proteins, but with much lower efficiency. Here, we present a unique case of enhanced recognition and degradation of an extended Mycoplasma pneumoniae (MP) tmRNA tag by the MP-Lon protease. We demonstrate that MP-Lon can efficiently and sele... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=2992474 Fri, 13 Nov 2009 00:00:00 +0100 2992474 http://www.medworm.com/index.php?rid=2984521&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06930.x In this study, we have characterized novel mechanisms of transcription control through which the system regulates itself. At low AHL levels a positive feedback loop activates expression of sinI (AHL synthase), resulting in amplification of AHL levels. At high AHL levels, expression of sinI is reduced by a negative feedback loop. These feedback mechanisms are mediated by the LuxR-type regulators ExpR and SinR. Expression of sinR and expR is regulated by ExpR in the presence of AHLs. A novel ExpR binding site in the promoter of sinR is responsible for the reduction of expression of this gene. In addition, expression of sinR, upon which sinI expression is dependent, is induced by phoB during growth under phosphate-limiting conditions. This indicates that this response ensures quorum sensing i... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=2984521 Thu, 12 Nov 2009 00:00:00 +0100 2984521 http://www.medworm.com/index.php?rid=3078919&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06958.x Microbial pathogens use adhesive surface proteins to bind to and interact with host tissues, events that are universal for the pathogenesis of infectious diseases. A surface adhesin of Bacillus anthracis, the causative agent of anthrax, required to mediate these steps has not been discovered. Previous work identified BslA, an S-layer protein, to be necessary and sufficient for adhesion of the anthrax vaccine strain, Bacillus anthracis Sterne, to host cells. Here we asked whether encapsulated bacilli require BslA for anthrax pathogenesis in guinea pigs. Compared with the highly virulent parent strain B. anthracis Ames, bslA mutants displayed a dramatic increase in the lethal dose and in mean time-to-death. Whereas all tissues of animals infected with B. anthracis Ames contained high numbers... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3078919 Tue, 10 Nov 2009 00:00:00 +0100 3078919 http://www.medworm.com/index.php?rid=3026366&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06943.x In recent years, small non-coding RNAs have emerged as important regulatory components in bacterial stress responses and in bacterial virulence. Many of these are conserved in related species and act on target mRNAs by sequence complementarity. They are tightly controlled at the transcription level, and are frequently elements of global regulatory systems. In Escherichia coli and Salmonella, almost one-third of the functional characterized small RNAs participate in control of outer membrane protein production. A subset of these genes is under the control of the [sigma]E-signalling system that monitors the folding status of the envelope and interacts with other regulatory systems to integrate multiple signals into a co-ordinated cellular response. In this issue of Molecular Microbiology, Mo... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3026366 Tue, 10 Nov 2009 00:00:00 +0100 3026366 http://www.medworm.com/index.php?rid=3026362&cid=s_32053_77_f&fid=32053&url=http%3A%2F%2Fdx.doi.org%2F10.1111%252Fj.1365-2958.2009.06957.x Mycobacterium tuberculosis H37Rv contains the kshA (Rv3526) and kshB (Rv3571) genes, encoding 3-ketosteroid 9[alpha]-hydroxylase (KSH). Consistent with their predicted roles, the [Delta]kshA and [Delta]kshB deletion mutants of M. tuberculosis H37Rv were unable to use cholesterol and 4-androstene-3,17-dione as primary carbon and energy sources. Interestingly, [Delta]kshA and [Delta]kshB mutants were also unable to metabolize the steroid substrate 5[alpha]-androstane-3,17-dione, whereas wild-type M. tuberculosis H37Rv could. The deletion of either of these genes lead to rapid death of the microorganism in murine infection models and in macrophages, showing that kshA and kshB are essential factors for M. tuberculosis pathogenesis. Penta-acylated trehalose (PAT) biosynthesis was altered in the... Molecular Microbiology journals http://www.medworm.com/rss/comments.php?id=3026362 Tue, 10 Nov 2009 00:00:00 +0100 3026362