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Molecular Microbiology

Mon, 07/08/2019 - 10:44
Vibrio cholerae mutants lacking lytic transglycosylases MltC and RlpA are defective for daughter cell separation. Our results suggest that lytic transglycosylases at the division septum serve as a back‐up mechanism to cleave peptidoglycan strands that cannot be cleared by highly‐regulated amidase activity and to clear peptidoglycan debris that may block the completion of outer‐membrane...
Wed, 06/12/2019 - 07:43
Bacteria use ECF sigma factors to maintain metal homeostasis. They regulate the expression of genes either to import metals under conditions of metal depletion or to reduce toxicity when metal concentrations are excessive. These adaptive mechanisms can be complex, consisting of several proteins with different cell locations, or very simple, consisting of only the sigma factor capable of sensing...
Thu, 05/23/2019 - 09:52
Abstract The general stress response (GSR) allows many bacterial species to react to myriad different stressors. In Alphaproteobacteria, this signaling pathway proceeds through the partner‐switching PhyR‐EcfG sigma‐factor mechanism and is involved in multiple life processes, including virulence in Brucella abortus. To date, details of the alphaproteobacterial GSR signaling pathway have been...
Sat, 05/11/2019 - 10:03
The signaling peptide NprX orchestrates the development of B. thuringiensis during the stationary phase. In the absence of NprX, NprR inhibits sporulation by impairing the phosphorylation of Spo0F‐P; in the presence of NprX, NprR–NprX ensures the survival of the bacteria in the insect cadaver. We show that NprX is imported in the bacteria by two olipeptide permease systems: Opp, known to be...
Thu, 05/09/2019 - 10:29
Campylobacter jejuni helical shape is key to its pathogenesis. Under stress, C. jejuni alters its shape from helical to coccoid. This study characterized C. jejuni bacterial cell wall peptidoglycan changes occurring during coccoid formation and identified a role for the peptidoglycan hydrolases Pgp1 and previously uncharacterized AmiA in the process. In addition, we determined that coccoid C....
Mon, 05/06/2019 - 07:48
How motile bacteria recognize their environment and decide whether to stay or move is a fundamental issue in survival. Here we established the molecular mechanism underlying the intimate relationship between nutrient availability and flagellum‐driven motility in Vibrio vulnificus; dephosphorylated EIIAGlc of the PEP:carbohydrate phosphotransferase system sequesters the flagellar assembly protein...
Thu, 04/04/2019 - 12:58
Alternaria alternata contaminates many crops and fruits. The mold produces a large variety of different mycotoxins, one of which is alternariol and its derivatives. We identified the gene cluster responsible for the biosynthesis. We show that alternariol is a colonization and virulence factor on tomato, apple and citrus. Abstract The filamentous fungus Alternaria alternata is a potent producer...
Tue, 04/02/2019 - 11:02
Bacteria can be social and move in groups. Here, we show that Vibrio parahaemolyticus coordinates motility using the S signal, a cell‐cell signaling molecule that serves as a chemoattractant during swimming and swarming. Two methyl‐accepting chemoreceptors detect this autoinducer. One is necessary for S signal reception by liquid‐grown bacteria, while the other is important for chemotaxis by...
Fri, 03/15/2019 - 15:30
Vibrio cholerae is an aquatic bacterium with the potential to infect humans. This study focuses on the DNA replication and cell division of this bi‐chromosomal bacterium during starvation stress. Surprisingly, cells temporarily restart their DNA replication after a first shut‐down period before finally reaching a state with fully replicated single chromosome sets. Abstract Vibrio cholerae is...
Wed, 02/27/2019 - 14:10
Listeria monocytogenes is a soil bacterium that can infect humans upon ingestion. Numerous genes are known that are specifically expressed during infection, but less is known about genes important for survival in the soil. We identified the first genetic module regulating and mediating resistance against the depsipeptide antibiotic aurantimycin A. This substance is produced by Streptomyces...
Sun, 02/17/2019 - 13:58
Synthetic peptide MciZ is a specific inhibitor of B. subtilis division, sporulation and germination that binds with high affinity to key cell division protein FtsZ, blocking its assembly and the formation of the cytokinetic Z‐ring. MciZ activity extends to other Bacillus, including pathogenic B. cereus – anthracis. MciZ is also recognized by FtsZ from S. aureus and intracellularly expressed...
Thu, 02/14/2019 - 13:14
Schematic showing the mechanisms that contribute to maintenance of the virulence plasmid in Shigella flexneri, indicating the position of its functional TA (ccdAB, gmvAT, and vapBC) and partitioning systems (parAB and stbAB) relative to the origin of replication. We showed previously that the plasmid can integrate into the chromosome Summary Members of the genus Shigella carry a large plasmid...
Wed, 02/13/2019 - 12:03
YadA is an essential virulence factor of Yersinia enterocolitica and Yersinia pseudotuberculosis. It is a well‐studied member of the trimeric autotransporter adhesins (TAAs). TAAs are exported to the bacterial cell surface by a peculiar mechanism called “Type Vc secretion”. In this work, we set out to understand the molecular mechanism of type Vc secretion, and found evidence of a hairpin...
Mon, 02/11/2019 - 13:52
The Cpx envelope stress response senses envelope protein misfolding and is required for virulence of many pathogens, including the murine gastrointestinal pathogen Citrobacter rodentium. Here, we show that the C. rodentium Cpx response promotes expression of numerous envelope‐localized proteases and chaperones – including DegP and DsbA, which are required for host infection – while inhibiting...
Mon, 02/11/2019 - 12:14
Cell‐cell communication called quorum sensing regulates numerous behaviors in bacteria, including bioluminescence, biofilm formation, and virulence. At the epicenter of quorum sensing pathways are the transcriptional regulators that respond to changes in bacterial cell density and accordingly alter gene expression. Here we show that the master quorum sensing transcription factors LuxR/HapR in...
Fri, 02/08/2019 - 11:57
Salmonella enterica genomes, as most other bacterial species, host multiple prophages whose genes can represent up to 5% of the genome content. In this review, we aim at putting into light the multiple genetic interactions that can be weaved between the host and its prophages and between prophages themselves within the host. Summary Thanks to the exponentially increasing number of publicly...
Fri, 02/08/2019 - 11:57
Enteroaggregative Escherichia coli (EAEC) is a commonly isolated human pathogen that causes mucoid diarrhoea. As EAEC virulence is controlled by the AggR master transcription factor, we use RNA‐sequencing to identify the AggR‐regulated genes in the pathogenic EAEC strain 042. We report the structure of several AggR‐dependent promoters in order to understand the mechanism of AggR‐mediated...
Fri, 02/08/2019 - 11:57
GcvB sRNA negatively regulates at least 31 target mRNAs mostly involved in amino acid metabolism in Escherichia coli and Salmonella Typhimurium. Two main regions of GcvB, referred to as R1 and R3, are required to base‐pair with described target mRNAs. Remarkably, SroC, a GcvB sRNA sponge, is of prime importance to release GcvB‐dependent repression in stationary phase of growth and in minimal...
Sun, 02/03/2019 - 11:04
Summary The bacterial envelope is a remarkable and complex compartment of the prokaryotic cell in which many essential functions take place. The article by Herrou and collaborators (Herrou et al., in press), by a clever combination of structural analysis, genetics and functional characterization in free‐living bacterial cells and during infection in animal models, elucidates a new factor,...
Mon, 01/21/2019 - 15:00
We have characterized a conserved protein of unknown function, which we have named EipA. EipA plays a role in maintenance Brucella cell envelope integrity and is genetically linked to O‐polysaccharide synthesis. EipA influences features of the envelope that are important for Brucella spp. replication and survival in the host intracellular niche. Summary Molecular components of the Brucella...
Wed, 12/12/2018 - 11:54
Salmonella is a leading cause of gastrointestinal disease worldwide. Proper temporal and spatial expression of the Salmonella SPI1 type three secretion system is critical for invasion of the host intestinal epithelium. Here, we show that two oxygen‐dependent sRNAs, FnrS and ArcZ, regulate production of the invasion machinery, tuning SPI1 expression to a particular oxygen level consistent with...
Tue, 12/11/2018 - 13:27
CalY is a biofilm protein produced in high quantities. We found that in early stationary phase, this protein is located at the cell surface where it promotes the bacterium binding to host cells. Later, in mid‐ or latestationary phase, CalY is released in the extracellular medium by the signal peptidase SipW and polymerizes as fibers promoting biofilm formation. Abstract The extracellular...
Tue, 03/06/2018 - 10:55
Summary Enteropathogenic Escherichia coli (EPEC) use a type 3 secretion system (T3SS) for injection of effectors into host cells and intestinal colonization. Here, we demonstrate that the multicargo chaperone CesT has two strictly conserved tyrosine phosphosites, Y152 and Y153, that regulate differential effector secretion in EPEC. Conservative substitution of both tyrosine residues to...
Sat, 02/17/2018 - 05:30
Summary Transcriptional silencing and anti-silencing mechanisms modulate bacterial physiology and virulence in many human pathogens. In Shigella species, many virulence plasmid genes are silenced by the histone-like nucleoid structuring protein H-NS and anti-silenced by the virulence gene regulator VirB. Despite the key role that these regulatory proteins play in Shigella virulence, their...
Mon, 02/05/2018 - 10:12
Summary Endolysins are bacteriophage-encoded peptidoglycan hydrolases that specifically degrade the bacterial cell wall at the end of the phage lytic cycle. They feature a distinct modular architecture, consisting of enzymatically active domains (EADs) and cell wall binding domains (CBDs). Structural analysis of the complete enzymes or individual domains is required for better understanding the...
Thu, 02/01/2018 - 04:45
Summary Integration of horizontally acquired genes into transcriptional networks is essential for the regulated expression of virulence in bacterial pathogens. In Salmonella enterica, expression of such genes is repressed by the nucleoid-associated protein H-NS, which recognizes and binds to AT-rich DNA. H-NS-mediated silencing must be countered by other DNA-binding proteins to allow expression...
Sat, 01/20/2018 - 05:14
Summary DNA in intracellular Salmonella enterica serovar Typhimurium relaxes during growth in the acidified (pH 4 to 5) macrophage vacuole and DNA relaxation correlates with upregulation of Salmonella genes involved in adaptation to the macrophage environment. Bacterial ATP levels did not increase during adaptation to acid pH unless the bacterium was deficient in MgtC, a cytoplasmic-membrane-...
Thu, 12/14/2017 - 09:01
Summary Genes required for fungal secondary metabolite production are usually clustered, co-regulated and expressed in stationary growth phase. Chromatin modification has an important role in co-regulation of secondary metabolite genes. The virulence factor dothistromin, a relative of aflatoxin, provided a unique opportunity to study chromatin level regulation in a highly fragmented gene cluster...
Thu, 12/07/2017 - 08:03
Abstract Listeria monocytogenes and other pathogenic bacteria modify their peptidoglycan to protect it against enzymatic attack through the host innate immune system, such as the cell wall hydrolase lysozyme. During our studies on GpsB, a late cell division protein that controls activity of the bi-functional penicillin binding protein PBP A1, we discovered that GpsB influences lysozyme resistance...
Mon, 11/20/2017 - 04:26
Abstract VieA is a cyclic diguanylate phosphodiesterase that modulates biofilm development and motility in Vibrio cholerae O1 of the classical biotype. vieA is part of an operon encoding the VieSAB signal transduction pathway that is nearly silent in V. cholerae of the El Tor biotype. A DNA pull-down assay for proteins interacting with the vieSAB promoter identified the LysR-type regulator LeuO....
Fri, 10/27/2017 - 08:20
Summary The AbcR small RNAs (sRNAs) are a fascinating example of two highly conserved sRNAs that differ tremendously at the functional level amongst organisms. From their transcriptional activation to their regulatory capabilities, the AbcR sRNAs exhibit varying characteristics in three well-studied bacteria belonging to the Rhizobiales order: the plant symbiont Sinorhizobium meliloti, the plant...
Tue, 09/19/2017 - 06:40
Summary The proton-driven flagellar motor of Salmonella enterica can accommodate a dozen MotA/B stators in a load-dependent manner. The C-terminal periplasmic domain of MotB acts as a structural switch to regulate the number of active stators in the motor in response to load change. The cytoplasmic loop termed MotAC is responsible for the interaction with a rotor protein, FliG. Here, to test if...
Thu, 09/14/2017 - 08:10
Summary In the environment and during infection, the human intestinal pathogen Vibrio cholerae must overcome noxious compounds that damage the bacterial outer membrane. The El Tor and classical biotypes of O1 V. cholerae show striking differences in their resistance to membrane disrupting cationic antimicrobial peptides (CAMPs), such as polymyxins. The classical biotype is susceptible to CAMPs,...
Fri, 09/01/2017 - 03:35
Abstract Microbial expression of genes for resistance to heavy metals and metalloids is usually transcriptionally regulated by the toxic ions themselves. Arsenic is a ubiquitous, naturally occurring toxic metalloid widely distributed in soil and groundwater. Microbes biotransform both arsenate (As(V)) and arsenite (As(III)) into more toxic methylated metabolites methylarsenite (MAs(III)) and...
Wed, 06/14/2017 - 05:45
Summary Anti-virulence (AV) compounds are a promising alternative to traditional antibiotics for fighting bacterial infections. The Type Three Secretion System (T3SS) is a well-studied and attractive AV target, given that it is widespread in more than 25 species of Gram-negative bacteria, including enterohemorrhagic E. coli (EHEC), and as it is essential for host colonization by many pathogens....
Tue, 06/06/2017 - 12:15
Summary The generation of a membrane potential (Δψ), the major constituent of the proton motive force (pmf), is crucial for ATP synthesis, transport of nutrients and flagellar rotation. Campylobacter jejuni harbors a branched electron transport chain, enabling respiration with different electron donors and acceptors. Here, we demonstrate that a relatively high Δψ is only generated in the presence...
Tue, 05/16/2017 - 06:20
Summary Through Minos transposon mutagenesis we obtained A. nidulans mutants resistant to 5-fluorouracil due to insertions into the upstream region of the uncharacterized gene nmeA, encoding a Major Facilitator Superfamily (MFS) transporter. Minos transpositions increased nmeA transcription, which is otherwise extremely low under all conditions tested. To dissect the function of NmeA we used...
Tue, 05/16/2017 - 00:10
Abstract To enable specific and tightly controlled gene expression both in-vitro and during the intracellular lifecycle of the pathogen Listeria monocytogenes, a TetR-dependent genetic induction system was developed. Highest concentration of cytoplasmic TetR and best repression of tetO-controlled genes was obtained by tetR expression from the synthetic promoter Pt17. Anhydrotetracycline (ATc) as...
Tue, 05/02/2017 - 11:59
Abstract ToxR is a transmembrane transcription factor that is essential for virulence gene expression and human colonization by Vibrio cholerae. ToxR requires its operon partner ToxS, a periplasmic integral membrane protein, for full activity. These two proteins are thought to interact through their respective periplasmic domains, ToxRp and ToxSp. In addition, ToxR is thought to be responsive to...
Fri, 04/07/2017 - 19:30
Summary Members of the multihaem cytochrome c (MCC) family such as pentahaem cytochrome c nitrite reductase (NrfA) or octahaem hydroxylamine oxidoreductase (Hao) are involved in various microbial respiratory electron transport chains. Some members of the Hao subfamily, here called εHao proteins, have been predicted from the genomes of nitrate/nitrite-ammonifying bacteria that usually lack NrfA....
Thu, 03/30/2017 - 04:45
Abstract Small RNAs (sRNAs), particularly those that act by limited base pairing with mRNAs, are part of most regulatory networks in bacteria. In many cases, the base-pairing interaction is facilitated by the RNA chaperone Hfq. However, not all bacteria encode Hfq and some base-pairing sRNAs do not require Hfq raising the possibility of other RNA chaperones. Candidates are proteins with homology...
Sat, 03/18/2017 - 11:55
SUMMARY Campylobacter jejuni helical shape is important for colonization and host interactions with straight mutants having altered biological properties. Passage on calcofluor white (CFW) resulted in C. jejuni 81-176 isolates with morphology changes: either a straight morphology from frameshift mutations and single nucleotide polymorphisms in peptidoglycan hydrolase genes pgp1 or pgp2 or a...
Thu, 03/02/2017 - 11:30
Summary LeuO is a conserved LysR-type transcription factor of pleiotropic function in Enterobacteria. Regulation of the leuO gene has been best studied in Escherichia coli and Salmonella enterica. Its expression is silenced by the nucleoid-associated proteins H-NS and StpA, autoregulated by LeuO, and in E. coli activated by the transcription regulator BglJ-RcsB. However, signals which induce leuO...
Sat, 02/18/2017 - 10:55
Summary Bacteria of the genera Bacillus and Clostridium form highly resistant spores, which in the case of some pathogens act as the infectious agents. An exosporium forms the outermost layer of some spores; it plays roles in protection, adhesion, dissemination, host targeting in pathogens, and germination control. The exosporium of the Bacillus cereus group, including the anthrax pathogen,...
Fri, 02/17/2017 - 03:20
Abstract The Escherichia coli K-12 nrf operon encodes a periplasmic nitrite reductase, the expression of which is driven from a single promoter, pnrf. Expression from pnrf is activated by the FNR transcription factor in response to anaerobiosis and further increased in response to nitrite by the response regulator proteins, NarL and NarP. FNR-dependent transcription is suppressed by the binding...
Tue, 02/14/2017 - 17:45
A common mechanism for high affinity carbohydrate uptake in microbial species is the phosphoenolpyruvate-dependent phosphotransferase system (PTS). This system consists of a shared component, EI, which is required for all PTS transport, and numerous carbohydrate uptake transporters. In V. cholerae, there are 13 distinct PTS transporters. Due to genetic redundancy within this system, the...
Fri, 01/27/2017 - 03:26
Abstract Methylation of inorganic arsenic is a central process in the organoarsenical biogeochemical cycle. Members of every kingdom have ArsM As(III) S-adenosylmethionine (SAM) methyltransferases that methylates inorganic As(III) into mono- (MAs(III)), di- (DMAs(III)) and tri- (TMAs(III)) methylarsenicals. Every characterized ArsM to date has four conserved cysteine residues. All four cysteines...
Wed, 01/18/2017 - 04:10
Summary Cyclic di-adenosine monophosphate (c-di-AMP) is a conserved nucleotide second messenger critical for bacterial growth and resistance to cell wall-active antibiotics. In Listeria monocytogenes, the sole diadenylate cyclase, DacA, is essential in rich, but not synthetic media and ΔdacA mutants are highly sensitive to the β-lactam antibiotic cefuroxime. In this study, loss of function...
Mon, 12/26/2016 - 05:31
Abstract Invasion of intestinal epithelial cells by Campylobacter jejuni is a critical step during infection of the intestine by this important human pathogen. In this study we investigated the role played by DNA supercoiling in the regulation of invasion of epithelial cells and the mechanism by which this could be mediated. A significant correlation between more relaxed DNA supercoiling and an...
Fri, 12/23/2016 - 18:48
Summary In bacteria, the RNA chaperone Hfq enables pairing of small regulatory RNAs with their target mRNAs and therefore is a key player of post-transcriptional regulation network. As a global regulator, Hfq is engaged in the adaptation to external environment, regulation of metabolism and bacterial virulence. In this study we used RNA-sequencing and quantitative proteomics (LC-MS/MS) to...

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