554 research outputs found
Cyclic Dinucleotides and the Innate Immune Response
Cyclic dinucleotides (CDNs) have been previously recognized as important secondary signaling molecules in bacteria and, more recently, in mammalian cells. In the former case, they represent secondary messengers affecting numerous responses of the prokaryotic cell, whereas in the latter, they act as agonists of the innate immune response. Remarkable new discoveries have linked these two patterns of utilization of CDNs as secondary messengers and have revealed unexpected influences they likely had on shaping human genetic variation. This Review summarizes these recent insights and provides a perspective on future unanswered questions in this exciting field
Characterization of the RpoN Regulon Reveals Differential Regulation of T6SS and New Flagellar Operons in Vibrio cholerae O37 Strain V52
The alternative sigma factor RpoN is an essential colonization factor of Vibrio cholerae and controls important cellular functions including motility and type VI secretion (T6SS). The RpoN regulon has yet to be clearly defined in T6SS-active V. cholerae isolates, which use T6SS to target both bacterial competitors and eukaryotic cells. We hypothesize that T6SS-dependent secreted effectors are co-regulated by RpoN. To systemically identify RpoN-controlled genes, we used chromatin immunoprecipitation coupled with sequencing (ChIP-Seq) and transcriptome analysis (RNA-Seq) to determine RpoN-binding sites and RpoN-controlled gene expression. There were 68 RpoN-binding sites and 82 operons positively controlled by RpoN, among which 37 operons had ChIP-identified binding sites. A consensus RpoN-binding motif was identified with a highly conserved thymine (−14) and an AT-rich region in the middle between the hallmark RpoN-recognized motif GG(−24)/GC(−12). There were seven new RpoN-dependent promoters in the flagellar regions. We identified a small RNA, flaX, downstream of the major flagellin gene flaA. Mutation of flaX substantially reduced motility. In contrast to previous results, we report that RpoN positively regulates the expression of hcp operons and vgrG3 that encode T6SS secreted proteins but has no effect on the expression of the main T6SS cluster encoding sheath and other structural components
Exopolysaccharide protects Vibrio cholerae from exogenous attacks by the type 6 secretion system
The type 6 secretion system (T6SS) is a nanomachine used by many
Gram-negative bacteria, including Vibrio cholerae, to deliver toxic
effector proteins into adjacent eukaryotic and bacterial cells. Because
the activity of the T6SS is dependent on direct contact between
cells, its activity is limited to bacteria growing on solid
surfaces or in biofilms. V. cholerae can produce an exopolysaccharide
(EPS) matrix that plays a role in adhesion and biofilm formation.
In this work, we investigated the effect of EPS production on
T6SS activity between cells. We found that EPS produced by V.
cholerae cells functions as a unidirectional protective armor that
blocks exogenous T6SS attacks without interfering with its own
T6SS functionality. This EPS armor is effective against both samespecies
and heterologous attackers. Mutations modulating the
level of EPS biosynthesis gene expression result in corresponding
modulation in V. cholerae resistance to exogenous T6SS attack.
These results provide insight into the potential role of extracellular
biopolymers, including polysaccharides, capsules, and S-layers in
protecting bacterial cells from attacks involving cell-associated
macromolecular protein machines that cannot readily diffuse
through these mechanical defenses
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MetR-Regulated Vibrio cholerae Metabolism Is Required for Virulence
LysR-type transcriptional regulators (LTTRs) are the largest, most diverse family of prokaryotic transcription factors, with regulatory roles spanning metabolism, cell growth and division, and pathogenesis. Using a sequence-defined transposon mutant library, we screened a panel of V. cholerae El Tor mutants to identify LTTRs required for host intestinal colonization. Surprisingly, out of 38 LTTRs, only one severely affected intestinal colonization in the suckling mouse model of cholera: the methionine metabolism regulator, MetR. Genetic analysis of genes influenced by MetR revealed that glyA1 and metJ were also required for intestinal colonization. Chromatin immunoprecipitation of MetR and quantitative reverse transcription-PCR (qRT-PCR) confirmed interaction with and regulation of glyA1, indicating that misregulation of glyA1 is likely responsible for the colonization defect observed in the metR mutant. The glyA1 mutant was auxotrophic for glycine but exhibited wild-type trimethoprim sensitivity, making folate deficiency an unlikely cause of its colonization defect. MetJ regulatory mutants are not auxotrophic but are likely altered in the regulation of amino acid-biosynthetic pathways, including those for methionine, glycine, and serine, and this misregulation likely explains its colonization defect. However, mutants defective in methionine, serine, and cysteine biosynthesis exhibited wild-type virulence, suggesting that these amino acids can be scavenged in vivo. Taken together, our results suggest that glycine biosynthesis may be required to alleviate an in vivo nutritional restriction in the mouse intestine; however, additional roles for glycine may exist. Irrespective of the precise nature of this requirement, this study illustrates the importance of pathogen metabolism, and the regulation thereof, as a virulence factor
Single amino acid substitutions in the N-terminus of Vibrio cholerae TcpA affect colonization, autoagglutination, and serum resistance
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74620/1/j.1365-2958.1995.mmi_17061133.x.pd
Quorum Regulated Resistance of Vibrio cholerae against Environmental Bacteriophages.
Predation by bacteriophages can significantly influence the population structure of bacterial communities. Vibrio cholerae the causative agent of cholera epidemics interacts with numerous phages in the aquatic ecosystem, and in the intestine of cholera patients. Seasonal epidemics of cholera reportedly collapse due to predation of the pathogen by phages. However, it is not clear how sufficient number of the bacteria survive to seed the environment in the subsequent epidemic season. We found that bacterial cell density-dependent gene expression termed "quorum sensing" which is regulated by signal molecules called autoinducers (AIs) can protect V. cholerae against predatory phages. V. cholerae mutant strains carrying inactivated AI synthase genes were significantly more susceptible to multiple phages compared to the parent bacteria. Likewise when mixed cultures of phage and bacteria were supplemented with exogenous autoinducers CAI-1 or AI-2 produced by recombinant strains carrying cloned AI synthase genes, increased survival of V. cholerae and a decrease in phage titer was observed. Mutational analyses suggested that the observed effects of autoinducers are mediated in part through the quorum sensing-dependent production of haemaglutinin protease, and partly through downregulation of phage receptors. These results have implication in developing strategies for phage mediated control of cholera
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