scholarly journals The Cpx System Regulates Virulence Gene Expression in Vibrio cholerae

2015 ◽  
Vol 83 (6) ◽  
pp. 2396-2408 ◽  
Author(s):  
Nicole Acosta ◽  
Stefan Pukatzki ◽  
Tracy L. Raivio
Keyword(s):  
Vibrio Cholerae ◽  
Response Regulator ◽  
Bacterial Species ◽  
Virulence Gene ◽  
Receptor Protein ◽  
Virulence Determinants ◽  
Content Type ◽  
Virulence Gene Expression ◽  
Envelope Stress ◽  
El Tor

Bacteria possess signal transduction pathways capable of sensing and responding to a wide variety of signals. The Cpx envelope stress response, composed of the sensor histidine kinase CpxA and the response regulator CpxR, senses and mediates adaptation to insults to the bacterial envelope. The Cpx response has been implicated in the regulation of a number of envelope-localized virulence determinants across bacterial species. Here, we show that activation of the Cpx pathway inVibrio choleraeEl Tor strain C6706 leads to a decrease in expression of the major virulence factors in this organism, cholera toxin (CT) and the toxin-coregulated pilus (TCP). Our results indicate that this occurs through the repression of production of the ToxT regulator and an additional upstream transcription factor, TcpP. The effect of the Cpx response on CT and TCP expression is mostly abrogated in a cyclic AMP receptor protein (CRP) mutant, although expression of thecrpgene is unaltered. Since TcpP production is controlled by CRP, our data suggest a model whereby the Cpx response affects CRP function, which leads to diminished TcpP, ToxT, CT, and TCP production.

scholarly journals The Fatty Acid Regulator FadR Influences the Expression of the Virulence Cascade in the El Tor Biotype of Vibrio cholerae by Modulating the Levels of ToxT via Two Different Mechanisms

2017 ◽  
Vol 199 (7) ◽  
Author(s):  
Gabriela Kovacikova ◽  
Wei Lin ◽  
Ronald K. Taylor ◽  
Karen Skorupski
Keyword(s):  
Gene Expression ◽  
Vibrio Cholerae ◽  
Virulence Gene ◽  
Enteric Bacteria ◽  
Posttranslational Regulation ◽  
Content Type ◽  
Virulence Gene Expression ◽  
Expression Of Genes ◽  
El Tor ◽  
Virulence Regulator

ABSTRACT FadR is a master regulator of fatty acid (FA) metabolism that coordinates the pathways of FA degradation and biosynthesis in enteric bacteria. We show here that a ΔfadR mutation in the El Tor biotype of Vibrio cholerae prevents the expression of the virulence cascade by influencing both the transcription and the posttranslational regulation of the master virulence regulator ToxT. FadR is a transcriptional regulator that represses the expression of genes involved in FA degradation, activates the expression of genes involved in unsaturated FA (UFA) biosynthesis, and also activates the expression of two operons involved in saturated FA (SFA) biosynthesis. Since FadR does not bind directly to the toxT promoter, we determined whether the regulation of any of its target genes indirectly influenced ToxT. This was accomplished by individually inserting a double point mutation into the FadR-binding site in the promoter of each target gene, thereby preventing their activation or repression. Although preventing FadR-mediated activation of fabA, which encodes the enzyme that carries out the first step in UFA biosynthesis, did not significantly influence either the transcription or the translation of ToxT, it reduced its levels and prevented virulence gene expression. In the mutant strain unable to carry out FadR-mediated activation of fabA, expressing fabA ectopically restored the levels of ToxT and virulence gene expression. Taken together, the results presented here indicate that V. cholerae FadR influences the virulence cascade in the El Tor biotype by modulating the levels of ToxT via two different mechanisms. IMPORTANCE Fatty acids (FAs) play important roles in membrane lipid homeostasis and energy metabolism in all organisms. In Vibrio cholerae, the causative agent of the acute intestinal disease cholera, they also influence virulence by binding into an N-terminal pocket of the master virulence regulator, ToxT, and modulating its activity. FadR is a transcription factor that coordinately controls the pathways of FA degradation and biosynthesis in enteric bacteria. This study identifies a new link between FA metabolism and virulence in the El Tor biotype by showing that FadR influences both the transcription and posttranslational regulation of the master virulence regulator ToxT by two distinct mechanisms.

scholarly journals Use of a Phosphorylation Site Mutant To Identify Distinct Modes of Gene Repression by the Control of Virulence Regulator (CovR) in Streptococcus pyogenes

2017 ◽  
Vol 199 (18) ◽  
Author(s):  
Nicola Horstmann ◽  
Pranoti Sahasrabhojane ◽  
Hui Yao ◽  
Xiaoping Su ◽  
Samuel A. Shelburne
Keyword(s):  
Gene Expression ◽  
Streptococcus Pyogenes ◽  
Response Regulator ◽  
Phosphorylation Site ◽  
Virulence Gene ◽  
Content Type ◽  
Virulence Gene Expression ◽  
Superficial Skin ◽  
Virulence Regulator ◽  
The Impact

ABSTRACT Control of the virulence regulator/sensor kinase (CovRS) two-component system (TCS) serves as a model for investigating the impact of signaling pathways on the pathogenesis of Gram-positive bacteria. However, the molecular mechanisms by which CovR, an OmpR/PhoB family response regulator, controls virulence gene expression are poorly defined, partly due to the labile nature of its aspartate phosphorylation site. To better understand the regulatory effect of phosphorylated CovR, we generated the phosphorylation site mutant strain 10870-CovR-D53E, which we predicted to have a constitutive CovR phosphorylation phenotype. Interestingly, this strain showed CovR activity only for a subset of the CovR regulon, which allowed for classification of CovR-influenced genes into D53E-regulated and D53E-nonregulated groups. Inspection of the promoter sequences of genes belonging to each group revealed distinct promoter architectures with respect to the location and number of putative CovR-binding sites. Electrophoretic mobility shift analysis demonstrated that recombinant CovR-D53E protein retains its ability to bind promoter DNA from both CovR-D53E-regulated and -nonregulated groups, implying that factors other than mere DNA binding are crucial for gene regulation. In fact, we found that CovR-D53E is incapable of dimerization, a process thought to be critical to OmpR/PhoB family regulator function. Thus, our global analysis of CovR-D53E indicates dimerization-dependent and dimerization-independent modes of CovR-mediated repression, thereby establishing distinct mechanisms by which this critical regulator coordinates virulence gene expression. IMPORTANCE Streptococcus pyogenes causes a wide variety of diseases, ranging from superficial skin and throat infections to life-threatening invasive infections. To establish these various disease manifestations, Streptococcus pyogenes requires tightly coordinated production of its virulence factor repertoire. Here, the response regulator CovR plays a crucial role. As an OmpR/PhoB family member, CovR is activated by phosphorylation on a conserved aspartate residue, leading to protein dimerization and subsequent binding to operator sites. Our transcriptome analysis using the monomeric phosphorylation mimic mutant CovR-D53E broadens this general notion by revealing dimerization-independent repression of a subset of CovR-regulated genes. Combined with promoter analyses, these data suggest distinct mechanisms of CovR transcriptional control, which allow for differential expression of virulence genes in response to environmental cues.

scholarly journals MroQ Is a Novel Abi-Domain Protein That Influences Virulence Gene Expression in Staphylococcus aureus via Modulation of Agr Activity

2019 ◽  
Vol 87 (5) ◽  
Author(s):  
Stephanie Marroquin ◽  
Brittney Gimza ◽  
Brooke Tomlinson ◽  
Michelle Stein ◽  
Andrew Frey ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Virulence Gene ◽  
Transcriptional Analysis ◽  
Data Sets ◽  
Virulence Determinants ◽  
Sequencing Data ◽  
Content Type ◽  
Virulence Gene Expression ◽  
Function Mechanism ◽  
Family Protein

ABSTRACT Numerous factors have, to date, been identified as playing a role in the regulation of Agr activity in Staphylococcus aureus, including transcription factors, antisense RNAs, and host elements. Herein we investigated the product of SAUSA300_1984 (termed MroQ), a transmembrane Abi-domain/M79 protease-family protein, as a novel effector of this system. Using a USA300 mroQ mutant, we observed a drastic reduction in proteolysis, hemolysis, and pigmentation that was fully complementable. This appears to result from diminished agr activity, as transcriptional analysis revealed significant decreases in expression of both RNAII and RNAIII in the mroQ mutant. Such effects appear to be direct, rather than indirect, as known agr effectors demonstrated limited alterations in their activity upon mroQ disruption. A comparison of RNA sequencing data sets for both mroQ and agr mutants revealed a profound overlap in their regulomes, with the majority of factors affected being known virulence determinants. Importantly, the preponderance of alterations in expression were more striking in the agr mutant, indicating that MroQ is necessary, but not sufficient, for Agr function. Mechanism profiling revealed that putative residues for metalloprotease activity within MroQ are required for its Agr-controlling effect; however, this was not wielded at the level of AgrD processing. Virulence assessment demonstrated that both mroQ and agr mutants exhibited increased formation of renal abscesses but decreased skin abscess formation alongside diminished dermonecrosis. Collectively, we present the characterization of a novel agr effector in S. aureus which would appear to be a direct regulator, potentially functioning via interaction with the AgrC histidine kinase.

scholarly journals Integration of Cyclic di-GMP and Quorum Sensing in the Control ofvpsTandaphAin Vibrio cholerae

2011 ◽  
Vol 193 (22) ◽  
pp. 6331-6341 ◽  
Author(s):  
Disha Srivastava ◽  
Rebecca C. Harris ◽  
Christopher M. Waters
Keyword(s):  
Quorum Sensing ◽  
Binding Site ◽  
Vibrio Cholerae ◽  
Biofilm Formation ◽  
Virulence Gene ◽  
Transcriptional Activator ◽  
Transcriptional Regulators ◽  
Content Type ◽  
Virulence Gene Expression ◽  
Signaling Systems

Vibrio choleraetransitions between aquatic environmental reservoirs and infection in the gastrointestinal tracts of human hosts. The second-messenger molecule cyclic di-GMP (c-di-GMP) and quorum sensing (QS) are important signaling systems that enableV. choleraeto alternate between these distinct environments by controlling biofilm formation and virulence factor expression. Here we identify a conserved regulatory mechanism inV. choleraethat integrates c-di-GMP and QS to control the expression of two transcriptional regulators:aphA, an activator of virulence gene expression and an important regulator of the quorum-sensing pathway, andvpsT, a transcriptional activator that induces biofilm formation. Surprisingly,aphAexpression was induced by c-di-GMP. Activation of bothaphAandvpsTby c-di-GMP requires the transcriptional activator VpsR, which binds to c-di-GMP. The VpsR binding site at each of these promoters overlaps with the binding site of HapR, the master QS regulator at high cell densities. Our results suggest thatV. choleraecombines information conveyed by QS and c-di-GMP to appropriately respond and adapt to divergent environments by modulating the expression of key transcriptional regulators.

scholarly journals A Quinazoline-2,4-Diamino Analog Suppresses Vibrio cholerae Flagellar Motility by Interacting with Motor Protein PomB and Induces Envelope Stress

2013 ◽  
Vol 57 (8) ◽  
pp. 3950-3959 ◽  
Author(s):  
Hongxia Wang ◽  
Li Zhang ◽  
Anisia J. Silva ◽  
Jorge A. Benitez
Keyword(s):  
Cholera Toxin ◽  
Vibrio Cholerae ◽  
Motor Protein ◽  
Polar Flagellum ◽  
Flagellar Motility ◽  
Extracellular Rna ◽  
Content Type ◽  
Envelope Stress ◽  
Causative Agents ◽  
El Tor

ABSTRACTVibrio choleraestrains of serogroups O1 and O139, the causative agents of the diarrheal illness cholera, express a single polar flagellum powered by sodium motive force and require motility to colonize and spread along the small intestine. In a previous study, we described a high-throughput assay for screening for small molecules that selectively inhibit bacterial motility and identified a family of quinazoline-2,4-diamino analogs (Q24DAs) that (i) paralyzed the sodium-driven polar flagellum ofVibriosand (ii) diminished cholera toxin secreted by El Tor biotypeV. cholerae. In this study, we provide evidence that a Q24DA paralyzes the polar flagellum by interacting with the motor protein PomB. Inhibition of motility with the Q24DA enhanced the transcription of the cholera toxin genes in both biotypes. We also show that the Q24DA interacts with outer membrane protein OmpU and other porins to induce envelope stress and expression of the extracellular RNA polymerase sigma factor σE. We suggest that Q24DA-induced envelope stress could affect the correct folding, assembly, and secretion of pentameric cholera toxin in El Tor biotypeV. choleraeindependently of its effect on motility.

scholarly journals A Genome-Wide Screen Reveals that the Vibrio cholerae Phosphoenolpyruvate Phosphotransferase System Modulates Virulence Gene Expression

2015 ◽  
Vol 83 (9) ◽  
pp. 3381-3395 ◽  
Author(s):  
Qiyao Wang ◽  
Yves A. Millet ◽  
Michael C. Chao ◽  
Jumpei Sasabe ◽  
Brigid M. Davis ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cholera Toxin ◽  
Vibrio Cholerae ◽  
Insertion Site ◽  
Virulence Gene ◽  
Loss Of Function ◽  
Phosphotransferase System ◽  
Content Type ◽  
Virulence Gene Expression ◽  
A Genome

Diverse environmental stimuli and a complex network of regulatory factors are known to modulate expression ofVibrio cholerae's principal virulence factors. However, there is relatively little known about how metabolic factors impinge upon the pathogen's well-characterized cascade of transcription factors that induce expression of cholera toxin and the toxin-coregulated pilus (TCP). Here, we used a transposon insertion site (TIS) sequencing-based strategy to identify new factors required for expression oftcpA, which encodes the major subunit of TCP, the organism's chief intestinal colonization factor. Besides identifying most of the genes known to modulatetcpAexpression, the screen yieldedptsIandptsH, which encode the enzyme I (EI) and Hpr components of theV. choleraephosphoenolpyruvate phosphotransferase system (PTS). In addition to reduced expression of TcpA, strains lacking EI, Hpr, or the associated EIIAGlcprotein produced less cholera toxin (CT) and had a diminished capacity to colonize the infant mouse intestine. The PTS modulates virulence gene expression by regulating expression oftcpPHandaphAB, which themselves control expression oftoxT, the central activator of virulence gene expression. One mechanism by which PTS promotes virulence gene expression appears to be by modulating the amounts of intracellular cyclic AMP (cAMP). Our findings reveal that theV. choleraePTS is an additional modulator of the ToxT regulon and demonstrate the potency of loss-of-function TIS sequencing screens for defining regulatory networks.

scholarly journals A Vibrio cholerae LysR Homolog, AphB, Cooperates with AphA at the tcpPH Promoter To Activate Expression of the ToxR Virulence Cascade

1999 ◽  
Vol 181 (14) ◽  
pp. 4250-4256 ◽  
Author(s):  
Gabriela Kovacikova ◽  
Karen Skorupski
Keyword(s):  
Vibrio Cholerae ◽  
Virulence Genes ◽  
Virulence Gene ◽  
Growth Conditions ◽  
Culture Conditions ◽  
Virulence Gene Expression ◽  
Environmental Stimuli ◽  
High Level ◽  
El Tor

ABSTRACT We describe here a new member of the LysR family of transcriptional regulators, AphB, which is required for activation of the Vibrio cholerae ToxR virulence cascade. AphB activates the transcription of the tcpPH operon in response to environmental stimuli, and this process requires cooperation with a second protein, AphA. The expression of neither aphA or aphB is strongly regulated by environmental stimuli, raising the possibility that the activities of the proteins themselves may be influenced under various conditions. Strains of the El Tor biotype of V. choleraetypically exhibit lower expression of ToxR-regulated virulence genes in vitro than classical strains and require specialized culture conditions (AKI medium) to induce high-level expression. We show here that expression of aphB from the tac promoter in El Tor biotype strains dramatically increases virulence gene expression to levels similar to those observed in classical strains under all growth conditions examined. These results suggest that AphB plays a role in the differential regulation of virulence genes between the two disease-causing biotypes.

scholarly journals Bicarbonate Induces Vibrio cholerae Virulence Gene Expression by Enhancing ToxT Activity

2009 ◽  
Vol 77 (9) ◽  
pp. 4111-4120 ◽  
Author(s):  
Basel H. Abuaita ◽  
Jeffrey H. Withey
Keyword(s):  
Gene Expression ◽  
Carbonic Anhydrase ◽  
Vibrio Cholerae ◽  
Regulatory Protein ◽  
Virulence Gene ◽  
Chemical Stimulus ◽  
High Concentration ◽  
Virulence Gene Expression ◽  
Regulatory Cascade ◽  
El Tor

ABSTRACT Vibrio cholerae is a gram-negative bacterium that is the causative agent of cholera, a severe diarrheal illness. The two biotypes of V. cholerae O1 capable of causing cholera, classical and El Tor, require different in vitro growth conditions for induction of virulence gene expression. Growth under the inducing conditions or infection of a host initiates a complex regulatory cascade that results in production of ToxT, a regulatory protein that directly activates transcription of the genes encoding cholera toxin (CT), toxin-coregulated pilus (TCP), and other virulence genes. Previous studies have shown that sodium bicarbonate induces CT expression in the V. cholerae El Tor biotype. However, the mechanism for bicarbonate-mediated CT induction has not been defined. In this study, we demonstrate that bicarbonate stimulates virulence gene expression by enhancing ToxT activity. Both the classical and El Tor biotypes produce inactive ToxT protein when they are cultured statically in the absence of bicarbonate. Addition of bicarbonate to the culture medium does not affect ToxT production but causes a significant increase in CT and TCP expression in both biotypes. Ethoxyzolamide, a potent carbonic anhydrase inhibitor, inhibits bicarbonate-mediated virulence induction, suggesting that conversion of CO2 into bicarbonate by carbonic anhydrase plays a role in virulence induction. Thus, bicarbonate is the first positive effector for ToxT activity to be identified. Given that bicarbonate is present at high concentration in the upper small intestine where V. cholerae colonizes, bicarbonate is likely an important chemical stimulus that V. cholerae senses and that induces virulence during the natural course of infection.

scholarly journals The Vibrio cholerae Cpx Envelope Stress Response Senses and Mediates Adaptation to Low Iron

2014 ◽  
Vol 197 (2) ◽  
pp. 262-276 ◽  
Author(s):  
Nicole Acosta ◽  
Stefan Pukatzki ◽  
Tracy L. Raivio
Keyword(s):  
Vibrio Cholerae ◽  
Stress Responses ◽  
Bacterial Species ◽  
Membrane Pore ◽  
Toxic Compounds ◽  
Content Type ◽  
Major Function ◽  
Pathway Activation ◽  
Envelope Stress ◽  
Cpx Pathway

The Cpx pathway, a two-component system that employs the sensor histidine kinase CpxA and the response regulator CpxR, regulates crucial envelope stress responses across bacterial species and affects antibiotic resistance. To characterize the CpxR regulon inVibrio cholerae, the transcriptional profile of the pandemicV. choleraeEl Tor C6706 strain was examined upon overexpression ofcpxR. Our data show that the Cpx regulon ofV. choleraeis enriched in genes encoding membrane-localized and transport proteins, including a large number of genes known or predicted to be iron regulated. Activation of the Cpx pathway further led to the expression of TolC, the major outer membrane pore, and of components of two RND efflux systems inV. cholerae. We show that iron chelation, toxic compounds, or deletion of specific RND efflux components leads to Cpx pathway activation. Furthermore, mutations that eliminate the Cpx response or members of its regulon result in growth phenotypes in the presence of these inducers that, together with Cpx pathway activation, are partially suppressed by iron. Cumulatively, our results suggest that a major function of the Cpx response inV. choleraeis to mediate adaptation to envelope perturbations caused by toxic compounds and the depletion of iron.

scholarly journals Modulation of Expression of the ToxR Regulon in Vibrio cholerae by a Member of the Two-Component Family of Response Regulators

1998 ◽  
Vol 66 (12) ◽  
pp. 5854-5861 ◽  
Author(s):  
Sandy M. Wong ◽  
Patricia A. Carroll ◽  
Laurence G. Rahme ◽  
Frederick M. Ausubel ◽  
Stephen B. Calderwood
Keyword(s):  
Gene Expression ◽  
Vibrio Cholerae ◽  
Virulence Factors ◽  
Bacterial Species ◽  
Virulence Gene ◽  
Response Regulators ◽  
Key Factors ◽  
Virulence Gene Expression ◽  
The Family ◽  
Two Component

ABSTRACT The ToxRS system in Vibrio cholerae plays a central role in the modulation of virulence gene expression in response to environmental stimuli. An integration of multiple signalling inputs mediated by ToxR, -S, and -T controls virulence gene expression leading to cholera toxin (CT) production. Recently, we identified a new virulence locus, varA (virulence associated regulator), in classical V. cholerae O1 that positively controls transcription of tcpA, the major subunit of the toxin-coregulated pilus (TCP) and the production of CT, two key factors in cholera pathogenesis. The varA locus is a homolog ofgacA (originally described for the soil organismPseudomonas fluorescens), which encodes a conserved global regulator belonging to the family of two-component signal transducing molecules. GacA homologs in a number of diverse gram-negative pathogenic bacterial species have been implicated in controlling the production of diverse virulence factors.varA mutants showed reduced levels of tcpAmessage and TcpA protein, lacked visible signs of autoagglutination (a phenotype associated with functional TCP), produced decreased levels of CT, and were attenuated in colonizing infant mice. Transcription ofvarA appears to be independent of ToxR, and overexpression of the regulators tcpPH and toxT from plasmids in the varA mutant restored wild-type levels of CT production and the ability to autoagglutinate. varArepresents an additional modulating factor in the coordinate expression of virulence factors in V. cholerae.

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