Vibrio cholerae TolC Is Required for Expression of the ToxR Regulon

Abstract

Vibrio cholerae is a Gram-negative bacterium that causes the enteric disease cholera. V. cholerae colonization of the human intestine is dependent on the expression of both virulence genes and environmental adaptation genes involved in antimicrobial resistance. The expression of virulence genes, including the genes encoding for the main virulence factors cholera toxin (CT) and the toxin coregulated pilus (TCP), are coordinately regulated by the ToxR regulon. Tripartite transport systems belonging to the ATP binding cassette, major facilitator, and Resistance-Nodulation-Division families are critical for V. cholerae pathogenesis. Transport systems belonging to these families contribute to myriad phenotypes including protein secretion, antimicrobial resistance and virulence. TolC plays a central role in bacterial physiology by functioning as the outer membrane pore protein for tripartite transport systems. Consistent with this, V. cholerae tolC was previously found to be required for MARTX toxin secretion and antimicrobial resistance. Herein we investigated the contribution of TolC to V. cholerae virulence. We documented that tolC was required for CT and TCP production in O1 El Tor V. cholerae . This phenotype was linked to repression of the critical ToxR regulon transcription factor aphA . Decreased aphA transcription correlated with increased expression of the LysR-family transcription factor leuO . Deletion of leuO restored aphA expression, and CT and TCP production, in a tolC mutant. The collective results document that tolC is required for ToxR regulon expression and further suggest that tolC may participate in a efflux-dependent feedback circuit to regulate virulence gene expression.

Holistic analysis of lysine acetylation in aquaculture pathogenic bacteria Vibrio alginolyticus under bile salt stress

“…For example, secretion system related genes secA, secD , secF, yajC, yidC and tolC , which prior to studies reported that secretion system genes played roles in the bacterial adhesion, thereby promoting the adhesion of V. alginolyticus to the host surface and causing bacterial infection ( 46 ). In Vibrio cholerae , the outer membrane protein TolC is necessary for the expression of toxR regulon and participates in an efflux dependent feedback loop to regulate the expression of virulence genes, MARTX toxin secretion and resistance to antimicrobial compounds present in the host ( 47 ). In this study, we also found that ToxR protein, a key transcription activator, is acetylated.…”

Vibrio cholerae RND efflux systems: mediators of stress responses, colonization and pathogenesis

“…The tolC (VC2436) coding sequence is encoded as a single, self-standing gene on the large chromosome ( Bina and Mekalanos, 2001 ). TolC’s RND pore function was inferred from experiments showing that a tolC deletion mutant exhibited the same antimicrobial resistance and virulence factor production phenotypes as an otherwise isogenic RND efflux pump negative strain that retains tolC ( Bina and Mekalanos, 2001 ; Weng et al., 2021 ). VexR, a transcriptional regulator belonging to the TetR family has been reported to positively regulate the expression of the vexRAB operon ( Bina et al., 2008 ; Taylor et al., 2015 ), while BreR, another member of the TetR family is a transcriptional regulator that represses vexCD expression ( Cerda-Maira et al., 2008 ; Cerda-Maira et al., 2013 ).…”

“…V. cholerae lacking RND efflux systems exhibits severe attenuation in infant mouse colonization which was hypothesized to result from an abundance of antimicrobial compounds in the gastrointestinal tract ( Bina et al., 2008 ). RND-mediated efflux together with outer membrane selective permeability is hypothesized to synergistically allow bacteria to overcome the cytotoxic effect of bile acids, detergents and antimicrobial peptides commonly found in the intestine ( Bina and Mekalanos, 2001 ; Bina et al., 2008 ; Weng et al., 2021 ). Competitive index experiments in which strains are compared pairwise for infant mouse colonization revealed that the vexBDH , vexBDK and RND null mutants could not be recovered from infant mice when administered at a 1:1 ratio with WT.…”

“…Separate from the strictly protective physiological function which impact colonization of the small intestine by enhancing antimicrobial resistance, RND efflux evolved to tie into virulence gene expression. CT and TCP transcription in RND-efflux deficient V. cholerae is decreased by ~70% when the bacteria are grown in laboratory conditions that induce virulence factor expression, suggesting a regulatory link between RND-mediated efflux and expression of the ToxR regulon ( Bina and Mekalanos, 2001 ; Bina et al., 2008 ; Weng et al., 2021 ). Interestingly, the contribution of individual RND efflux systems towards antimicrobial resistance mirrored their impact on virulence factor production.…”

Membrane Efflux Pumps of Pathogenic Vibrio Species: Role in Antimicrobial Resistance and Virulence

“…Similarly, the RND efflux pumps of E. coli could not function with the TolC from V. parahaemolyticus, suggesting a species-specific preference for the TolC component [71,72]. TolC in the V. cholerae O1 El Tor strain has been reported to play an essential role in the transcription of the ToxR regulon, a finding that emphasizes the importance of efflux pump-mediated regulation of virulence in pathogenic bacteria [73].…”