ToxT Regulon Is Nonessential for Vibrio cholerae Colonization in Adult Mice

Carbon source, cell density, and the microbial community control inhibition of V. cholerae surface colonization by environmental nitrate

The intestinal diarrheal pathogen Vibrio cholerae colonizes the host terminal ileum, a microaerophilic, glucose-poor, nitrate-rich environment. In this environment, V. cholerae respires nitrate and increases transport and utilization of alternative carbon sources via the cAMP receptor protein (CRP), a transcription factor that is active during glucose scarcity. Here, we show that V. cholerae nitrate respiration in aerated cultures is under control of CRP and, therefore, glucose availability. V. cholerae nitrate respiration results in extracellular accumulation of nitrite because V. cholerae does not possess the machinery for nitrite reduction. This nitrite inhibits V. cholerae biofilm formation via an as-yet unelucidated mechanism that depends on the high cell density master regulator HapR. The genome of Paracoccus aminovorans, an intestinal microbe identified in the microbiome of cholera patients that has been shown to enhance V. cholerae biofilm accumulation in the neonatal mouse gut, encodes enzymes that reduce nitrite to nitrogen gas. We report that, in nitrate-supplemented co-cultures, P. aminovorans metabolizes the nitrite generated by V. cholerae and, thereby, enhances V. cholerae surface accumulation. We propose that V. cholerae biofilm formation in the host intestine is limited by nitrite production but can be rescued by intestinal microbes such as P. aminovorans that have the capacity to metabolize nitrite. Such microbes increase V. cholerae colonization of the host ileum and predispose to symptomatic infection.IMPORTANCEVibrio cholerae colonizes the terminal ileum where both oxygen and nitrate are available as terminal electron acceptors. V. cholerae biofilm formation is inhibited by nitrate due to its conversion to nitrite during V. cholerae respiration. When co-cultured with a microbe that can further reduce nitrite, V. cholerae surface accumulation in the presence of nitrate is rescued. The contribution of biofilm formation to ileal colonization depends on the composition of the microbiota. We propose that the intestinal microbiota predisposes mammalian hosts to cholera by consuming the nitrite generated by V. cholerae in the terminal ileum. Differences in the intestinal abundance of nitrite-reducing microbes may partially explain the differential susceptibility of humans to cholera and the resistance of non-human mammalian models to intestinal colonization with V. cholerae.

Carbon source, cell density, and the microbial community control inhibition of V. cholerae surface colonization by environmental nitrate

The intestinal diarrheal pathogen Vibrio cholerae colonizes the host terminal ileum, a microaerophilic, glucose-poor, nitrate-rich environment. In this environment, V. cholerae respires nitrate and increases transport and utilization of alternative carbon sources via the cAMP receptor protein (CRP), a transcription factor that is active during glucose scarcity. Here we show that V. cholerae nitrate respiration in aerated cultures is under control of CRP and, therefore, glucose availability. V. cholerae nitrate respiration results in extracellular accumulation of nitrite because V. cholerae does not possess the machinery for nitrite reduction. This nitrite inhibits V. cholerae biofilm formation via an as yet unelucidated mechanism that depends on the high cell density master regulator HapR. The genome of Paracoccus aminovorans , an intestinal microbe shown to enhance V. cholerae biofilm accumulation in the neonatal mouse gut and predispose household contacts to cholera, encodes enzymes that reduce nitrite to nitrogen gas. We report that, in nitrate-supplemented co-cultures, P. aminovorans metabolizes the nitrite generated by V. cholerae and, thereby, enhances V. cholerae surface accumulation. We propose that V. cholerae biofilm formation in the host intestine is limited by nitrite production but can be rescued by intestinal microbes such as P. aminovorans that have the capacity to metabolize nitrite. Such microbes increase V. cholerae colonization of the host ileum and predispose to infection.

Importance

V. cholerae colonizes the terminal ileum where both oxygen and nitrate are available as terminal electron acceptors. V. cholerae biofilm formation is inhibited by nitrate due to its conversion to nitrite during V. cholerae respiration. When co-cultured with a microbe that can further reduce nitrite, V. cholerae surface accumulation in the presence of nitrate is rescued. The contribution of biofilm formation to ileal colonization depends on the composition of the microbiota. We propose that the intestinal microbiota predisposes mammalian hosts to cholera by consuming the nitrite generated by V. cholerae in the terminal ileum. Differences in the intestinal abundance of nitrite-reducing microbes may partially explain the differential susceptibility of humans to cholera and the resistance of non-human mammalian models to intestinal colonization with V. cholerae .

Precisely Controlling Csr sRNA Levels by MshH Enhances Vibrio cholerae Colonization in Adult Mice

Vibrio cholerae is the causative agent of cholera. Effective intestinal colonization is a key step for V. cholerae pathogenicity and transmission. In this study, we found that deleting mshH, a homolog of the Escherichia coli CsrD protein, caused a V. cholerae colonization defect in the intestine of adult mice. By analyzing the RNA levels of CsrB, CsrC, and CsrD, we found that deleting mshH increased the levels of CsrB and CsrD but decreased the level of CsrC. However, deleting CsrB and -D not only recovered the mshH deletion mutant colonization defect but also recovered CsrC to wild-type levels. These results indicated that controlling the RNA levels of CsrB, -C, and -D is crucial for V. cholerae colonization of adult mice. We further demonstrated that the RNA levels of CsrB and CsrD were mainly controlled by MshH-dependent degradation, yet the level of CsrC was mainly determined by the CsrA-dependent stabilization. Our data show that V. cholerae differentially controls CsrB, -C, and -D abundance through the MshH-CsrB/C/D-CsrA regulatory pathway to finely regulate the activity of CsrA targets such as ToxR, so as to better survive in adult mouse intestine. IMPORTANCE The ability of V. cholerae to colonize the intestine is a key factor for its fitness and transmissibility between hosts. Here, we investigated the mechanism of V. cholerae colonization of adult mammal intestine and found that precisely controlling the CsrB, -C, and -D contents by MshH and CsrA plays an essential role for V. cholerae colonization in the adult mouse intestine. These data expand our knowledge on the mechanism of V. cholerae controlling the RNA level of CsrB, -C, and -D and highlight the importance that the different strategies used by V. cholerae to regulate the RNA level of CsrB, -C, and -D confer the bacterium with a survival advantage.