Vibrio cholerae VttR A and VttR B Regulatory Influences Extend beyond the Type 3 Secretion System Genomic Island

A subset of non-O1/non-O139 serogroup strains ofVibrio cholerae cause disease using type 3 secretion system (T3SS)-mediated mechanisms. An ∼50-kb genomic island carries genes encoding the T3SS structural apparatus, effector proteins, and two transmembrane transcriptional regulators, VttRA and VttRB , which are ToxR homologues. Previous experiments demonstrated that VttRA and VttRB are necessary for colonizationin vivo and promote bile-dependent T3SS gene expressionin vitro . To better understand the scope of genes that are potential targets of VttRA and VttRB regulation, we performed deep RNA sequencing using O39 serogroup strain AM-19226 and derivatives carrying deletions invttR A andvttR B grown in bile. Comparison of the transcript profiles from ΔvttR A and ΔvttR B mutant strains to the isogenic parent strain confirmed that VttRA and VttRB regulate expression of some T3SS island genes and provided additional information about relative expression levels and operon organization. Interestingly, the data also suggested that additional genes, located outside the T3SS island and encoding functions involved in motility, chemotaxis, type 6 secretion, transcriptional regulation, and stress responses, may also by regulated by VttRA and VttRB . We verified transcript levels for selected genes by quantitative reverse transcription (RT)-PCR and then focused additional studies on motility and biofilm formation. The results suggest that VttRA and VttRB act as part of a complex transcriptional network that coordinates virulence gene expression with multiple cellular phenotypes. VttRA and VttRB therefore represent horizontally acquired transcriptional regulators with the ability to influence global gene expression in addition to modulating gene expression within the T3SS genomic island.