PhoB regulates both environmental and virulence gene expression in Vibrio cholerae

Vibrio cholerae is a facultative pathogen that thrives in two nutritionally disparate environments, aquatic and human small intestine. Phosphate (P(i) ) is an essential nutrient that is limited in aquatic ecosystems and of unknown availability in the small intestine. Here, we show that the P(i) (Pho) regulon, which is controlled by the P(i)-specific transporter (Pst) and two-component system PhoBR, is required for V. cholerae survival in both environments, though for differing reasons. While induction of P(i) acquisition systems including Pst is critical for survival in the aquatic environment, regulation of virulence genes by PhoB and not P(i) transport per se is required for colonization of the small intestine. We show that PhoB regulates virulence genes by directly controlling expression of a key upstream transcriptional regulator, tcpPH. Thus, the Pho regulon includes virulence genes and represents a diverse gene set essential to pathogenic V. cholerae throughout its life cycle.

Roles of cyclic diguanylate in the regulation of bacterial pathogenesis

Cyclic diguanylate (c-di-GMP) is a bacterial second messenger of growing recognition involved in the regulation of a number of complex physiological processes. This review describes the biosynthesis and hydrolysis of c-di-GMP and several mechanisms of regulation of c-di-GMP metabolism. The contribution of c-di-GMP to regulating biofilm formation and motility, processes that affect pathogenesis of many bacteria, is described, as is c-di-GMP regulation of virulence gene expression. Finally, ways in which c-di-GMP may mediate these regulatory effects are proposed.

PilZ domain proteins bind cyclic diguanylate and regulate diverse processes in Vibrio cholerae

Cyclic diguanylate (c-di-GMP) is an allosteric activator and second messenger implicated in the regulation of a variety of biological processes in diverse bacteria. In Vibrio cholerae, c-di-GMP has been shown to inversely regulate biofilm-specific and virulence gene expression, suggesting that c-di-GMP signaling is important for the transition of V. cholerae from the environment to the host. However, the mechanism behind this regulation remains unknown. Recently, it was proposed that the PilZ protein domain represents a c-di-GMP-binding domain. Here we show that V. cholerae PilZ proteins bind c-di-GMP specifically and are involved in the regulation of biofilm formation, motility, and virulence. These findings confirm a role for PilZ proteins as c-di-GMP-sensing proteins within the c-di-GMP signaling network.