PROJECT SUMMARY/ABSTRACT Cholera is an acute diarrheal disease that affects 3-5 million people each year. Cholera iscaused by Vibrio cholerae; a Gram-negative bacterium and facultative human pathogen that is native toaquatic ecosystems around the world. The worldwide distribution of V. cholerae makes it a significanthealth threat anytime human populations lack access to clean water and good sanitation; a factexemplified by the ongoing cholera epidemics in Haiti and Yemen. The devastating consequences ofcholera combined with the rapidity with which it can spread, evolving antibiotic resistance, and its abilityto persist in aquatic ecosystems, have underscored the need for the development of novel approachesto limit the spread of this epidemic disease. We recently discovered that cellular metabolites producedby V. cholerae can serve as environmental cues to downregulate the production of the virulence factorscholera toxin and the toxin coregulated pilus. In this proposal, we will investigate how cell metabolitesand other environmental signals modulate transcriptional responses involved in the V. cholerae lifecycle. Two specific aims are proposed. The first aim will characterize the role of the LysR-familytranscriptional regulator LeuO in V. cholerae pathogenesis and environmental adaptation. The secondaim will investigate how the membrane-bound transcriptional regulator ToxR senses and responds toenvironmental stimuli. Determining the regulatory mechanisms and environmental cues that modulateadaptive responses will illuminate important aspects of V. cholerae pathogenesis, provide a betterunderstanding of the factors that contribute to the epidemic spread, and may lead to the developmentof novel approaches to combat the disease cholera.