PROJECT SUMMARY/ABSTRACT Cholera is an acute diarrheal disease that is caused by Vibrio cholerae. V. cholerae is a Gram- negative bacterium and facultative human pathogen that is native to aquatic ecosystems around the world. The worldwide distribution of V. cholerae makes it a significant health threat anytime human populations lack access to clean water; a fact exemplified by the ongoing cholera epidemic in Yemen. The devastating consequences of cholera combined with its ability to persist in the environment have accentuated the need for new therapeutic approaches to limit the epidemic spread of this disease. We recently discovered that RND-mediated efflux is linked to V. cholerae adaptive responses. In the absence of RND-mediated efflux unknown cell metabolites accumulate in V. cholerae can serve as cues to repress V. cholerae virulence. The overarching goal of this proposal is to identify these metabolites and characterize the role of the V. cholerae RND transporters in their efflux. Two specific aims are proposed. The first aim will identify the metabolites that are substrates of the RND efflux systems. The second aim will identify regulators of the RND efflux systems and determine how the metabolites affect the expression of the RND systems. Determining the regulatory mechanisms and environmental cues that modulate V. cholerae adaptive responses will illuminate important aspects of V. cholerae pathogenesis, provide a better understanding of the factors that contribute to epidemic spread, and may lead to the development of novel approaches to combat the disease cholera.