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Abstract
Quorum sensing (QS) is a mechanism of chemical communication that bacteria use to monitor cell-population density and coordinate group behaviors. QS relies on the production, detection, and group-wide response to extracellular signal molecules called autoinducers. Vibrio cholerae employs parallel QS circuits that converge into a shared signaling pathway. At high cell density, the CqsS and LuxPQ QS receptors detect the intra-genus and inter-species autoinducers CAI-1 and AI-2, respectively, to repress virulence factor production and biofilm formation. In this work, natural and synthetic mechanisms of QS regulation are explored for the purpose of better understanding QS signal transduction and for possible applications in controlling V. cholerae virulence. First, this thesis shows that positive feedback, mediated by the QS pathway, increases CqsS but not LuxQ levels during the transition into QS-mode, which amplifies the CAI-1 input into the pathway relative to the AI-2 input. Asymmetric feedback on CqsS enables responses exclusively to the CAI-1 autoinducer. Because CqsS exhibits the dominant QS signaling role in V. cholerae, agonism of CqsS with synthetic compounds could be used to control pathogenicity and host dispersal. Nine synthetic compounds are identified that share no structural similarity to CAI-1, yet potently agonize CqsS via inhibition of CqsS autokinase activity. Second, this thesis shows that the central QS signal integrator, LuxO, employs an unprecedented competitive mechanism of natural negative regulation of its ATPase activity. Synthetic compounds that target LuxO mimic this natural form of inhibition. LuxO is conserved among vibrios, so these compounds have the potential to be developed into broad-spectrum vibrio anti-virulence molecules.
