Quorum sensing regulation of bacterial development

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Project Summary Bacteria communicate using the cell-cell signaling system called quorum sensing to collectively alter gene expression in response to changes in population density and composition. Quorum sensing controls behaviors that benefit the group for adaption and survival, including biofilm formation, motility, bioluminescence, and toxin production and secretion. A more comprehensive understanding of how cell-cell signaling regulates virulence and impacts bacteria in their environmental niches can lead to the development of anti-microbial molecules that modulate quorum sensing to mitigate pathogenesis. Despite advances in elucidating the quorum signaling inputs, comparatively less is known about the output – the transcriptional regulation program that controls group behaviors and development in bacteria. The objective of the proposed research is to define how bacteria use quorum sensing signaling to control virulence gene expression, using Vibrio bacteria as established quorum sensing model systems and relevant pathogens. In Vibrio species, LuxR is the master transcription factor and the conserved core regulator of quorum sensing genes and virulence. Previous work identified important and highly conserved biochemical, biophysical, and genetic features of LuxR and Vibrio quorum signaling systems that govern gene expression. Yet, the influence of quorum sensing on numerous developmental pathways varies even among closely related Vibrio strains through means that are not understood. The proposed research will expand upon these findings to examine gene regulation by LuxR at the mechanistic level and then more broadly connect this information to the conservation and impact of quorum signaling networks across Vibrio species. First, the proposed research will determine the connections between spatial organization of the chromosome and LuxR regulation based on established findings that nucleoid structuring proteins impinge on quorum sensing gene expression in several Vibrio species. Second, to more broadly examine the influence of signals from “self” (quorum sensing autoinducers) and “other” (environment), quorum sensing gene expression will be assessed at the single-cell and population- wide level in response to variations in autoinducer signaling and nutrient availability. The proposed microfluidics, cell culture, and host infection experiments combined with comparative genomics will provide key links between quorum sensing signaling and Vibrio adaptation to environmental and host signals. Third, the van Kessel lab recently developed thiophenesulfonamide inhibitors that specifically block LuxR protein function in Vibrio bacteria. These molecules are key tools that will guide our understanding of LuxR function and inform structure-activity modeling and inhibitor design for potential therapeutic compounds. Collectively, the proposed research will provide fundamental data critical to understanding quorum signaling and how it impacts bacterial pathogenesis to contribute to future advances in vibriosis disease treatment.