PROJECT SUMMARY Quorum sensing describes the signaling mechanism that promotes intercellular communication among bacteria. Bacteria synthesize small, signaling molecules called autoinducers that freely diffuse across cellular membranes. Detection of autoinducers by a cell typically causes a change in gene expression, which alters its physiology. Because quorum sensing regulates genes encoding factors that enable bacteria to associate with host tissue, determining the molecular mechanisms underlying quorum sensing is significant for understanding how microbes initially interact with a host. The overall goal of this proposal is to increase understanding of strain-specific differences in quorum sensing. Vibrio fischeri is a bacterium that produces bioluminescence in response to quorum sensing within its natural host, the Hawaiian bobtail squid Euprymna scolopes. To achieve this goal, an undergraduate summer research program that investigates natural strain variation in quorum sensing is proposed. Students will participate remotely in two primary research activities: 1) genome and phylogenetic analyses of different V. fischeri isolates, and 2) in silico simulations of quorum sensing. The proposed research will reveal how a quorum-sensing system varies among different V. fischeri strains, which is significant because this knowledge provides insight into the evolution of a bacterial symbiont. Students are expected to make gains in technical, operational, and professional skills associated with the genomic and phylogenetic analyses of microbes.