Sensing more than a quorum: The role of pheromones in the light-organ symbiont Vibrio fischeri

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Plants and animals are consistently colonized by bacteria, and thesesymbiotic microorganisms often contribute to beneficial processes and/or diseasein their hosts. Many symbiotic bacteria communicate using pheromone signals,allowing them to coordinate group behaviors during infection. Such pheromonesignaling is typically called ?quorum sensing?, because high cell density isnecessary for pheromones to build up. However, a ?quorum? is typically notsufficient to induce pheromone-mediated behaviors fully, and bacterialpheromones are not simply census-taking signals. Importantly, the pheromonesmay also function to communicate aspects of the host environment among thebacteria. This project will use genetic, molecular, microscopic, and microbiologicalapproaches in exploiting the tractable model symbiosis between thebacterium Vibrio fischeri and its natural host squid Euprymna scolopes toexamine the relationship between conditions in the host and the symbiont?s useof pheromones. Pheromone signaling was discovered in V. fischeri and itremains among the best-understood model systems for such study. Thesymbiotic infection occurs in transparent tissue that is only colonized by V.fischeri, and pheromone signaling during infection results in the emission ofbioluminescence by the bacteria, making the infection relatively simple and theregulatory output easy to monitor. The scientific aims of this project are todetermine what aspects of the host environment lead to the induction of bacterialbioluminescence and to determine what role pheromones play in communicatingconditions in the host. A third aim is to integrate research on bacteria-hostsymbioses into undergraduate education, both through direct emersion inresearch and through the generation of materials to facilitate in-class discussionof scientific papers. The project will provide insight into the environmentsymbiotic bacteria encounter in a host, and how their perception of the hostenvironment can be integrated with their use of pheromones. The project willalso help train young scientists.