The Molecular Basis of Host Adaptation and Origin of New Mutualisms

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Beneficial bacteria are the foundation of health in both plants and animals. Although disease-causing bacteria have received intensive scientific attention, the processes that drive the evolution of beneficial bacterial symbioses are still poorly understood. This project will apply the techniques and conceptual perspectives of molecular genetics, microbiology and evolutionary biology to document the genetic processes involved in evolution of beneficial symbiosis. The project will make use of an unusually tractable experimental model involving marine animals and their symbiotic bacteria: the symbiosis between bobtail squid and a light-producing bacterium, Vibrio fischeri. Some strains of Vibrio fischeri form life-long symbioses with squid and fish, whereas other strains are free-living in the marine environment. Exploiting the natural variation in this bacterium, the investigators will compare six V. fischeri strains with diverse environmental histories and differing initial capacities for colonization of squid hosts to identify bacterial mutations correlated with successful animal colonization, and with evolution of beneficial symbiotic interactions. This is among the first experimental evolution models, and the only natural model, to explore the mechanistic basis of beneficial host-adaptation in symbiotic microbes. The project includes interdisciplinary training for several graduate and undergraduate students, and capitalizes upon an engaging model system to promote an understanding of evolution and of symbiosis among students at all educational levels. The project will also develop educational resources for middle and high school teachers, including hands-on experiments using beneficial microbes in the classroom.