Partner association and adaptation in the Dictyostelium-Burkholderia proto-farming symbiosis

Washington University, Saint Louis MO

Investigators

Abstract

Members of different species sometimes associate and adapt to each other. Sometimes the associations are mutually beneficial, as in many of the bacteria associated with the human gut. In this work, the investigators will explore the mostly beneficial interactions in a much simpler system where several bacterial species are carried in the gut of an amoeba. The bacteria gain by being transported to new localities in amoeba spores while the amoeba gains by being able to seed out populations of food bacteria in new areas. The result is a sort of primitive farming. The investigators will first explore how selection works on this system using experiments to test new theory that could also be applied to more complex systems. Second, they will explore how the partnerships are formed. Are the partners attracted to each other and are particularly good food bacteria favored? Finally, the investigators will determine many of the amoeba and bacterial genes that control this interaction, exploiting the fact that both partners can be genetically manipulated. The students and post-doctoral individuals in this project will gain valuable training in important areas like genomics. The investigators will also impact high school students through on-campus workshops, undergrads and grads via a blog on being an academic, and the local community via an innovative science booth at the Ferguson farmer's market. The social amoeba Dictyostelium discoideum and two clades of Burkholderia bacteria engage in a remarkable microbiome-like symbiosis. The Burkholderia gain dispersal inside amoeba spores and also induce carriage of food bacteria that are released after spore dispersal to seed new food crops for the amoebas. This model system for symbiosis exploits short lifespans, small genomes, genetically manipulability, and other advantages. The PIs will use a new theoretical framework to estimate components of selection for both partners (Aim 1). This framework draws on analogies with kin selection theory and promises to be similarly useful. Second, they will explore partner association, testing how Burkholderia and Dictyostelium find each other, whether they succeed at choosing beneficial partners, and whether there is preferential association with beneficial food bacteria. Finally, they will discover many of the genes involved in the symbiosis and how they have evolved (Aim 3). Insertional mutant libraries of both partners will be constructed, put through various selection regimes, and sequenced to determine frequency changes that will identify relevant genes.