Kith and kin in amoeba-bacteria cooperation

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Understanding cooperation among microbes is vital. Pathogenic microbes sometimes cooperate in ways that harm us. The bacteria comprising our gut microbiome can cooperate in ways that benefit us. Microbes can cooperate both with members of their own species and with other species. This project will show how within- and between species cooperation are actually closely related. First, the two processes often work together. Cooperation among microbial populations is required for them to cooperate with a larger host organism. This study will examine how favoring relatives affects cooperation with their host by using a simple, understandable model system. Many Burkholderia bacteria inhabit an amoeba host, conferring both helpful and harmful effects. The study will show how the ability of bacteria to cooperate, especially among relatives, affects host survival and reproduction. There are similarities between the theories of within- and between-species cooperation. The investigators will construct mathematical models for a more unified theory that will allow insights about one type of cooperation to be applied to the other type. Finally, this study will test these theories by putting the microbial partners together in the lab to see what changes occur over time using experimental evolution. The results of this work will explain microbial interactions far beyond this bacteria-amoeba system, with potential insights for medicine and agriculture. The investigators will develop active learning modules that allow students to manipulate models of microbial interactions and see the consequences. They will also produce short educational videos that will be widely available.Cooperation occurs both within and between species, but these two realms have been studied rather separately. This study will bridge these research traditions in three ways, by studying the importance of kin selection in an amoeba-bacteria mutualism, by developing kith selection models of mutualism that are formally similar to kin selection models, and by applying those models to an amoeba-bacteria mutualism. First, the investigators will study the importance of within-species kin selection in a between-species symbiosis, the amoeba-bacteria proto-farming system. They will investigate relatedness of the bacteria, their kin recognition, and the effects of these on host fitness. Second, they will model understudied aspects of kith selection in which cooperators pay a direct fitness cost but can be compensated by an indirect benefit from the other species, modeled by a regression coefficient that is formally similar to genetic relatedness. Finally, the investigators will evolve the participants under different interaction circumstances in the amoeba-bacteria mutualism to apply and test the models. They will determine the relative roles of direct selection, indirect selection due to partners, and their interaction. The theory will help unify disparate schools of thought and the empirical methods will be transferable to many other systems. Furthermore, the investigators will develop educational modules on the topic of their research, will involve undergraduates, and K12 students, and make presentations to the public. They also will facilitate diversification of the professoriate with informative pieces on academic success strategies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.