Functional transitions in an insect-bacteria symbiosis

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Insects are ideal model systems for studying associations between animals and microorganisms because of the diversity of interactions formed between them. These interactions, or symbioses, span a wide continuum of types, from those that are pathogenic and short-lived to those that are beneficial and stable over extremely long periods of time. Sap-feeding insects in particular have been shown to form intimate and stable symbioses with bacteria that live exclusively within insect cells. This strict intracellular lifestyle has profound effects on the symbiotic bacteria, effects that are dramatically manifest in their highly reduced genomes. This project will investigate a symbiosis involving a cicada that lives in the southwestern United States and its dual bacterial symbionts. One of these symbionts, named Hodgkinia, has a remarkably small genome encoding many fewer genes than was thought possible for an autonomous organism. The investigators will use both genetic and molecular techniques to uncover the mechanistic changes that have allowed Hodgkinia's extreme genome reduction. It is expected that adaptations in both the host insect and symbiont will be found that enable such dramatic gene loss. This work has broad-reaching consequences for the way we understand genome reduction in bacteria, the integration of organisms in the context of intimate symbioses, and the formation of cellular organelles such as mitochondria. The broader impacts of this project will involve the training of several undergraduate students, one graduate student, one postdoctoral fellow, and several K-12 teachers and students through collaboration with the Missoula County Public Schools and College of Education and Human Sciences at the University of Montana.