Dr. Jennifer Wernegreen of the Marine Biological Laboratory at Woods Hole, MA, has been awarded a grant to study unique features of the genomes of bacteria that live permanently in the tissues of certain insects. Bacterial species show a wide variation in rates and patterns of DNA sequence evolution in their genomes, but few comparative studies have explored the mechanisms that produce this variation. Distinct patterns of molecular evolution may result from mechanisms related to changes in habitat, genes present in the genome, and/or other natural genetic processes. The objective of this project is to distinguish how these different mechanisms contribute to how and why genomes evolve in the ways that they do. This project focuses on Candidatus, a bacterial symbiont of carpenter ants, and Buchnera, a bacterial symbiont of aphids, as model systems to explore the molecular evolutionary consequences of this unusual lifestyle. These obligate bacterial symbionts are closely related to free-living bacterial species such as Escherichia coli. Wernegreen's lab group will sequence several protein coding genes from multiple, diverse lineages of Candidatus, Buchnera, and E. coli to compare patterns of molecular evolution in each group. This will permit them to test for different phenomena that might be responsible for evolutionary changes in the genomes of Candidatus and Buchnera. Analyses will include contrasting the symbionts and E. coli with regard to rates and patterns of protein and DNA sequence evolution. The results of this project will provide a framework to understand the vast diversity of evolutionary rates, compositions and architectures of bacterial genomes.