Abstract for presentation at 11th International Congress of Human Genetics

Wolbachia pipientis is a bacterial endosymbiont present in a wide range of arthropods and in several lineages of filarial nematodes. The symbiont can induce a number of reproductive manipulations in its hosts including cytoplasmic incompatibility, feminization, and parthenogenesis. All of these modifications enhance spread of the symbiont infection through populations while providing few benefits to hosts. The clear exception to this rule is in filarial nematodes where removal of Wolbachia infection by antibiotic treatment leads to death of the host. The genetic basis of Wolbachia-host interactions is poorly understood. We have used a comparative genomics approach to identify candidate genes that may play a role in these lineage specific life history adaptations. An evolutionary model that estimated lineage specific dN/dS (ratio of nonsynonymous substitution to synonymous substitution rate) was applied to a three-way genome comparison between the insect (wMel) and worm (wBm) Wolbachia genomes and that of Anaplasma marginale as the outgroup. Genes bearing the signature of positive selection (dN/dS > 1) in either or both of the Wolbachia lineages were identified. In wBm a number of DNA repair/replication, peptidase, and transporter genes exhibited positive selection, while in wMel cell wall biosynthesis, energy metabolism, and protein fate/folding genes were more commonly affected. An emphasis on cell wall biosynthesis is a characteristic expected from a more parasitic symbiont. Genes involved with type IV secretion and iron transport were shown to be under selection in both Wolbachia lineages as well as a number of genes of unknown function.