Comparative and evolutionary genomics of vent and seep symbionts
Chemosynthetic communities inhabiting hydrothermal vents and cold seeps depend on bacteria that metabolize reduced compounds such as sulfide and methane as primary producers. Many taxa inhabiting these environments, including clams, mussels, and tubeworms have developed intracellular symbioses with these bacteria. Symbiont transmission varies among these taxa from environmental acquisition to vertical, maternal transmission through eggs, and these different transmission strategies have led to differing selection pressures on symbiont populations resulting in highly variable symbiont genomes. Vesicomyid clams are a group that possess vertically-transmitted, intracellular symbionts whose symbiotic association has recently evolved (approx. 50-100 MY). As such, the symbiont genomes are in a state of flux characterized by a reduction in size, variable gene content, and genomes with elevated AT content. Vertical, maternal transmission can create epistatic interactions between host and symbiont cytoplasmic genomes, which can lead to a buildup of excess deleterious mutations; conversely, recombination can ameliorate these effects. I am interested in understanding how these evolutionary processes operate as a symbiont transitions into a plastid and effectively becomes part of the host genome. I will present results from a taxonomically broad genomic survey of symbiont genomes and host mitochondrial genomes and discuss the evolutionary implications of transmission strategy across these organisms.