N-190. Detection of Free-Living Symbionts of Bathymodioline Mussels (Bivalvia: Mollusca) at Deep-Sea Hydrothermal Vents

K. M. Fontanez, C. M. Cavanaugh;
Harvard Univ., Cambridge, MA.

Studies of mutualistic symbioses between marine invertebrates and intracellular chemoautotrophic bacteria have yielded remarkable insights into the physiology and evolution of prokaryote-eukaryote symbioses, as well as the ecology and primary production potential of marine reducing environments. These symbioses are ubiquitous at deep-sea vents and cold seeps, environments in which mussels of the genus Bathymodiolus are found distributed across the globe. A reliable mechanism of symbiont transmission to the next generation is essential to the maintenance of the symbiosis. Whereas symbionts of some hosts are transmitted vertically via the egg, Bathymodiolus sp. are hypothesized to acquire their symbionts from the environment, a mechanism which necessitates a free-living population of symbionts. This study addresses the hypothesis that free-living symbionts of the mussel, Bathymodiolus brevior, exist in the hydrothermal vent environment. Microbial communities were analyzed on basalt blocks deployed at, and collected from, the Lau Basin hydrothermal vents in the Western Pacific Ocean. The B.brevior symbiont was detected by PCR using primers for, and sequence analysis of, symbiont-specific genes. The recent availability of 454 sequence databases (based on regions of the 16S rRNA gene) allowed us to explore whether Bathymodiolus symbionts exist as free-living bacteria at other hydrothermal vents. The V6 region (~60 nucleotides), determined to be 100% identical for the majority of Bathymodiolus sp. symbionts, was detected in two 454 databases from vent water filtered from the Juan de Fuca hydrothermal vents. Collectively, these results suggest that bathymodioline symbionts occur as free-living bacteria in the environment and provide corroborative evidence for environmental transmission in these symbioses.