Meeting Abstract
The evolution of gutless siboglinids, which are important members of chemosynthetic communities, has been hypothesized to be driven by preference for reducing habitats and their dependence on endosymbionts. However, genomes from only a few vent-dwelling vestimentiferan and bone-eating Osedax symbiont genomes have been sequenced and characterized. Here we focus on the genomes of gamma proteobacteria symbionts from vestimentiferan and frenulate siboglinids. Vestimentiferans tend to grow to relatively large sizes whereas frenulates are typically more diminutive. To understand differences in these holobiont systems, we sequenced 3 vestimentiferan and 1 frenulate symbiont genomes collected at hydrocarbon seeps and compared them to endosymbiont genomes from hydrothermal vent regions. All sampled endosymbionts from seep-dwelling siboglinids are also able to use rTCA cycle in addition to Calven-Benson cycle for carbon fixation. However, representative of frenulates, the Galathealinum symbionts lack key enzymes associated with rTCA and can only use Calvin cycle for carbon fixation. Thus, we hypothesize that symbionts with higher metabolic flexibility in carbon fixation may allow tubeworms to thrive in more reducing environments, such as seeps and vents. In addition, we show that metabolisms of sulfur, nitrogen are largely conserved across all siboglinid chemoautotrophic symbionts. Surprisingly, we find that the ability to use hydrogen as an additional energy source is probably also widespread in cold seeps than previous recognized, especially for siboglinid symbionts. Lastly, we take a comparative approach to systematically characterize the molecular mechanisms related to the process of infection. These results suggest that there are previously unrecognized links among siboglinid symbionts from different deep-sea chemosynthetic environments and shed light on understanding of evolutionary trends of siboglinid host-symbiont evolution.
