One of the most exiting mutualisms is the association between the sulfur-oxidizing bacterium, Candidatus Endoriftia persephone, and its host Riftia pachyptila. These giant tubeworms live in the deep sea at hydrothermal vents in the Pacific Ocean. The tubeworms reproduce through larvae that do not carry the symbionts. They migrate through the seawater and settle at vents. There, the uptake of the symbiont into the host happens in each host generation anew from a pool of free-living symbionts from the environment. The host has no mouth and gut as adult and is nourished by its symbiont, housed in an organ deep inside the host body. The symbionts receive all chemicals necessary for chemoautotrophy. In return they feed the host. The tubeworms, however, are highly dependent on the environment in which sulfide and oxygen fluctuate. How the symbiont reacts to variable concentrations is not known yet. Upon cessation of vent flow, supplies of chemicals stop and the host dies. The symbionts, however survive because they leave the dead host. How they manage is not known yet.

The overall goal of this project is to investigate the molecular response of host-associated and free-living life style in Endoriftia using metatransciptomics. In specifics, we will study in a suite of experiments how Endoriftia reacts to hosts differing in cooperativeness, to a dead host, and to deep-sea conditions when free-living.