PRJNA534438
Host-symbiont interactions in the chemosynthetic Riftia model symbiosis
The deep-sea tubeworm Riftia pachyptila is a model system for a mutualistic association: The adult worm has no digestive system, but completely relies on one phylotype of endosymbiotic chemosynthetic bacteria for nutrition. The bacteria, in turn, are provisioned by the host. Metabolism and physiology of this symbiosis, particularly of the uncultured symbiont, have been subject to various studies. Yet, how both partners interact on the molecular level remains largely unknown. To study these host-symbiont interactions in detail, we sequenced the R. pachyptila host transcriptome de novo, and conducted comprehensive metaproteomic comparisons of symbiont-containing and symbiont-free R. pachyptila tissues under energy-rich and energy-limiting conditions.Our results demonstrate that R. pachyptila invests a considerable part of its proteome to provision the symbionts with inorganic compounds. It acquires symbiont-derived biomass primarily by digesting parts of the symbiont population. The R. pachyptila immune system apparently not only protects the holobiont from pathogens, but is also involved in symbiont population control. The symbiont expresses a repertoire of proteins dedicated to communication with the host, including eukaryote-like proteins that may counteract phagocytosis. During energy limitation, i.e., when reduced sulfur compounds are lacking, the host apparently increases symbiont digestion.We show here an intricate network of interaction pathways that shapes the R. pachyptila holobiont. Together with the metabolic flexibility of the association under varying energy conditions, this probably forms the basis for the success of this tight association under the highly challenging deep-sea conditions.