https://www.researchgate.net/figure/Sources-of-sulphide-and-respiratory-pathways-at-contrasting-habitats-in-siboglinid_fig8_49853885

Sulfide Oxidizing Symbionts

symbiotic endosymbiotic sulfide-oxidizing bacteria mostly belong to the γ-proteobacteria, whereas the endosymbiotic methane oxidizers belong to the α-proteobacteria. Chemolithotrophic endosymbionts are either digested by their host, or the host depends on excretion of organic matter from the symbionts.

Sources of sulphide and respiratory pathways at contrasting habitats in siboglinid tubeworms. At hydrothermal vents, sulphide is produced through the inorganic reaction of sulphate with geothermal energy. By contrast, sulphide has a microbial origin at cold seeps, organic-rich sediments, and whale-falls. At cold seeps, the source of sulphide is the anaerobic oxidation of methane coupled to sulphate reduction. At organic-rich sediments, sulphide is produced during the anaerobic degradation of a range of organic compounds. At whale-falls, although sulphide is produced, Osedax worms are thought to rely only on heterotrophic digestion of bone by the endosymbionts. The trophosome (light grey) houses endosymbiotic bacteria (orange ovals). White open circles represent methane and hydrocarbon seepage. Full arrow = reaction, dashed arrow = diffusion, and dotted arrow = acquisition or excretion by the host/symbiont.