Sulphur-isotopic composition of the deep-sea mussel Bathymodiolus marisindicus from currently active hydrothermal vents in the Indian Ocean

Sulphur-isotopic composition of soft tissues from Bathymodiolus marisindicus collected from hydrothermal vents in the Indian Ocean was reported. The δ³⁴S values of the soft tissues (+3∼+5‰ vs Cañyon Diablo troilite) were nearly identical to those from the associated hydrothermal fluid and chimney sulphides (+5 to 4-8‰), but were significantly different from that of the common seawater sulphate (+21‰), which suggested that the endosymbiotic bacteria used sulphide in the fluid as an energy source. Transmission electron microscopic observation of the endosymbionts also suggested that the symbiont is a thioautotroph. Bathymodiolus species, which depend on either sulphide or methane oxidation, or both, have a worldwide distribution. Bathymodiolus marisindicus from the Indian Ocean has a close relationship with congeners in the Pacific Ocean as evidenced by form of symbiosis. Biogeography and migration of the genus Bathymodiolus based on the relevant data are briefly discussed.