Densely packed invertebrate communities have been observed around deep-sea hydrothermal vents and cold seeps, despite the high concentrations of hydrogen sulfide present in these environments. The species that inhabit these environments have been reported to accumulate the sulfur-containing amino acid, thiotaurine. This non-toxic amino acid is synthesized from its precursor, hypotaurine and ambient hydrogen sulfide. In this study, we compared the levels of thiotaurine and hypotaurine in the gills and mantles of two deep-sea mussels (Bathymodiolus septemdierum and B. platifrons) and a shallow-water mussel (Mytilus galloprovincialis) to investigate their degree of dependence on the thiotaurine/hypotaurine system. The levels of thiotaurine and hypotaurine in the gill were higher than those present in the mantle in the two deep-sea species but lower or similar in M. galloprovincialis. The levels of thiotaurine and hypotaurine were the highest in the gill of B. septemdierum, estimated at 6.56 and 13.50 µmol/g wet weights, respectively. Moreover, B. septemdierum exhibited a higher thiotaurine/(hypotaurine+thiotaurine) ratio in the gill, B. septemdierum than that did B. platifrons and M. galloprovincialis. These results suggest that the levels of thiotaurine and hypotaurine in Bathymodiolus may be related to the ambient sulfide levels in their habitats.
2016 The Plankton Society of Japan, The Japanese Association of Benthology