HUDSON, H.A.*; HOM, J.R.; FIESS, J.C.; KATO, C.; YANCEY, P.H.: Corelations of hypotaurine and thiotaurine contents with sulfide metabolism in gills of vesicomyid bivalves from different cold seeps

Most marine invertebrates use organic solutes such as taurine, glycine, and betaine as cell osmolytes. But recent studies show that deep-sea, hydrothermal-vent, and cold-seep animals have different osmolytes, possibly adaptations to pressure or metabolism. In particular, vesicomyid bivalves from sulfide seeps, which have sulfide-oxidizing symbionts, have high contents of hypotaurine and thiotaurine, postulated to be used in sulfide transport or detoxification rather than primarily as osmolytes. To investigate roles of these and other osmotically significant solutes, we analyzed major solutes in gills of vesicomyids from a variety of depths and sulfide exposures. Specimens (Calyptogena/Vesicomya species) were collected from sulfide and methane seeps at 0.5 km (Eel River, California), 1.1 km (Okinawa Trough, Sagami Bay), 2 km (Oregon Margin), 4.4 km (Kodiak Trench), and 6.4 km (Japan Trench). In gills, hypotaurine plus thiotaurine contents showed no relation to habitat depth, but were significantly higher in gills (which house the symbionts) than in foot and mantle. In Eel River specimens, gill thiotaurine levels were significantly higher in clams from deeper in the sediment with higher sulfide exposure. These data support the hypothesis that these solutes are related to sulfide metabolism. No thiotaurine was found in the Oregon clams, suggesting methylotropic rather than sulfide-using symbionts in that species. Finally, echinoderms, polychaetes, gastropods and anthozoans (Anthomastus ritteri) from Eel River seeps were also collected. The anthozoan (but no other species) contained hypotaurine and thiotaurine, suggesting that this species also has symbionts.