FIESS, J.C.*; HUDSON, H.A.; HOM, J.R.; KATO, C.; YANCEY, P.H.: Depth correlations of organic osmolytes in foot and mantle tissues of vesicomyid bivalves

Osmoconforming invertebrates such as bivalves use organic osmolytes such as free amino acids to maintain cell volume against the osmotic pressure of seawater. Recent studies have demonstrated that certain osmolytes can also stabilize proteins against hydrostatic pressure. We studied foot and mantle tissues of Vesicomya/Calyptogena bivalves from a range of depths-0.5km (Eel River seeps, California), 1.1km (Okinawa Trough, Sagami Bay), 2km (Oregon Margin seeps), 4.4km(Kodiak Trench, Alaska), and 6.4km (Japan Trench). The osmolytes in the clams from the Kodiak and Japan Trenches differed markedly from the other, more shallow clams. Of the common osmolytes, taurine decreased exponentially with depth, betaine remained nearly constant until decreasing sharply at 6.4km, and glycine peaked at 1.1km before declining exponentially. In addition, an unidentified amine (ninhydrin-positive) compound peaked at 2km then declined sharply, and an unidentified trimethylamine (Dragendorff-positive) compound increased sharply between 2 and 6.4km. A potentially new class of osmolyte, a serine-phosphate compound, increased linearly from 2 to 6.4km making it the dominant osmolyte in the deepest clams. The presence of this and the other unknown compounds in high levels at depths of 2km and greater, as well as the decrease of taurine, betaine, and glycine, suggests a replacement of the more common osmolytes in favor of compounds that can protect cells from the effects of both seawater and high pressure.