Taurine-related compounds and other free amino acids in deep-sea hydrothermal vent and non-vent invertebrates

Several hydrothermal vent-endemic invertebrates detoxify sulfide by reacting toxic H2S with the taurine derivative, hypotaurine to produce non-toxic thiotaurine, but dependence on this system appears to vary among species. In this study, free amino acids and taurine and its related compounds, hypotaurine and thiotaurine, were quantified in vent-specific invertebrates with different lifestyles, including two polychaetes (the tube-dwelling Paralvinella hessleri and an unidentified, motile scale worm, Polynoidae. gen. sp.) and two sessile cirripedes (Neoverruca sp. and Ashinkailepas seepiophila). The two polychaetes and Neoverruca sp. were collected from the same active chimney on the Myojin Knoll (32 degrees 06.278N, 139 degrees 52.081E, June 2011) where they were directly exposed to the vent fluid and relatively close to the vents. By contrast, A. seepiophila was collected on a dead chimney in the same area (32 degrees 06.254N, 139 degrees 52.086E, June 2011). The two polychaetes contained completely different amounts of taurine-related compounds, despite being sympatric whereas the two cirripedes had similar amounts of taurine-related compounds although they were allopatric, suggesting that the amounts of taurine-related compounds were not influenced by habitat alone. The proportions of the other free amino acids were generally similar among the four species, with glycine being the highest, but they were more similar between the two polychaetes and between the two cirripedes despite the different lifestyles and habitats. This suggests a taxonomic similarity in the metabolic pathways.