AMINO-ACID AND RELATED COMPOUND COMPOSITION IN 2 SYMBIOTIC MYTILID SPECIES FROM HYDROTHERMAL VENTS

Two species of deep-sea mussels belonging to the genus Bathymodiolus w ere collected from 5 vent fields distributed over 2 basins of a hydrot hermal system in the South Pacific. Free and bound primary amino compo unds were analysed in gills and mantles using OPA-HPLC. The method all owed the detection of 32 amino acids and related compounds (AARCs). An undetermined free chemical was found at high levels (up to 30% of the total free AARCs) in vent mussel tissues. This amino compound is pres umed to be an end-product from specific metabolism occurring in vent m ussels. Except for this unknown compound, comparison of the biochemica l composition between vent and littoral mussels revealed that the gene ral nitrogenous requirement as well as the endogenous metabolic pathwa ys of the main amino acids seem to be similar for the 2 mussel types. Ultrastructural observations indicated that these deep mussels harbour bacteria in their gills. Indices of high metabolic rates found in the se organs appear to be related to the presence of endobacterial. It se ems that symbionts could provide a preponderant fraction of essential amino acids to their host. In particular, free thiotaurine displayed h igh concentrations (up to 13% of the total free AARCs). This sulphur-c ontaining compound could be involved in a specific metabolism related to toxic forms of sulphur. Variations of the AARC composition between the 2 vent mussel species do not appear to be species related but appe ar to be due to environmental constraints. As shown by stress indices, deterioration of the physiological condition in these mussels is dire ctly linked to the quantity and/or the quality of the hydrothermal ven t emissions.