Metabolic responses of the hydrothermal vent tube worm Riftia pachyptila to severe hypoxia

The metabolic capabilities of the hydrothermal vent tube worm Riftia pachyp tila to tolerate short- and long-term exposure to hypoxia were investigated . After incubating specimens under anaerobic conditions the metabolic chang es in body fluids and tissues were analyzed over time. The tube worms toler ated anoxic exposure up to 60 h. Prior to hypoxia the dicarboxylic acid, ma late, was found in unusually high concentrations in the blood (up to 26 mM) and tissues (up to 5 pmol g(-1) fresh wt). During hypoxia, most of the mal ate was degraded very quickly, while large quantities of succinate accumula ted (blood: about 17 mM; tissues: about 13 mu mol g(-1) fresh wt). Volatile , short-chain fatty acids were apparently not excreted under these conditio ns. The storage compound, glycogen, was mainly found in the trophosome and appears to be utilized only during extended anaerobiosis. The succinate for med during hypoxia does not account for the use of malate and glycogen, whi ch possibly indicates the presence of yet unidentified metabolic end produc ts. Glutamate concentration in the trophosome decreased markedly during hyp oxia, presumably due to a reduction in the autotrophic function of the symb ionts during hypoxia. In conclusion, R. pachyptila is physiologically well adapted to the oxygen fluctuations frequently occurring in the vent habitat .