ADAPTATIONS TO SULFIDE BY HYDROTHERMAL VENT ANIMALS: SITES AND MECHANISMS OF DETOXIFICATION AND METABOLISM

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Abstract
The detoxification and metabolism of sulfide were studied in three symbiont-containing invertebrates from the deep-sea hydrothermal vents: the tube worm, Riftia pachyptila: the clam, Calyptogena magnifica; and the mussel, Bathymodiolus thermophilus. Sulfide oxidizing activities, due to specific sulfide oxidase enzymes, were found in all tissues, with the greatest activities occurring in the symbiont-containing tissues: the trophosome of the tube worm and the gills of the bivalves. Sulfide oxidase activity was correlated with the bacterial content of the tissues. The sulfide oxidases in the outer cell layer(s) of symbiont-free tissues, e.g., body wall muscle of Riftia and foot and mantle of the bivalves, may detoxify sulfide as soon as it enters the body. Sulfide entering the blood in Riftia and Calyptogena may be bound by sulfide-binding factors that transport sulfide to the symbionts and protect against sulfide inhibition of aerobic respiration [via effects on the cytochrome-c oxidase (CytOx) system]. Sulfide strongly inhibited the CytOx systems of these animals, but this inhibition was offset by the addition to the CytOx assay mixture of blood of Riftia or Calyptogena. Reduced sulfur compounds, sulfide, sulfide, sulfite, and thiosulfate, were effective in stimulating ATP synthesis in homogenates of symbiont-containing tissues. The most effective reduced sulfur compound varied among the three symbioses.