ENERGY METABOLISM PATHWAYS OF HYDROTHERMAL VENT ANIMALS: ADAPTATIONS TO A FOOD-RICH AND SULFIDE-RICH DEEP-SEA ENVIRONMENT

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Abstract
The activities of enzymes of the major pathways of energy metabolism (glycolysis, the citric acid cycle and the electron transport system) were measured in tissues of animals from the deep-sea hydrothermal vent site at 21.degree. N latitude. Enzymic activities of related shallow-living marine animals were assayed for comparison. Vent species studied were the large pogonophoran tube worm, Riftia pachyptila, the clam, Calyptogena magnifica, the crab Bythograea thermydron, the polychaete worm, Alvinella pompejana and an unidentified zoarcid fish. The enzymic activities found in the tissues of the vent animals were qualitatively and quantitatively similar to those of phylogenetically related shallow-living marine species, suggesting that the types of energy metabolism pathways, and the potential flux rates through these pathways, are similar in both groups. The enzymic activities of the vent zoarcid fish were much higher than those of all other deep-sea fishes studied to date. Despite the occurrence in the vent waters of high concentrations of HS-, a potent inhibitor of the cytochrome c oxidase system, most of the vent animals possessed cytochrome c oxidase activities comparable to those of related shallow-living species. The cytochrome c oxidase systems of the vent species and shallow-living species so examined were half-inhibited by HS- concentrations in the nanomolar to micromolar range. The mechanisms by which the vent animals avoid poisoning of respiration by HS- are discussed. C. magnifica was the only vent species that appeared to have a minimal capacity for aerobic respiration, as judged by extremely low activities of the cytochrome c oxidase system and citrate synthase in its tissues compared to other bivalves. C. magnifica may rely largely on anaerobic pathways of energy metabolism.