Sulfide Detoxification by the Hydrothermal Vent Crab Bythograea thermydron and Other Decapod Crustaceans

Abstract

Bythograea thermydron, a brachyuran crab endemic to the deep-sea hydrothermal vent habitats, encounters concentrations of hydrogen sulfide of up to 318 μM. To determine how B. thermydron avoids the potentially lethal effects of these high concentrations of sulfide, we examined several physiological and biochemical systems to determine, first, this species' sensitivity to sulfide, and, second, how sulfide entering the body is detoxified. The heart rate of B. thermydron was unaffected by ambient sulfide concentrations of up to 1,400 μM. The toxic effects of sulfide were not avoided by exclusion of sulfide from the body. Protection from sulfide poisoning appears to be achieved by a sulfide detoxification system located in the hepatopancreas. The initial step in this process was the oxidation of sulfide by a sulfide oxidase enzyme. The hepatopancreas of B. thermydron produced thiosulfate and sulfate as the major products of sulfide oxidation. Thiosulfate accumulated to >1 mM in the blood. The toxicity of sulfide, sulfide-oxidizing activities, and products of sulfide metabolism were compared in three nonvent crabs, Cancer antennarius, Pachygrapsus crassipes, and Portunis xantusii. These species exhibited qualitatively similar adaptations. However, the nonvent species were significantly more sensitive to sulfide poisoning than was the vent crab.