Sulfide-Driven Autotrophic Balance in the Bacterial Symbiont-Containing Hydrothermal Vent Tubeworm, Riftia pachyptila Jones

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Abstract
Hydrothermal vent tubeworms, Riftia pachyptila Jones, were maintained alive and studied on board ship using flow-through pressure aquaria. Simultaneous measurements of O2, ΣCO2, ΣH2S fluxes showed that the intact symbioses reach maximum rates of uptake of ΣCO2 (>2 μmole g-1 h-1) at about 90 μM ΣH2S. Measurements were made of hemolymph and coelomic fluid ΣCO2, ΣH2S, thiosulfate, pH, and hemoglobin concentrations in worms kept under various conditions of O2 and ΣH2S. Normal hemolymph pH appears to be about 7.5 and is not affected by ΣH2S and ΣCO2 concentrations within the ranges observed. We conclude that Riftia is specialized to provide sulfide to its symbionts with minimal interaction of sulfide with the animal metabolism. The uptake of sulfide is apparently by diffusion into the hemolymph, facilitated by the sulfide-binding properties of the hemoglobins. Both ΣCO2 and PCO2 are elevated in the hemolymph above their levels in the medium, although they are reduced under autotrophic conditions. Thus inorganic carbon is apparently concentrated from the medium into the hemolymph by an unknown mechanism.

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