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

Hydrothermal vent tubeworms, Riftia pachyptila Jones, were maintained alive and studied on board ship using flow-through pressure aquaria. Simultaneous measurements of O2,Σ CO2,Σ H2S fluxes showed that the intact symbioses reach maximum rates of uptake of $\Sigma {\rm CO}_{2}(>2\ \mu {\rm mole}\ {\rm g}^{-1}{\rm h}^{-1})$ at about 90 μM Σ H2S. Measurements were made of hemolymph and coelomic fluid Σ CO2,Σ H2S, thiosulfate, pH, and hemoglobin concentrations in worms kept under various conditions of O2and Σ H2S. Normal hemolymph pH appears to be about 7.5 and is not affected by Σ H2S and Σ CO2concentrations 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 Σ CO2and 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.