THE BACTERIAL SYMBIONT FROM THE HYDROTHERMAL VENT TUBEWORM RIFTIA-PACHYPTILA IS A SULFIDE SPECIALIST

We have investigated the metabolic adaptations of the chemolithotrophic bacterial symbionts of Riftia pachyptila. Specimens of the tubeworm were collected by submersible from depths of 2600 m at 13°N on the East Pacific Rise in 1987, and 2450 m at the Galápagos Rift in 1988. Isolated bacteria utilize sulfide, but not thiosulfate or sulfite, as their sole reduced-sulfur energy source. The bacteria rapidly oxidize a wide range of sulfide concentrations (5 μM to 2 m M), with maximal respiration rates at concentrations >1 m M, and unlike many sulfur-oxidizing bacteria, show no inhibition in oxygen consumption at sulfide concentrations up to 2 m M. Incubations of freshly homogenized trophosome tissue or isolated bacteria with sodium [35S] sulfide and subsequent analysis of sulfur products by high-performance liquid chromatography and flow-through scintillation counting showed that sulfide disappeared almost completely within 1 min. Both soluble and insoluble products of sulfide oxidation were produced. The soluble fraction contained sulfate and polysulfides, with no thiosulfate produced. However, the majority of the radioactivity was in the water-insoluble fraction, mostly as elemental sulfur. Whole-worm experiments under pressure showed a rapid removal of35S-sulfide from the incubation water, with sulfide, sulfate, and polysulfides appearing in the blood within 4 h. There was no utilization of thiosulfate by the whole worms, freshly homogenized trophosome tissue, or isolated bacteria. © 1990 Springer-Verlag.