Minimal sulfur requirement for growth and sulfur-dependent metabolism of the hyperthermophilic archaeonStaphylothermus marinus

Staphylothermus marinusis an anaerobic hyperthermophilic archaeon that uses peptides as carbon and energy sources. Elemental sulfur (S°) is obligately required for its growth and is reduced to H2S. The metabolic functions and mechanisms of S° reduction were explored by examining S°-dependent growth and activities of key enzymes present in this organism. All three forms of S° tested—sublimed S°, colloidal S° and polysulfide—were used byS. marinus, and no other sulfur-containing compounds could replace S°. Elemental sulfur did not serve as physical support but appeared to function as an electron acceptor. The minimal S° concentration required for optimal growth was 0.05% (w/v). At this concentration, there appeared to be a metabolic transition from H2production to S° reduction. Some enzymatic activities related to S°-dependent metabolism, including sulfur reductase, hydrogenase, glutamate dehydrogenase and electron transfer activities, were detected in cell-free extracts ofS. marinus.These results indicate that S° plays an essential role in the heterotrophic metabolism ofS. marinus. Reducing equivalents generated by the oxidation of amino acids from peptidolysis may be transferred to sulfur reductase and hydrogenase, which then catalyze the production of H2S and H2, respectively.