Mix ingredients, except yeast extract, sulfur and Na2S·9H2O, and autoclave. Separately autoclave 10% (w/v) yeast extract solution, and 5% Na2S·9H2O solution under a N2 atmosphere. Steam sulfur for 3 hr on each of 3 successive days. Distribute the medium into culture vessels (e.g., 20 ml of the medium in 120 ml serum bottles) containing sulfur under a stream of H2-CO2 (4:1, v/v) gas mixture, add the yeast extract solution, and seal with butyl rubber stoppers. Prior to inoculation, add the sterile Na2S·9H2O solution, and adjust pH to 5.5 with sterile 1 N H2SO4. Pressurize the inoculated bottles to 200 kPa H2-CO2 (4:1, v/v) gas mixture.