ANAEROBIC DEGRADATION OF METHYLMERCAPTAN AND DIMETHYL SULFIDE BY NEWLY ISOLATED THERMOPHILIC SULFATE-REDUCING BACTERIA

The complete oxidation of methylmercaptan (MSH) and dimethyl sulfide (DMS) with sulfate or nitrate as electron accepters was observed in enrichment cultures and dilution series using thermophilic fermenter sludge as the inoculum. Three new strains of thermophilic sulfate reducers were isolated in pure culture (strains MTS5, TDS2, and SDN4). Strain MTS5 grew on MSH and strain TDS2 grew on DMS whereas strain SDN4 grew on either MSH or DMS. The cellular growth yields were 2.57 g (dry weight)/mol of MSH for strain MTS5 and 6.02 g (dry weight)/mol of DMS for strain TDS2. All strains used sulfate, sulfite, or thiosulfate as electron accepters, but only strain SDN4 used nitrate. DMS and MSH were oxidized to CO, and sulfide with either sulfate or nitrate as the electron acceptor. Sulfate was stoichiometrically reduced to sulfide while nitrate was reduced to ammonium. All strains were motile rods, required biotin for growth, lacked desulfoviridin, had DNA with G+C contents of 48 to 57 mol%, and probably belonged to the genus Desulfotomaculum. This is the first report of the oxidation of MSH and DMS by pure cultures of sulfate-reducing bacteria.