Abstract

A novel alkaliphilic, sulfate-reducing bacterium, strain MLF1^T, was isolated from sediments of soda Mono Lake, California. Gram-negative vibrio-shaped cells were observed, which were 0·6–0·7×1·2–2·7 μm in size, motile by a single polar flagellum and occurred singly, in pairs or as short spirilla. Growth was observed at 15–48 °C (optimum, 37 °C), >1–7 % NaCl, w/v (optimum, 3 %) and pH 8·0–10·0 (optimum, 9·5). The novel isolate is strictly alkaliphilic, requires a high concentration of carbonate in the growth medium and is obligately anaerobic and catalase-negative. As electron donors, strain MLF1^T uses hydrogen, formate and ethanol. Sulfate, sulfite and thiosulfate (but not sulfur or nitrate) can be used as electron acceptors. The novel isolate is a lithoheterotroph and a facultative lithoautotroph that is able to grow on hydrogen without an organic source of carbon. Strain MLF1^T is resistant to kanamycin and gentamicin, but sensitive to chloramphenicol and tetracycline. The DNA G+C content is 63·0 mol% (HPLC). DNA–DNA hybridization with the most closely related species, Desulfonatronum lacustre Z-7951^T, exhibited 51 % homology. Also, the genome size (1·6×10⁹ Da) and T_m value of the genomic DNA (71±2 °C) for strain MLF1^T were significantly different from the genome size (2·1×10⁹ Da) and T_m value (63±2 °C) for Desulfonatronum lacustre Z-7951^T. On the basis of physiological and molecular properties, the isolate was considered to be a novel species of the genus Desulfonatronum, for which the name Desulfonatronum thiodismutans sp. nov. is proposed (the type strain is MLF1^T=ATCC BAA-395^T=DSM 14708^T).