METHANOHALOPHILUS-OREGONENSE SP-NOV, A METHYLOTROPHIC METHANOGEN FROM AN ALKALINE, SALINE AQUIFER

Methanohalophilus oregonense WAL1(T) (= OGI 99(T) = DSM 5435(T)) (T = type strain) was isolated from an anoxic aquifer (pH 10, with 100 g of dissolved solids per liter of pore water) 3 m deep near Alkali Lake, an alkaline, desert lake in south central Oregon. An examination of the subsurface sediments revealed no methanogens that were capable of growth on methanogenic substrates, such as H2-CO2, formate, or acetate, which is consistent with the results of other studies of hypersaline, sulfate-containing anoxic environments. Strain WAL1(T) grew on trimethylamine and grew slowly on methanol or dimethylsulfide, but did not catabolize H2-CO2, formate, or acetate. The cells were irregular coccoids (diameter, 1 to 1.5 μm), and cells growing in liquid media also formed clumps of 2 to 15 or more cells. The cells were mesophilic and required one or more vitamins present in yeast extract. Like the only previously described strain of alkaliphilic, methylotrophic methanogen (Methanohalophilus zhilinae WeN5(T)), strain WAL1(T) grew most rapidly in medium of moderate salinity; strain WAL1(T) grew well in the presence of 0.1 to 1.4 M Na+ and grew most rapidly at an Na+ concentration of 0.35 M (specific growth rate, 0.1 h-1). Best growth occurred with about 50 mM Mg2+ and at a pH of 8.4 to 9.0. K+ appeared to be required, with 13 to 130 mM K+ supporting most rapid growth. The guanine-plus-cytosine content of the DNA was 40.9 ± 0.1 mol%.