Methanobacterium alcaliphilum sp. nov., an H2-Utilizing Methanogen That Grows at High pH Values

Four strains of alkaliphilic methanogens (strains WeN1, WeN2, WeN3, and WeN4T [T = type strain]) previously enriched and isolated from sediments of four low-salt, high-pH (pH 8.3 to 9.3) lakes in the Wadi el Natrun of Egypt were further characterized. These organisms were H2-oxidizing, CO2-reducing, rod-shaped bacteria which grew best at high pH values (strains WeN1, WeN2, and WeN4T preferred pH 8.4 and grew at pH values up to 9.9; strain WeN3 grew best at pH 7.8 and grew at pH values up to 9.2). Each strain required sulfide as a sulfur source and was resistant to elevated concentrations (growth rates in the presence of 0.5% Na2S · 9H2O were one-third to one-half the maximum observed rates). The guanine-plus-cytosine content of the deoxyribonucleic acid of strain WeN4T was 57 mol%. A new species of methanogen, Methanobacterium alcaliphilum, is described; strain WeN4 (= DSM 3387) is the type strain.