sp. nov. was isolated from the perennially cold, anoxic hypolimnion of Ace Lake in the Vesfold Hills of Antarctica. The cells were psychrophilic, exhibiting most rapid growth at 15°C and no growth at temperatures above 18 to 20°C. The cells were irregular, nonmotile coccoids (diameter, 1.2 to 2.5 μm) that occurred singly and grew by CO reduction by using H as a reductant Formate could replace H, but growth was slower. Acetate, methanol, and trimethylamine were not catabolized. Cells grew with acetate as the only organic compound in the culture medium, but growth was much faster in medium also supplemented with peptones and yeast extract. The cells were slightly halophilic; good growth occurred in medium supplemented with 350 to 600 mM Na, but no growth occurred with 100 or 850 mM Na. The pH range for growth was 6.5 to 7.9; no growth occurred at pH 6.0 or 8.5. Growth was slow (maximum specific growth rate, 0.24 day; doubling time, 2.9 days). This is the first report of a psychrophilic methanogen growing by CO reduction.


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