Two irregular coccoid methanogens designated SEBR 4845and FR1T were isolated from an oilfield in Alsace, France. Strain SEBR 4845(T = type strain) is a hydrogenotrophic halotolerant methanogen, which grows optimally at 5% NaCI (w/v) and tolerates up to 12% NaCI. It does not use methylated compounds and therefore cannot be ascribed to any of the known genera of the halophilic methylotrophic methanogens. It differs from hydrogenotrophic members of the orders and in the NaCI growth range (0–12% NaCI), which is the widest reported to date for any hydrogenotrophic methanogen. 16S rRNA gene sequence analysis indicated that strain SEBR 4845is a novel isolate for which a new genus is proposed, gen. nov., sp. nov. (= OCM 470) that might be indigenous to the oilfield ecosystem. Strain FR1T (= OCM 471) is a moderately halophilic methanogen which grows optimally at 10% NaCI and tolerates up to 20% NaCI. It grows on trimethylamine and methanol as carbon and energy sources. The G+C content of its DNA is 43 mol%. It is therefore phenotypically and genotypically related to members of the genus This report provides evidence that methylotrophic and hydrogenotrophic, but not aceticlastic methanogens are present in a saline subsurface oilfield environment, as already observed in surface saline to hypersaline environments.


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