Summary auto-generated
This study reports the isolation and characterization of two methanogenic archaea from a saline oil-producing well in Alsace, France. Strain SEBR 4845T is a novel hydrogenotrophic (hydrogen-utilizing) methanogen that tolerates an exceptionally wide salt range of 0-12.5% NaCl, with optimal growth at 5% NaCl and 38°C—matching the well's temperature. This irregular coccoid organism produces methane from hydrogen and formate but cannot use methylated compounds. Based on 16S rRNA gene sequencing and phenotypic analysis, it represents a new genus and species, Methanocalculus halotolerans, positioned within the order Methanomicrobiales. Strain FR1T, a moderately halophilic methanogen optimally growing at 10% NaCl and tolerating up to 20%, utilizes trimethylamine and methanol, with DNA composition suggesting relation to the genus Methanohalophilus. Notably, no aceticlastic methanogens were detected. The results indicate that hydrogenotrophic and methylotrophic methanogens inhabit subsurface saline ecosystems, with the hydrogenotrophic types adapted to lower salt concentrations than methylotrophs, similar to surface saline environments.
Key findings
- Methanocalculus halotolerans is a novel hydrogenotrophic methanogen with the widest reported NaCl tolerance range (0-12.5%) for hydrogen-oxidizing methanogens, previously documented at only 8.3% maximum
- The new organism's optimal growth conditions (38°C, 5% NaCl) closely match the oil well environment, suggesting it is indigenous to subsurface ecosystems
- 16S rRNA analysis places Methanocalculus halotolerans in the order Methanomicrobiales as a distinct genus, related to but separate from Methanogenium and Methanocorpusculum genera
- Methylotrophic methanogens tolerate higher salt concentrations than hydrogenotrophic types in both surface and subsurface saline environments
- Aceticlastic methanogens were absent from the saline oilfield sample, indicating their exclusion from high-salinity subsurface ecosystems
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Abstract
B Ollivier, ML Fardeau, JL Cayol, M Magot, BK Patel, G Prensier and JL Garcia
Laboratoire ORSTOM de Microbiologie des Anaerobies, Universite de Provence, Marseille, France. ollivier@esil.univ-mrs.fr
Two irregular coccoid methanogens designated SEBR 4845T and FR1T were isolated from an oilfield in Alsace, France. Strain SEBR 4845T (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 Methanococcales and Methanomicrobia les in the NaCI growth range (0-12% NaCI), which is the widest reported to data for any hydrogenotrophic methanogen. 16S rRNA gene sequence analysis indicated that strain SEBR 4845T is a novel isolate for which a new genus is proposed, Methanocalculus halotolerans gen. nov., sp. nov. (= OCM470T) that might be indigenous to the oilfield ecosystem. Strain FR1T (=OCM 471) is a moderately halophilic methanogen which growths 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 Methanohalophilus. 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.