A novel thermophilic acetotrophic strain was isolated from a thermophilic anaerobic digest or by using acetate enrichment and serial dilution in the presence of vancomycin and neomycin. This isolate, designated sp. strain P, resembled sp. strain CALS-1 morphologically; however, it occasionally formed filaments longer than 100 μm and exhibited autofluorescence. The content of coenzyme F was much higher than that of reference strains, and coenzyme F with four glutamyl residues on the side chain was the predominant component. Furthermore, a comparative analysis of the antigenic fingerprint of strain P with the fingerprints of reference organisms showed that this isolate was not related antigenically to the reference methanogens, including sp. (“” sp.) strain CALS-1 and (“”) Opfikon. Strain P formed visible colonies in a deep agar medium when high cell concentrations were present. However, transfer of a colony into liquid medium resulted in no growth. Strain P could utilize only acetate as a sole carbon and energy source. The optimum temperature and optimum pH for methanogenesis were near 55°C and 6.7, respectively. The specific methane formation rate μ under optimum conditions was 0.47 day, and the doubling time was 1.49 days. The DNA base composition was 52.7 mol% guanine plus cytosine.


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