Isolation and Characterization of a Novel Thermophilic Methanosaeta Strain

Abstract

A novel thermophilic acetotrophic Methanosaeta 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 Methanosaeta sp. strain PT, resembled Methanosaeta sp. strain CALS-1 morphologically; however, it occasionally formed filaments longer than 100 μm and exhibited autofluorescence. The content of coenzyme F420 was much higher than that of Methanosaeta reference strains, and coenzyme F420 with four glutamyl residues on the side chain was the predominant component. Furthermore, a comparative analysis of the antigenic fingerprint of strain PT with the fingerprints of reference organisms showed that this isolate was not related antigenically to the reference methanogens, including Methanosaeta sp. (“Methanothrix” sp.) strain CALS-1 and Methanosaeta concilii (“Methanothrix soehngenii”) Opfikon. Strain PT 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 PT 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 μCH 4 under optimum conditions was 0.47 day−1, and the doubling time was 1.49 days. The DNA base composition was 52.7 mol% guanine plus cytosine.