A new methanogen, strain 7T, was isolated from the rumen of a cow (Moscow region, Russia). Morphologically, the strain is composed of non-motile coccoid cells of irregular shape, 1.3–4.3 μm in size, and small aggregates thereof. The strain uses exclusively a mixture of hydrogen and carbon dioxide as energy substrates for methanogenesis and requires the presence of acetate in the culture medium. The cells grow at a temperature of 20–53°C (optimum 45°C), pH 6.5–7.8 (optimum pH 7.2–7.4), and are tolerant to NaCl levels up to 0.34 M. According to the 16S rRNA gene sequence analysis, the new methanogen belongs to the genus Methanoculleus, sharing a gene similarity level of 98.16% with the closest species of this genus, M. bourgensis MS2. The average nucleotide similarity (ANI) between the genomes of strains 7T and M. bourgensis MS2 was 88.24%, and the virtual estimate of hybridization of the genomes of these two strains was 31.40%. The G + C content of genomic DNA is 61.27% mol. %. Based on the phylogenetic analysis and physiological and biochemical properties of the isolate, we propose to classify the isolated strain 7T (= VKM B-3409 = JCM 39547) as a new species Methanoculleus bovis sp. nov.
V. E. Trubitsyn (2025) studied this question.