Methanobacterium kanagiense sp. nov., a hydrogenotrophic methanogen, isolated from rice-field soil

Abstract

A pure culture of an obligately anaerobic, hydrogenotrophic, methanogenic archaeon, designated strain 169T, which grows with hydrogen and carbon dioxide as the sole energy and carbon sources, was isolated from an anaerobic propionate-oxidizing enrichment culture originally obtained as an inoculant from rice-field soil in Japan. Cells of strain 169T were non-motile, Gram-reaction-variable and rod-shaped or slightly curved rods with rounded ends (1.6–5.0×0.35–0.5 µm). Strain 169T had fimbriae at both ends of the cell (up to ~10 per cell) but did not possess flagella. Ultrathin sections showed a single-layered, electron-dense cell wall about 6 nm thick, which is typical of Gram-positive bacteria. Growth was observed at 15 °C–45 °C (optimum 40 °C), at pH  6.5–9.6 (optimum pH 7.5–8.5) and in 0–70 g NaCl l−1 (0–1.2 M) (optimum 5 g NaCl l−1; 0.086 M). Strain 169T utilized only hydrogen and carbon dioxide as energy and carbon sources. The DNA G+C content was 39.3 mol%. The results of 16S rRNA gene sequence analysis indicated that strain 169T was most closely related to Methanobacterium subterraneum DSM 11074T (96.8 % sequence similarity) and Methanobacterium formicicum DSM 1535T (96.4 %). On the basis of its morphological, physiological and phylogenetic characteristics, strain 169T ( = DSM 22026T = JCM 15797T) represents a novel species of the genus Methanobacterium, for which the name Methanobacterium kanagiense sp. nov. is proposed.