Methanoculleus hydrogenitrophicus sp. nov., a methanogenic archaeon isolated from wetland soil

<jats:p>An obligately anaerobic, methanogenic archaeon, strain HC<jats:sup>T</jats:sup>, was isolated from soil of the Zoige wetland on the Tibetan plateau, China. The strain was isolated through construction of an artificial butyrate-degrading consortium in co-culture with a syntrophic bacterium, ‘<jats:italic>Syntrophomonas erecta</jats:italic> subsp. <jats:italic>sporosyntropha</jats:italic>’ JCM 13344. Cells of strain HC<jats:sup>T</jats:sup> were irregular coccoids, 0.8–2 μm in diameter, that occurred singly and utilized only H<jats:sub>2</jats:sub>/CO<jats:sub>2</jats:sub> for growth and methane production. Growth occurred at 18–45 °C (optimum around 37 °C). The pH for growth was 5.0–8.5 (optimal growth around pH 6.6). The G+C content of the genomic DNA was 60.2 mol%. 16S rRNA gene sequence analysis indicated that strain HC<jats:sup>T</jats:sup> was affiliated to the genus <jats:italic>Methanoculleus</jats:italic>, with sequence similarities of 94.8–97.2 % to existing members. However, strain HC<jats:sup>T</jats:sup> was distinguished from described <jats:italic>Methanoculleus</jats:italic> species by not using formate for growth or methane formation and not requiring acetate as a growth factor. On the basis of phylogenetic analysis and phenotypic characteristics, the novel species <jats:italic>Methanoculleus hydrogenitrophicus</jats:italic> sp. nov. is proposed, with strain HC<jats:sup>T</jats:sup> (=CGMCC 1.5146<jats:sup>T</jats:sup> =JCM 16311<jats:sup>T</jats:sup>) as the type strain.</jats:p>