Methanobacterium nebraskense sp. nov., a hydrogenotrophic methanogen isolated from saline wetland soil

A hydrogenotrophic methanogen, designated strain ACI-7 ^T , was isolated from an alkaline, saline wetland located in eastern Nebraska, USA. Cells were identified as non-motile rods (0.9–4.2 μm in length and 0.2–0.4 µm in diameter) that occurred singly, in chains, and as long filaments and twisted aggregates. Strain ACI-7 ^T utilized H ₂ + CO ₂ or formate as methanogenic substrates and required growth factors present in yeast extract for continuous cultivation. The strain grew at 20–45°C (optimum, 40°C), at pH 6.5–8.5 (optimum, pH 7.3) and with 0–2.5% NaCl (optimum, 0–1%). The genomic G+C content of ACI-7 ^T was 31.79 mol%. Phylogenetic analysis of the 16S rRNA gene sequence indicated strain ACI-7 ^T was affiliated with the genus Methanobacterium, most closely related to Methanobacterium oryzae FPi ^T (97.1% sequence similarity) and Methanobacterium veterum MK4 ^T (96.9% sequence similarity). Overall genome relatedness indices for strain ACI-7 ^T compared to other Methanobacterium species ranged from 68.45–78.17% for average nucleotide identity and 18.9–25.7% for digital DNA–DNA hybridization. Morphological, physiological, and genomic characteristics indicate that strain ACI-7 ^T represents a novel species, for which the name Methanobacterium nebraskense sp. nov. is proposed. The type strain is ACI-7 ^T (=DSM 118696 ^T =ATCC TSD-487 ^T ).