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, or as twisted chains and aggregates. Strain ACI-7^T utilized H₂+CO₂ 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 to 78.17% for average nucleotide identity and 18.9 to 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).