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

A hydrogenotrophic methanogen, designated strain ACI-7T, was isolated from an alkaline, saline wetland located in eastern Nebraska, USA. Cells were identified as non-motile rods (0.9-4.2 m in length and 0.2-0.4 {micro}m in diameter) that occurred singly, in chains, and as long filaments and twisted aggregates. Strain ACI-7T 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{degrees}C (optimum, 40{degrees}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-7T was 31.79 mol%. Phylogenetic analysis of the 16S rRNA gene sequence indicated strain ACI-7T was affiliated with the genus Methanobacterium, most closely related to Methanobacterium oryzae FPiT (97.1% sequence similarity) and Methanobacterium veterum MK4T (96.9% sequence similarity). Overall genome relatedness indices for strain ACI-7T 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-7T represents a novel species, for which the name Methanobacterium nebraskense sp. nov. is proposed. The type strain is ACI-7T (=DSM 118696T=ATCC TSD-487T).