Abstract
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)).