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 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 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
).