A novel anaerobic, mesophilic, non-spore-forming bacterium (strain m25 ) was isolated from methanogenic enrichment cultures obtained from a lab-scale methanogenic landfill bioreactor containing anaerobic digester sludge. Cells were Gram-stain-negative, catalase-positive, oxidase-negative, rod-shaped, and motile by means of a flagellum. The genomic DNA G+C content was 40.11 mol%. The optimal NaCl concentration, temperature and pH for growth were 2.5 g l , 35 °C and at pH 7.0, respectively. Strain m25 was able to grow in the absence of yeast extract on glycerol, pyruvate, arginine and cysteine. In the presence of 0.2 % yeast extract, strain m25 grew on carbohydrates and was able to use glucose, cellobiose, fructose, raffinose and galactose. The novel strain could utilize glycerol, urea, pyruvate, peptone and tryptone. The major fatty acids were iso-C , C , C DMA (dimethyl acetal) and iso-C DMA. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the new isolate was closely related to EBR46 (95.02 % 16S rRNA gene sequence similarity). Genome relatedness was determined using both average nucleotide identity and amino acid identity analyses, the results of which both strongly supported that strain m25 belongs to the genus . Based on its unique phylogenetic features, strain m25 is considered to represent a novel species within the genus . Moreover, based on its unique physiologic features, mainly the lack of spore formation, a proposal to amend the genus is also provided to include the non-spore-forming and mesophilic species. sp. nov. is proposed. The type strain of the species is m25 (=DSM 112749 =ATCC TSD-268 ).