ABSTRACT: A thermophilic, anaerobic, fermentative bacterium, strain A6T, was obtained from an anaerobic batch digester treating animal manure and rice straw. Cells were Gram-stain-positive, slightly curved rods with a size of 0.6-1×2.5-8.2?µm, non-motile and produced terminal spores. The temperature, pH and NaCl concentration ranges for growth were 40-60?°C, 6.5-8.0 and 0-15.0?g l-1, with optimum growth noted at 50-55?°C, pH 7.5 and in the absence of NaCl, respectively. Yeast extract was required for growth. d-Glucose, maltose, d-xylose, d-galactose, d-fructose, d-ribose, lactose, raffinose, sucrose, d-arabinose, cellobiose, d-mannose and yeast extract were used as carbon and energy sources. The fermentation products from glucose were ethanol, lactate, acetate, propionate, butyrate, valerate, iso-butyrate, iso-valerate, H2 and CO2. The G+C content of the genomic DNA was 36.6?mol%. The predominant fatty acids were C16?:?0, iso-C17?:?1, C14?:?0, C16?:?1?7c, C16?:?0 N-alcohol and C13?:?0 3-OH. Respiratory quinones were not detected. The polar lipid profile comprised phosphoglycolipids, phospholipids, glycolipids, a diphosphatidylglycerol, a phosphatidylglycerol and an unidentified lipid. Phylogenetic analyses of the 16S rRNA gene sequence indicated that the strain was closely related to Defluviitalea saccharophila DSM 22681T with a similarity of 96.0?%. Based on the morphological, physiological and taxonomic characterization, strain A6T is considered to represent a novel species of the genus Defluviitalea, for which the name Defluviitalea raffinosedens sp. nov. is proposed. The type strain is A6T (=DSM 28090T=ACCC 19951T).