A new strictly anaerobic, alkaliphilic, moderately thermophilic, fermentative, spore-forming bacterium, strain K1T, was isolated from manure samples (pH 6-8). Cells were Gram-positive, straight, non-motile rods that grew at temperatures of 37-66 degrees C (optimum at 62 degrees C) and in a pH range of 8.0-10.5 (optimum at 9.5-9.7). The bacterium fermented D-glucose, sucrose, D-fructose, D-trehalose and starch as carbon and energy sources. It required vitamins and its growth is stimulated by yeast extract. The major metabolic products were H2 and acetate. Cells were catalase-negative and could reduce nitrate to nitrite. The G+C content of the DNA was 42.2 mol%. Based on the phenotypic properties and 16S rDNA sequencing and DNA-DNA hybridization data, strain K1T (= DSM 12423T = ATCC 700785T = VKM B-2193T) was assigned to the new genus Anoxybacillus gen. nov., as a representative of a new species, Anoxybacillus pushchinensis sp. nov. 'Bacillus flavothermus' strain d.y., which was found to be closely related to strain K1T, is described as Anoxybacillus flavithermus comb. nov. (type strain = d.y.T = DSM 2641T).