A strict anaerobe (strain GB8-1(T)) that degraded straight-chain fatty acids with C(4)-C(18) in syntrophic association with methanogens was isolated from an up-flow anaerobic sludge blanket reactor treating beer wastewater. Strain GB8-1(T) degraded 1 mol butyrate into about 2 mol acetate and 1 mol (presumably) H(2) in co-culture with a methanogen. Neither branched-chain fatty acids nor benzoate could be degraded. Strain GB8-1(T) could grow on crotonate in pure culture and converted 1 mol crotonate to 0.5 mol butyrate and 1 mol acetate. Generation time was about 11 h when grown on crotonate at 37 degrees C. Fumarate, sulfate, thiosulfate, sulfur and nitrate could not serve as electron acceptors for strain GB8-1(T) to degrade butyrate. Cells of strain GB8-1(T) were curved rods with Gram-negative cell walls; no spores were observed. The DNA G+C content was 46.6 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain GB8-1(T) was related most closely to the fatty acid-oxidizing, syntrophic bacterium Syntrophomonas sapovorans DSM 3441(T); however, the relationship was not very close (95.4 % sequence similarity). Some phenotypic features also differentiated strain GB8-1(T) from Syntrophomonas sapovorans DSM 3441(T). Therefore, a novel species, Syntrophomonas curvata sp. nov., is proposed. The type strain is GB8-1(T) (=CGMCC 1.5010(T)=DSM 15682(T)).