From granular sludge of an upflow anaerobic sludge bed (UASB) reactor treating paper-mill wastewater, a sulfate-reducing bacterium (strain ASRB1) was isolated with acetate as sole carbon and energy source. The bacterium was rod-shaped, (1.4-1.9 x 2.5-3.4 microns), nonmotile, and gram-negative. Optimum growth with acetate occurred around 37 degrees C in freshwater medium (doubling time: 3.5-5.0 days). The bacterium grew on a range of organic acids, such as acetate, propionate, and butyrate, and on alcohols, and grew autotrophically with H2, CO2, and sulfate. Fastest growth occurred with formate, propionate, and ethanol (doubling time: approx. 1.5 days). Strain ASRB1 clusters with the delta subdivision of Proteobacteria and is closely related to Syntrophobacter wolinii, a syntrophic propionate oxidizer. Strain ASRB1 was characterized as a new genus and species: Desulforhabdus amnigenus.