A gram-positive, facultatively anaerobic, rod-shaped bacterium was isolated from selenium-polluted sediment and identified as Bacillus sp. The bacterium, designated strain SF-1, grows with lactate as an electron donor and selenate as an electron acceptor in the absence of oxygen and presence of yeast extract (selenate respiration). There is a stoichiometric balance between the cell growth, lactate consumption and selenate reduction. Strain SF-1 can completely reduce up to 1 mM selenate to amorphous elemental selenium with transient accumulation of selenite. Although about 20 mM selenate can be converted to selenite, only a small portion of the accumulated selenite is further reduced to elemental selenium probably due to its inhibitory effect. The optimal pH and temperature for the selenate reduction of strain SF-1 are approximately 8.0 and 30 degrees C, respectively. The presence of nitrate inhibits the selenate reduction, suggesting a relationship between the nitrate and selenate reduction mechanisms. As strain SF-1 possesses the ability to convert toxic soluble selenium, selenate and selenite to insoluble elemental selenium which can easily be removed from an aqueous phase, it seems useful for detoxification and/or removal of soluble selenium from selenium-contaminated wastewater.