Dissimilatory arsenate reduction by a facultative anaerobe, Bacillus sp. strain SF-1

Bacillus sp. strain SF-1, isolated first as a selenate-reducing bacterium, was characterized as a novel arsenate-reducing bacterium. Strain SF-1 rapidly reduced 10 mM levels of arsenate to arsenite with concomitant cell growth and lactate oxidation under anoxic conditions, indicating that arsenate can act as the terminal electron acceptor for anaerobic respiration (dissimilatory arsenate reduction). Strain SF-1 can use various organic compounds including synthetic sewage mainly composed of peptone and meat extract as the electron donors for arsenate reduction. Although strain SF-1 can grow aerobically, which is very rare for dissimilatory arsenate-reducing bacteria, the presence of oxygen inhibited the arsenate reduction. On the other hand, the presence of nitrate or selenate, which can support the growth of strain SF-1 as electron acceptors, did not significantly inhibit the arsenate reduction. Arsenate-reducing activity, that is, arsenate reductase, was exhibited in strain SF-1 only when grown on arsenate, but the enzyme could not reduce other oxyanions including nitrate and selenate. It was presumed that arsenate reduction was carried out by an enzyme system separate from those of nitrate and selenate reduction, and the arsenate reductase was inducible and specific for arsenate. These results suggest that strain SF-1 may be utilized for extracting arsenic from contaminated soil for the purpose of bioremediation.