Chromate reduction by Bacillus megaterium TKW3 isolated from marine sediments

Bacillus megaterium strain TKW3 was isolated from multiple-metal-contaminated marine sediments of Tokwawan, Hong Kong SAR. This facultative aerobe utilized arabinose, mannitol, N-acetylglucosamine, maltose, caprate, citrate, butyrate or lactate as the sole source of carbon and energy for growth. B. megaterium TKW3 reduced highly toxic and soluble Cr6+ (as CrO42-) into almost non-toxic and insoluble Cr3+ under aerobic conditions. Complete reduction of 0.20 mM Cr6+ by B. megaterium TKW3 was achieved within 360 h. Initial Cr6+ concentration below 0.90 mM or inoculum less than 10(7) cells ml(-1) did not have significant effect on Cr6+ reduction, while the residue Cr6+ concentration was the lowest at 10(7) cells ml(-1). Cr6+ reduction by this strain was inhibited by high levels of NaCl (55 parts per thousand). B. megaterium TKW3 was also resistant to other oxyanions including 0.34 mM Cr2O72- mM AsO43-, 0.58 mM SeO32- and 0.53 mM SeO42-, and reduced soluble Se4+ ( as SeO32-) to insoluble red amorphous Se-0. B. megaterium TKW3 might have potential application in bioremediation of Cr-laden sediments associated with other oxyanions.