Bioreduction and biosorption of Cr(VI) by a novel Bacillus sp. CRB-B1 strain

This study reported an efficient novel chromium reducing bacteria (Bacillus sp. CRB-B1) and investigated its removal mechanism. Bacillus sp. CRB-B1 could effectively reduce high level Cr(VI), under a wide range of shaking velocity (125-200 rpm), temperature (33-41 °C), pH (6-9). The co-existing ions Cd²⁺ and NO₃- inhibited its Cr(VI) reduction capacity, while Cu²⁺ enhanced the reduction efficiency. In addition, Bacillus sp. CRB-B1 could reduce Cr(VI) using glucose and fructose as an electron donor. Micro-characterization analysis confirmed the Cr(VI) reduction and adsorption ability of Bacillus sp. CRB-B1. Cells degeneration result indicated that Cr(VI) removal was mainly bioreduction rather than biosorption. The cell-free suspension had a Cr(VI) removal rate of 68.5.%, which was significantly higher than that of cell-free extracts and cell debris, indicating Cr(VI) reduction mainly occurs extracellularly, and possibly mediated by extracellular reductase. The reduced Cr was mainly distributed in the extracellular suspension, and a small amount was accumulated in the cells. In conclusion, Bacillus sp. CRB-B1 was a highly efficient Cr(VI) reducing bacteria, which has potential in the remediation of Cr(VI)-containing water and soil.