Coupling heavy metal resistance and oxygen flexibility for bioremoval of copper ions by newly isolated Citrobacter freundii JPG1.

The potential for bioremoval of copper ions was investigated by a novel strain of bacterium Citrobacter freundii JPG1, which was newly isolated from gold mining tailing in China and grew either aerobically or anaerobically. The strain cross-tolerated heavy metals of Ag+, Cd2+, Co2+, Cr6+, Cu2+ and Ni2+ and removed copper under both aerobic and anaerobic conditions with the stress of copper. Under aerobic conditions, the cells grew rapidly and exhibited higher biomass at low copper concentrations (<1 mmol L-1), while the growth of cells was almost completely inhibited at high copper concentrations (2 mmol L-1). However, the cell growths were less affected by copper under anaerobic conditions. Similarly, the copper-removal efficiency was affected by oxygen and the capability of copper removal by anaerobic cells was significantly higher than that of aerobic cells (P < 0.05). The quantitative measurement of extracellular biosorption and intercellular bioaccumulation of copper indicated that biosorption efficiencies for aerobic cells (37%) and anaerobic cells (38%) were similar but the bioaccumulation by anaerobic cells was almost ten-fold higher than that by aerobic cells, indicating bioaccumulation contributed most in copper reduction under anaerobic conditions. Overall, the results suggested the facultative strain C. freundii JPG1 had great potential in the treatment of copper-laden industrial wastewater under both aerobic and anaerobic conditions.