Enhanced chromate reduction by resting Escherichia coli cells in the presence of quinone redox mediators

The reduction of Cr(VI) by resting Escherichia coli cells was significantly enhanced by the quinone redox mediators, lawsone, menadione, anthraquinone-2-sulfonate and anthraquinone-2,6-disulfonate. In the presence of 0.2 mM lawsone, over 97.5% Cr(VI) (100 mg l−1) was reduced in 4 h. The mediated reduction occurred at initial Cr(VI) concentrations of 50–250 mg l−1, and increased with increasing initial biomass concentrations from 0.05 to 1.2 g l−1. The addition of glucose as electron donor promoted the reduction process. Cu2+, Ni2+ and Co2+ inhibited, whereas Mn2+ and Pb2+ stimulated reduction. Four rounds of mediated reduction were completed in 19 h, suggesting its stability and persistence. The efficient mediated microbial reduction of Cr(VI) is promising for rapid anaerobic removal of chromate.