The biocathode of a microbial fuel cell (MFC) offers a promising potential for the reductive treatment of oxidized pollutants. In this study, we demonstrated biological Cr(VI) reduction in the cathode of a MFC and identified putative Cr(VI) reducing microorganisms. The MFC was continuously monitored for Cr(VI) reduction and power generation. Acetate was provided to the anode compartment as substrate and bicarbonate was added to the cathode compartment as the sole external carbon source. The contribution of biomass decay and abiotic processes on Cr(VI) reduction was minimal, confirming that most of the Cr(VI) reduction was assisted by microbial activity in the cathode, which utilizes electrons and protons generated from the oxidation of acetate in the anode compartment. Relatively fast Cr(VI) reduction was observed at initial Cr(VI) concentrations below 80 mg/L. However, at 80 mg Cr(VI)/L, Cr(VI) reduction was extremely slow. A maximum Cr(VI) reduction rate of 0.46 mg Cr(VI)/g VSS.h was achieved, which resulted in a current and power density of 123.4 mA/m(2) and 55.5 mW/m(2), respectively. The reduced chromium was nondetectable in the supernatant of the catholyte which indicated complete removal of chromium as Cr(OH)(3) precipitate. Analysis of the 16S rRNA gene based clone library revealed that the cathode biomass was largely dominated by phylotypes closely related to Trichococcus pasteurii and Pseudomonas aeruginosa, the putative Cr(VI) reducers.