Reduction of chromate by bacteria isolated from the cooling water of an electricity generating station

Abstract

Chromate-reducing bacteria were isolated from the cooling water of an electricity generating station where reduction of chromate had caused blockage of pipes by precipitation of chromium(III) oxide. Isolates identified included the genera Alcaligenes, Vibrio, Bacillus, Micrococcus, Staphylococcus and Corynebacterium. Isolate VMC-2 with the highest chromate-reducing activity was tentatively identified as Comanonas testosteroni. The concentration of added chromate (K2CrO4, 20 μM)_decreased by 95% during 45 min incubation with whole cells of VMC-2. In comparison, two Fe(III)-reducing isolates, Vibrio metschnikovii and Aeromonas hydrophila, from lake sediments, showed similarly high chromate-reducing activities, and were able to reduce 99% of added chromate (20 μM) in 45 min. Moderate Cr(VI)-reducers included strains of Bacillus, Vibrio and Corynebacterium. Micrococcus and Staphylococcus did not reduce Cr(VI). Sulfate (0.5 and 1.0 mM) inhibited the reduction of chromate by VMC-2 suggesting competition between the two oxyanions. Chromate-reducing activity was located in the soluble fraction of this isolate. The intermediacy of Cr(V)_in the reduction of chromate was confirmed by EPR spectroscopy. The bactericidal activity of hypochlorite towards isolate VMC-2 was determined. © 1995 Society for Industrial Microbiology.