Characterization of enzymatic reduction of hexavalent chromium by Escherichia coli ATCC 33456

Abstract

Chromium reduction by Escherichia coli ATCC 33456 quantitatively transferred hexavalent chromium, Cr(VI), to trivalent chromium, Cr(m). The reduced chromium was predominantly present in the external medium. Supernatant fluids of cell extract, obtained by centrifugation at 12,000 and 150,000 x g, showed almost the same Cr(VI) reduction activity, indicating that Cr(VI) reduction by E. coli ATCC 33456 was a largely soluble reductase activity. In studies with respiratory inhibitors, no inhibitory effects on aerobic and anaerobic Cr(VI) reduction were demonstrated by addition of cyanide, azide, and rotenone into both intact cell cultures and supernatant fluids of E. coli ATCC 33456. Although cytochromes b and d were identified in the membrane fraction of cell extracts, Cr(VI) was not reduced by the membrane fraction alone. The cytochrome difference spectra analysis also indicated that these cytochromes of the respiratory chain require the presence of the soluble Cr(VI) reductase to mediate electron transport to Cr(VI). Stimulation of Cr(VI) reduction by an uncoupler, 2,4-dinitrophenol, indicated that the respiratory-chain-linked electron transport to Cr(VI) was limited by the rate of dissipation of the proton motive force.

Survival and chromate reducing ability ofPseudomonas aeruginosain industrial effluents

“…In addition to sulphate, the high salinity of the tannery effluent may also effect chromium toxicity to the cells (Reidel 1984). The electroplating effluent contained high concentrations of Cu 2¦ (65 ppm) and Zn 2¦ (133 ppm), which have been shown to be highly toxic to chromate reduction by Enterobacter cloacae (Ohtake et al 1990b) and Escherichia coli ATCC3456 (Shen and Wang 1993). An increased population size but a lower rate of chromate reduction in C-, N-and P-supplemented electroplating effluent suggests that because of the 200-fold dilution, the effluent became highly nutrient deficient, but concentrations of metals and other factors toxic to chromate reduction may still have remained at a toxic level.…”

Chromate Reduction in Shewanellaoneidensis MR‐1 Is an Inducible Process Associated with Anaerobic Growth

“…One way to remediate Cr(VI) contamination is by microbial reduction of Cr(VI) to trivalent chromium (Cr-(III)), which is less water-soluble, less mobile, and much less toxic than Cr(VI) (3,9,10). Numerous bacterial genera including Pseudomonas, Bacillus, Enterobacter, Deinococcus, Desulfovibrio, Rhodobacter, Shewanella, Microbacterium, and Escherichia (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21) have been shown to reduce Cr(VI). Reduction of Cr(VI) has been reported under both aerobic and anaerobic conditions (22)(23)(24) and has been shown to be a redox-sensitive process (25,26).…”

Isolation and characterization of a chromium‐reducing bacterium from a chromated copper arsenate‐contaminated site

“…Several species use Cr(VI) as a terminal electron acceptor in their respiratory chains and these include Pseudomonas aeruginosa (Gvozdyak et al, 1986), Bacillus subtilis (Gvozdyak et al, 1986), Pseudomonas fluorescens (Bopp and Ehrlich, 1988), Enterobacter cloacae (Wang et al, 1989) and some sulphatereducing bacteria (Fude et al, 1994;Tebo and Obraztsova, 1998). Other strains utilize a soluble enzyme that catalyses the reduction of Cr(VI) to Cr(III), leading to decreased uptake of chromium; this is thought to be a detoxification strategy (Horitsu et al, 1987;Ishibashi et al, 1990;Shen and Wang, 1993). Once reduced by microbial processes, the Cr(III) can then bind to electronegatively charged surface functional groups in the cell layers (Beveridge and Murray, 1976) and form stable nucleation sites for further precipitation of Cr(III) mineral phases (McLean et al, 1999).…”