Isolation of hexavalent chromium-reducing anaerobes from hexavalent-chromium-contaminated and noncontaminated environments

Abstract

Hexavalent chromium [Cr(VI)], is a toxic, water-soluble contaminant present in many soils and industrial effluents. Bacteria from various soils were examined for Cr(VI) resistance and reducing potential. Microbes selected from both Cr(VI)-contaminated and -noncontaminated soils and sediments were capable of catalyzing the reduction of Cr(VI) to Cr(III) a less toxic, less water-soluble form of Cr, demonstrating the utility of using a selection strategy for indigenous Cr(VI)-reducing bacteria in a bioprocess. As a result, indigenous Cr(VI)- reducing microbes from contaminated sites should provide the means for developing a bioprocess to reduce Cr(VI) to Cr(III) in nonsterile effluents such as those from soil washes. This approach also avoids the contamination problems associated with pure cultures of allochthonous microorganisms. In addition the apparent ubiquity of Cr(VI)-reducing bacteria in soil and sediments indicates potential for in situ bioremediation of Cr(VI)-contaminated soils and ground water.

Genesis of hexavalent chromium from natural sources in soil and groundwater

“…Considering chromite as a conservative phase of Cr(III), our experiments reveal that even at circumneutral pH, Cr(VI) formation rates of 4.1 nM h Ϫ1 can lead to aqueous Cr(VI) concentrations exceeding World Health Organization standards of 50 g liter Ϫ1 within 100 days; within soils/sediments at pH 5, pore-water residence time of Ͻ10 days could lead to concentrations Ͼ50 g liter Ϫ1 . Countering production, however, will be Cr(VI) reduction, a process transpiring through biologically mediated and abiotic pathways and dominating the fate of Cr under anaerobic conditions (26)(27)(28)(29). Reduction within aerobic soils/sediments will be linked primarily to microbial oxidation of organic matter.…”

Comparative Uptake and P Hytoextraction Study of Soil Induced Chromium by Accumulator and High Biomass Weed Species

“…Leather tanning, electroplating and stainless steel industries contribute to most of the chromium contamination, by disposal of wastewater directly to the streams and/or by over land disposal of sludge or solid waste [21,24]. Non-biodegradability of chromium is responsible for its persistence in the environment; once mixed in soil, it undergoes transformation into various mobile forms before ending into environmental sink.…”

Developments in Bioremediation of Soils and Sediments Polluted with Metals and Radionuclides – 1. Microbial Processes and Mechanisms Affecting Bioremediation of Metal Contamination and Influencing Metal Toxicity and Transport

“…Numerous such bacteria have been isolated, including species of Bacillus, Desulfovibrio, Achromobacter, Aeromonas, Escherichia, Enterobacter and Pseudomonas (Lovley & Phillips 1994;Turick et al 1996). Mechanisms of chromate reduction in anaerobic bacteria appear to involve respiratory electron-transport enzymes (Bopp & Ehrlich 1988;Shen & Wang 1993), with convincing evidence for catalysis by cytochrome c 3 in Desulfovibrio vulgaris (Lovley & Phillips 1994).…”

“…Mechanisms of chromate reduction in anaerobic bacteria appear to involve respiratory electron-transport enzymes (Bopp & Ehrlich 1988;Shen & Wang 1993), with convincing evidence for catalysis by cytochrome c 3 in Desulfovibrio vulgaris (Lovley & Phillips 1994). While it is thermodynamically possible for chromate reduction to generate enough energy to support respiration (Table 2), true chromate respiration remains to be discovered (Lovley & Phillips 1994;Shen & Wang 1993;Turick et al 1996). In aerobic chromate-reducers, reduction may be fortuitously catalyzed by enzymes that have other natural substrates (Cervantes 1991).…”