Chromate removal from contaminated groundwater using indigenous bacteria

Total Forest Industries Ltd., is a Canadian company, which owns a wood preserving business in Acton, Ontario. Over the many years of operation, the chromated copper-arsenate (CCA) solution used to preserve the wood has contaminated the underlying soils and groundwaters at the site. Copper and arsenic are bound to the soil, however due to unfavourable environmental conditions, chromium which is a highly toxic water-soluble metal in its hexavalent state, Cr(VI), has become mobile in the groundwaters and therefore demands immediate corrective action. After ceasing operations, the company is interested in using in situ or on-site bioremediation as a possible strategy to clean up the toxic metal contamination as opposed to using potentially hazardous chemical remediation alternatives. Recently, a bacterium capable of reducing chromium to an insoluble solid Cr(III) precipitate on its surface, thereby effectively removing the toxic Cr(VI) from solution, has been isolated from the contaminated site. An 16s rRNA sequence indicated that this efficient chromium reducer might be a yet unidentified gram-negative strain, which is tolerant to high levels of Cr(VI) (similar to 500 mg/L) and, possibly, to Cu and As (40 mg/L). The exact mechanism by which this indigenous microorganism reduces aqueous Cr(VI) to a solid Cr(III) precipitate are varied since our results indicate there are a combination of biochemical and surface mediated reactions implicated in the process. The crude enzyme activity in a soluble cytoplasmic fraction of the cell yielded an estimated K-m, of 23 mg/L and a V-max,, of 0.98 mgCr/h mg protein(-1).