A Soluble Flavoprotein Contributes to Chromate Reduction and Tolerance by Pseudomonas putida

As a consequence of its toxicity, the accumulation of chromate [Cr(VI)] in drinking water poses a serious risk to human health. Conventional approaches to groundwater remediation and the regeneration of potable water supplies are expensive and have, to date, been limited in their effect. From a biological perspective, chromium(III) compounds, the end products of bacterial chromate reduction, are less dangerous; not only are they less toxic than chromate, they also have very low solubility, restricting their spread and their biological availability. Thus, reduction of chromate by bacteria is an attractive strategy for its remediation. Through biomolecular engineering, it should be possible to improve the chromate‐reducing activities of wild type bacterial enzymes, and to produce bacteria capable of expressing such activities at a high level under nutrient‐poor and stressful field conditions. With this goal in mind, we have identified, purified and characterised a chromate‐reducing flavoenzyme from Pseudomonas putida . The results presented here indicate that this enzyme is an efficient reducer of Cr(VI) in vitro , and also plays an important role in chromate detoxification in vivo . Our ongoing studies have also identified areas where improvement in these enzymes would enhance chromate bioremediation.