Metabolic pathway of Cr(VI) reduction by bacteria: A review

Heavy metal wastes, particularly hexavalent chromium [Cr(VI)], are generated from anthropogenic activities, and their increasing abundance has been a research concern due to their toxicity, genotoxicity, carcinogenicity and mutagenicity. Exposure to these dangerous pollutants could lead to chronic infections and even mortality in humans and animals. Bioremediation using microorganisms, particularly bacteria, has gained considerable interest because it can remove contaminants naturally and is safe to the surrounding environment. Bacteria, such as Pseudomonas putida and Bacillus subtilis, can reduce the toxic Cr(VI) to the less toxic trivalent chromium Cr(III) through mechanisms including biotransformation, biosorption and bioaccumulation. These mechanisms are mostly linked to chromium reductase and nitroreductase enzymes, which are involved in the Cr(VI) reduction pathway. However, relevant data on the nitroreductase route remain insufficient. Thus, this work proposes an alternative metabolic pathway of nitroreductase, wherein nitrate activates the reaction and indirectly reduces toxic chromium. This nitroreductase pathway occurs concurrently with the chromium reduction pathway.

Automated summary

Heavy metal wastes, like hexavalent chromium [Cr(VI)], are a growing concern due to their toxicity, genotoxicity, carcinogenicity, and mutagenicity. Exposure to these pollutants can result in chronic infections and mortality in humans and animals. Bioremediation using bacteria, such as Pseudomonas putida and Bacillus subtilis, is a promising approach for removing these contaminants naturally and safely. The bacteria can reduce the toxic Cr(VI) to less toxic Cr(III) through mechanisms involving chromium reductase and nitroreductase enzymes. However, more research is needed on the nitroreductase pathway.