ABSTRACT
The rapidly increasing industrialization has mobilized chromium into the pristine environment. This has resulted in an increase in the concentration of chromium severalfold than usually found in nature. Given its potential mutagenic and carcinogenic effects in humans, hexavalent chromium has been prioritized as one of the major inorganic environmental pollutants by environmental agencies of different countries. In the environment, chromium is prevalent in several oxidation states; however, the two most ecologically stable forms are the Cr(III)–trivalent chromium and Cr(VI)–hexavalent chromium. The toxicity potential of Cr(VI) is considered higher than Cr(III) due to its high solubility and mobility in the aqueous environment. Many indigenous bacterial species have been identified at chromium-contaminated sites. These bacterial strains have evolved different strategies to evade chromium toxicity and also have the ability to detoxify or transform the toxic hexavalent chromium. This ability of certain bacterial species for reductive immobilization of Cr(VI) to innocuous Cr(III) via soluble or cytoplasmic enzymes or via other mechanisms offers a great advantage in the biological treatment of hexavalent chromium. The bacterial mechanisms to evade chromium toxicity generally involve decreased uptake or exclusion of Cr(VI) compounds through the cell membranes, upregulation of genes associated with oxidative stress response, or biosorption. Given the successful results of several studies using microorganisms to mitigate chromium pollution, eco-friendly bioremediation approaches are nowadays considered to be pragmatic over physicochemical treatment processes. This chapter focuses on the bacterial interactions with chromium and bacterial detoxification strategies in treating hexavalent chromium pollution.
