Detoxification and Bioremediation of Hexavalent Chromium Using Microbes and Their Genes: An Insight into Genomic, Proteomic and Bioinformatics Studies

Abstract

Chromium (Cr) is one of the important environmental pollutant generated from various industrial processes as well as extensive mining activities. Contamination of the soil, surface and ground water with Cr6+ is an issue of potential concern due to its toxicity to plant, animal and human. Remediation of chromium contaminated medium is a challenge to modern day research to formulate safe, viable and cost effective technology. There are different methods available for remediation of chromium, but microbial bioremediation is found to be a promising method. Microbial bioremediation of toxic hexavalent chromium to non-toxic trivalent chromium found to be economic and eco-friendly method for chromate detoxification due to their diversity, versatility, and adaptability. The bacterial species those are able to survive under such toxic conditions prevalent in Cr6+contaminated environments are generally tolerant or resistant to chromium. Such bacteria exhibit various mechanism of chromate resistance such as, ion transport, reduction, DNA repair and other. Bacteria employ both enzymatic and non-enzymatic methods of chromate reduction. Enzymatic Cr6+ reduction occurs either in aerobic or anaerobic conditions or both. Anaerobic reduction is carried out by membrane bound reductases such as flavin reductases, cytochromes and hydrogenases and use chromate as terminal electron acceptor while aerobic reduction is associated with soluble proteins and requires nicotinamide adenine dinucleotide phosphate (NADPH) and flavin mononucleotide (FMN) as an electron donor.