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

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 bioremediationMicrobial 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 detoxificationChromate detoxification due to their diversity, versatility, and adaptability. The bacterial species those are able to survive under such toxic conditions prevalent in Cr6+ contaminated environmentsContaminated environments are generally tolerant or resistant to chromium. Such bacteriaBacteria 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 aerobic and anareobic reduction enzymatic reduction is associated with soluble proteins and requires nicotinamide adenine dinucleotide phosphate (NADPH) and flavin mononucleotide (FMN) as an electron donor. Assessment of bacterial communities surviving under such hostile conditions i.e. chromium contaminated environment Contaminated environments is important for bioremediation study which can be made by culture dependent and culture independent (metagenomics) methods. Thus, many bacteriaBacteria were isolated and identified from different contaminated environment and their Cr6+ reduction potentials were evaluated. Several study reports on bacterial communities from other contaminated environments provided the structural, functional and metabolic characteristics to understand their mechanisms of resistance. In recent years, bioinformatics have been demonstrated to be a useful tool for determination of structure and function of genes and proteins associated in chromate reduction. In this chapter, a detailed description on various methods of assessing the microbial community patterns in chromium contaminated soils as well as identification of underlying mechanisms involved in chromate resistance have been provided which could be further exploited biotechnologically for bioremediation of hexavalent chromium from the polluted environment. Apart from this, in silico analysis of the genes and proteins associated in chromate resistance and reduction using various bioinformatics tools and techniques were also discussed.