Toxicity of Hexavalent Chromium and Its Microbial Detoxification Through Bioremediation
Chromium exists in different oxidation states ranging from −IV to +VI, in relation to human exposure. Chromium contaminated ecosystems through ore refining, chemical and refractory processing, cement plants, automobile brake lining and catalytic converter
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Abstract
Chromium exists in different oxidation states ranging from IV to +VI, in relation to human exposure. Chromium contaminated ecosystems through ore refining, chemical and refractory processing, cement plants, automobile brake lining and catalytic converters for automobiles, leather tanneries and chrome pigments. It’s having carcinogenic and mutagenic effects upon both acute and chronic exposures because of its high water solubility, etc. Hexavalent chromium (Cr6+) is known to have 100-fold more toxicity than its other forms. Chromium reduction has been evaluated in both aerobic and anaerobic conditions by a group of microorganisms. Bioremediation is a viable, environment-friendly technology for cleaning up the chromium-contaminated sites. Bacterial strains such as Klebsiella pneumoniae, Bacillus firmus, Pseudomonas maltophilia and Mycobacterium sp. are capable of absorbing Cr6+ efficiently into their biomass. The fungal strains, Aspergillus flavus, Aspergillus sp. and A. niger, are also capable of transforming Cr6+ to Cr3+ relative to cell-wall-binding properties by their soluble enzymes and membrane-associated reductases of electron transfer systems. Infrared spectral analysis showed that bacterial isolates having the binding groups – OH, –NH2 and C¼O conjugated with –NH were responsible for Cr6+ adsorption within the cell. Cr6+ serves as electron acceptor involving cytochromes b and c. Genetic and protein engineering may further enhance the Cr6+ reductase efficiency. The direct application of Cr6+ reductases may be a promising approach both in situ and ex situ bioremediation in a wide range of environments.
S. Chaturvedi · S. M. P. Khurana (*) Amity Institute of Biotechnology, Amity University Haryana, Gurgaon, India A. Khare Amity School of Applied Sciences, Amity University, Mumbai, India # Springer Nature Singapore Pte Ltd. 2021 M. P. Shah (ed.), Removal of Emerging Contaminants Through Microbial Processes, https://doi.org/10.1007/978-981-15-5901-3_25
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Keywords
Cr6+ · Cr3+ · Bioremediation · Biotransformation · Bioreduction · Bioabsorption · Cytochromes
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Introduction
Chromium is increasing in the environment by different industries as a result of metallurgical refractory, chemical industries, tannery, agriculture and many more anthropogenic activities. It is one of the most toxic metals and abundant pollutants in both aquatic and terrestrial ecosystem (Costa et al. 2003). It exists in environment in different oxidation states; it is found that hexavalent Cr(VI) and trivalent Cr(III) are more stable in nature and enter in bacterial and mammalian cells via transport system (Ackerley et al. 2004). Cr(III) is a less toxic, trace element essential for functioning of the environment. It is readily converted into Cr(VI) under natural conditions, and it reacts with nucleic acid and other cell components and causes mutagenic, carcinogenic effects on biological system (Wang et al. 2009). Cr bioremediation mechanisms include biosorption, bioaccumulation, complexation, electrosta
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