Toxicity of Hexavalent Chromium and Its Microbial Detoxification Through Bioremediation

2021 
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 C=O 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.
    • Correction
    • Source
    • Cite
    • Save
    • Machine Reading By IdeaReader
    110
    References
    0
    Citations
    NaN
    KQI
    []