Assessment of Tolerance and Bio-reductive Potential of Hexavalent Chromium (VI) to Trivalent Chromium (III) via Isolated Microorganisms from Contaminated Soil
Abstract
This study addresses the growing environmental concern of chromium contamination, particularly the toxicity of hexavalent chromium [Cr (VI)] in soil and aquatic systems. The primary objective of this study is to evaluate the mechanisms by which soil microorganisms tolerate and detoxify hexavalent chromium [Cr (VI)] and to assess their potential for sustainable bioremediation through bio-reductive transformation into the less toxic trivalent form [Cr (III)]. The research problem focuses on understanding how soil microorganisms tolerate and detoxify Cr (VI), a highly toxic, carcinogenic, and mobile form of chromium, and how these biological processes can be harnessed for sustainable bioremediation. The methodology of this study is based on a comprehensive review of existing literature focusing on the isolation, identification, and characterization of chromium-resistant microorganisms. Techniques such as 16S rRNA gene sequencing, Diphenylcarbazide (DPC) assays, and agar well diffusion methods have been analyzed to evaluate microbial resistance and reduction efficiency. Various microbial mechanisms, including biosorption, bioaccumulation, and biotransformation, are examined under different environmental conditions such as pH, temperature, and oxygen availability. Key findings reveal that several bacterial genera, including Bacillus, Pseudomonas, and Streptomyces, demonstrate high tolerance and efficiency in reducing Cr (VI) to Cr (III). Microbial detoxification occurs through enzymatic reduction, intracellular sequestration, efflux systems, and extracellular binding. Biosorption efficiencies exceeding 70–80% have been reported under optimal conditions. Overall, the study concludes that microbial bioremediation is a cost-effective, environmentally friendly, and efficient approach for mitigating chromium pollution and restoring ecosystem balance. This review provides a critical framework linking microbial physiology, enzymatic mechanisms, and environmental application, highlighting microbial bioremediation as a cost-effective and eco-friendly strategy while identifying future directions for improving field-scale implementation.
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