Deciphering chromate tolerance and reduction ability of an indigenous Bacillus strain isolated from polluted pond sludge for chromium bioremediation

Industrial development has caused significant environmental pollution by discharging chromium (Cr) contaminated hazardous effluents into the ecosystem. The main goal of this study was to isolate, characterize, and assess the Cr(VI) resistance potential of indigenous naturally occurring chromate-resistant bacteria from the Uttar Dinajpur region of West Bengal. Based on the maximum tolerable concentration (MTC) to Cr(VI), a potent indigenous bacterial isolate with an MTC of 400 µg mL^- 1 was selected for a detailed assessment of its Cr(VI) tolerance and reducing abilities. Molecular identification and phylogenetics revealed the isolate as a strain of Bacillus wiedmannii. Cr(VI) resistance ability of the isolate in different pH was analyzed, and a Fourier-transform infrared spectroscopy analysis under different pH in the presence of Cr(VI) was performed to capture the preliminary variation in the metabolic fingerprints. The isolate demonstrated Cr(VI) removal efficiency of 70.27% Cr(VI) at pH 8. The expression of chromate reductase enzyme in constitutive and Cr(VI) induced conditions was measured using different electron donors, and a detailed statistical analysis was performed to determine whether there exists a significant difference in the specific activity of chromate reductase in constitutive and induced conditions. The extracellular chromate reductase had a 98.42% Cr(VI) reduction rate using glucose as an electron donor and it was significantly higher than that of other electron donors, indicating glucose as the preferred electron source for Cr(VI) reduction. The genes responsible for coding enzymes responsible for chromate reduction viz., azoreductase, FMN-dependent NADH-azoreductase type1, and chromate reductase were also detected in the studied isolate. The findings of this study may contribute to the pool of indigenous isolates in countering chromate toxicity and their efficient utilization in chromate detoxification and bioremediation.