Cloning and expression of chromate reductase from Bacillus paramycoides S48 for chromium remediation

Abstract

This study explores the production and characterization of chromium reductase from Bacillus paramycoides S48, focusing on its ability to effectively reduce toxic hexavalent chromium to less harmful chromium. The strain exhibited 65% reduction in Cr(VI) within 96 h at 30 °C. Clear morphological and functional group shifts on strain S48 cell surface treated with metal were noted using analytical tools i.e. SEM–EDX and FT-IR. The physico-chemical conditions such as temperature, pH and nutritional factors were optimized for better chromate reductase yield using Placket-Burman and Central Composite design software. The purified chromate reductase, obtained through size exclusion column chromatography, demonstrated a specific activity of 1416.5 U/mg, and 6.6-fold increase in purity, with a molecular mass of approximately 35 kDa. The enzyme exhibited stability at temperature 30–40 °C and pH 5.0–8.0. Furthermore, the purified chromium reductase achieved, 80% reduction of toxic Cr(VI) at temperature 35 °C after 96 h. The BparChR gene was successfully cloned into the pET-28a vector, expressed in E. coli BL21, and purified through Ni-Affinity ion exchange chromatography. The recombinant BparChR protein displayed a specific activity of 1680 U/mg, and a purification fold of 5.73 times. The BparChR exhibited a remarkable 90% reduction in chromium after 96 h, surpassing the efficacy of whole-cell and native chromium reductase. This study concludes that B. paramycoides S48, holds promise for the cost-effective and environmentally friendly detoxification of chromium in contaminated industrial effluents.