A Rice Rhizosphere-Associated Bacillus sp. With Dual Biosorption and Enzymatic Pathways for Chromium (VI) Detoxification.

Hexavalent Cr(VI) is well known hazardous pollutant which not only impairs the soil health but also drastically reduces the plant developmental processes. Here, we observed a plant growth promoting rhizobacterium (Bacillus sp. AKS_bp1) isolated from rice rhizosphere modulating dual roles in Cr(VI) detoxification and plant responses. Initially, Bacillus sp. (AKS_bp1) showing PGPR characteristic along with a high tolerance to varying Cr(VI) concentrations in laboratory condition. Moreover, the strain also reduce the Cr(VI) concentration (~80%) with a bio-sorption capacity reaching 95.21% under 72 h incubation followed by pseudo first order kinetics. Further, biosorption studies through infrared spectroscopy and scanning micrograph showing the presence of hydroxyl, polysaccharides, and amino-nitrogen based functional groups for Cr binding. Likewise, internal Cr(VI) bio-removal the activity of Cr reductase was recorded with changes through 20, 40, 60, and 80 ppm of Cr(VI) in solution. Enzyme activity was validated with varying pH (5-8), temperature (21°C-45°C) and metal (Ag2+), salt (sodium dodecyl sulphate) etc. In detoxification pathways, the strain recorded further upregulation of antioxidative enzymes highlighting a well-established defence against Cr induced toxicity. Remarkably, application the strain was able to remove 36.86% of Cr(VI) when incubated in tannery effluents through 72 h. Conclusively, the present work provides importance of Bacillus sp. (AKS_bp1) mediated bio-removal of contaminated industrial effluents, which predominantly rich in Cr(VI). This bacterial strain also significantly reduced lipid peroxidation and polyphenol oxidation. Moreover, it offers potential for additional chemical modifications and sustainable bioremediation of Cr and other toxic metals, thereby improving crop growth and productivity.