Mechanism of Cr(VI) reduction by an indigenous Rhizobium pusense CR02 isolated from chromite mining quarry water (CMQW) at Sukinda Valley, India

Abstract

Toxicological assessment of CMQW generated due to chromite mining activities at Sukinda, valley has revealed high chromium contamination along with Zn and Fe. The present study focused on mechanism of chromate reduction by an indigenous multi-metal tolerant bacterium Rhizobium pusense CR02 isolated from CMQW. Isolated strain has shown resistance upto (520 mg/L) of Cr(VI) with IC50 value of 385.4 mg/L. The highest reduction rate 8.6×10 -2 /h was recorded with 20 mg/L of initial concentration of Cr(VI). Extracellular (3.06±0.012 U/mL), intracellular (3.60±0.13 U/mL) and membrane (1.89±0.01 U/mL) associated chromate reductases were found to be involved for reduction. The extracellular polymeric substances (EPS) produced by the isolate also enhanced reduction activity of 46.32±1.69 mg/L after 72 h with initial concentration of 50 mg/L. FTIR analysis revealed the involvement of functional groups -OH, -CO and -NH for Cr(VI) biosorption whereas P=O, -CO-NH-and -COOH interacted with Cr(III). Zeta potential with less negative surface charge favored reduction of Cr(VI). Treatment of CMQW by bacterial isolate detoxi ed Cr(VI) minimizing chromosomal aberrations in root cells of Allium cepa L., suggesting the role of Rhizobium pusense CR02 as a promising bio-agent for Cr(VI) detoxi cation. DeclarationsCredit author statement Hrudananda Sahoo: Conceptualization, methodology, execution of all experiments, data analysis, validation, manuscript writing, review and editing. Kanika Kisku, Kumar S. K. Varadwaj, and Prasannajit Acharya: Data analysis, review, and editing. Umesh Chandra Naik: Conceptualization, validation of data, review, and editing.Acknowledgments would like to express our sincere thanks to SERB, Govt. of India (YSS/2015/001089) for the nancial support. We would also acknowledge University Grants Commission (UGC), Govt. of India for providing Fellowship. We would also like to acknowledge CIF, OUAT, Bhubaneswar for ICP-OES and Zeta potential analysis; CSIR-NIIST, Thiruvananthapuram, Kerala for XPS analysis, and ILS, Bhubaneswar for DNA sequencing facilities. We are also highly thankful to the research