Cr(VI) reduction by Enterobacter sp. DU17 isolated from the tannery waste dump site and characterization of the bacterium and the Cr(VI) reductase

• Newly isolate Enterobacter sp. DU17 reduced Cr(VI) extracellularly.
• Complete reduction of 100 mg L−1 Cr(VI) noticed within 16 h in presence of glucose.
• Maximum homology of Cr(VI) reducing gene was established with flavoprotein.
• Strain DU17 showed low multiple antibiotic resistance (MAR) index.

Out of nineteen bacteria screened from the tannery waste dump site, the most effective isolate, strain DU17 was selected for Cr(VI) reduction process among the non-pathogenic once. Based on 16S rRNA gene sequence analysis, the bacterium was identified as Enterobacter sp. DU17. Its amplified Cr(VI) reductase gene showed maximum homology with flavoprotein of Enterobacter cloacae. Enterobacter sp. DU17 reduced Cr(VI) maximally at 37 °C and pH 7.0. Various co-metals, electron (e−) donors and inhibitors were tested to study their effect on Cr(VI) reduction. In presence (0.2% each) of glucose and fructose, Enterobacter sp. DU17 reduced Cr(VI) completely after 16 and 20 h, respectively. Since the concentration of total Cr was invariable after remediation as detected through AAS analysis, this experiment disclosed that responsible operation was associated with extracellular Cr(VI) reduction process rather than uptake mechanism. Multiple antibiotic resistance index of 0.08 for this bacterium was very low as compared to standard risk assessment value of 0.20. With high Cr(VI) reducing capability, non-pathogenicity and antibiotic sensitivity, Enterobacter sp. DU17 is found to be very efficient in removing Cr(VI) toxicity from the environment.

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