UNLABELLED

A novel Cr(VI)-resistant haloalkaliphilic bacterial strain NRC-R, identified as , was isolated from hypersaline soda lakes and characterized for its Cr(VI) bioreduction efficiency. Strain NRC-R grew well and effectively reduced Cr(VI) under a wide range of sodium chloride, pH, shaking velocity and temperature, showing maximum Cr(VI) reduction at 8% NaCl, pH 10, 150 rpm and 35 °C, respectively. Strain NRC-R was able to grow and reduce Cr(VI) effectively in the presence of different heavy metals and oxyanions (Pb, Zn, Co, Mn, Ni, Mo, HPO , NO , SO and HCO ). Furthermore, Fe and Cu significantly enhanced the Cr(VI) removal by about 1.5 fold. Strain NRC-R could reduce Cr(VI) using a variety of electron donors, exhibiting a maximum reduction in the presence of NADH and fructose. The bioremoval of Cr(VI) using strain NRC-R was due to direct enzymatic reduction and the chromate reductase activity was mainly detected in the bacterial cell membrane. Under the optimized conditions, strain NRC-R showed a remarkable Cr(VI) bioreduction with highest reduction rate of 240 uM/h. Cr(VI) concentrations of up to 3 mM (888.5 mg/L) and 4 mM (1177 mg/L) were completely reduced within 16 h and 32 h, respectively. TEM and SEM-EDX analyses confirmed the biosorption of chromium species into the cells. To the best of our knowledge, this is the first report about Cr(VI) reduction by In conclusion, . NRC-R was a highly efficient Cr(VI) reducing haloalkaliphilic bacterium that has a significant potential in the bioremediation of Cr(VI)-contaminated environments.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03082-2.