Bacterial reduction of toxic Cr (VI) into Cr (III)

Two chromium-resistant bacterial strains CrT-1 and CrT-13, which can tolerate K2CrO4 up to 40 mg x mL(-1) on nutrient agar, 25 mg x mL(-1) K2 CrO4 in nutrient broth, and up to 10 mg x mL(-1) in acetate-minimal media, were used in this study. On the basis of 16S rRNA, strain CrT-1 was identified as Ochrobactrum intermedium and CrT-13 as Brevibacterium sp.. Uptake of chromate was greater in living cells than in heat-killed cells. Ochrobactrum intermedium CrT-1 reduced 73% and 41% of Cr(V) while Brevibacterium CrT-13 reduced 62% and 48% Cr(VI) at an initial chromate concentration of 750, and 1500 microg x mL(-1), after 96 hours with an inoculum size of 9.6 x 10(7) cells mL(-1). Different heavy metals at low concentrations did not affect the reduction potential of the strains significantly. Ochrobactrum intermedium CrT-1 reduced 84% and 65% while Brevibacterium CrT-13 reduced 60% and 44% of Cr(VI) at an initial Cr(VI) concentration of 250 and 500 microg x mL(-1), respectively, in an industrial effluent sample.