CR(VI) REDUCTION BY BACILLUS-COAGULANS ISOLATED FROM CONTAMINATED SOILS

Investigation on Cr(VI) reduction was conducted using bacteria isolate d from soil samples receiving electroplating wastewater. Chromium redu ction capacity of these isolates was compared with that of Pseudomonas aeruginosa, a pure culture procured from the Institute of Microbial T echnology, as well as Bacillus circulans, a laboratory isolate from ga rden soil. Bacillus coagulans, isolated and identified from chromium p olluted soil, gave maximum reduction potential among all organisms stu died. Malate was found to yield maximum biotransformation out of four electron donors employed. B. coagulans was able to reduce Cr(VI) even at 10 mM initial Cr(VI) concentration. With an increase in initial cel l density, Cr(VI) reduction capacity was also increased; however, maxi mum specific biotransformation occurred at low cell densities. The opt imum pH for Cr(VI) reduction was 7. Sulphates and nitrates did not com pete with Cr(VI) for accepting the electrons. The presence of respirat ory inhibitors like DNP and NaN3 marginally reduced the Cr(VI) reducti on capacity. Cell free extracts were able to reduce Cr(VI) even in the absence of external electron donors; however, marginal increase was f ound in the presence of malate, nicotinamide adenine dinucleotide, and reduced nicotinamide adenine dinucleotide. The contribution of cell m embrane in Cr(VI) reduction was negligible. Hence, the soluble enzymes appear to be responsible for Cr(VI) reduction by B. coagulans.