Cadmium resistant bacteria from industrial wastewater and their use as bioremediator

The present study is aimed at assessing the ability of six Zn 2 + resistant bacterial strains (CM BL.Zn 4-Zn9), isolated from industrial waste of Lahore Chemicals and Medi Pak Pharmaceutical Company, Lahore, to decontaminate the industrial effluents of Zn 2 + . The minimum inhibitory concentrations (MICs) of Zn 2 + ranged between 450-450 m/ml. They also tolerated Pb 2 + (1.6-2 mg/ml), Ni 2 + (300-480 μg/ml), Cu 2 + (350-370 μg/ml), Cd 2 + (260-500 μg/ml) and Cr 6 + (375 μg/ml). All isolates were resistant to Ceftizoxime and Cefuroxime. CMBL Zn9 was resistant to Kanamycin, CMBL.Zn5 to Cephalothin and CMBL.Zn5 and Zn9 to Tetracycline. All other bacterial strains were sensitive to respective antibiotics. The isolates showed typical growth curves, but they showed optimum growth at 37°C and pH varying between 6-8. Large sized plasmids (23 kb) were present in all the bacterial strains, which could not be cured with Ethidium Bromide, Acridine Orange or SDS. For determination of location of the gene for zinc resistance on chromosomes or plasmid the DH5 a cells of E. coli were transformed with the plasmids of bacterial isolates. The transformed cells did not grow on selective medium containing 300 μg/ml of Zn 2 + , which showed that resistant gene was not located on the plasmids. The growth of these transformed cells on selective medium containing 200 mg/ml Cd 2 + (which was used as a control) was, however, an indication that transformation itself was successfully done. Metal processing ability of the isolates was determined in a medium containing 100 mg/ml of Zn 2 + for 24 hours. CMBL.Zn4, CMBL.Zn5 CMBL.Zn6, CMBL.Zn7, CMBL.Zn8 and CMBL.Zn9 reduced 28%, 10%, 20% 14%, 15% and 18% zinc from the medium after 24 hours. These strains were hence not very efficient zinc accumulators.