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Abstract

Four chromium resistant bacterial strains CrT-4, CrT-S, CrT-6, and CrT-7 that reduce hexavalent chromium C(VI) to trivalent chromium were isolated from the effluents of East-Pak Chrome tannery situaled near Lahore-Sheikhupura road. These chromium resistant bacterial strains were able to grow both an liquid as well as in solid media in the presence of very high concentration of chromate i.e. up to 25mg ml in nutrient broth and 40 mg ml in nutrient agar, Strains CrT-4, C7T-6, and CrT-7 were gram-negative motile rods. They have circular convex colonies with entire margins whereas strain CrT-5 was gram-positive cocci with irregular flat colonies. All the strains were facultatively anerobes. CYT-4, CrT-6. and CrT-7 showed affinities with Pseudomonadacee while CrT-S shared character with Micrococcaccac. In majority of strains optimum pliwas 8 in chromate-supplemented media but they preferred pH 7 in Chromate free media. All of them give better growth at 37° C. They were resistant to different antibiotics and metallic salts and reduce hexavalent chromium acrobically. The rate of hexavalent chromium reduction is more with low initial chromate concentration (100 ug ml") and high inoculum size. For optimum chromate reduction all of them preferred pH 7 at 37° C. Four strains could also caused reduction of hexavalent chromium in industrial effluents and Crf-4 exhibited the highest reduction potential.

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