Comparative Chromium Bioremediation Efficiency of Planktonic and Biofilm Bacteria Isolated from Indigenous Sources

Abstract

The main purpose of this research project was to check the chromium reduction ability of indigenous bacteria in their biofilm modes of life and planktonic cells. For this purpose, Chromium resistant bacteria were isolated from soil samples and wastewater collected from tanneries and wastewater treatment plant in Kasur, Punjab, Pakistan. The selected bacterial isolates were checked for their biofilm forming ability both quantitatively and qualitatively in the absence and presence of chromium stress. Minimum inhibitory concentration (MIC) for the chromium metal of each selected bacterial isolate was found to be varied. The highest MIC value of the bacterial isolates was 950 µg/ml. On the basis of MIC and biofilm forming ability, four bacterial isolates AN1, AN2, AN4 and AN5 were selected for further studies. These bacterial isolates were characterized morphologically, physiologically and biochemically. The pH and optimum temperature were found to be 7 and 37ºC respectively for the growth of these bacterial isolates. On the basis of biochemical characteristics, these bacterial isolates were found to be the members of three different genera, i.e., AN1 and AN4 belonged to Bacillus, AN2 belonged to Pseudomonas and AN5 belonged to Salmonella. Chromium reduction ability of these selected bacterial isolates was checked with Diphenyl carbazide method. After 48 hours, the bacterial isolates showed increased rate of chromium reduction as compare to the 24 hours in both planktonic and biofilm mode of life. In biofilm mode of growth, bacterial isolates AN1 and AN4 (Bacillus) showed more chromium reduction as compared to their planktonic cells whereas in planktonic cells mode, AN2 (Pseudomonas) and AN5 (Salmonella) showed more chromium reduction as compared to their biofilm mode of growth.