Growth Responses of Chromium (vi) Tolerant Bacteria to Different Concentrations of Chromium

Chromium (vi) – tolerant bacterial strains, namely, Bacillus sp., Pseudomonas sp., Escherichia coli and Staphylococcus sp. were isolated from the oxidation ditch of a sewage treatment plant. All the isolates tolerated high concentrations of up to 500 μg/ml chromium (vi) in nutrient broth. The growth responses of the bacterial isolates to different concentrations of chromium (vi) were carried out in this study. The responses of the bacteria were dependent on time of incubation and chromium (vi) concentration. The analysis of the results showed that there was significant difference (P ˂ 0.05) in the growth of the isolates at different concentrations of hexavalent chromium. As the concentration of chromium increased, the growth of the bacterial isolates decreased. The growth of the isolates was slightly inhibited at hexavalent chromium concentration of 200 μg/ml and highly inhibited at 500 μg/ml when compared to other lower concentrations such as 50, 100 and 150 μg/ml. The present study revealed the capacity of the bacterial isolates to grow at different concentrations of Cr (vi) and such bacteria can be used to remove Cr (vi) from the