Is Cr(III) toxic to bacteria: toxicity studies using Bacillus subtilis and Escherichia coli as model organism

The objective of this work is to detect the mode of damage caused by Cr(III), one of the widely used industrial pollutant on Bacillus subtilis—industrial strain 168 and Escherichia coli MTCC 40. Bioassays are very sensitive, precise, economical and rapid for detecting early stages of pollution. The detrimental effect of trivalent chromium becomes clear from the growth profile and growth inhibition studies. Mode of action of damage by trivalent chromium in bacterial model was found to be oxidative, as chromium is one of the redox active metals. The generation of reactive oxygen species (ROS) resulted in membrane damage which in turn had a detrimental effect on the membrane proteins as well as the DNA. The structural changes in the SEM and AFM images clearly reveals the damage caused by Cr(III) to the test bacterial models. Trivalent chromium causes greater DNA, protein and membrane damage in case of E. coli than B. subtilis. Membrane damage caused by ROS becomes evident from the production of Thiobarbituric acid reactive substances (TBARs) as the mechanism of killing followed by DNA damage and the production of elevated levels of stress proteins known as extracellular cellular proteins.