Microcalorimetric study on effect of chromium(III) and Chromium(VI) species on the growth of Escherichia coli

The effects of Cr(III) and Cr(VI) species (Cr2O72 , CrO42- and Cr3+ on the growth of Escherichia coli (E. coli) have been investigated in detail by microcalorimetry at 37 degrees C. Parameters including the growth rate constant (k), inhibitory ratio (I), half-inhibitory concentration (IC50), total heat output (Q(total)), time of the maximum heat production (t(log)) in the log phase have been obtained. The results showed that Cr(VI) and Cr(Ill) had the inhibition effect on the growth of El. coli in aquatic environment; however, the inhibitory ratio of Cr(III) to E. coli was smaller than that of Cr(VI). The k values of E. coli in the presence of Cr(VI) and at high concentrations of Cr(III) were decreased with increasing the concentrations of these chromium species. Among the three chromium species investigated, CO2O72- 7 was found to be the most poisonous species against E. coli with an IC50 value of 35.52 mu g center dot mL(-1). Cr 4 exhibited moderate toxicity on E. coli with an IC50 of 50.24 mu g center dot-mL(-1), and Cr3+ had the lowest toxicity with an IC50 of 84.30 mu g center dot mL(-1). Microcalorimetry can provide a convenient, sensitive and reliable method to study the effect of various metal species on the growth of bacteria or other microorganisms.