Effect of heavy metals on the ferrous iron oxidizing ability of Thiobacillus ferrooxidans

The effect of mercury and some other heavy metals on the ferrous iron oxidizing ability of Thiobacillus ferrooxidans was studied using redox potential measurement, UV-VIS and atomic absorption (AA) spectroscopy, and electron microscopy, Results obtained suggest that the presence of some cations (e.g. Hg(II), Ag(I), Pb(II) and Cd(II) at a concentration level of 10 mg/l), inhibits the microbial oxidation of Fe(II). The presence of 10 mg/l of As(III), Mn(II), Sn(II), Co(II), Cu(lI) and Zn(II) and anions such as Cl- and NO3- did not have an observable effect on Fe(II) oxidizing activity of the bacteria. Our results also suggest that Hg(II) inhibits the microbial oxidation of Fe(II) in an uncompetitive mechanism, suggesting that it may bind with the enzyme-Fe(II) complex. In the presence of 10 mg/l Hg(II), microbial oxidation of Fe(II) is likely to be controlled by the rate of diffusion of Fe(II) into the periplasmic space of the T. ferrooxidans cells.