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 concentrat ion 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 sugges t that Hg(II) inhibits the microbial oxidation of Fe(II) in an uncompe titive mechanism, suggesting that it may bind with the enzyme-Fe(II) c omplex. In the presence of 10 mg/l Hg(II), microbial oxidation of Fe(I I) is likely to be controlled by the rate of diffusion of Fe(II) into the periplasmic space of the T. ferrooxidans cells.