Influence of heavy metals on growth and ferrous sulphate oxidation by Acidithiobacillus ferrooxidans in pure and mixed cultures

The work described here concerns the study of the tolerance limits of the acidophilic bacterium, Acidithiobacillus ferrooxidans, in the presence of a range of heavy metal concentrations. With the aim of reducing the inhibitory effect that organic matter has on ferrous iron oxidation by A. ferrooxidans, a heterotrophic bacterium, Acidiphilium, sp., was added to media supplemented with organic matter. The maximum tolerated concentrations (MTC) were measured. At. ferrooxidans tolerates high levels of the metals tested: 0.4 g Cr(III)/l, 10 g Cu(II)/l, 10 g Cd(II)/l, 30 g Zn(II)/l and 30 g Ni(II)/l. The addition of heterotrophic bacteria, Acidiphilium, changes the tolerance limits in different ways depending on the metal: 0.4 g Cr(III)/l, 4 g Cu(II)/l, 10 g Cd(II)/l, 40 g Zn(II)/l and 15 g Ni(II)/l.