Anilite oxidation was evaluated with two acidophilic thiobacilli that are important in bioleaching processes. The experiments were carried out in shake flasks in the absence and presence of energy sources such as 2 g/L powdered sulphur and 10 g/L Fe(2+) (as ferrous sulphate) at pH 2.0, 150 rpm, 35 degrees C. Tests showed that copper extraction in a mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus caldus was higher than in pure cultures with added sulphur in the presence of anilite. The effect of supplemental iron clearly improved Cu leaching by the A. ferrooxidans culture and the mixed culture. The oxidation of anilite by A. caldus was negligible and this bacterium seemed to have no ability to initiate anilite solubilization. On the other hand, an important potential of A. caldus to leaching anilite was indicated. It can decrease pH of the medium and supply a suitable bioleaching environment. (c) 2007 Elsevier Ltd. All rights reserved.