The extraction of precious metals, such as nickel (Ni) and cobalt (Co), from a low-grade nickel laterite ore - supplied from the Caldag deposits in Manisa, Turkey - has been investigated by employing pure and mixed cultures of mesophilic acidophiles (Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans). The study examines the effects of parameters such as the pulp density, the amount of externally added elemental sulphur and ferrous iron, and pure and mixed bacterial cultures on the bioleaching of the lateritic ore. The increase in the pulp density adversely influenced the leaching activity of the pure and mixed cultures. Mixed culture (At. ferrooxidans and At. thiooxidans) displayed a better performance than pure cultures on the extraction of nickel and cobalt from the ore. The maximum dissolution of Ni and Co after 40 days was found to be 97% and 95%, respectively, by a bioleaching process that contained 7% (w/v) elemental sulphur, 2.24 g/L of ferrous iron, 1% (w/v) solids and the mixed culture.