Screening of thermoacidophilic autotrophic bacteria for covellite solubilization

In an attempt to obtain suitable bacterial isolates for bioleaching of copper from chalcopyrite and covellite, soil samples taken from areas of the metal industry were screened using an enrichment procedure specially run at acidic pH and thermophilic temperature range, to overcome the limitations of mesophiles employed for the purpose besides having economic and environmental advantages. Of a total of 47 isolates, the most promising 3 having resistance to copper toxicity were evolved by subjecting them to gradually increasing concentrations of CuSO4 by acclimatization runs conducted on an environmental shaker for 125 d at 65 degrees C. The isolates, JVCu-8, JVCu-10, and JVCu-12, exhibited significantly enhanced bioleaching and copper tolerance ability at pH 3.5 and 60-70 degrees C. The total solubilization of copper recorded was 87, 89.4, and 91.2% by JVCu-8, JVCu-10, and JVCu-12, respectively, and these isolates exhibited tolerance to CuSO4 concentrations of 6.9, 7.2, and 7.2%, respectively. The isolates morphologically resembled Thiobacillus and Sulfolobus.