Isolation and characterization of mineral oxidizing bacteria from the obuasi gold mining site, Ghana.

Abstract

Ghana has one of the largest gold ore deposits in the world. Gold extraction by bioleaching technology which is more environmentally friendly and efficient compared to conventional mining methods is therefore preferred for processing refractory gold ores. The Ashanti Goldfields Company Limited in Ghana operates the world's largest commercial bioleaching plant.However, the same organisms are used to leach gold from surface arsenopyrite and underground sulphide ores even though the use of adapted local organisms for the different ore may improve gold recovery.

Efforts were therefore made to isolate and characterize local acidophilic bioleaching bacteria from surface arsenopyrite gold ore, underground sulphide gold ore, underground mine water and slurry from the commercial biooxidation tank at Obuasi. Isolation of the organisms was made using 9K enrichment medium and the bacteria identified using physiological, morphological, cultural and biochemical criteria.Thiobacillus ferrooxidans and ‘Leptospirillum ferrooxidans were isolated from each of the samples analysed. However, Thiobacillus thiooxidans was not found in underground mine water even though it was isolated from the other samples. It was also observed that bacteria isolates obtained from surface arsenopyrite and underground sulphide gold ores had higher oxidation rates compare with the isolates from the underground mine water. Further characterization was done using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) which clearly differentiated the various bacteria isolates at the species level.