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

Ghana has one of the largest gold ore deposits in the world. Gold extractio n by bioleaching technology which is more environmentally friendly and effi cient compared to conventional mining methods is therefore preferred for pr ocessing refractory gold ores. The Ashanti Goldfields Company Limited in Gh ana operates the world's largest commercial bioleaching plant. However, the same organisms are used to leach gold from surface arsenopyrite and underg round 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 b ioleaching bacteria from surface arsenopyrite gold ore, underground sulphid e gold ore, underground mine water and slurry from the commercial biooxidat ion tank at Obuasi. Isolation of the organisms was made using 9K enrichment medium and the bacteria identified using physiological, morphological, cul tural and biochemical criteria. Thiobacillus ferrooxidans and 'Leptospirill um ferrooxidans' were isolated from each of the samples analysed. However, Thiobacillus thiooxidans was not found in underground mine water even thoug h it was isolated from the other samples. It was also observed that bacteri a isolates obtained from surface arsenopyrite and underground sulphide gold ores had higher oxidation rates compare with the isolates from the undergr ound mine water. Further characterization was done using sodium dodecyl sul phate polyacrylamide gel electrophoresis (SDS-PAGE) which clearly different iated the various bacteria isolates at the species level.