Energy Gene Expressions And Electrical Characterization Of Acidophiles Interacting With Chalcopyrite

In order to better understand the bioleaching mechanism, the expression of genes involved in energy conservation in free and attached Acidithiobacillus ferrooxidans during bioleaching of chalcopyrite were studied using quantitative real-time PCR. Sulfur oxidation genes of attached A. ferrooxidans were up-regulated while ferrous iron oxidation genes were down-regulated compared with free Acidithiobacillus ferrooxidans in the culture solution. Sulfur oxidation genes sqr, p21were up15.9and5.9folds, and ferrous oxide gene rus, cycl were decreased by0.48and0.17folds.The up-regulation of sulfur oxidation genes may be induced by elemental sulfur on the mineral surface. This conclusion was supported by the results of high-performance liquid chromatography analysis.Sulfur-oxidizing Acidithiobacillus thiooxidans(A. thiooxidans) and ferrous-oxidizing Leptospirillum ferrooxidans(L. ferrooxidans) were mix cultured in chalcopyrite bioleaching. Study of the community structure of free and attached bacteria showed that A. thiooxidans is the dominant bacteria in attached bacteria while L. ferrooxidans is the dominant bacteria in free bacteria. The percentage of A. thiooxidans in the attached bacteria is68.25%, and the percentage of L. ferrooxidans in the free bacteria is88.03%.With respect to available energy sources during bioleaching of chalcopyrite, sulfur-oxidizers tend to be on the mineral surfaces whereas ferrous iron-oxidizers tend to be suspended in the aqueous phase. Taken together, these results indicate that the main role of attached acidophilic bacteria was to oxidize elemental sulfur and dissolution of chalcopyrite involved chiefly an indirect bioleaching mechanism.Electrochemical impedance spectroscopy (EIS) has emerged as a promising analytical tool for bacterial adhesion. Using the EIS method, kinetic adhesion of A. ferrooxidans to chalcopyrite surface was studied. At the first40minutes, most of the bacteria quickly absorbed the chalcopyrite electrode surface, therefore impedance increase rapidly from317.58kΩ to520.27kΩ EIS can be used to monitor attachment of bacteria. When bacteria were attached to the chalcopyrite surface, a new element was added to the equivalent circuit to represent the cell layer’s resistance (Rbl) and capacitance(Cbl). The intrinsic conducting and dielectric properties of the bacterial cell have decrease the charge transfer resistance and increased the a double-layer capacitance and causing a consequent in impedance magnitude. At temperature of30℃and concentration of8.0×108cells/ml, charge transfer resistance (Ret) reduced the maximum while electric double layer capacitance (CPEd1) increased the most, which means A. ferrooxidans attachment to chalcopyrite the most.