Abstract:Extracellular polymeric substances (EPS) were extracted from Acidithiobacillus ferrooxidans through sonication method associated with centrifugation, which was evaluated tentatively with 2-keto-3-deoxyoctonic acid (KDO) as the indicator of EPS by spectrophotometry. Then the effect of EPS of A. ferrooxidans on the adhesion on chalcopyrite and pyrite surfaces was studied through a series of comparative experiments. The untreated cells and EPS-free cells of A. ferrooxidans were mixed with EPS suspension, Fe²⁺ or Fe³⁺, respectively. The planktonic cells were monitored in 2 h during bioleaching. The results indicate that the presence of EPS on the cell is an important factor for the adhesion to chalcopyrite and pyrite. A decrease of attachment of A. ferrooxidans to minerals was produced by the deficiency of EPS, which can recover mostly when the EPS was re-added into the EPS-free cells. The restoring extent is more obvious in pyrite than in chalcopyrite. The extent of cell adhesion to chalcopyrite increased when EPS and Fe³⁺ added, and decreased when Fe²⁺ added, which imply the electrostatic interaction plays a main role in initial adhesion between bacteria and minerals and it is a driving force for bacteria to produce EPS probably as a result of regaining their attachment ability to copper sulphides.

Key words: attachment; Acidithiobacillus ferrooxidan; extracellular polymeric substances; chalcopyrite; pyrite