Extracellular DNA enhances the adsorption of Sulfobacillus thermosulfidooxidans strain ST on chalcopyrite surface

Extracellular polymeric substances (EPS) and their key components play an important role in bioleaching. Herein, the amount of extracellular DNA (eDNA) secreted by Sulfobacillus thermosulfidooxidans strain ST during bioleaching of chalcopyrite concentrate was investigated through traditional extraction method and confocal laser scanning microscope (CLSM) analysis. DNase I was added into the bioleaching system to degrade eDNA, and then the effects of eDNA deficiency on bacterial adsorption, copper extraction and the synthesis of other key components of EPS were evaluated. The results of adsorption experiment indicated that the adsorption time was prolonged and the equilibrium adsorption quantity was decreased when the eDNA was absent. The bioleaching experiment showed that eDNA in the EPS was favorable to the copper extraction, which increased by 18.5% compared with that of the eDNA-deficient group. Furthermore, it was found that the removal of eDNA decreased the formation of other key EPS components like polysaccharides and proteins. In situ observation and monitoring of eDNA on the chalcopyrite surface by CLSM were carried out. The results showed that the loss of eDNA attenuated the fluorescence intensity of each component of EPS, which was consistent with the above results. These studies suggested that eDNA in the EPS could enhance the adsorption of bacteria on the surface of chalcopyrite and further increase the copper extraction.