Exogenous intervention enhances the "contact" mechanism of A. caldus

• 1、Key Laboratory of Industrial Biotechnology, Ministry of Education, Wuxi 214122
• 2、 Biotechnology School, Jiangnan University, Wuxi 214122
• 3、National Engineering Research Center for Functional Food, School of Food Science and Technology, Jiangnan University, Wuxi 214122

Abstract：In order to enhance the "contact mechanism" governing the interaction of extracellular polymeric substances (EPS) with low-grade chalcopyrite for the bioleaching of copper, moderately thermophilic Acidithiobacillus caldus was subjected to exogenous intervention with iron and sulfur. The enhancement of the contact mechanism was systematically investigated by evaluating the attached cells/EPS dynamics, intracellular adenosine triphosphate (ATP), cell functional groups, gene transcriptional level, and ore characteristics. Confocal laser scanning microscopy (CLSM) revealed that exogenous intervention with iron and sulfur led to the production of a denser EPS layer and faster adsorption of the attached cells to the ore based on differential fluorescence staining, which indicated enhancement of the "contact mechanism". The increased intracellular ATP content of the attached cells in the exogenous substrate system provided the required energy for the adsorption processes associated with the "contact mechanism". Fourier-transform infrared spectroscopic (FTIR) analysis of the attached cells and the ore showed a dramatic shift of the N-H and C-O-S peaks (associated with EPS formation), whereas the FTIR peaks of S-Oassociated with sulfur metabolism were also significantly influenced. Moreover, reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that the expression of genes related to cellular energy metabolism, sulfur metabolism,biofilm formation and cell colonization was up-regulated after exogenous intervention, verifying enhancement of the "contact mechanism" at the transcriptional level. In addition, scanning electron microscopy (SEM) indicated more obvious adsorption traces on the ore surface. X-ray diffraction (XRD) indicated the presence of more complex derivatives, such as Fe3(SO4)4, FeSO4, Fe2(SO4)3, and Cu2S, which is suggestive of more active iron/sulfur metabolism with addition of the exogenous iron and sulfur. Overall, a model for bioleaching of low-grade chalcopyrite by moderately thermophilic A. caldus was constructed. The results of this investigation should provide a guide for similar industrial bioleaching processes.

Keywords： Bioleaching A. caldus Low-grade chalcopyrite Iron/sulfur metabolism Contact mechanism