| In the paper, four different sulfur-oxidizing thermophilic archaea Acidianus brierleyi (JCM8954), Metallosphaera Sedula (YN23), Acidianus manzaensis (YN25) and Sulfolobus metallicus (YN24) were chosen for bioleaching chalcopyrite and were investigated in the following research work. Firstly, the apparent sulfur oxidation activities of the four thermophilic archaea in bioleaching of chalcopyrite were studied. In way of characeterizing the apparent sulfur oxidation activity of the archea, the functional genes related to sulfur oxidation activity were screened and identified from the four strains. And based on this, a new molecular method for characterizing the thermophilic archaea sulfur oxidation activity was proposed and proved. Next, the community dynamics and function change of the consortium associated with chalcopyrite bioleaching rate at different temperatures and initial pH values were studied, and the relationship between their sulfur oxidation activities and sulfur speciation was analyzed. Finally, the factors, affecting the leaching rate of chalcopyrite were analyzed based on the grey correlation theory. The detailed research contents and the main conclusions are as follows:(1) Comparisons of the apparent sulfur oxidation activities of four pure thermophilic archea A. brierleyi, M. sedula, A. manzaensis and S. metallicus and their mixture showed that the mixed culture contributed significantly to the raising of leaching rate, which indicated that mixed culture had a higher sulfur oxidation activity than the pure culture. At the same time, we found it was difficult to explain accurately the relationship between the apparent parameters and the sulfur oxidation activities of various strains. Therefore, it was necessary to find a desirable method for characterizing efficiently the sulfate oxidation activities of various strains.(2) The functional genes in thermophilic archaea related to sulfur oxidation activity were screened and proved by real-time qPCR. It was found that soxB gene expression of four thermophilic archaea was significantly up-regulated grown on elemental sulfur than that on the ferrous sulfate, and soxB gene expression of each strain was also obvious different under the same energy substrate. It was noticeable that this was the first time to derive that soxB gene existed in the four thermophilic archaea of A. brierleyi, M. sedula, A. manzaensis and S. metallicus.(3) soxB gene expression of the four thermophilic archaea grew at two different temperatures were not obviously detected by real-time qPCR.The result suggested that soxB gene may be the constitutive gene for four thermophilic archaea, and the expression level of soxB gene could be better embodied the function change of the consortium owing to it was not be restricted by various environmental factors. It was the first time for mentioning that analysis and characterization of sulfur oxidation activities of different sulfur oxidizing strains based on the expression of functional gene in bioleaching chalcopyrite.(4) The community succession and function change of thermophilic archaea consortium were studied by denaturing gradient gel electrophoresis (DGGE) analysis and real-time qPCRanalysis associated with chalcopyrite bioleaching rate at different temperatures and initial pH values. The results indicated that the temperatures and initial pH values had a significant effect on the community structure, its function change and the bioleaching rate of chalcopyrite, in which the impact temperatures were more obvious. In the consortium, S. metallicus was most sensitive to the environment changes, which was the dominant species in the leaching system with initial pH1.5and at65℃, but it showed a weak growth in other conditions. A. brierley was the dominant species in all leaching systems and showed a best adaptability and sulfur oxidation ability. Furthermore, it was found that the leaching rate of chalcopyrite closely correlated with the function change of the consortium embodied by the expression level of soxB gene.(5) According to the analysis of the relevant surface sulfur speciation and the leaching character of chalcopyrite with thermophilic archaea, it could be inferred that the precipitation of jarosite hampered the leaching process, while elemental sulfur seemed to have no significant influence on it. In addition, the coexistence of covellite and chalcocite supports the former speculation that covellite might convert from chalcocite during the leaching experiments, as well as elemental sulfur may be partially the derivation of covellite and chalcocite.(6) The gray correlation theory was first time introduced into the bioleaching system for analysis of the correlations between the sulfur oxidation activities, archaeal communities and sulfur speciation in bioleaching chalcopyrite with thermophilic archaea under various affecting factors. The results showed that chalcopyrite dissolution was mainly caused by the ferric ion oxidation during the bioleaching process with thermophilic archaea at the higher temperature65℃and pH (1.5,2), while H+was the dominant factor to attack chalcopyrite at the lower pH (1.0). The passivation phenomenon has become more and more obvious with the intermediates and product accumulated during bioleaching process, and these effects were related to the microbial growth and their function mechanisms. Especially at lower temperature (55℃) leaching system, the grey correlation degree between the microbial actions and the formed intermediates and product and the leaching rate of chalcopyrite were significantly improved. Secondly, it was found that the grey correlation analysis of the chalcopyrite leaching rate applied in the expression level of soxB gene was more closed than that in the cell density in the consortium. It had once again proved that the expression analysis of the related sulfur oxidation function gene soxB could be better embodied the function change of the consortium in bioleaching chalcopyrite. |
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