| Bioleaching is an economical method for the recovery of metals from minerals, especially from low grade ores, overburden and waste from current mining operations, which requires moderate capital investment with low operating cost. Furthermore, bioleaching are environmentally friendly. In the present study, an extremely acidophilic and moderately thermophilic iron-oxidizing archaeon was isolated and characterized, and the strain represents a new species of genus Ferroplasma. To understand the role iron-oxidizing archaeon plays in mineral bioleaching, according to its physiological characteristics we focused on the effects of variously defined combinations of At. caldus, L. ferriphilum, S. acidophilus and F. thermophilum on copper dissolution from chalcopyrite. The variation of pH, ferrous iron, ferric iron and copper was also investigated. The real-time quantitative PCR was applied to investigate the population dynamics of moderate thermophiles during bioleaching and the bioleaching mechanisms of chalcopyrite by the above microorganisms were discussed.A ferrous iron-oxidizing archaeon, named L1, was isolated from a chalcopyrite-leaching bioreactor. Strain L1 is a non-motile coccus that lacks cell wall. The diameter of strain L1 ranges from 0.4 to 1.0μm. Strain L1 has a temperature optimum of45℃and the optimum initial pH for growth is 1.0. The generation time of strain L1 is 6.65 h. Strain L1 is capable of growth on ferrous iron and yeast extract. No growth occurred when ferrous iron or yeast extract presented as the sole energy source. The strain can not grow on following organic substrates: peptone, glucose, lactose and galactose. Strain L1 is also not capable of using elemental sulfur, sodium thiosulfate as energy sources. The morphological, biochemical and physiological characterization were investigated. The G+C content of strain L1 is 34.1%. Analysis based on 16S rRNA gene sequence indicated that the strain L1 should be grouped in the genus Ferroplasma, and stain L1 is most closely related to F. cupricumulans BH2~T with 99% similarity in gene sequence. The DNA-DNA similarity hybridization between F. cupricumulans BH2~T and strain L1 was 46.3%. Based on above results, strain L1 should represent a new species of genus Ferroplasma and is proposed the name F. thermophilum L1 (CCTCC AB207143~T).The bioleaching of chalcopyrite by variously defined combinations of At. caldus, L. ferriphilum, S. acidophilus and F. thermophilum was studied in shake flask cultures. The complex consortia containing both chemoautotrophic and chemomixotrophic moderate thermophiles were found to be the most efficient in all of those tested. Mutualistic interactions between physiologically distinct moderately thermophilic acidophiles, involving transformations of iron and sulfur and transfer of organic and inorganic compound, were considered to play a critical role in optimizing chalcopyrite dissolution. The decrease of chalcopyrite dissolution rate in leaching systems containing L. ferriphilum after 15-20 days coincided with the formation of jarosite precipitation on the mineral surface during the bioleaching as a passivation layer. The results of XRD indicated that low concentration of ferric iron reduced jarosite formation and the high concentration of ferric iron might be a more important parameter for forming jarosite precipitation than pH during bioleaching process.The results of real-time PCR analysis indicate At. caldus and L. ferriphilum were the dominant organisms initial during bioleaching. The proportion of L. ferriphilum in total prokaryotes decreased in the latter stages. F. thermophilum was detected the numerically dominant organism in the latter stages, though the proportion of F. thermophilum in total prokaryotes was small initially. The proportion of S. acidophilus did not change obvious during bioleaching of chalcopyrite. The analysis results were consistent with physiological characteristics of these strains.
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