| Benefiting from the advantages of greenness and economy,bioleaching is widely used in the extraction of non-ferrous metals from low-grade minerals.Efficient bioleaching is closely related to the active iron and sulfur metabolism mediated by microorganisms,and the lack of iron metabolism is a key factor restricting the leaching of chalcocite.In this study,the biological leaching of low-grade chalcocite was studied.The physiological and leaching characteristics of iron oxidizing and reducing bacteria,the difference at global transcription level of cells,and the improvement of the column bioleaching efficiency of chalcocite based on the collaborative leaching of leaching microorganisms were studied.The main research contents are as follows:(1)Screening and identification of iron-oxidizing and reducing bacteria L.ferriphilum and Acidiphilium sp.and analysis of basic physiological characteristics.The acidophilic heterotrophic bacteria Acidiphilium sp.DX-LIX2 was isolated from the leaching solution of Dexing Copper Mine using glucose as the matrix.The bacteria cells are Gram-stained negative,rod-shaped or spherical(0.6×0.8?1.0?m).The maximum specific growth rate(?max)is 0.19 h-1.Acidiphilium sp.DX-LIX2 uses organic matter such as glucose and galactose for heterotrophic growth.Additionally,it has a certain iron reduction activity and can synergistically extract chalcocite.The acidophilic iron oxidizing bacteria L.ferriphilum ZJ-AU1 was screened from the acid mine drainage(AMD)of the Zijinshan Copper Mine by combining the dilution separation route and the double-layer plate method.The bacterial cells are curved rod or spiral(length in 0.7?2.5?m,diameter in 0.25?0.5?m),and the?max reachs0.13 h-1.L.ferriphilum ZJ-AU1 utilizes ferrous iron as main energy source and exhibits strong iron oxidation activity.(2)Influence of exogenous intervention on bioleaching of low-grade chalcocite and its mechanism analysis.A combination of strains was constructed by L.ferriphilum,A.caldus and Acidiphilium sp.,external intervene with Fe2+/Fe3+-pyrite-acid hydrolysate of fibrous waste were applied to improve low-grade chalcocite bioleaching,and the differences in leaching were systematically analyzed.The biochemical parameters showed that exogenous intervention enhanced the iron and sulfur metabolism in the leaching systems and promoted the growth of bacteria,among them,the strategy of adding pyrite and aquatic weeds acid hydrolysate at the same time had the best strengthening effect.The free and attached biomass increased by 2.51and 5.73 times,respectively,and the leaching rate of copper ion reached 67.6%after 40 days of leaching.Adding strong oxidant Fe3+to directly react with minerals or adding pyrite can provide more energy substances for the growth of bacteria.The acid hydrolyzate promotes iron circulation and the bacteria attachment.The significant increase in attached cells and EPS secretion strengthens the"contact"mechanism,thus effectively accelerates the dissolution of minerals and promotes the leaching of copper ions.(3)Based on transcriptomics,the physiological response mechanism of L.ferriphilum ZJ-AU1during bioleaching of low-grade chalcocite under the intervention of exogenous acid hydrolysate of fibrous waste was systematically analyzed.616 differentially expressed genes(DEGs)were detected according to the gene expression level,among which 298 genes were up-regulated and related to flagellum assembly,two-component system and other pathways,318 down-regulated genes were involved in basic metabolic pathways such as oxidative phosphorylation and purine-pyrimidine synthesis.The physiological metabolic pathways related to DEGS were specifically analyzed,and the following inferences were drawn based on the experimental conditions.The acid stress and oxidative stress caused by the introduction of acid hydrolyzate might lead to the inhibition of intracellular basal metabolism,accordingly,the bacteria need to establish a complex regulatory network and mechanism to retain key and efficient metabolic pathways to maintain vitality.The bacteria migrate to the mineral surface through flagella and chemotactic proteins and strengthen the cell wall/EPS synthesis,thus resist adverse environment and effectively promote the"contact"mechanism,which plays an important role in the dissolution of minerals.Proton and reactive oxygen species(ROS)stress can be alleviated through efflux system or synthesis of buffer substances.In addition,various defense and repair mechanisms could timely deal with damaged DNA,protein and other important biological macromolecules.(4)Enhancement of biological column leaching of low grade chalcocite based on intervention strategy of exogenous bacteria.Combined with the physiological characteristics of each strain,the exogenous inoculation strategy was designed at different stages,and the changes of physicochemical parameters and community structure during the leaching process were analyzed.The continuous intervention strategy(inoculation of L.ferriphilum at protophase,A.caldus at middle stage,and Acidiphilium sp.at later period)strengthens the iron and sulfur metabolism of the leaching system,promotes more bacteria to grow,attach to the mineral surface and meanwhile secrete a large amount of EPS to accelarate the dissolution of copper ions.After 25 days of bioleaching,the copper ion concentration of the optimal system was325.5 mg·L-1,and the leaching rate reached 59.8%,which was 39.3%and 18.2%higher than that of the abiotic control and the biological control without reinoculation strategy,respectively.The community structure analysis showed that the main genus were Leptospirillum,Acidithiobacillus,Acidiphilium and Alicyclobacillus.Under the condition of no external intervention,Acidiphilium occupied a dominant position.Inoculation of L.ferriphilum could significantly increase the relative abundance of Acidithiobacillus and Leptospirillum.The inoculation of A.caldus was beneficial to Leptospirillum but might intensify the competition between strains of the same nutritional type. |
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