An-an Peng

Sulfur oxidation activities of pure and mixed thermophiles and sulfur speciation in bioleaching of chalcopyrite

The sulfur oxidation activities of four pure thermophilic archaea Acidianus brierleyi (JCM 8954), Metallosphaera sedula (YN 23), Acidianus manzaensis (YN 25) and Sulfolobus metallicus (YN 24) and their mixture in bioleaching chalcopyrite were compared. Meanwhile, the relevant surface sulfur speciation of chalcopyrite leached with the mixed thermophilic archaea was investigated. The results showed that the mixed culture, with contributing significantly to the raising of leaching rate and accelerating the formation of leaching products, may have a higher sulfur oxidation activity than the pure cultures, and jarosite was the main passivation component hindering the dissolution of chalcopyrite, while elemental sulfur seemed to have no influence on the dissolution of chalcopyrite. In addition, the present results supported the former speculation, i.e., covellite might be converted from chalcocite during the leaching experiments, and the elemental sulfur may partially be the derivation of covellite and chalcocite.

A new strain Acidithiobacillus albertensis BY-05 for bioleaching of metal sulfides ores

Abstract An acidophilic, rod-shaped Gram-negative sulfur oxidizing strain BY-05 was isolated from an acid mine drainage of copper ore in Baiyin area, Gansu Province, China. Ultrastructural studies show that the isolate has a tuft of polar flagella and possesses sulfur granules with clear membrane adhering to the cell innermembrane. Physiological study shows that this isolate grows autotrophically and aerobically by oxidizing S0 and reduced inorganic sulfur compounds (S2O2-3, S2O2-4, S2- and ZnS) with the optimum growth at pH 3.5–4.0 and at the temperature range of 25–30 °C. The 16S rRNA gene sequence (DQ 423683) of strain BY-05 has 100% sequence similarity to that of Acidithiobacillus albertensis (DSM 14366). So it is identified and named as A. albertensis BY-05. Bioleaching experiments with this new strain show that it can play an important role in recovery of metals from chalcopyrite and sphalerite.

Comparative study on effects of Tween-80 and sodium isobutyl-xanthate on growth and sulfur-oxidizing activities of Acidithiobacillus albertensis BY-05

Abstract Effects of two typical surfactants, Tween-80 and sodium isobutyl-xanthate (NaIBX), with different concentrations on the growth and sulfur-oxidizing activities of a new strain Acidithiobacillus albertensis BY-05, an acidophilic sulfur-oxidizing bacterium, were investigated. The results indicate that both surfactants can enhance the growth and sulfur-oxidizing activities of A. albertensis BY-05 only at some special concentrations, e.g., 10−4–10−8 g/L for NaIBX and lower than 10−8 g/L for Tween-80, but were inhibited and even harmful at higher concentrations. Both surfactants can not be metabolized by A. albertensis BY-05. The contact between the bacteria and the sulfur particles may be dependent upon both the extracellular substance and the surfactants, both of which provide the amphiphilic environment improving the attachment for bacteria to the sulfur particles surface. These data could be significant for enlarging the applications of both A. albertensis BY-05 and some typical surfactants for industrial bioleaching of sulfides minerals.

Investigation of Elemental Sulfur Speciation Transformation Mediated by Acidithiobacillus ferrooxidans

The speciation transformation of elemental sulfur mediated by the leaching bacterium Acidithiobacillus ferrooxidans was investigated using an integrated approach including scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, and X-ray absorption near edge spectroscopy (XANES). Our results showed that when grown on elemental sulfur powder, At. ferrooxidans ATCC23270 cells were first attached to sulfur particles and modified the surface sulfur with some amphiphilic compounds. In addition, part of the elemental sulfur powder might be converted to polysulfides. Furthermore, sulfur globules were accumulated inside the cells. XANES spectra of these cells suggested that these globules consisted of elemental sulfur bound to thiol groups of protein.

Thermophilic archaeal community succession and function change associated with the leaching rate in bioleaching of chalcopyrite.

The community succession and function change of thermophilic archaea Acidianus brierleyi, Metallosphaera sedula, Acidianus manzaensis and Sulfolobus metallicus were studied by denaturing gradient gel electrophoresis (DGGE) analysis of amplifying 16S rRNA genes fragments and real-time qPCR analysis of amplifying sulfur-oxidizing soxB gene associated with chalcopyrite bioleaching rate at different temperatures and initial pH values. The analysis results of the community succession indicated that temperature and initial pH value had a significant effect on the consortium, and S. metallicus was most sensitive to the environmental change, A. brierleyi showed the best adaptability and sulfur oxidation ability and predominated in various leaching systems. Meanwhile, the leaching rate of chalcopyrite closely related to the consortium function embodied by soxB gene, which could prove a desirable way for revealing microbial sulfur oxidation difference and tracking the function change of the consortium, and for optimizing the leaching parameters and improving the recovery of valuable metals.

Effect of surfactant Tween-80 on sulfur oxidation and expression of sulfur metabolism relevant genes of Acidithiobacillus ferrooxidans

Abstract The effects of surfactant Tween-80 on the growth, sulfur oxidation, and expression of selected typical sulfur metabolism relevant genes of Acidithiobacillus ferrooxidans ATCC 23270 were investigated. The results showed that in the presence of 10 −2 g/L Tween-80, the growth of A. ferrooxidans and its metabolism on the insoluble substrate S 0 and CuFeS 2 were promoted. After 24 d of bioleaching, the copper extraction yield of chalcopyrite at 10 −2 g/L Tween-80 increased by 16% compared with the bioleaching experiment without Tween-80. FT-IR spectra analysis revealed that the result was probably caused by the extracellular polymeric substances whose composition could be changed by the surfactant addition. RT-qPCR was used to analyze the differential expressions of 17 selected sulfur metabolism relevant genes in response to the addition of Tween-80. Down-regulation of the extracellular protein genes indicated the influence of Tween-80 on bacteria-sulfur adsorption. Variation of the expression level of the enzymes provided a supplement to sulfur metabolism investigation.

Synchrotron radiation based STXM analysis and micro-XRF mapping of differential expression of extracellular thiol groups by Acidithiobacillus ferrooxidans grown on Fe2 + and S0

The differential expression of extracellular thiol groups by Acidithiobacillus ferrooxidans grown on substrates Fe(2+) and S(0) was investigated by using synchrotron radiation based scanning transmission X-ray microscopy (STXM) imaging and microbeam X-ray fluorescence (μ-XRF) mapping. The extracellular thiol groups (SH) were first alkylated by iodoacetic acid forming Protein-SCH2COOH and then the P-SCH2COOH was marked by calcium ions forming P-SCH2COOCa. The STXM imaging and μ-XRF mapping of SH were based on analysis of SCH2COO-bonded Ca(2+). The results indicated that the thiol group content of A. ferrooxidans grown on S(0) is 3.88 times to that on Fe(2+). Combined with selective labeling of SH by Ca(2+), the STXM imaging and μ-XRF mapping provided an in situ and rapid analysis of differential expression of extracellular thiol groups.

Isolation, characterization of Acidiphilium sp. DX1-1 and ore bioleaching by this acidophilic mixotrophic organism

The isolation and characterization of a subspecies of Acidiphilium that not only acts as an enhancer of other autotrophic acidophiles in bioleaching, but also has significant leaching capacity towards marmatite was described. Acidiphilium sp. DX1-1, a Gram-negative, motile, short rod-shaped bacterium that accumulates intracellular polyhydroxybutyrate, was isolated from the Dexing copper mine area in China. It is mesophilic and acidophilic with an optimum growth at 30 °C and pH 3.5. Phylogenetic analyses identify that it is a member of genus Acidiphilium and closely related to Acidiphilium cryptum and Acidiphilium multivorum. It is mixotrophic, utilizing organic substrates and a range of inorganic substrates, such as sulfur, ferric iron and a variety of sulfide minerals. Acidiphilium sp. DX1-1 is able to bioleach 40% of the zinc content of marmatite with the initial pH 3.5 within a month, which is even higher than that of A. ferrooxidans or the mixed culture with A. ferrooxidans at even lower pH.

Differential utilization of cyclic, orthorhombic α- and chain-like polymeric μ-sulfur by Acidithiobacillus ferrooxidans

Abstract The differential utilization of cyclic, orthorhombic α-sulfur (α-S) and chain-like polymeric μ-sulfur (μ-S) by Acidithiobacillus ferrooxidans was investigated. The growth and sulfur oxidation results indicated that utilization of μ-S by A. ferrooxidans was clearly different from α-S. Even if the planktonic cells were produced, the fall of pH and the rise of sulfate concentration were the same after 300 h on each substrate, the speeds of the planktonic cells increase, pH decrease and sulfate concentration increase in the earlier cultivation stage were faster on polymeric sulfur compared with the orthorhombic form. The adsorption capacity of the cells was higher on μ-S than on α-S. The results of SEM, DRIFTS and XRD analyses indicated that the surfaces of α-S and μ-S were modified differently by cells. Differential expression of 11 selected sulfur adsorption-activation and metabolism relevant genes was detected by RT-qPCR. The results showed that the expression of the hydrophobic substrate transport proteins and the sulfur metabolism related proteins was up-regulated, and the adsorption and activation related proteins were down-regulated when the cells were grown on μ-S, suggesting that μ-S could be more easily bio-adapted and activated than α-S.

Characterization of apparent sulfur oxidation activity of thermophilic archaea in bioleaching of chalcopyrite

Abstract The apparent sulfur oxidation activities of four pure thermophilic archaea, Acidianus brierleyi (JCM 8954), Metallosphaera sedula (YN 23), Acidianus manzaensis (YN 25) and Sulfolobus metallicus (YN 24) and their mixture in bioleaching chalcopyrite were compared, which were characterized indirectly by the evolution of the cells concentration, pH value and sulfate ions concentration in solution. The results show that the mixed culture contributed significantly to the raising of leaching rate, which suggests that the mixed culture had a higher sulfur oxidation activity than the pure culture. Meanwhile, the results also indicate that the changes of parameters characterizing the sulfur oxidation activity of thermophilic archaea are often influenced by many factors, so it is hard to reflect accurately the specific sulfur oxidation activities among the different sulfur-oxidizing microbes when bioleaching chalcopyrite at different conditions. Accordingly, an efficient method to characterize microbial sulfur oxidation activity appears to be desirable.