An extremely acidophilic sulfur-oxidizing bacterium was isolated from an industrial-scale bioheap of the Zijinshan copper mine and was named ZJJN. A tuft of flagella and a layer of thick capsule outside the cell envelope were clearly observed under transmission electron microscopy (TEM), which might be closely related to the extremely acid-proof capacity of ZJJN cells in the bioleaching system; 16S ribosomal RNA (rRNA) phylogeny showed that the isolated strain was highly homologous to the genera of Acidithiobacillus. The optimum temperature of ZJJN was determined at 30 °C and pH at 1.0. It was capable of growth at even pH 0. Strain ZJJN can utilize reduced sulfur as an energy source but not with organics or ferrous ion. Strain ZJJN was sensitive to all antibiotics with different concentrations; when it showed a certain resistance to different concentrations of Cu(2+). In the mixed strains of ZJJN and A. ferrooxidans system (initial pH 1.0), the copper-leaching efficiency was up to 60.1 %, which was far higher than other systems. Scanning electron microscopy (SEM) analysis showed that less jarosite precipitation was produced in the most efficient system. The extremely acidophilic strain ZJJN would be of great potential in the application of chalcopyrite bioleaching.

In previous study, two extremely acidophilic strains Acidithiobacillus thiooxidans ZJJN-3 (collection site: bioleaching leachate) and ZJJN-5 (collection site: bioleaching wastewater) were isolated from a typical industrial bio-heap in China. Here, we unraveled the potential acid-tolerance components of ZJJN-3 by comparing the physiological differences with ZJJN-5 under different acid stresses. The parameters used for comparison included intracellular pH (pHin), capsule morphology, fatty acid composition of cell membrane, transcription of key molecular chaperones, H(+)-ATPase activities and NAD(+)/NADH ratio. It was indicated that the acid-tolerance of A. thiooxidans ZJJN-3 was systematically regulated. Capsule first thickened and then shed off along with increased acid stress. Cell membrane maintained the intracellular stability by up-regulating the proportion of unsaturated fatty acid and cyclopropane fatty acids. Meanwhile, the transcription of key repair molecular chaperones (GrpE-DnaK-DnaJ) was up-regulated by 2.2-3.5 folds for ensuring the proper folding of peptide. Moreover, low pHin promoted ZJJN-3 to biosynthesize more H(+)-ATPase for pumping H(+) out of cells. Furthermore, the NAD(+)/NADH ratio increased due to the decreased H(+) concentration. Based on the above physiological analysis, the potential acid-tolerance components of A. thiooxidans ZJJN-3 were first proposed and it would be useful for better understanding how these extremophiles responded to the high acid stress.

No abstract

No abstract

In this study, two typical bioleaching strains (A. ferrooxidansandA. thiooxidans) were employed for exploring the enhancement mechanism of the adapted adsorption behavior in the bioleaching of copper-bearing sulfide ore.