| As two of the most important acidophilic, chemoautotrophic bioleaching microorganisms, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans are widely used in biooxidation and bioleaching of various sulfides ores and other fields.Twenty-seven strains of bioleaching bacteria have been isolated from Chinese representative orefields. Nineteen strains were classified as members of A. ferrooxidans, and the other eight strains belonged to A. thiooxidans. Besides, A. ferrooxidans ATCC19859 and A. thiooxidans ATCC19377 were also introduced into this study.After adaptation of these experimental strains to inorganic arsenical compounds, it was found that resistances of fifteen strains of A. ferrooxidans and four strains of A. thiooxidans were not high. The remaining four strains of A. ferrooxidans (i.e., BY-3, FY-3, H-3, TKY-2) and ATCC 19859 typical strain, and the remaining four strains of A. thiooxidans (i.e., DX-3, JY, LYS, YP-2) and ATCC 19377 typical strain, could resist high concentrations of arsenite and arsenate. Furthermore, the strong resistances could pass on steadily to their daughter cells. The predominances of those adapted strains were significant when compared with wild or unadapted strains. Among these adapted strains, A. thiooxidans LYS and A. ferrooxidans BY-3 were two of the best performers that could resist more than 80 mM and 60 mM As(III), respectively, and A. thiooxidans JY and A. ferrooxidans TKY-2 were the other two of the best performers that could tolerate more than 120 mM and 100 mM As(V), respectively. So far, the resistances of these adapted strains to inorganic arsenical compounds reported here were the highest among all of the bioleaching microorganisms.Realgar and arsenic-bearing refractory gold ore are two kinds of representative arsenic-containing sulfides, and can be oxidized and decomposed by bioleaching microorganisms. The medium containing a small amount of elemental sulfur and Fe2＋was selected as the bioleaching system, and mixed bacterial cultures were introduced to biooxidize them in the bioleaching experiment. The results indicated that the abilities of mixed arsenic-resistant cultures to biooxidize and decompose these two sulfides ores were stronger than those of mixed unadapted bioleaching bacteria. In detail, arsenic bioleaching ratios from realgar and arsenic-bearing refractory gold ore by mixed adapted cultures were 28.6% and 45.0%, respectively, while arsenic bioleaching ratios by mixed unadapted cultures were 12.4% and 22.9%, respectively. Besides, bioleaching of arsenic by the control was insignificant, as the maximum leaching ratios of arsenic in these two ores by sulfuric acid in the whole observation were only 2.8% and 11.2%, respectively, which were significantly lower than the values of the other two biological treatments.arsC gene that is one of the most important genes in the ars operon was cloned. After sequencing, comparison and cluster analysis of various arsC gene sequences from different bioleaching strains, it was concluded that arsC gene sequences from both A. ferrooxidans and A. thiooxidans were very similar to those arsC gene sequences provided by GenBank database. Therefore, it can be deduced that arsC genes from different sources are highly conserved.The proteins related to inorganic arsenic resistances in the bioleaching bacterial arsenic-resistant cells were activated in the presence of arsenic, and performed respective biological functions to survive in the harsh environment. However, different concentrations of arsenic would probably induce different varieties and quantities of the arsenic-resistant proteins. The results showed that there has not been significant difference of the contents of total membrane proteins between adapted strains in the presence of arsenic and unadapted strains in the absence of arsenic. SDS-PAGE was introduced to isolate every sample of total membrane proteins, and preliminary analysis of expression differences among those isolated protein subunits was conducted. The electrophoresis graphs indicated that significant expression differences of total membrane proteins of A. ferrooxidans and A. thiooxidans experimental strains do exist between when cultured in the absence of arsenic and when cultured in the presence of arsenic. For these two kinds of bioleaching bacteria, when cultured in the presence of arsenic, both the brightness and width of the proteins bands were more predominant than from those strains cultured in the absence of arsenic. And the higher the concentration of soluble arsenic in the bioleaching system was, the more significant the phenomenon appeared. |
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