Effects of pH value on the expression of key iron/sulfur oxidation genes during bioleaching of chalcopyrite on thermophilic condition

Physicochemical factors such pH value would affect the microbial metabolism during chalcopyrite bioleaching. To this end, the effects of pH on the expression of critical functional genes during bioleaching were evaluated. A mixed culture of moderate thermophiles was used for chalcopyrite bioleaching at initial pH values of 1.0, 2.0, and 3.0, and bioleaching processes were monitored via measuring the physicochemical parameters. Quantitative real-time PCR assay was used to monitor the dynamics of microbial community structures and the expression of critical iron/sulfur oxidation genes (4Fe-4S ferredoxin and sulfate adenylyltransferase genes, respectively). Redundancy analysis and calculation of correlation coefficients were used to reveal linkages between gene expression and various physicochemical factors. The leaching processes at initial pH of 1.0 and 3.0 were prolonged compared with that at initial pH of 2.0. It was shown that Sulfobacillus thermosulfidooxidans and Acidithiobacillus caldus were the dominant species during the early stage in free and attached cells, respectively, while Ferroplasma thermophilum became predominant in the later phase. The gene expression in Sulfobacillus thermosulfidooxidans and Ferroplasma thermophilum was greatly affected by pH values. On the other hand, the relationship between pH and gene expression in Acidithiobacillus caldus was not significant. The study unraveled the importance of pH value on chalcopyrite bioleaching, and pH selectively influenced the expression of key functional genes of some specific species.