Evaluating the Expression of Iron and Sulfur Oxidation Genes related to Sulfobacillus Thermosulfidooxidans Strains under the Influence of Effective Parameters in the Bioleaching Process

Sulfate adenylyltransferase catalyzes adenosine phosphosulfate (APS) to generate ATP and sulfate, which is the final stage of the sulfite oxidation to obtain energy, and 4Fe_4S ferredoxin as an enzyme member of the electron transfer chain plays an important role in the oxidation of ferrous iron in the bioleaching system. Efforts to optimize bacterial growth conditions will also increase the gene expression, which will be accompanied by an increase in the efficiency of the microbial leaching system. Accordingly, the present study aimed to investigate the gene expression related to the proteins in Sulfobacillus thermosulfidooxidans along with the application of changing factors in the culture medium.

For culture, different concentrations of chalcopyrite, yeast extract, and ferrous iron ion were added to a 9K medium. Bacteria were purified and bacterial RNA extraction and cDNA synthesis were performed. To investigate the expression level of the genes under study, the Real-time PCR reaction was performed and the results were analyzed by the 2-∆∆CT method. The results were also analyzed by Tukey and Duncan tests using SPSS version 21 with the P-value of ˂0.05.

Using the results of the PCR, the genes in question were identified and primers were confirmed. The highest percentage of copper extraction in the four test environments was in the No. 2 environment with 48.75% in which the 4Fe_4Sferredoxin gene had the highest expression than the other test environments. The highest expression of the Sulfate adenylyltransferase gene was related to the medium No. 4 in which the percentage of copper extraction was 39.16%.

The composition of the bacterial culture medium can change the expression of genes and the percentage of copper extraction. The most suitable test medium was obtained for the extraction of copper in a 10-micron size, the presence of 1.5 g/L ferrous ion, and the absence of yeast extract.