Optimization of Acidithiobacillus ferrooxidans at low temperature for bioleaching process

Bioleaching is an economic process in which by using proper bacteria. One of the most important bacteria in this field is Acidithiobacillus ferrooxidans. This bacterium has an optimum growth in temperature interval 25-35 degrees centigrade and it has no desirable growth in lower than 20°C temperature. The main purpose of this research is to adapt these bacteria in lower temperatures, so that bioleaching process can be performed in all seasons of year including cold seasons. In this research, At.ferrooxidans is extracted from Pregnant leaching solution (PLS) of Sarcheshmeh copper mine and inoculated in TK and 9K media in 30°C. Then in order to adapt of At.ferrooxidans in low temperatures, this bacteria was enriched gradually at temperatures 25, 22, 18, 15, 12 and 4°C. In order to ensure the viability of bacteria at low temperatures and performing bioleaching process, the growth of At.ferrooxidans and ferric iron concentrations was measured by a spectrophotometer. The concentration of Cu (II) has been measured by Neocuprion at that temperature. In order to confirm At.ferrooxidans growth at 4°C extracellular proteins was measured by Bradford methods after six days. DNA of At.ferrooxidans strain has been extracted and region genes of 16SrDNA were amplified by PCR and gene sequencing was done. At.ferrooxidans has logarithmic growth at low temperatures such as 25, 22, 18, 15, 12 and 4 °C and is able to oxidize ferrous iron to ferric iron in bioleaching process and release Cu II in soluble form. It is shown that bacteria has the best growth at 25°C after 18 days and the rate of growth decrease with temperature reduction. Comparing the results of nucleotide sequence superior strains with the related strains showed that the bacteria is Acidithiobacillus ferrooxidans and was named as AL strain. At.ferrooxidans is able to adapt and perform bioleaching at low temperatures. Thus, according to the results, the process of iron oxidation and bioleaching at low temperatures is possible and precious metals such as gold and copper can be extracted at low temperatures.