Shifts in the Microbial Populations of Bioleach Reactors Are Determined by Carbon Sources and Temperature

SIMPLE SUMMARY: The application of extremophilic, acidophilic microbial populations for the bio-oxidation of gold-bearing sulfide concentrates in industry is a source of great interest in the research of these populations. Understanding the effects of different factors on the activity of such acidophilic populations may allow for the performance of the bio-oxidation of sulfide concentrates to be regulated. In the present work, we studied the effects of different temperatures as well as carbon sources (carbon dioxide and molasses) on the rate of the bio-oxidation of a gold-bearing pyrite–arsenopyrite concentrate as well as on the composition of the microbial population performing this process. It was shown that an increase in the temperature from 40 to 50 °C led to a decrease in the intensity of bio-oxidation, while the application of additional carbon dioxide as a carbon source made it possible to prevent the inhibition of bio-oxidation due to a temperature increase. An analysis of the populations formed under different experimental conditions revealed that both temperature and carbon dioxide affected the composition of the microbial population which, in turn, may explain the effect on the bio-oxidation performance. Thus, the use of additional carbon dioxide may be proposed as the method to increase the efficiency of bio-oxidation and to prevent the negative effect of a temperature increase on the activity of bio-oxidation. ABSTRACT: In the present study, the effect of additional carbon sources (carbon dioxide and molasses) on the bio-oxidation of a pyrite–arsenopyrite concentrate at temperatures of 40–50 °C was studied, and novel data regarding the patterns of the bio-oxidation of gold-bearing sulfide concentrates and the composition of the microbial populations performing these processes were obtained. At 40 °C, additional carbon sources did not affect the bio-oxidation efficiency. At the same time, the application of additional carbon dioxide improved the bio-oxidation performance at temperatures of 45 and 50 °C and made it possible to avoid the inhibition of bio-oxidation due to an increase in the temperature. Therefore, the use of additional carbon dioxide may be proposed to prevent the negative effect of an increase in temperature on the bio-oxidation of sulfide concentrates. 16S rRNA gene profiling revealed archaea of the family Thermoplasmataceae (Acidiplasma, Ferroplasma, Cuniculiplasma, and A-plasma group) and bacteria of the genera Leptospirillum, with Sulfobacillus and Acidithiobacillus among the dominant groups in the community. Temperature influenced the composition of the communities to a greater extent than the additional sources of carbon and the mode of operation of the bioreactor. Elevating the temperature from 40 °C to 50 °C resulted in increases in the shares of Acidiplasma and Sulfobacillus and decreases in the relative abundances of Ferroplasma, Leptospirillum, and Acidithiobacillus, while Cuniculiplasma and A-plasma were more abundant at 45 °C. A metagenomic analysis of the studied population made it possible to characterize novel archaea belonging to an uncultivated, poorly-studied group of Thermoplasmatales which potentially plays an important role in the bio-oxidation process. Based on an analysis of the complete genome, we propose describing the novel species and novel genus as “Candidatus Carboxiplasma ferriphilum” gen. nov., spec. nov.