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

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.

Hydrometallurgical Processing of a Low-Grade Sulfide Copper–Nickel Ore Containing Pt and Pd

“…Representatives of A-plasma, Acidiphilum, and Leptospirillum were detected in the population, but their proportion was comparatively low. It may explain the comparatively low iron-oxidizing activity of the population at 45 • C. It should be noted that the presence of Acinetobacter in the population of bioleach reactors was shown in our recent work, but its role in the bioleaching process has not yet been understood [25].…”

“…It may explain the comparatively low iron-oxidizing activity of the population at 45 °C. It should be noted that the presence of Acinetobacter in the population of bioleach reactors was shown in our recent work, but its role in the bioleaching process has not yet been understood [25].…”

“…The initial pH value of the leaching solution was 1.5. The experiment was carried out at different temperatures (25,35, and 45 • C), since temperature has a significant effect on bioleaching processes. In industrial processes of heap bioleaching of sulfide ores, the ore heaps always heat up, and the temperature changes deep in the ore layer.…”

“…The analysis of the composition of microbial populations that formed under the experimental conditions was carried out by high-throughput sequencing on the MiSeq system (Illumina, San Diego, CA, USA) of the V3-V4 region of the 16S rRNA gene. The analysis was described in detail in our previous work [25]. In the present work, we analyzed samples of biomass from the inoculum as well as the microbial population formed in the column at each temperature after 140 days of bioleaching.…”

“…Molecular biological analysis of the microbial population in the columns formed for 140 days showed that the species composition of microorganisms changed at different temperatures (Figure 7). In the inoculum obtained at 25 • C, representatives of the genera Ferroplasma, Cunuciliplasma, uncultivated group A-plasma (which were recently described as the iron-oxidizing archaea "Candidatus Carboxiplasma ferriphilum" based on metagenomic analysis) [25], and Ferrimicrobium were predominant. After long-term bioleaching of the ore at 25 Thus, at 45 °C, typical acidophilic microorganisms were replaced by heterotrophic microorganisms, the role of which in bioleaching has not been described.…”