Pyrite-bioleaching microbial community: domestication, identification of dominant species, and characterization of functions

Abstract:

[Background]The bioleaching performance is closely related to the microbial community structure and its dynamics during the bioleaching process. Understanding the changes in microbial community structure and function during the bioleaching process is crucial for elucidating the role of microorganisms in this process and building efficient microbial combinations.[Objective] To obtain the microbial community with stable and high pyrite-leaching efficiency by domestication, and analyze the structure and function of the microbial community. [Methods]The microbial community was subcultured in the 9K medium with pyrite as the energy source. The iron and sulfur oxidation capacity of the microbial community was measured before and after domestication. The structure of the domesticated microbial community was analyzed by metagenomic sequencing combined with 16S rRNA gene clone library. Differentiation culture experiments were carried out to study the functions of dominant microorganisms in the domesticated microbial community during pyrite bioleaching. The functional annotation of metagenomic sequencing results was carried out to analyze the functional changes of the microbial community before and after domestication.[Results]The microbial community with a stable structure, improved bioleaching ability, and adaptability to the pyrite leaching environment was obtained after domestication. The metagenomic sequencing results showed that the relative abundance of the genus Acidithiobacillusand Sulfobacillus were both increased. Detection results from the 16S rRNA gene clone library showed that the domesticated microbial community mainly consisted of Acidithiobacillus thiooxidans and Sulfobacillus thermotolerans, with the iron and sulfur oxidation capacity increasing by 15.15% and 70.86%, respectively. The leaching effects were compared between the bacterial community and the dominant species alone. In terms of total iron leached from pyrite, the 16-day leaching rate of the domesticated community 5Biol reached 81.18%, while those of A.thiooxidans and S.thermotolerans were 51.86% and 37.65%, respectively. The better leaching ability of 5Biol than that of single dominant species indicated that the existence of synergistic effect between dominant species in the community, which endowed 5Biol with the leaching effect that a single species cannot achieve. The differentiation culture experiments showcased that A.thiooxidans primarily contributed to sulfur oxidation, while S.thermotolerans was mainly responsible for iron oxidation. S.thermotolerans was dependent on A.thiooxidans for iron oxidation. This indicated that different strains within the community may collaborate synergistically, leveraging their respective strengths to enhance the overall leaching efficiency. This is consistent with the increases in the relative abundance of Acidithiobacillus and Sulfobacillus and the enhancement of leaching ability of 5Biol after domestication. After domestication, sulfocyanin-like proteins were the key proteins involved in iron oxidation, while sulfur oxidation included the sox system, sor system, and non-sox subsystems. [Conclusion] Long-term domestication by passages with a specific ore can yield a stable microbial community with enhanced bioleaching performance. The simplified stable microbial community makes it easy to elucidate the functional roles of different microbial species. The findings provide insights into the construction of efficient microbial communities for bioleaching.