16S-rRNA gene-targeted amplicon sequence analysis of an enargite-dominant bioleach demonstration in Peru

Newmont Mining Corporation initiated a large-scale (ca. 1 million tonne) copper heap bioleach demonstration targeting enargite-dominant ore in northern Peru beginning in 2012. The Verde Bioleach Demonstration Facility has now concluded operations after over 4 years of active leaching, making it possible to perform microbiological analyses on residual ore samples from the heaps. 16S-rRNA gene targeted metagenomics analysis was performed on spatially-distributed samples obtained from the Run-of-Mine (ROM) heap by sonic drilling in late 2016, as well as leach solution samples obtained through the course of the demonstration, from 2013 to 2016. The results indicate substantial alteration of the planktonic microbial populations as applied raffinate solution chemistry changed, leading to the dominance of heterotrophic bacteria atypical of previously-described bioleach environments (predominantly Microbacterium and Achromobacter species), and an archaeal population completely dominated by Ferroplasma species. Inferred attached microbial populations from the single samples obtained near the end of the heap leach operation resembled populations more in line with past studies, containing Acidithiobacillus, Sulfobacillus, and Leptospirillum species, and archaeal populations containing Ferroplasma and Acidiplasma species. These results are described in the context of the heap leach chemistry observed during the course of the demonstration