The Duluth Complex in northeastern Minnesota hosts economically significant deposits of copper, nickel, and platinum group elements (PGEs). The primary sulfide mineralogy of these deposits includes the minerals pyrrhotite, chalcopyrite, pentlandite, and cubanite, and weathering experiments show that most sulfidebearing rock from the Duluth Complex generates moderately acidic leachate (pH 4 to 6). Microorganisms are important catalysts for metal sulfide oxidation and could influence the quality of water from mines in the Duluth Complex. Nevertheless, compared with that of extremely acidic environments, much less is known about the microbial ecology of moderately acidic sulfide-bearing mine waste, and so existing information may have little relevance to those microorganisms catalyzing oxidation reactions in the Duluth Complex. Here, we characterized the microbial communities in decade-long weathering experiments (kinetic tests) conducted on crushed rock and tailings from the Duluth Complex. Analyses of 16S rRNA genes and transcripts showed that differences among microbial communities correspond to pH, rock type, and experimental treatment. Moreover, microbial communities from the weathered Duluth Complex rock were dominated by taxa that are not typically associated with acidic mine waste. The most abundant operational taxonomic units (OTUs) were from the genera Meiothermus and Sulfuriferula, as well as from diverse clades of uncultivated Chloroflexi, Acidobacteria, and Betaproteobacteria. Specific taxa, including putative sulfur-oxidizing Sulfuriferula spp., appeared to be primarily associated with Duluth Complex rock, but not pyrite-bearing rocks subjected to the same experimental treatment. We discuss the implications of these results for the microbial ecology of moderately acidic mine waste with low sulfide content, as well as for kinetic testing of mine waste.
Bibliographical noteFunding Information:
We thank the Minnesota Department of Natural Resources Division of Lands and Minerals for facilitating sampling of the weathered rock samples used in this study. Special thanks to S. Koski and P. Geiselman for advice and assistance with sample collection, to D. Gohl, A. Hague, A. MacLean, and K. Beckman for insightful discussion and assistance with amplicon sequencing at the UMGC, to T. Lösekann and D. Bond for advice and the use of laboratory equipment for cell counting, and to N. Seaton and K. Hobart for assistance with scanning electron microscope analyses. C. Nguyen, L. Thomas, the University of Minnesota College of Science and Engineering systems staff, and the Minnesota Supercomputing Institute provided computing support and the use of facilities. This work was supported by University of Minnesota MnDRIVE initiative and the University of Minnesota BioTechnology Institute.
© 2017 American Society for Microbiology.
- 16S rRNA
- Duluth Complex
- Humidity cell
- Microbial communities
- Mine waste
- Sulfide mineral