46-10 Microbial community development and evolution in kinetic tests of sulfide-bearing rock over two years of operation

Session: Research to Accelerate Recovery of Critical Minerals from Primary and Secondary Resources

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Despite their importance as catalysts for sulfide mineral oxidation, microorganisms are usually not often considered in the design of humidity cells and other widely-used kinetic tests for pre-assessment of mine waste. Microbial communities respond to different environmental conditions such as temperature, chemistry, and moisture, which may affect mineral oxidation rates within the test cell. Here we report new DNA- and RNA-based analyses of microbial communities in laboratory kinetic tests and field piles of pyrite-bearing Ely Greenstone with different sulfide mineral contents that were operated under a range of test conditions, in order to evaluate microbiological influences on sulfide oxidation and considerations for kinetic test work. rRNA gene libraries from humidity cells were dominated by genera including Bradyrhizobium, Paucibacter, and Alicyclobacillus, with other groups such as Arsenicitalea, Acidibacter, and Sulfuritalea present at lower abundance. In contrast, large field piles of the same rock that have been weathered outside for more than 20 years were dominated by uncultured Ktedonobacteria and Acidobacteria. Most of these taxa were present in both rRNA gene and transcript libraries, indicating that they are active members of the rock weathering community. The field pile communities were both more diverse, and had a higher species richness than the humidity cells. In both the field piles and humidity cells, material with the highest sulfide mineral content had the lowest diversity. Metagenomic libraries show that the community included taxa capable of chemolithoautotrophic growth, including Bradyrhizobium spp. that are especially abundant and have multiple pathways for the oxidation of reduced inorganic sulfur compounds and genes that encode CO₂ and N₂ fixation, as well as uncultured taxa that have the potential for ferrous iron oxidation. We will discuss differences in microbial community development in different experimental treatments, and implications for considering microbial community analysis in kinetic tests of sulfide-bearing rock.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8567

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