INTEGRATING GEOCHEMICAL, MAGNETIC, AND GENOMIC ANALYSES TO UNDERSTAND STRAIN-SPECIFIC DIFFERENCES IN MICROBIALLY-MEDIATED PYRRHOTITE DISSOLUTION

Sulfur-oxidizing microorganisms play an important role in the dissolution of iron sulfide minerals and the generation of acid rock drainage. Pyrrhotite, (Fe_1-xS, 0 ≤ x ≤ 0.125), is the second most abundant iron sulfide mineral in the Earth’s crust, and is frequently associated with copper, nickel, and platinum-group element ores, so understanding pyrrhotite dissolution in the environment is critical to predicting the quality and improving management of mine waste and water. However, little is known about the influence of microorganisms on the rate of pyrrhotite dissolution, particularly at near-neutral or mildly acidic pH. We have isolated five sulfur-oxidizing microorganisms from sulfide-bearing rocks from Minnesota's Duluth Complex. These organisms have a substantial effect on the rate of pyrrhotite dissolution and the precipitation of secondary minerals in laboratory experiments. In addition to using traditional geochemical methods to track dissolution rate in these experiments, bulk magnetic susceptibility can be used to track the dissolution of pyrrhotite and the accumulation of magnetic secondary minerals. Further, the composition and concentration of secondary minerals can be characterized using low- and high-temperature magnetic methods with higher sensitivities than conventional geochemical or mineralogical techniques allow. We find strain-specific differences in dissolution rate and types of precipitates formed. We then sequenced the genomes of the five strains, and identified properties of their sulfur, carbon, and nitrogen metabolic pathways that may explain some of the strain-specific differences in pyrrhotite oxidation and inorganic sulfur compound transformation. Combining geochemical, genomic, and magnetic analysis techniques can identify differences in the accumulation and mineralogy of secondary minerals that we observed in our experiments with and without sulfur-oxidizing microorganisms, and could be used as a proxy for microbiologically-influenced acid production and mineral dissolution in the environment.