STRAIN-SPECIFIC GENOMIC DIFFERENCES IN PYRRHOTITE OXIDIZING BACTERIA ISOLATED FROM THE DULUTH COMPLEX, MINNESOTA

Microorganisms are an important catalyst for sulfide mineral oxidation and contribute to the formation of acid mine drainage. Pyrrhotite is the second most abundant metal sulfide mineral, and understanding pyrrhotite dissolution under realistic environmental conditions is critical to predicting the impact 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 conducted laboratory experiments using sulfur-oxidizing isolates and enrichments collected from sulfide-bearing rocks from Minnesota’s Duluth Complex, which hosts a large undeveloped disseminated Cu-Ni-PGE deposit. The presence of these organisms results in a substantial acceleration of pyrrhotite dissolution as compared to controls. Different isolates and enrichment communities not only result in different dissolution rates, but also affect the amount of elemental sulfur formed and the precipitation of secondary minerals. 16S rRNA gene sequencing of the enrichment experiments, as well as complete genome sequencing of the isolates, allow us to link the differences in dissolution rates to strain or community specific elements. We found that enrichments with sulfur and iron-oxidizing members only slightly increased rates over isolate sulfur oxidizers, although less elemental sulfur was produced. Among the sulfur-oxidizing isolates, the fastest rates occurred with an obligately aerobic autotrophic strain of Sulfuriferula that had a partial SOX system and sulfide quinone reductase (SQR). Other strains with slower pyrrhotite oxidation included strains with dissimilatory nitrate reductases and dissimilatory sulfate reduction/oxidation pathways.