Microbial community composition influences pyrrhotite dissolution rates: Insights from paired mineral magnetic and genomics studies.

Abstract:

Pyrrhotite (Fe_1-xS, 0 ≤ x ≤ 0.125) is the second most abundant sulfide mineral in the Earth’s crust, and is frequently associated with copper, nickel, and platinum-group element ores. Microorganisms are known to catalyze and accelerate the dissolution of sulfide minerals under environmental conditions thereby negatively impacting water quality. Thus, quantifying microbially-mediated pyrrhotite dissolution under circumneutral environmental pH conditions is critical to improving management of mine waste and water.

We have conducted laboratory experiments using isolated sulfur-oxidizing microorganisms and enrichment cultures obtained from pyrrhotite-bearing rocks from Minnesota’s Duluth Complex, which hosts a large, undeveloped deposit of disseminated Cu-Ni-PGE ore minerals. The presence of these organisms results in a substantial acceleration of pyrrhotite dissolution as compared to abiotic conditions. Different isolates and enrichment communities result in varying dissolution rates and affect the amount of elemental sulfur formed and the precipitation of secondary iron minerals. Small subunit 16S rRNA gene sequencing of the enrichment experiments, as well as whole genome sequencing of several isolates, allows us to link the differences in dissolution rates to strain or community specific elements.

Both dissolution rate and differences in type and quantity of secondary minerals can be characterized using low- and high-temperature magnetic techniques with higher sensitivities and increased specificity than traditional geochemical or mineralogical techniques. The clear morphological and magnetic differences observed in our experiments with and without sulfur-oxidizing microorganisms can be used to evaluate microbiologically influenced acid production and mineral dissolution in the environment.