S9: Adaptation of soil-associated microbial communities to intrusion of acid mind drainage

Coal mine derived acid mine drainage (AMD) is produced by oxidation iron sulfide phases that are exposed during mining, resulting in fluids that are acidic and contain abundant dissolved Fe(II).  In some cases, upon emergence at the terrestrial surface, AMD moves in a sheet-flow fashion, with a fluid depth of ≤0.5 cm.  This flow characteristic facilitates AMD aeration, and consequently the activities of Fe(II) oxidizing bacteria (FeOB), leading to the formation of massive Fe(III) (hydr)oxide deposits referred to as “iron mounds.” FeOB activities in iron mounds result in the removal of dissolved Fe(II) from AMD, which is a major goal of AMD treatment.  The robust FeOB activity associated with iron mounds develops with no human intervention, suggesting that treating AMD based on the iron mound concept could be a reliable, inexpensive, and sustainable approach to removal of Fe from AMD.  However, the dynamics of initial iron mound development are unclear. To determine how iron mound microbial communities and activities develop, we incubated pristine soil from an area adjacent to an iron mound with AMD. Rates of Fe(II) oxidation, culturable FeOB abundances, and changes in microbial communities associated with the incubations were determined at periodic intervals. FeOB abundances and rates of biological Fe(II) oxidation increased over 24 days of incubation, approching levels comparable to those of iron mound sediments. These data suggest that microbial communities associated pristine soil adapt to the harsh conditions of AMD, such that efficient Fe removal can be accomplished.