Acid mine drainage (AMD) is a major environmental problem affecting tens of thousands of km of waterways worldwide. Passive bioremediation of AMD relies on microbial communities to oxidize and remove iron from the system; however, iron-oxidation rates in AMD environments are highly variable across sites. At Scalp Level Run (Cambria County PA), first-order iron-oxidation rates are ten times faster than at other coal associated iron mounds in the Appalachians. We examined the bacterial community at Scalp Level Run to determine whether a unique community is responsible for the rapid iron oxidation rate. Despite strong geochemical gradients including an over 10-fold change in the concentration of ferrous iron from 57.3 mg/L at the emergence to 2.5 mg/L at the base of the coal tailings pile, the bacterial community composition was nearly constant with distance from the spring outflow. Scalp Level Run contains many of the same taxa present in other AMD sites, but the community is dominated by two strains of Ferrovum myxofaciens, a species that is associated with high rates of Fe(II) oxidation in laboratory studies.
Importance Acid mine drainage pollutes more than 19,300 km of rivers and streams and 72,000 ha of lakes worldwide (1). Remediation is frequently ineffective and costly, upwards of US$100 billion globally (2, 3, 4) and nearly US$5 billion in Pennsylvania alone (5). Microbial Fe(II) oxidation is more efficient than abiotic Fe(II) oxidation at low pH (6). Therefore, AMD bioremediation could harness microbial Fe(II) oxidation to fuel more cost-effective treatments. Advances will require a deeper understanding of the ecology of Fe(II)-oxidizing microbial communities and the factors that control their distribution and rates of Fe(II) oxidation. We investigated bacterial communities that inhabit an AMD site with rapid Fe(II) oxidation and found that they were dominated by two OTUs of Ferrovum myxofaciens, a taxon associated with high laboratory rates of iron-oxidation. This research represents a step forward in identifying taxa that can be used to enhance cost-effective AMD bioremediation.