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Acid mine drainage (AMD) is a major environmental problem affecting tens of thousands of kilometers 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 among sites. At Scalp Level Run (Cambria County, PA), first-order iron oxidation rates are 10 times greater 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 a >10-fold change in the concentration of ferrous iron from 57.3 mg/liter at the emergence to 2.5 mg/liter 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. Remediation is frequently ineffective and costly, upwards of $100 billion globally and nearly $5 billion in Pennsylvania alone. Microbial Fe(II) oxidation is more efficient than abiotic Fe(II) oxidation at low pH (P. C. Singer and W. Stumm, Science 167:1121-1123, 1970, https://doi.org/10.1126/science.167.3921.1121). 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 operational taxonomic units (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.

Lehman Caves is an extensively decorated high desert cave that represents one of the main tourist attractions in Great Basin National Park, Nevada. Although traditionally considered a water table cave, recent studies identified abundant speleogenetic features consistent with a hypogenic and, potentially, sulfuric acid origin. Here, we characterized white mineral deposits in the Gypsum Annex (GA) passage to determine whether these secondary deposits represent biogenic minerals formed during sulfuric acid corrosion and explored microbial communities associated with these and other mineral deposits throughout the cave. Powder X‐ray diffraction (pXRD), scanning electron microscopy with electron dispersive spectroscopy (SEM‐EDS), and electron microprobe analyses (EPMA) showed that, while most white mineral deposits from the GA contain gypsum, they also contain abundant calcite, silica, and other phases. Gypsum and carbonate‐associated sulfate isotopic values of these deposits are variable, with δ34SV‐CDT between +9.7‰ and +26.1‰, and do not reflect depleted values typically associated with replacement gypsum formed during sulfuric acid speleogenesis. Petrographic observations show that the sulfates likely co‐precipitated with carbonate and SiO2 phases. Taken together, these data suggest that the deposits resulted from later‐stage meteoric events and not during an initial episode of sulfuric acid speleogenesis. Most sedimentary and mineral deposits in Lehman Caves have very low microbial biomass, with the exception of select areas along the main tour route that have been impacted by tourist traffic. High‐throughput 16S rRNA gene amplicon sequencing showed that microbial communities in GA sediments are distinct from those in other parts of the cave. The microbial communities that inhabit these oligotrophic secondary mineral deposits include OTUs related to known ammonia‐oxidizing Nitrosococcales and Thaumarchaeota, as well as common soil taxa such as Acidobacteriota and Proteobacteria. This study reveals microbial and mineralogical diversity in a previously understudied cave and expands our understanding of the geomicrobiology of desert hypogene cave systems. [ABSTRACT FROM AUTHOR]

A legacy of coal mining in the Appalachians has provided a unique opportunity to study the ecological niches of iron-oxidizing microorganisms. Mine-impacted, anoxic groundwater with high dissolved-metal concentrations emerges at springs and seeps associated with iron oxide mounds and deposits. These deposits are colonized by iron-oxidizing microorganisms that in some cases efficiently remove most of the dissolved iron at low pH, making subsequent treatment of the polluted stream water less expensive. We used full-cycle rRNA methods to describe the composition of sediment communities at two geochemically similar acidic discharges, Upper and Lower Red Eyes in Somerset County, PA, USA. The dominant microorganisms at both discharges were acidophilic Gallionella-like organisms, “Ferrovum” spp., and Acidithiobacillus spp. Archaea and Leptospirillum spp. accounted for less than 2% of cells. The distribution of microorganisms at the two sites could be best explained by a combination of iron(II) concentration and pH. Populations of the Gallionella-like organisms were restricted to locations with pH>3 and iron(II) concentration of >4 mM, while Acidithiobacillus spp. were restricted to pH4 mM. Our findings offer a predictive framework that could prove useful for describing the distribution of microorganisms in acid mine drainage, based on readily accessible geochemical parameters.

Premise: A family‐specific probe set for sunflowers, Compositae‐1061, enables family‐wide phylogenomic studies and investigations at lower taxonomic levels, but may lack resolution at genus to species levels, especially in groups complicated by polyploidy and hybridization. Methods: We developed a Hyb‐Seq probe set, Compositae‐ParaLoss‐1272, that targets orthologous loci in Asteraceae. We tested its efficiency across the family by simulating target enrichment sequencing in silico. Additionally, we tested its effectiveness at lower taxonomic levels in the historically complex genus Packera. We performed Hyb‐Seq with Compositae‐ParaLoss‐1272 for 19 Packera taxa that were previously studied using Compositae‐1061. The resulting sequences from each probe set, plus a combination of both, were used to generate phylogenies, compare topologies, and assess node support. Results: We report that Compositae‐ParaLoss‐1272 captured loci across all tested Asteraceae members, had less gene tree discordance, and retained longer loci than Compositae‐1061. Most notably, Compositae‐ParaLoss‐1272 recovered substantially fewer paralogous sequences than Compositae‐1061, with only ~5% of the recovered loci reporting as paralogous, compared to ~59% with Compositae‐1061. Discussion: Given the complexity of plant evolutionary histories, assigning orthology for phylogenomic analyses will continue to be challenging. However, we anticipate Compositae‐ParaLoss‐1272 will provide improved resolution and utility for studies of complex groups and lower taxonomic levels in the sunflower family. [ABSTRACT FROM AUTHOR]