Bacterial community responses to a gradient of alkaline mountaintop mine drainage in Central Appalachian streams

Abstract

Microbial community composition and diversity change along chemical gradients, leading to the expectation that microbial community information might provide new gradient characterizations. Here we examine stream bacteria composition and diversity along a strong chemical gradient in Central Appalachian streams. Coal mining in the region generates alkaline mine drainage (AlkMD), causing dramatic increases in conductivity, alkalinity, sulfate and metals sufficient to degrade stream macrobiota communities throughout the ecoregion. In this study, we examined the relationship between water and biofilm chemistry and biofilm bacteria taxonomic composition in streams where active and reclaimed surface coal mines occupied 0-96% of watershed surface area. We incubated wood veneers in each stream site for 4 months to develop biofilms on similar substrates. We sampled water chemistry at the time of deployment and collection, and after 1 month. Following incubation, we collected biofilms for microbial and chemical characterization. Microbial composition was determined by pyrosequencing 16S rRNA amplicons. Biofilm subsamples were analyzed by inductively coupled plasma mass spectrometry to determine metal concentrations. Our results show that microbial community composition differed significantly between AlkMD-exposed and AlkMD-unexposed sites, and that compositional dissimilarity increased with AlkMD loading. Diversity was not correlated with pH or extent of upstream mining, but instead correlated with biofilm concentrations of Cd, Mn, Zn and Ni. Within mined sites, the extent of upstream mining was negatively correlated with taxonomic richness. Despite major compositional shifts, functional capacity predicted with PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) correlated with mining in only 3 of 43 level-2 KEGG (Kyoto Encyclopedia of Genes and Genomes) Orthology groups.