Investigation of microbial populations in the extremely metal-contaminated Coeur d'Alene River sediments

The deposition of mine tailings generated from 125 years of sulfidic ore mining resulted in the enrichment of Coeur d'Alene River (CdAR) sediments with significant amounts of toxic heavy metals. A review of literature suggests that microbial populations play a pivotal role in the biogeochemical cycling of elements in such mining-impacted sedimentary environments. To assess the indigenous microbial communities associated with metal-enriched sediments of the CdAR, high-density 16S microarray (PhyloChip) and clone libraries specific to bacteria (16S rRNA), ammonia oxidizers (amoA), and methanogens (mcrA) were analyzed. PhyloChip analysis provided a comprehensive assessment of bacterial populations and detected the largest number of phylotypes in Proteobacteria followed by Firmicutes and Actinobacteria. Furthermore, PhyloChip and clone libraries displayed considerable metabolic diversity in indigenous microbial populations by capturing several chemolithotrophic groups such as ammonia oxidizers, iron-reducers and -oxidizers, methanogens, and sulfate-reducers in the CdAR sediments. Twenty-two phylotypes detected on PhyloChip could not be classified even at phylum level thus suggesting the presence of novel microbial populations in the CdAR sediments. Clone libraries demonstrated very limited diversity of ammonia oxidizers and methanogens in the CdAR sediments as evidenced by the fact that only Nitrosospira- and Methanosarcina-related phylotypes were retrieved in amoA and mcrA clone libraries, respectively.