Ecology of sulfate-reducing bacteria in an iron-dominated, mining-impacted freshwater sediment

The bacterial community of Quesnel Lake sediments impacted by a catastrophic mine tailings spill differ in composition from those at undisturbed locations - two years post-spill

The West Basin of Quesnel Lake (British Columbia, Canada) suffered a catastrophic disturbance event in August 2014 when mine tailings and scoured natural material were deposited into the lake’s West Basin due to an impoundment failure at the adjacent Mount Polley copper-gold mine. The deposit covered a significant portion of the West Basin floor with a thick layer of material. Since lake sediments host bacterial communities that play key roles in the geochemical cycling in lacustrine environments, it is important to understand which groups inhabit the newly deposited material and what this implies for the ecological function of the West Basin. Here we report a study conducted two years post-spill, comparing the bacterial communities from sediments of both disturbed and undisturbed sites. Our results show that sediments from disturbed sites differed in physical and chemical properties than those in undisturbed sites (e.g. higher pH, particle size and Cu concentration). Furthermore, bacterial communities from the disturbed sites appeared to be legacy communities from the tailings impoundment, with metabolic potential revolving mainly around the cycling of S and metals, whereas the ones from the undisturbed sites were associated with the cycling of N.

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.

Formation of Fe-sulfides in cultures of sulfate-reducing bacteria

The purpose of this study was to synthesize Fe-sulfides produced with sulfate-reducing bacteria under experimental laboratory conditions. Fe-sulfides were precipitated with biologically produced sulfide in cultures growing at 22, 45, and 60 degrees C for up to 16 weeks. Abiotic controls were prepared by reacting liquid media with Na(2)S solutions. Precipitates were collected anaerobically, freeze-dried and analyzed by X-ray diffraction. Additional analyses included total Fe and S content, magnetic susceptibility, specific surface area, and scanning electron microscopy. Mackinawite (FeS) and greigite (Fe(3)S(4)) were the dominant iron sulfide phases formed in sulfate-reducing bacterial cultures. An increase in the incubation temperature from 22 to 60 degrees C enhanced the crystallinity of the Fe-sulfides. Generally, greigite was more prevalent in abiotic samples and mackinawite in biogenic materials. Pyrite (FeS(2)) was also found in abiotic precipitates. Abiotic samples had a higher magnetic susceptibility because of the greigite and displayed improved crystallinity compared to biotic materials.