Abstract
ABSTRACTMicrobe-mediated precipitation of Mn-oxides enriched in rare earth elements (REE) and other trace elements was discovered in tunnels leading to the main shaft of the Ytterby mine, Sweden. Defining the spatial distribution of microorganisms and elements in this ecosystem provide a better understanding of specific niches and parameters driving the emergence of these communities and associated mineral precipitates. Along with elemental analyses, high-throughput sequencing of the following four subsystems were conducted: (i) water seeping from a rock fracture into the tunnel, (ii) Mn-oxides and associated biofilm; referred to as the Ytterby Black Substance (YBS) biofilm (iii) biofilm forming bubbles on the Mn-oxides; referred to as the bubble biofilm and (iv) fracture water that has passed through the biofilms. Each subsystem hosts a specific collection of microorganisms. Differentially abundant bacteria in the YBS biofilm were identified within the Rhizobiales (e.g. Pedomicrobium), PLTA13 Gammaproteobacteria, Pirellulaceae, Hyphomonadaceae, Blastocatellia and Nitrospira. These taxa, likely driving the Mn-oxide production, were not detected in the fracture water. This biofilm binds Mn, REE and other trace elements in an efficient, dynamic process, as indicated by substantial depletion of these metals from the fracture water as it passes through the Mn deposit zone. Microbe-mediated oxidation of Mn(II) and formation of Mn(III/IV)-oxides can thus have considerable local environmental impact by removing metals from aquatic environments.
Highlights
Metal contamination in aquatic environments is a major concern in many areas of the world due to adverse ecological effects
Each of the four subsystems in the underground Mn-oxide producing ecosystem serves as a distinct ecological niche hosting a specific collection of microorganisms
The production of the rare earth elements (REE)-enriched Mn-oxides is likely driven by the group of differentially abundant bacterial taxa in the Ytterby Black Substance (YBS) biofilm: Rhizobiales (e.g. Pedomicrobium), PLTA13 Gammaproteobacteria, Pirellulaceae, Hyphomonadaceae, Blastocatellia and Nitrospira
Summary
Metal contamination in aquatic environments is a major concern in many areas of the world due to adverse ecological effects. Microbial activity can limit the mobility of contaminants by producing highly reactive minerals with strong sorption capacities. Most Mn-oxidation in nature is believed to be microbially driven (Tebo et al 2004). These microbially produced Mn-oxides have substantially higher sorption capacities than their abiotic-synthetic analogs (Zhou, Kim and Ko 2015). Microbial oxidation of Mn(II) and subsequent formation of sparingly soluble oxides of Mn(III) and Mn(IV) can have considerable local environmental impact and could have an important role in removal of Mn and trace metals from aquatic environments
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