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Mn oxide precipitation by epilithic biofilms in the Ytterby mine, Sweden: formation of an YREE-enriched birnessite
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Biofilms scavenge and bind reduced Mn(II) as well as stabilize highly reactive Mn(III), favouring formation of Mn oxides. Mn oxidation and precipitation involve closely connected and concomitant abiotic and biotic biogeochemical mechanisms, often making the biogenicity of the mineral product difficult to determine. In order to use these precipitates as potential biosignatures, profound knowledge of the formation pathways is required. Here we have access to an underground Mn oxide producing ecosystem in which epilithic biofilms precipitate yttrium and rare earth element enriched birnessite-type Mn oxides. Microbial community composition combined with elemental data is investigated to provide insight into how different subsystems of this ecosystem (fracture water, Mn oxide producing biofilm, and bubble biofilm) interact with each other to form the birnessite. We find that the microbial assembly of the feeding water has little impact on the derived biofilms, in which the signature microbial groups rather results from water chemistry and environmental conditions. In the Mn oxide producing biofilm, bacteria  are adapted to the emerging extreme environment (low temperature, no light, high metal concentration) which is generated by the biofilm itself. Microstructural characterizations show that the birnessite has a dendritic/shrublike or spherulitic/botryoidal growth pattern. Nucleation occurs in close association to the biofilm and Mn encrustations of cells and other organic structures serve as stable nuclei for further growth. The influence of organics decrease in importance as precipitates grow. In more evolved crystals, a repetitive pattern, Liesegang-type of rings, implies that abiotic factors dominate. Grown on a solid substrate, four bacterial (Hydrogenophaga sp., Pedobacter sp., Rhizobium sp. and Nevskia sp.) and one fungal species (Cladosporium sp.) are involved in Mn oxide production. Hydrogenophaga and Pedobacter oxidize Mn independently while Rhizobium needs a synergistic relationship with selected species (e.g., Nevskia). Members of the Pedobacter and Nevskia genera are previously not known Mn oxidizers. The onset of Mn precipitaiton takes place at different locations with respect to the cells for the different species. Precipitates are located intracellularly (possibly post mortem), on the bacterial cell walls, at the outer edges of more well developed crystals, within the extracellular organic matter (EOM) and on hyphal surfaces.

Keywords [en]
Mn oxidizers, birnessite, ecosystem, epilithic biofilms, shallow subsurface, YREE, Ytterby mine
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
URN: urn:nbn:se:su:diva-174773OAI: oai:DiVA.org:su-174773DiVA, id: diva2:1362601
Available from: 2019-10-21 Created: 2019-10-21 Last updated: 2019-10-23Bibliographically approved
In thesis
1. Microbially mediated manganese oxides enriched in yttrium and rare earth elements in the Ytterby mine, Sweden
Open this publication in new window or tab >>Microbially mediated manganese oxides enriched in yttrium and rare earth elements in the Ytterby mine, Sweden
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Microorganisms are able to manipulate redox reactions and thus exert extensive control on chemical speciation and element partitioning in nature, affecting the formation and dissolution of certain minerals. One of these redox active elements is manganese (Mn), which in its oxidized states (III/IV), commonly forms Mn oxide-hydroxide minerals. A microbially mediated birnessite-type Mn oxide enriched in yttrium (Y) and rare earth elements (REE) has been studied in our research. The YREE-enriched birnessite was found in a tunnel to the main shaft of the former Ytterby mine in Sweden, well known as the place of discovery of scandium, yttrium, tantalum and five of the REEs. The thesis aims to define preconditions and processes leading to the formation of this Ytterby birnessite, with particular focus on microbial involvement and the potentially promoting role of biofilms. Dynamics and mineral products of the natural system are studied in combination with analyses of Mn phases produced in vitro by microbes isolated from this system. In addition, the nature of the YREE association with the birnessite-type Mn oxides is investigated.

Natural birnessite has the composition Mx(Mn3+, Mn4+)2O4•(H2O)n  with M ususally being (Na,Ca) and x=0.5. An empirical formula based on element analyses for the Ytterby birnessite has been assessed as M = (Ca0,37-0,41YREE0.02Mg0.04Other metals0.02-0.03), with [Mn3+]/[Mn4+] = 0.86-1.00 to achieve charge balance. We find that there is a preference for the trivalent YREEs over divalent and monovalent metals. There is also a preferential uptake of light rare earth elements (LREE) relative to heavy rare earth elements (HREE), likely due to mineralogical preferences for charge and ionic radius. The YREEs are strongly bound to the mineral structure and not merely adsorbed on the surface. The Mn deposit subsystems (fracture water, Mn oxide precipitating biofilm and bubble biofilm) are phylogenetically significantly different and the microbial community composition of the feeding water has little impact on the derived biofilms. The signature microbial groups of the Mn oxide producing biofilm Rhizobiales (e.g., Pedomicrobium), PLTA13 Gammaproteobacteria, Pirellulaceae, Blastocatellia and Nitrospira are adapted to the specific characteristics of the biofilm: an emerging extreme environment (low temperature, no light, high metal concentration) which is in part generated by the biofilm components themselves. Known Mn oxidizers are identified among these niched microbial groups and four of the isolated bacterial species (Hydrogenophaga sp., Pedobacter sp., Rhizobium sp. and Nevskia sp.) as well as one fungal species (Cladosporium sp.) are involved in Mn oxide production. Hydrogenophaga sp. and Pedobacter sp. produce Mn oxides independently while results imply a synergistic relationship between Rhizobium sp. and selected species. Members of the Pedobacter and Nevskia genera are previously not known to oxidize Mn. Microstructural characterizaton show that the growth pattern of the birnessite-type Mn oxides is either dendritic/shrublike or spherulitic/botryoidal. Nucleation takes place in close association to the biofilm and initial Mn precipitates are observed at different locations depending on the mediating species. Encrustations of cells and other organic structures by Mn precipitates serve as stable nuclei for further growth. The close relationship appears to decrease in importance as the aggregates of poorly crystalline precipitates grow. In the more developed crystals, a repetitive pattern, Liesegang-type of rings, suggests that abiotic factors take over.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2019. p. 63
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper ; 378
Keywords
manganese oxidizers, birnessite, yttrium and rare earth elements (YREE), biofilms, shallow subsurface, Ytterby mine, geomicrobiology, microbial geochemistry, manganoxiderare, birnessit, yttrium och sällsynta jordartsmetaller (YREE), underjordisk, Ytterby mine, geomikrobiologi, mikrobiell kemi
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-175390 (URN)978-91-7797-841-1 (ISBN)978-91-7797-842-8 (ISBN)
Public defence
2019-12-11, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, 10:00 (English)
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Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2019-11-18 Created: 2019-10-23 Last updated: 2019-11-07Bibliographically approved

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