title: Submicron-Scale Heterogeneities in Nickel Sorption of Various Cell-Mineral Aggregates Formed by Fe(II)-Oxidizing Bacteria.
abstract: Fe(II)-oxidizing bacteria form biogenic cell-mineral aggregates (CMAs) composed of microbial cells, extracellular organic compounds, and ferric iron minerals. CMAs are capable of immobilizing large quantities of heavy metals, such as nickel, via sorption processes. CMAs play an important role for the fate of heavy metals in the environment, particularly in systems characterized by elevated concentrations of dissolved metals, such as mine drainage or contaminated sediments. We applied scanning transmission (soft) X-ray microscopy (STXM) spectrotomography for detailed 3D chemical mapping of nickel sorbed to CMAs on the submicron scale. We analyzed different CMAs produced by phototrophic or nitrate-reducing microbial Fe(II) oxidation and, in addition, a twisted stalk structure obtained from an environmental biofilm. Nickel showed a heterogeneous distribution and was found to be preferentially sorbed to biogenically precipitated iron minerals such as Fe(III)-(oxyhydr)oxides and, to a minor extent, associated with organic compounds. Some distinct nickel accumulations were identified on the surfaces of CMAs. Additional information obtained from scatter plots and angular distance maps, showing variations in the nickel-iron and nickel-organic carbon ratios, also revealed a general correlation between nickel and iron. Although a high correlation between nickel and iron was observed in 2D maps, 3D maps revealed this to be partly due to projection artifacts. In summary, by combining different approaches for data analysis, we unambiguously showed the heterogeneous sorption behavior of nickel to CMAs.
authors.affiliation: Environmental Analytical Microscopy, Center for Applied Geoscience, University of Tübingen , Hölderlinstrasse 12, 72074 Tübingen, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Schmid
authors.affiliation: Environmental Analytical Microscopy, Center for Applied Geoscience, University of Tübingen , Hölderlinstrasse 12, 72074 Tübingen, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Zeitvogel
authors.affiliation: Environmental Analytical Microscopy, Center for Applied Geoscience, University of Tübingen , Hölderlinstrasse 12, 72074 Tübingen, Germany.
authors.forename: Likai
authors.initials: L
authors.lastname: Hao
authors.affiliation: Environmental Analytical Microscopy, Center for Applied Geoscience, University of Tübingen , Hölderlinstrasse 12, 72074 Tübingen, Germany.
authors.forename: Pablo
authors.initials: P
authors.lastname: Ingino
authors.affiliation: Environmental Analytical Microscopy, Center for Applied Geoscience, University of Tübingen , Hölderlinstrasse 12, 72074 Tübingen, Germany.
authors.forename: Irini
authors.initials: I
authors.lastname: Adaktylou
authors.affiliation: Environmental Analytical Microscopy, Center for Applied Geoscience, University of Tübingen , Hölderlinstrasse 12, 72074 Tübingen, Germany.
authors.forename: Merle
authors.initials: M
authors.lastname: Eickhoff
authors.affiliation: Environmental Analytical Microscopy, Center for Applied Geoscience, University of Tübingen , Hölderlinstrasse 12, 72074 Tübingen, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Obst
mesh_terms: D000327:Adsorption; D001419:Bacteria / Q000737:chemistry* / Q000378:metabolism*; D005296:Ferrous Compounds / Q000737:chemistry* / Q000378:metabolism*; D009532:Nickel / Q000737:chemistry* / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D005296:Ferrous Compounds; D009532:Nickel