title: Iron Isotope Fractionation during Fe(II) Oxidation Mediated by the Oxygen-Producing Marine Cyanobacterium Synechococcus PCC 7002.
abstract: In this study, we couple iron isotope analysis to microscopic and mineralogical investigation of iron speciation during circumneutral Fe(II) oxidation and Fe(III) precipitation with photosynthetically produced oxygen. In the presence of the cyanobacterium Synechococcus PCC 7002, aqueous Fe(II) (Fe(II)aq) is oxidized and precipitated as amorphous Fe(III) oxyhydroxide minerals (iron precipitates, Feppt), with distinct isotopic fractionation (ε56Fe) values determined from fitting the δ56Fe(II)aq(1.79‰ and 2.15‰) and the δ56Feppt(2.44‰ and 2.98‰) data trends from two replicate experiments. Additional Fe(II) and Fe(III) phases were detected using microscopy and chemical extractions and likely represent Fe(II) and Fe(III) sorbed to minerals and cells. The iron desorbed with sodium acetate (FeNaAc) yielded heavier δ56Fe compositions than Fe(II)aq. Modeling of the fractionation during Fe(III) sorption to cells and Fe(II) sorption to Feppt, combined with equilibration of sorbed iron and with Fe(II)aqusing published fractionation factors, is consistent with our resulting δ56FeNaAc. The δ56Fepptdata trend is inconsistent with complete equilibrium exchange with Fe(II)aq. Because of this and our detection of microbially excreted organics (e.g., exopolysaccharides) coating Fepptin our microscopic analysis, we suggest that electron and atom exchange is partially suppressed in this system by biologically produced organics. These results indicate that cyanobacteria influence the fate and composition of iron in sunlit environments via their role in Fe(II) oxidation through O2production, the capacity of their cell surfaces to sorb iron, and the interaction of secreted organics with Fe(III) minerals.
authors.affiliation: Iowa State University , Department of Geological & Atmospheric Sciences, 2237 Osborn Drive, 253 Science I, Ames, Iowa 50011-1027, United States.
authors.forename: E D
authors.identifier: http://orcid.org/0000-0001-9507-0893
authors.initials: ED
authors.lastname: Swanner
authors.affiliation: University of Tuebingen , Department of Geosciences, Tuebingen, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Bayer
authors.affiliation: University of Tuebingen , Department of Geosciences, Tuebingen, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Wu
authors.affiliation: University of Tuebingen , Department of Geosciences, Tuebingen, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Hao
authors.affiliation: University of Bayreuth , Bayreuth Center of Ecology and Environmental Research, Dr-Hans-Frisch-Str. 1-3, 95448 Bayreuth, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Obst
authors.affiliation: University of Tuebingen , Department of Geosciences, Tuebingen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Sundman
authors.affiliation: University of Tuebingen , Department of Geosciences, Tuebingen, Germany.
authors.forename: J M
authors.initials: JM
authors.lastname: Byrne
authors.affiliation: Department of Geosciences, Virginia Tech , Blacksburg, Virginia 24061-0420, United States.
authors.forename: F M
authors.initials: FM
authors.lastname: Michel
authors.affiliation: University of Tuebingen , Department of Geosciences, Tuebingen, Germany.
authors.forename: I C
authors.initials: IC
authors.lastname: Kleinhanns
authors.affiliation: University of Tuebingen , Department of Geosciences, Tuebingen, Germany.
authors.forename: A
authors.identifier: http://orcid.org/0000-0002-3558-9500
authors.initials: A
authors.lastname: Kappler
authors.affiliation: University of Tuebingen , Department of Geosciences, Tuebingen, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Schoenberg
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D007503:Iron Isotopes / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen; D046940:Synechococcus / Q000378:metabolism*
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D007503:Iron Isotopes; D007501:Iron; D010100:Oxygen