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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, Fe ppt), with distinct isotopic fractionation (ε 56Fe) values determined from fitting the δ 56Fe(II) aq (1.79‰ and 2.15‰) and the δ 56Fe ppt (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 δ 56Fe 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) aq using published fractionation factors, is consistent with our resulting δ 56FeNaAc. The δ 56Fe ppt data 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 Feppt in our microscopic analysis, we suggest that electron and atom exchange is partially suppressed inmore » 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 O 2 production, the capacity of their cell surfaces to sorb iron, and the interaction of secreted organics with Fe(III) minerals.« less

Authors:
ORCiD logo; ; ; ; ; ; ; ; ; ORCiD logo;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1372246
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Science and Technology; Journal Volume: 51; Journal Issue: 9
Country of Publication:
United States
Language:
ENGLISH
Subject:
54 ENVIRONMENTAL SCIENCES

Citation Formats

Swanner, E. D., Bayer, T., Wu, W., Hao, L., Obst, M., Sundman, A., Byrne, J. M., Michel, F. M., Kleinhanns, I. C., Kappler, A., and Schoenberg, R. Iron Isotope Fractionation during Fe(II) Oxidation Mediated by the Oxygen-Producing Marine Cyanobacterium Synechococcus PCC 7002. United States: N. p., 2017. Web. doi:10.1021/acs.est.6b05833.
Swanner, E. D., Bayer, T., Wu, W., Hao, L., Obst, M., Sundman, A., Byrne, J. M., Michel, F. M., Kleinhanns, I. C., Kappler, A., & Schoenberg, R. Iron Isotope Fractionation during Fe(II) Oxidation Mediated by the Oxygen-Producing Marine Cyanobacterium Synechococcus PCC 7002. United States. doi:10.1021/acs.est.6b05833.
Swanner, E. D., Bayer, T., Wu, W., Hao, L., Obst, M., Sundman, A., Byrne, J. M., Michel, F. M., Kleinhanns, I. C., Kappler, A., and Schoenberg, R. Tue . "Iron Isotope Fractionation during Fe(II) Oxidation Mediated by the Oxygen-Producing Marine Cyanobacterium Synechococcus PCC 7002". United States. doi:10.1021/acs.est.6b05833.
@article{osti_1372246,
title = {Iron Isotope Fractionation during Fe(II) Oxidation Mediated by the Oxygen-Producing Marine Cyanobacterium Synechococcus PCC 7002},
author = {Swanner, E. D. and Bayer, T. and Wu, W. and Hao, L. and Obst, M. and Sundman, A. and Byrne, J. M. and Michel, F. M. and Kleinhanns, I. C. and Kappler, A. and Schoenberg, R.},
abstractNote = {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)aq using published fractionation factors, is consistent with our resulting δ56FeNaAc. The δ56Feppt data 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 Feppt in 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 O2 production, the capacity of their cell surfaces to sorb iron, and the interaction of secreted organics with Fe(III) minerals.},
doi = {10.1021/acs.est.6b05833},
journal = {Environmental Science and Technology},
number = 9,
volume = 51,
place = {United States},
year = {Tue Apr 11 00:00:00 EDT 2017},
month = {Tue Apr 11 00:00:00 EDT 2017}
}