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Simin Zhao Master's Thesis.pdf (2.37 MB)

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The effects of organic ligands on biotic oxidation of structural Fe(II) in reduced nontronite by Pseudogulbenkianiasp. strain 2002

Zhao, Simin
http://orcid.org/0000-0003-2452-7475
http://rave.ohiolink.edu/etdc/view?acc_num=miami1556873530093781

Abstract Details

2019, Master of Science, Miami University, Geology and Environmental Earth Science.
Nitrate-dependent Fe(II) oxidation (NDFO) is important for multiple environmental processes including nitrate remediation, heavy metal mobility and transport, and nuclear waste disposal. Past research has focused on microbial oxidation of either aqueous Fe2+ or structural Fe(II) in minerals, however, the effects of organic ligands on this process are not yet well understood, though organic ligands are ubiquitous in natural environments. The aim of this research was to study the NDFO process of structural Fe(II) in reduced nontronite (rNAu-2) by lithoautotrophic Pseudogulbenkiania sp. Strain 2002 in the presence oxalate (OXA) and nitrilotriacetic acid (NTA), to determine their effects on Fe(II) oxidation and mineral transformations. Bio-oxidation experiments were conducted using microbially reduced NAu-2 and nitrate as the sole electron donor and acceptor, respectively, under bicarbonate buffered neutral pH condition. A much faster rate of Fe(II) oxidation by strain 2002 than that of chemical oxidation by nitrite suggests a dominating biological role in the NDFO process. Fe(II) oxidation rate and extent were much higher in OXA and NTA groups than in no-ligand group. The ligand-promoted dissolution of rNAu-2 and the formation of highly bio-oxidizable Fe(II)-ligand complex and reduction of Fe(III)-ligand complex back to Fe(II)-ligand complex by structural Fe(II) in rNAu-2 via a process called interfacial electron transfer are the mechanisms for the enhanced oxidation rate and extent. In all biotic treatments, nitrate was predominantly reduced to N2 with a small amount of N2O gas and a negligible amount of nitrite. The ratio of oxidized Fe(II) to reduced nitrate was non-stoichiometric, probably resulting from heterotrophic nitrate reduction by cell-stored carbon. Structural Fe in rNAu-2 was more susceptible to chelation and liberation by organic ligands compared to unreduced NAu-2, but the structure of rNAu-2 was nearly restored to unreduced NAu-2 upon microbial oxidation in the presence of oxalate and NTA. Ferrosilite precipitated in abiotic oxalate group but not in biotic oxalate group, apparently due to oxidation of Fe(II) to Fe(III). No new minerals precipitated in NTA groups (biotic or abiotic), apparently due to its strong chelating ability. The results of this study highlight the importance of organic ligands on microbially-mediated Fe(II) oxidation kinetics and mineral transformations. These findings have important implications for iron and nitrogen biogeochemical cycles in natural environments.
Hailiang Dong (Advisor)
Rakovan John (Committee Member)
Levy Jonathan (Committee Member)
65 p.
Geobiology; Geochemistry

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Citations

  • Zhao, S. (2019). The effects of organic ligands on biotic oxidation of structural Fe(II) in reduced nontronite by Pseudogulbenkianiasp. strain 2002 [Master's thesis, Miami University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=miami1556873530093781

    APA Style (7th edition)

  • Zhao, Simin. The effects of organic ligands on biotic oxidation of structural Fe(II) in reduced nontronite by Pseudogulbenkianiasp. strain 2002. 2019. Miami University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=miami1556873530093781.

    MLA Style (8th edition)

  • Zhao, Simin. "The effects of organic ligands on biotic oxidation of structural Fe(II) in reduced nontronite by Pseudogulbenkianiasp. strain 2002." Master's thesis, Miami University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=miami1556873530093781

    Chicago Manual of Style (17th edition)

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This open access ETD is published by Miami University and OhioLINK.