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    Extracellular electron transfer-dependent metabolism of anaerobic ammonium oxidation (Anammox) bacteria

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    Name:
    PhD Dissertation_Dario Rangel Shaw_Final.pdf
    Size:
    13.75Mb
    Format:
    PDF
    Description:
    PhD Dissertation
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    Type
    Dissertation
    Authors
    Shaw, Dario Rangel
    Advisors
    Saikaly, Pascal cc
    Committee members
    Hong, Pei-Ying cc
    Daffonchio, Daniele cc
    Jetten, Mike
    Program
    Environmental Science and Engineering
    KAUST Department
    Biological and Environmental Sciences and Engineering (BESE) Division
    Date
    2020-08
    Embargo End Date
    2020-12-17
    Permanent link to this record
    http://hdl.handle.net/10754/666479
    
    Metadata
    Show full item record
    Access Restrictions
    At the time of archiving, the student author of this dissertation opted to temporarily restrict access to it. The full text of this dissertation became available to the public after the expiration of the embargo on 2020-12-17.
    Abstract
    Anaerobic ammonium oxidation (anammox) by anammox bacteria contributes significantly to the global nitrogen cycle and plays a major role in sustainable wastewater treatment. To date, autotrophic nitrogen removal by anammox bacteria is the most efficient and environmentally friendly process for the treatment of ammonium in wastewaters; its application can save up to 60% of the energy input, nearly 100% elimination of carbon demand and 80% decrease in excess sludge compared to conventional nitrification/denitrification process. In the anammox process, ammonium (NH4+) is directly oxidized to dinitrogen gas (N2) using intracellular electron acceptors such as nitrite (NO2–) or nitric oxide (NO). In the absence of NO2– or NO, anammox bacteria can couple formate oxidation to the reduction of metal oxides such as Fe(III) or Mn(IV). Their genomes contain homologs of Geobacter and Shewanella cytochromes involved in extracellular electron transfer (EET). However, it is still unknown whether anammox bacteria have EET capability and can couple the oxidation of NH4+ with transfer of electrons to extracellular electron acceptors. In this dissertation, I discovered by using complementary approaches that in the absence of NO2–, freshwater and marine anammox bacteria couple the oxidation of NH4+ with transfer of electrons to carbon-based insoluble extracellular electron acceptors such as graphene oxide (GO) or electrodes poised at a certain potential in microbial electrolysis cells (MECs). Metagenomics, fluorescence in-situ hybridization and electrochemical analyses coupled with MEC performance confirmed that anammox electrode biofilms were responsible for current generation through EET-dependent oxidation of NH4+. 15N-labelling experiments revealed the molecular mechanism of the EET-dependent anammox process. NH4+ was oxidized to N2 via hydroxylamine (NH2OH) as intermediate when electrode was used as the terminal electron acceptor. Comparative transcriptomics analysis supported isotope labelling experiments and revealed an alternative pathway for NH4+ oxidation coupled to EET when electrode was used as electron acceptor. The results presented in my dissertation provide the first experimental evidence that marine and freshwater anammox bacteria can couple NH4+ oxidation with EET, which is a significant breakthrough that is promising in the context of implementing EET-dependent anammox process for energy-efficient treatment of nitrogen using bioelectrochemical systems.
    Citation
    Shaw, D. R. (2020). Extracellular electron transfer-dependent metabolism of anaerobic ammonium oxidation (Anammox) bacteria. KAUST Research Repository. https://doi.org/10.25781/KAUST-E5V2Y
    DOI
    10.25781/KAUST-E5V2Y
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-E5V2Y
    Scopus Count
    Collections
    Biological and Environmental Sciences and Engineering (BESE) Division; Environmental Science and Engineering Program; Dissertations

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