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Mechanisms of Phenazine-Mediated Extracellular Electron Transfer by Pseudomonas aeruginosa


Saunders, Scott Harrison (2020) Mechanisms of Phenazine-Mediated Extracellular Electron Transfer by Pseudomonas aeruginosa. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/P4Z5-5445.


Extracellular electron transfer (EET), the process whereby cells access electron acceptors or donors that reside many cell lengths away, enables metabolic activity by microorganisms, particularly under oxidant-limited conditions that occur in multicellular bacterial biofilms. Although different mechanisms underpin this process in individual organisms, a potentially widespread strategy involves extracellular electron shuttles, redox-active metabolites that are secreted and recycled by diverse bacteria. Here, I first review general aspects of the electron shuttling strategy, such as the chemical diversity and potential distribution of electron shuttle producers and users, and the costs associated with electron shuttle biosynthesis. Then I address the long-standing question: how do these electron shuttles catalyze electron transfer within biofilms without being lost to the environment? I show that phenazine electron shuttles mediate efficient EET through interactions with extracellular DNA (eDNA) in Pseudomonas aeruginosa biofilms, which are important in nature and disease. Retention of pyocyanin (PYO) and phenazine carboxamide in the biofilm matrix is facilitated by binding to eDNA. In vitro, different phenazines can exchange electrons in the presence or absence of DNA and phenazines can participate directly in redox reactions through DNA; the biofilm eDNA can also support rapid electron transfer between redox-active intercalators. Electrochemical measurements of biofilms indicate that retained PYO supports an efficient redox cycle with rapid EET and slow loss from the biofilm. Together, these results establish that eDNA facilitates phenazine metabolic processes in P. aeruginosa biofilms, suggesting a model for how extracellular electron shuttles achieve retention and efficient EET in biofilms.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Microbiology, electrochemistry, phenazine, pseudomonas aeruginosa, bacteria, biofilm, electron transfer, metabolism
Degree Grantor:California Institute of Technology
Division:Biology and Biological Engineering
Major Option:Microbiology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Newman, Dianne K.
Thesis Committee:
  • Meyerowitz, Elliot M. (chair)
  • Barton, Jacqueline K.
  • Murray, Richard M.
  • Newman, Dianne K.
Defense Date:26 March 2020
Funding AgencyGrant Number
Army Research Office (ARO)W911NF-17-1-0024
Record Number:CaltechTHESIS:04022020-212557295
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 1 adapted for Chapter 2 2 github repository files: Appendix data Phenazine survival TnSeq
Saunders, Scott Harrison0000-0003-4224-9106
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13667
Deposited By: Scott Saunders
Deposited On:06 Apr 2020 21:21
Last Modified:08 Nov 2023 00:46

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