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The Role of Context-Dependent Metabolic Interactions in Organizing Microbial Communities


Wilbert, Steven Alexander (2023) The Role of Context-Dependent Metabolic Interactions in Organizing Microbial Communities. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/7sv2-gj10.


We can image the strikingly beautiful compositions of natural microbial communities, but we still lack an understanding of the factors that shape their organization. Understanding the drivers of these structures at the microscale may allow us to better predict and control large-scale community functions in dynamic environments. In this thesis, I developed quantitative image analysis pipelines for uncovering the spatiotemporal growth of aggregate biofilms within a developing oxygen gradient by expanding upon the Agar Block Biofilm Assay (ABBA). I then developed the Agar Disk Biofilm Assay (ADBA) for improved imaging resolution. These tools push the bounders of laboratory experiments to better capture the complexity of natural environments. Next, I built a synthetic microbial community reflecting a metabolic pathway often partitioned between members found in nature: Pseudomonas aeruginosa (PA) strains with a denitrification pathway genetically split at the nitric oxide (NO) node. I characterized the growth of a strict consumer and a strict producer of NO and found that PA metabolizes NO in a manner that supports growth, a previously underappreciated energy conservation strategy. Local oxygen flips this interaction from beneficial to detrimental by increasing toxicity. I found these principles drive context-dependent cellular organization. This work underscores the contributions of partitioned metabolic pathways, redox-active metabolites, and dynamic micro-niches to the organization of microbial communities. Finally, combining my efforts towards method development and an appreciation for how redox-active metabolites drive context-dependent microbial interactions, I show how phenazines promote a previously unrecognized form of slow growth under nutrient limited environments. Taken together, this thesis highlights the importance of understanding dynamic micron-scale microbial interactions and presents several methodological improvements to capture it.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:polymicrobial communities metabolism metabolic cross-feeding nitric oxide nitrate denitrification spatial organization microenvironment oxygen gradients Pseudomonas aeruginosa
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:
  • Gradinaru, Viviana (chair)
  • Orphan, Victoria J.
  • Mazmanian, Sarkis K.
  • Newman, Dianne K.
Defense Date:9 June 2023
Non-Caltech Author Email:swilbert88 (AT)
Funding AgencyGrant Number
Record Number:CaltechTHESIS:06122023-184806431
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Ch. 4
Wilbert, Steven Alexander0009-0008-4409-8974
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16110
Deposited By: Steven Wilbert
Deposited On:12 Jun 2023 23:18
Last Modified:08 Nov 2023 00:46

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