Quantitative Biosciences Thesis Proposal
School of Physics
Advisor: Dr. Jennifer Curtis (School of Physics – GT)
Co-advisor: Dr. Steve Diggle (School of Biology – GT)
Open to the Community
Bacteriophage-driven morphological spatial structuring of Pseudomonas aeruginosa biofilms
Tuesday, September 28th, 2021 at 8:00 am
Dr. Joshua Weitz (School of Biology – GT)
Dr. Yao Yao (Dept. of Mathematics – National University of Singapore)
Bacteria, while single-celled organisms, often exist as biofilms, which are normally defined as surface-attached bacterial communities enmeshed in a self-produced, slimy matrix of extracellular polymeric substances. Moreover, within typical biofilms, constituent bacteria are not homogeneously distributed, but are spatially structured along numerous dimensions: metabolic, social, morphological, etc. The focus of this proposal is morphological spatial structuring, which I intend to refer to the presence of distinct shapes and patterns of bacterial structures within biofilms. My overall goal is to investigate how a specific form of morphological spatial structuring in a model organism is driven by lytic bacteriophage, and how the resulting picture impacts efforts to employ phage therapeutically.
Pseudomonas aeruginosa is a rod-shaped, Gram-negative bacterium that opportunistically infects patients with preexisting health conditions, such as traumatic burns and cystic fibrosis (CF). It has been shown that P. aeruginosa biofilms grown in polymer-rich environments similar to the CF lung exhibit aggregates consisting of cells aligned laterally in columnar stacks. These “stacked aggregates” form due to the cell-polymer system’s tendency to maximize its entropy: at sufficiently high concentrations, lateral alignment of cells provides extracellular polymers (termed “depletants”) with the maximum amount of volume in which to move, and hence the maximum number of configurational microstates. We have discovered that phage can induce the formation of stacked aggregates in P. aeruginosa by this very mechanism; indeed, as infection proceeds, depletants from lysis accumulate in the extracellular matrix, eventually attaining the requisite densities for the depletion force to operate. This phenomenon presents a novel problem: the very agent used to eradicate infecting bacteria may instead promote their eventual flourishing by structuring surviving cells into phage-resistant aggregates.
My proposed research program consists of three primary aims. The first aim is to experimentally characterize the precise role of phage in stacked aggregation. For example, in what region of parameter space does phage generate stacked aggregates? And does phage itself serve as a depletant? The second aim is to determine whether stacked aggregation of P. aeruginosa does in fact confer protection from phage, and whether such protection differs from that afforded by other clinically relevant forms of morphological spatial structuring. The final aim involves the construction of a computational model of stacked aggregation in the presence of phage. I intend for this model to share a reciprocal relationship with the first two aims and to act as a useful testing ground for later hypotheses concerning the phage-bacteria dynamics of stacked aggregation.