In partial fulfillment of the requirements for the degree of 

Doctor of Philosophy in Quantitative Biosciences

in the School of Biological Sciences

Stephen Thomas

Defends his thesis:

Title: Linking Molecular Mechansims to Population-level Behavior using Mathematical Models of Pseudomonas aeruginosa Quorum Sensing

Thursday, January 5, 2023

10:00am Eastern Time

Engineered Biosystems Building (EBB) Seminar Room (CHoA, 1005)

https://gatech.zoom.us/j/95288429704

Open to the Community

Advisor:

Dr. Sam P. Brown
School of Biological Sciences
Georgia Institute of Technology

Committee Members:

Dr. Joshua S. Weitz
School of Biological Sciences
Georgia Institute of Technology

Dr. Steve Diggle
School of Biological Sciences
Georgia Institute of Technology

Dr. Marvin Whitely
School of Biological Sciences
Georgia Institute of Technology

Dr. Josephine Chandler
Dept. Of Molecular Biosciences
University of Kansas

Abstract: 

Bacterial cells of many species communicate with each other by exchanging diffusible signal molecules. This mechanism, known as quorum sensing, has been well-studied at the level of specific molecular interactions. We now understand how those interactions shape the creation of and response to signal molecules in model organisms such as Pseudomonas aeruginosa. What is less clear is how quorum sensing operates at the population level. How can we characterize population-level quorum sensing responses to defined environmental variables? What types of responses are possible? What are the important constraints on those responses?

The chapters that follow contribute answers to some of those questions. They focus on characterizing and modeling the overall population response to quorum sensing, and how heterogenous individual cells contribute systematically to that response. The results combine experimental observations conducted with P. aeruginosa and mathematical models. The models allow interpretation of the data, identification of key qualities and quantities, and exploration of alternatives.

Chapter 2 demonstrates that both populations and individual cells are not limited to the on or off reaction implied by simple quorum sensing narratives. Rather, cells and populations can fine-tune their behavior, giving them a richer repertoire of responses to variable environments. Chapter 3 examines the ways multiple quorum sensing systems within a species can interact and how the specific form of those interactions can significantly affect population-level behavior. Chapter 4 reveals temporal diversity in cells’ responses and suggests a way in which this behavior may benefit the population in unpredictable environments. Finally, Chapter 5 discusses key elements common to all of the chapters, and it outlines a path for future research that can extend their findings.