Author ORCID Identifier

Date of Award

Winter 3-1-2024

Document Type

Thesis (Ph.D.)

Department or Program

Microbiology and Immunology

First Advisor

George A. O'Toole Jr.


Biofilms are surfaced attached communities of cells encased in an extracellular matrix. The transition from free-swimming planktonic cells to a surface attached biofilm begins with cellular changes that occur after surface contact. This process is known as "surface sensing" and the opportunistic pathogen Pseudomonas aeruginosa PA14 uses its two motility appendages, type IV pili (T4P) and a single, polar flagellum to sense and traverse surfaces. The first cellular changes to occur within this organism upon surface contact is an increase in the second messengers cAMP and cdi- GMP. While the genes involved in surface sensing by P. aeruginosa are known, the mechanism by which these molecular machines sense and relay surface contact to the rest of the cell has remained a mystery. This thesis focuses on how T4P and flagellar surface contact lead to increases in cAMP and c-di-GMP, respectively. I show that the primary T4P retraction motor likely relays a surface signal to the Pil-Chp system, leading to CyaB activation and cAMP production. I also present data that supports a model whereby the stators of the flagellar motor senses surface contact and relay this information to a diguanylate cyclase leading to c-di-GMP production. These studies demonstrate how mechanical perturbations to these molecular motility machines upon surface contact can serve as cellular signals to initiate biofilm formation.