School of Physics Thesis Dissertation Defense

Presenter:        Aawaz Pokhrel 

Title:                     Biophysical basis of bacterial colony growth  

Date:                    Thursday, June 27, 2024

Time:                    10:00 a.m.  

Location:           Howey Physics Building, N201/202

Virtual link:      https://gatech.zoom.us/j/93911211652

 Committee members: 

Dr. Peter J. Yunker, School of Physics, Georgia Institute of Technology  (Advisor)

Dr. Jennifer Curtis, School of Physics, Georgia Institute of Technology

Dr. Brian K. Hammer, School of Biological Science, Georgia Institute of Technology

Dr. Itamar Kolvin, School of Physics, Georgia Institute of Technology

Dr. Zeb Rocklin, School of Physics, Georgia Institute of Technology

Abstract:

Bacteria often attach to surfaces and grow densely-packed communities called biofilms. As biofilms grow, they expand across the surface, granting them more access to nutrients. Thus, the overall growth rate of a biofilm is directly dependent on its "range expansion" rate. While individual-based discrete models and continuum models have provided valuable insights into biofilm development, a quantitative understanding and experimental validation of basic vertical and horizontal growth are still lacking.

In this thesis, we address this issue directly by experimentally observing the growth dynamics and morphologies of biofilms using interferometry. The use of interferometry allowed us to measure biofilm topography with nanometer resolution out-of-plane, providing insights into the emergent dynamics and morphologies of microbial colonies. We found that the geometry of the exponentially growing edge of a biofilm can be well described by a spherical-cap-napkin-ring geometry. We present a robust analysis of this geometry, showing the exact expression for the growth of such geometry explaining the growth of a biofilm. We then show that a simple biophysical model connecting vertical and horizontal growth dynamics can reproduce the experimental observations, suggesting that the spherical cap and spherical-cap-napkin-ring shapes emerge due to the biophysical consequences of diffusion-limited growth.