Biophysical Modeling of the Growth and Motion of Bacterial Populations

Abstract

The growth and spread of bacterial populations are processes of broad significance. The coupling between cells, the structures of their environment, and the chemical makeup of their environment underlies how bacteria survive and spread. For example, the environments bacteria inhabit often confine individual cells, modifying both their individual and collective motion in previously overlooked ways. Thus, in this thesis, I first use biophysical modeling and numerical simulations to uncover new features of cell motion that arise due to confinement within a heterogeneous medium. In particular, I develop a continuum model to better understand experimental observations of traveling bacterial fronts in highly-confining porous media. Using this model, I explore the influence of confinement on (i) the dynamics of bacteria spreading, (ii) the overall morphology of a migrating population, and (iii) the robustness of the population to morphological perturbations. Then, as a step toward similarly describing the dynamics of mixed communities---which are often composed of different species requiring different chemical conditions to thrive---I use biophysical modeling and numerical simulations to study the growth of aerobes and anaerobes in an environment of shared nutrient. In this case, the coupling between nutrient consumption, oxygen consumption, and growth leads to striking new dynamics, such as hysteresis/bistability and growth oscillations, amidst varying chemical conditions. Altogether, this work establishes a quantitative framework to predict, and potentially guide strategies to control, microbial behavior for diverse applications in biomedical science and the environment.