PhD Defense by Alba Garcia Vazquez

The title: Space matters: growth, death, and competition in spatially structured bacterial colonies

The abstract: This thesis investigates the emergence of spatial self-organization within bacterial colonies and its impact on their growth dynamics and survival. By using novel experimental setups and employing Escherichia coli as a model organism, I explored how space, death, and competition shape bacterial communities.

The first study introduces a novel model for investigating competition within three-dimensional bacterial colonies. The study reveals that  cell density controls the size, patterning, and growth dynamics of 3D colonies. Additionally, it shows that sectors in 3D colonies exhibit dynamic behavior, merging and splitting over time.

The second study explores the growth dynamics of three-dimensional bacterial colonies under varying glucose concentrations. At higher glucose concentrations, 3D colonies can grow to larger sizes. However, growth occurs only in the outer layers, while our experiments show that the cells in the core of the 3D colony are dead.

The third study examines the effect of cell shape on the self-organization of bacterial communities. Different cell morphologies result in distinct macroscopic patterns. Additionally, cell shape gives longer cells a competitive advantage in surface-attached colonies, enabling them to dominate the colony edge when competing with rounder cells. Furthermore, we investigated how cell alignment occurs when a colony collides with a neighboring colony.

Overall, this thesis focuses on how various factors such as the dimensionality of the environment, bacterial shape, and competition—influence the structure and development of bacterial colonies.