Emergent Escherichia coli Colony Morphogenesis in Polymer Solutions

Abstract

Many bacteria live in polymeric environments such as biofilms and mucosal linings of the body. Experimental knowledge of bacterial behavior in complex, polymeric media is limited, inhibiting the applicability of current understanding in clinical, real-world contexts. This thesis seeks to answer the following question: How do interactions with polymers influence growing bacterial colonies? Growth experiments of non-motile E. coli in aqueous solutions of polyethylene glycol, Ficoll, and carboxymethyl cellulose show that, when polymer in sufficiently concentrated, cells grow in striking “cable-like” morphologies that contrast from the conventionally-studied polymer-free case. Solution analysis reveals that neither viscosity nor overlap concentration indicate if cable morphology will emerge. It is proposed that a polymer-induced entropic attraction between cells is responsible for the onset of these cable-like morphologies. These results suggest a pivotal role of polymers in regulating bacterial community morphology, evoking new quantitative principles governing the morphogenesis of diverse forms of growing active matter in polymeric environments.