Motility of Escherichia coli Near Biomimetic Surfaces

Many bacteria, including the well-studied Escherichia coli, transition between two modes of life: individual free-swimming cells, and surface-aggregated communities called biofilms. When a swimming E. coli approaches solid surfaces, interactions between the bacterium and the surrounding environment change, altering the bacterium’s motion. This behavior provides a measure of the interactions E. coli experiences as it transitions from free swimming to surface aggregation – a key step in early biofilm formation. Properties of the surface such as charge and viscosity can affect near-surface motility. However, the relationship between such properties and motility has yet to be described quantitatively. We aim to investigate how surface viscosity influences a bacterium’s speed, height above the surface, and the curvature of the bacterium’s trajectory. 

First, we recorded the motion of E. coli engaged in near-surface swimming above a glass coverslip using Total Internal Reflection Fluorescence (TIRF) microscopy. We developed MATLAB code to track, model, and extract dynamical measurements from the bacteria. Preliminary results matched theoretical considerations of the effects of cell-surface distance on speed and trajectory curvature. Next, we constructed biomimetic surfaces with tunable viscosity for use in near-surface motility studies. Our surface consists of a supported lipid bilayer conjugated to polystyrene microspheres through biotin-avidin binding. By adjusting the density of microspheres atop the bilayer, it is possible to control the viscosity of the colloidal surface. The viscosity can then be measured by analyzing the Brownian motion of microspheres diffusing along the bilayer. Future work will aim to measure surface viscosity as a function of microsphere density, and to use these surfaces in bacterial motility experiments.