Analyzing Bacterial Motility Near a Smooth Surface

Motile bacteria play a pivotal role for life on Earth and studying them has many real-world applications. In particular, studying how motile bacteria interact with a smooth surface provides fundamental understanding about their transition from living as free-swimmers in the fluid to being a part of a surface aggregated community. Such knowledge can be useful in the resolution of medical problems like infections in the lungs of cystic fibrosis patients. In this work, we report the reconstructed three-dimensional motion of a motile bacterium from its two-dimensional images generated by total internal reflection fluorescence microscopy. First, the Trackpy package keeps track of the bacterium's position on a plane parallel to the surface at each time step. Then, our in-house Ellipsoid Fitting Algorithm analyzes the intensity profile of the bacterium to reconstruct its three-dimensional position and orientation relative to the surface. From these parameters, we further extract the velocity and the localized turning radii of the bacterium's trajectory in space.