Measuring the Motility of Pseudomonas aeruginosa Near Surfaces*

Many motile bacteria, including Pseudomonas aeruginosa, achieve motility by using their flagellar motor to generate a torque that rotates a helical filament and propels their body forward. When swimming near a surface, P. aeruginosa follows relatively curved trajectories, spontaneously retreating by switching the direction of the flagellar motor’s rotation. With its simple body structure, P. aeruginosa is a prime model organism for performing numerical simulations of bacterial motility near a surface. The aim of this work is to experimentally measure the motion of P. aeruginosa near a surface and input those measurements to a numerical model to compute the torque required to rotate the flagellum. 

We have developed an automated tracking and positioning algorithm for motile bacteria imaged near a surface. The algorithm takes a video of bacteria imaged under total internal reflection fluorescence microscopy and efficiently reconstructs their trajectories. Intensity profiles of the bacteria are saved at each point in their trajectories and used to extract each bacterium’s spatial orientation. This algorithm has already been implemented to study the motility of Escherichia coli near surfaces and preliminary results confirm its accuracy. Future experiments will focus on implementing this algorithm to study P. aeruginosa motility near surfaces and flagellar motor mechanics.