Time dependence of trajectories and motor torque in Vibrio anguillarum *

The flagellar motor is at the center of bacterial motility.  In this work we study the motor torque of the monotrichous bacterium Vibrio Anguillarum through experimental observations and numerical simulations. We observe the bacterial cells and their flagella while freely swimming to obtain the cell and the flagellum geometry, the cell’s trajectory, and its kinematics. We use our experimental data to compute the motor torque using a numerical model based on the method of regularized Stokeslets and the assumption of a force-free swimmer. The variance in the size of the studied cells creates different motor loads and allows us to measure a torque versus motor speed curve for this species. We compare our torque-speed data with the data in the literature published for other species. Our method allows us to measure the time-dependent torque along a freely swimming cell’s trajectory, including variations in torque and speed as the cell swims forward and in reverse.