Vibrio anguillarum swims with variable speeds during runs*

Singly-flagellated bacteria perform run-and-reverse, or run-reverse-flick motility, in which reorientation mostly occurs during isolated reversal or flick events. During runs, the cell is thought to move with a constant velocity determined by motor torque, motor speed, and cell geometry, with changes in direction caused by Brownian diffusion. We perform experiments on

Vibrio anguillarum, which undergoes run-reverse-flick motility. Under darkfield video microscopy we observe that during runs, cells often slow down then speed up again over tenth of a second timescales, which may be due to the motor stopping entirely on timescales faster than our framerates or slower changes in motor speed. We characterize these events in terms of timescale, changes in cell speed, trajectory direction, and flagellar configuration. We use this data to estimate the change in motor speed and torque through time with numerical simulations. Our results help in understanding the mechanism of these slowdowns. These events may provide ways for bacteria to reorient during motility in addition to reversals or flicks, and impact their chemotactic ability.