New Directions in Actin‐Based Motility of Intracellular Bacterial Pathogens

Abstract

Actin‐based motility by the intracellular bacterial pathogen Listeria monocytogenes is typically persistent and unidirectional, with the rod‐shaped bacteria moving nearly parallel to their long axis, while tracing out gently curving paths that can form circles, sine waves, figure eights, or spirals. We have taken two different approaches to understanding the shapes of these trajectories. First, we find that a simple kinematic model for motion that incorporates two different torque terms (for rotations both parallel to and perpendicular to the long axis of the bacterium) along with the speed can predict many of the observed bacterial trajectories, even those with very complex shapes. Second, we have explored the physical forces that govern the trajectories of movement for artificial particles resembling the bacteria in size and shape. Our results suggest that the polar comet tail orientation on moving wild‐type L. monocytogenes is due to polar protein expression and not to any mechanical or physical preference for movement parallel to the bacterial long axis, and that simple models for slight imbalances of force and torque are sufficient to explain many complex aspects of bacterial movement.