Quantifying the Influence of Stator Expression on E. coli Motility

Bacterial swimming is powered by protein complexes, stators, which produce the torque necessary to spin the bacterial flagella. Stators are found either freely diffusing in the inner membrane or attached to a motor in a torque generating configuration. The motor’s speed changes in response to external conditions, recruiting a full complement of stators under high load and releasing them under low load. This behavior has been described using models that combine statistical physics and mechanics, focusing on the dwell time of a stator. Previous models have assumed that the cell has enough stators such that the number of diffusing stators can be considered infinite. However, other studies have estimated that a single E. coli cell has ~100 stators, more than enough to power each motor at maximum capacity but small enough to not be considered infinite. Here, we study the effect of the total number of stators on the motility of E. coli through overexpression of the stators. We propose an extended model that includes the number of diffusing stators, using statistical physics methodology. To test this model we use precise biophysical experiments, bead assays, to measure the rotation of a single motor in vivo.