Mechanobiology of Stator Remodeling in the Bacterial Flagellar Motor

Abstract

Motility is critical for the survival and dispersal of bacteria, and it plays an important role during infection. How bacteria regulate motility is thus of great interest to microbiologists, ecologists, and infectious disease researchers alike. Regulation of motility via chemotaxis and gene regulation is well studied. However, recent work has added a new dimension to this problem. The flagellar motor of bacteria autonomously assembles and disassembles torque-generating stator complexes in response to changes in the external viscous load. in the bacterium Escherichia coli, up to 11 stator complexes drive the motor at high load while all the stator complexes are released at low load. We study this process by artificially manipulating the motor load using electrorotation, where a high frequency rotating electric field applies an external torque on the flagellar motor. Using this technique, we can increase or decrease the motor load at will and measure the resulting stator assembly dynamics. From detailed measurements of stator remodeling in both clockwise and counterclockwise rotating motors, we have found that the motor's response has a conserved torque dependence. increased torque decreases the dissociation rate of stator complexes from the motor, thereby increasing the steady state stoichiometry. We built an equilibrium model that captures the observed dynamics and provides insight into the underlying molecular interactions. Torque-dependent stator remodeling takes place within tens of seconds, making it a highly responsive autonomous control mechanism.