Coupling between switching regulation and torque generation in bacterial flagellar motor

Area of Science:

• Microbiology
• Biophysics
• Systems Biology

Background:

• The bacterial flagellar motor is essential for bacterial movement and sensing chemical gradients (chemotaxis).
• Experimental data show a nonmonotonic relationship between flagellar motor speed (and torque) and its switching dynamics.

Purpose of the Study:

• To develop a unified mathematical model of bacterial flagellar motor switching dynamics.
• To explain the nonmonotonic dependence of switching rate on motor rotation speed and torque.

Main Methods:

• Developed a mathematical model integrating experimental torque-speed curves.
• Incorporated a conformational spread model for torque-dependent switching.
• Analyzed the contributions of two stator-mediated switching mechanisms.

Main Results:

• The model accurately reproduces the observed switching rate as a function of rotation speed.
• Identified two key mechanisms by which stators influence switching: flipping rate acceleration (dominant at low speed/high torque) and increased unit influence (dominant at high speed).
• The switching rate peaks at an intermediate speed due to the optimal balance of these two mechanisms.

Conclusions:

• The model provides a generic physical explanation for flagellar motor switching dynamics, independent of specific molecular details.
• The load-switching relationship may function as an environmental sensing mechanism, analogous to chemotaxis.
• This mechanism could potentially coordinate switching behavior across multiple flagellar motors within a single cell.