Constraints on models for the flagellar rotary motor

Area of Science:

• Microbiology
• Biophysics
• Molecular Motors

Background:

• Bacteria utilize flagellar filaments for motility, driven by a sophisticated rotary motor.
• This motor, approximately 45 nm in diameter, comprises around 20 distinct parts and is assembled internally.

Purpose of the Study:

• To review and highlight key operational characteristics of the bacterial flagellar rotary motor.
• To identify the discrepancies between observed motor behaviors and current theoretical models.

Main Methods:

• Analysis of existing literature on bacterial flagellar motor function.
• Comparison of experimental data on motor speed, torque, and environmental factor dependencies.

Main Results:

• The motor operates via proton or sodium-ion flux, achieving at least 400 steps per revolution.
• At low speeds, motor speed correlates with protonmotive force, while torque is largely independent of temperature and hydrogen isotope.
• At high speeds, torque increases with temperature and is sensitive to hydrogen isotope, showing complex behavior with speed.

Conclusions:

• Observed motor behaviors, including torque-speed profiles and environmental sensitivities, present significant challenges for existing models.
• Further development of theoretical frameworks is needed to comprehensively explain the flagellar rotary motor's mechanics.