The flagellar motor sits in the bacterial cell envelope and turns a long helical filament. Stator units in the inner membrane let ions flow into the cell and push on a rotor ring, the C-ring. When the signal protein CheY-P binds the C-ring, the motor reverses. The switch between runs and tumbles steers the cell toward food.
- Where
- Cell envelope of flagellated bacteria such as Escherichia coli, Salmonella, Vibrio, Campylobacter and spirochetes. The rotor spans the cytoplasm, inner membrane, peptidoglycan and outer membrane.
- Power
- Inward flow of protons (E. coli, Salmonella, Campylobacter) or sodium ions (Vibrio polar flagella) across the inner membrane.
1,260 pN·nm
Stall torque, E. coli (fully induced)
1Measured at 63 Hz with 1 µm beads, so a high-load torque close to stall; 146 pN·nm per stator unit
≥11
~200 Hz
Knee speed, E. coli (23 °C)
2Later work gives 170–175 Hz (Yuan and Berg 2008)
~350 Hz
Zero-torque speed, E. coli (23 °C)
226
Measured at low driving force. A Salmonella C-ring has 34 FliG subunits (Tan et al. 2024), so the two counts differ
~3,800 pN·nm
Plateau torque, Vibrio Na+ motor
350 mM NaCl, up to ~300 Hz
Hill coefficient ~10
Switch sensitivity to CheY-P
8Motors with a fixed number of FliM gave 16.5–20.7 (Yuan and Berg 2013)
~20
Motor diameter about 45 nm