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Bacterial Flagella: Flagellar Motor

  1. George H Wadhams,
  2. Yoshiyuki Sowa

Published Online: 15 SEP 2009

DOI: 10.1002/9780470015902.a0000744.pub3



How to Cite

Wadhams, G. H. and Sowa, Y. 2009. Bacterial Flagella: Flagellar Motor. eLS. .

Author Information

  1. University of Oxford, Oxford, UK

Publication History

  1. Published Online: 15 SEP 2009

This is not the most recent version of the article. View current version (15 AUG 2014)


The bacterial flagellar motor is a complex biological rotary molecular motor which is situated in the cell envelopes of bacteria. Whereas most biological motors use adenosine triphosphate (ATP) as their energy source, the rotation of the flagellar motor is driven by a flow of charged ions across the bacterial plasma membrane. The motor powers the rotation of helical flagellar filaments at speeds of up to several hundred hertz. These rotating filaments act like propellers, pushing the cells through their environment. The motors are regulated by one of the best-characterized biological signalling pathways, the chemotaxis pathway. This pathway changes the swimming pattern of the bacteria in response to changes in the concentration of external chemicals so that they move into environments which are optimal for their growth.

Key concepts:

  • Bacteria swim using a small biological rotary motor which is powered by the movement of charged ions across the plasma membrane.

  • The flagellar motor consists of a rotor which rotates against stator units that are anchored to the peptidoglycan cell wall.

  • Torque is generated by the interaction of the stator units, MotA and MotB, with FliG in the rotor.

  • Despite the fact that the driving ions always flow in one direction through the stator units, many flagellar motors can switch between clockwise and counterclockwise rotation.

  • A complex signalling pathway regulates the motor output in response to environmental signals ensuring that bacteria swim towards nutrient rich environments.


  • bacterial motility;
  • molecular motors;
  • protein machines;
  • chemotaxis;
  • signalling