Hybrid-fuel bacterial flagellar motors in Escherichia coli

Yoshiyuki Sowa, Michio Homma, Akihiko Ishijima, Richard M. Berry

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)


The bacterial flagellar motor rotates driven by an electrochemical ion gradient across the cytoplasmic membrane, either H+ or Na+ ions. The motor consists of a rotor ∼50 nm in diameter surrounded by multiple torque-generating ion-conducting stator units. Stator units exchange spontaneously between the motor and a pool in the cytoplasmic membrane on a timescale of minutes, and their stability in the motor is dependent upon the ion gradient. We report a genetically engineered hybrid-fuel flagellar motor in Escherichia coli that contains both H+- and Na+-driven stator components and runs on both types of ion gradient. We controlled the number of each type of stator unit in the motor by protein expression levels and Na+ concentration ([Na+]), using speed changes of single motors driving 1-μm polystyrene beads to determine stator unit numbers. De-energized motors changed from locked to freely rotating on a timescale similar to that of spontaneous stator unit exchange. Hybrid motor speed is simply the sum of speeds attributable to individual stator units of each type. With Na+ and H+ stator components expressed at high and medium levels, respectively, Na+ stator units dominate at high [Na+] and are replaced by H+ units when Na+ is removed. Thus, competition between stator units for spaces in a motor and sensitivity of each type to its own ion gradient combine to allow hybrid motors to adapt to the prevailing ion gradient. We speculate that a similar process may occur in species that naturally express both H+ and Na+ stator components sharing a common rotor.

Original languageEnglish
Pages (from-to)3436-3441
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number9
Publication statusPublished - 2014 Mar 4
Externally publishedYes


  • Hybrid-fuel motor
  • Molecular motor
  • Na+-driven flagella
  • Nano-machine
  • Stator dynamics

ASJC Scopus subject areas

  • General


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