Direct observation of speed fluctuations of flagellar motor rotation at extremely low load close to zero

Shuichi Nakamura, Yuta Hanaizumi, Yusuke V. Morimoto, Yumi Inoue, Marc Erhardt, Tohru Minamino, Keiichi Namba

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


The bacterial flagellar motor accommodates ten stator units around the rotor to produce large torque at high load. But when external load is low, some previous studies showed that a single stator unit can spin the rotor at the maximum speed, suggesting that the maximum speed does not depend on the number of active stator units, whereas others reported that the speed is also dependent on the stator number. To clarify these two controversial observations, much more precise measurements of motor rotation would be required at external load as close to zero as possible. Here, we constructed a Salmonella filament-less mutant that produces a rigid, straight, twice longer hook to efficiently label a 60 nm gold particle and analyzed flagellar motor dynamics at low load close to zero. The maximum motor speed was about 400 Hz. Large speed fluctuations and long pausing events were frequently observed, and they were suppressed by either over-expression of the MotAB stator complex or increase in the external load, suggesting that the number of active stator units in the motor largely fluctuates near zero load. We conclude that the lifetime of the active stator unit becomes much shorter when the motor operates near zero load.

Original languageEnglish
Pages (from-to)755-765
Number of pages11
JournalMolecular Microbiology
Issue number4
Publication statusPublished - 2020 Apr 1


  • MotAB stator complex
  • bacterial flagellar motor
  • duty ratio
  • hook
  • torque generation


Dive into the research topics of 'Direct observation of speed fluctuations of flagellar motor rotation at extremely low load close to zero'. Together they form a unique fingerprint.

Cite this