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Proc Natl Acad Sci U S A. 2017 Oct 31;114(44):11603-11608. doi: 10.1073/pnas.1708054114. Epub 2017 Oct 16.

Speed of the bacterial flagellar motor near zero load depends on the number of stator units.

Author information

1
Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom.
2
Single Molecule Biophysics Department, Centre de Biochimie Stucturale, CNRS UMR 5048 UM INSERM U 1054, 34090 Montpellier, France.
3
Department of Frontier Bioscience, Hosei University, Tokyo 184-8584, Japan.
4
Department of Physics, National Central University, Jhongli 32001, Taiwan, Republic of China.
5
Graduate Institute of Biophysics, National Central University, Jhongli 32001, Taiwan, Republic of China.
6
Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom; richard.berry@physics.ox.ac.uk.

Abstract

The bacterial flagellar motor (BFM) rotates hundreds of times per second to propel bacteria driven by an electrochemical ion gradient. The motor consists of a rotor 50 nm in diameter surrounded by up to 11 ion-conducting stator units, which exchange between motors and a membrane-bound pool. Measurements of the torque-speed relationship guide the development of models of the motor mechanism. In contrast to previous reports that speed near zero torque is independent of the number of stator units, we observe multiple speeds that we attribute to different numbers of units near zero torque in both Na+- and H+-driven motors. We measure the full torque-speed relationship of one and two H+ units in Escherichia coli by selecting the number of H+ units and controlling the number of Na+ units in hybrid motors. These experiments confirm that speed near zero torque in H+-driven motors increases with the stator number. We also measured 75 torque-speed curves for Na+-driven chimeric motors at different ion-motive force and stator number. Torque and speed were proportional to ion-motive force and number of stator units at all loads, allowing all 77 measured torque-speed curves to be collapsed onto a single curve by simple rescaling.

KEYWORDS:

Escherichia coli; bacterial flagellar motor; hybrid fuel motor; molecular motor; motility

PMID:
29078322
PMCID:
PMC5676901
DOI:
10.1073/pnas.1708054114
[Indexed for MEDLINE]
Free PMC Article

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