Torque–speed relationship of the bacterial flagellar motor

^*Departments of Molecular and Cell Biology and Environmental Science, Policy and Management, University of California, Berkeley, CA 94720-3112; and ^‡Department of Physics, The Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, United Kingdom

Edited by Charles S. Peskin, New York University, New York, NY, and approved December 2, 2005 (received for review September 12, 2005)

Abstract

Many swimming bacteria are propelled by flagellar filaments driven by a rotary motor. Each of these tiny motors can generate an impressive torque. The motor torque vs. speed relationship is considered one of the most important measurable characteristics of the motor and therefore is a major criterion for judging models proposed for the working mechanism. Here we give an explicit explanation for this torque–speed curve. The same physics also can explain certain puzzling properties of other motors.

Footnotes

↵ § To whom correspondence should be addressed. E-mail: goster{at}nature.berkeley.edu.
↵ † Present address: Physical Biosciences Institute, Lawrence Livermore National Laboratory, Livermore, CA 94550-9234.
Author contributions: R.B. and G.O. designed research; J.X., F.B., and G.O. performed research; J.X., R.B., and G.O. analyzed data; and J.X., F.B., R.B., and G.O. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: BFM, bacterial flagellar motor; pmf, proton motive force; DoF, degrees of freedom.