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Press Release 08-105

Microscopic "Clutch" Puts Flagellum in Neutral

Insights into the workings of the flagellum may advance nanotechnology

Illustration of the mechanism that stops the flagellum of a bacteria.

A bacterium releases a protein (red) that disengages the clutch on its flagellum.
Credit and Larger Version

June 19, 2008

It has been long been known that bacteria swim by rotating their tail-like structure called the flagellum. (See the swimming bacteria in the figure.) The rotating motion of the flagellum is powered by a molecular engine located at the base of the flagellum. Just as engaging the clutch of a car connects its gear to its engine and delivers power to its wheels, engaging the molecular clutch of a bacterium connects its gear to its engine and delivers power to its flagellum.

Now, a paper appearing in the June 20 issue of Science describes, for the first time, how the flagellum's rotations are stopped so that bacteria stop moving. Here's how the stopping mechanism works: while a bacterium is swimming, it releases a protein (shown in red in the stationary bacterium in the figure) that flows between its gear and engine. The presence of this protein detaches the bacterium's gear from its engine and thereby stops the delivery of power to its flagellum. This process is analogous to disengaging the clutch of a car, which detaches its gear from its engine and thereby stops the delivery of power to its wheels.

Once the delivery of power to bacterium's flagellum stops, the flagellum stops rotating, and the bacterium's swimming ends.

An improved understanding of how flagella work may give nanotechnologists ideas about how to regulate tiny engines of their own creation. The flagellum is one of nature's smallest and most powerful motors. The flagellum of some bacteria can, for example, rotate more than 200 times per second, driven by 1,400 piconewton-nanometers of torque. That's quite a bit of (miniature) horsepower for a machine whose width stretches only a few dozen nanometers.

The research team was led by Kris Blair of the University of Indiana and included Daniel Kearns of the University of Indiana and Linda Turner and Howard Berg of Harvard University. Their study was funded by the National Science Foundation and the National Institutes of Health.


Media Contacts
Lily Whiteman, National Science Foundation, (703) 292-8310,
David Bricker, University of Indiana, (812) 856-9035,

Program Contacts
John Rogers, National Science Foundation, (703) 292-7139,

Principal Investigators
Daniel Kearns, University of Indiana, (812) 856-2523,

The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2016, its budget is $7.5 billion. NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Each year, NSF receives more than 48,000 competitive proposals for funding and makes about 12,000 new funding awards. NSF also awards about $626 million in professional and service contracts yearly.

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Photo of the June 20, 2008 issue of Science.
The June 20, 2008 issue of Science.
Credit and Larger Version