’Clutch’ Stops Flagella
BLOOMINGTON, Inc., June 23, 2008 -- The flagellum -- a rotating, tail-like structure that makes a bacterium swim, is powered by a molecular engine at its base. But what makes it stop?
Answer: It uses its clutch.
A tiny but powerful engine that propels the bacterium Bacillus subtilis through liquids is disengaged from the corkscrew-like flagellum by a protein clutch, Indiana University Bloomington and Harvard University scientists have learned. Scientists have long known what drives the flagellum to spin, but what causes the flagellum to stop spinning -- temporarily or permanently -- was unknown.
A bacterium releases a protein (red) that disengages the clutch on its flagellum. (Image: Zina Deretsky, National Science Foundation. Courtesy Indiana University)
The action of the protein they discovered, EpsE, is very similar to that of a car clutch. In cars, the clutch controls whether a car's engine is connected to the parts that spin its wheels. With the engine and gears disengaged from each other, the car may continue to move, but only because of its prior momentum; the wheels are no longer powered.
The discovery 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 -- ones like those produced by B. subtilis can rotate more than 200 times per second, driven by 1400 piconewton-nms of torque. That's a lot of horsepower for a machine only a few nms wide.
"We think it's pretty cool that evolving bacteria and human engineers arrived at a similar solution to the same problem," said Indiana University Bloomington biologist Daniel Kearns, who led the project. "How do you temporarily stop a motor once it gets going?"
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Science 20 June 2008:
Vol. 320. no. 5883, pp. 1636 - 1638
DOI: 10.1126/science.1157877
A Molecular Clutch Disables Flagella in the Bacillus subtilis Biofilm
Kris M. Blair,1 Linda Turner,2 Jared T. Winkelman,1 Howard C. Berg,2,3 Daniel B. Kearns1*
Biofilms are multicellular aggregates of sessile bacteria encased by an extracellular matrix and are important medically as a source of drug-resistant microbes. In Bacillus subtilis, we found that an operon required for biofilm matrix biosynthesis also encoded an inhibitor of motility, EpsE. EpsE arrested flagellar rotation in a manner similar to that of a clutch, by disengaging motor force-generating elements in cells embedded in the biofilm matrix. The clutch is a simple, rapid, and potentially reversible form of motility control.
1 Department of Biology, Indiana University, Bloomington, IN 47405, USA.
2 Rowland Institute at Harvard, Cambridge, MA 02142, USA.
3 Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
* To whom correspondence should be addressed. E-mail: dbkearns@indiana.edu
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