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A new twist on bacterial rotary engines.

Like tiny submarines, some bacteria move by spinning their tails rather than flailing them about like whips.

In such cases, the tails - stiff, helical flagella that resemble elongated corkscrews - hook on to a primitive driveshaft, which is spun by what biologists call a "rotary engine."

At a recent meeting of the Materials Research Society in Boston, Howard C. Berg, a biologist at Harvard University, described his groups efforts to show how rotary motors propel bacteria forward. While they know that protons moving through the cell membrane power the engine, the scientists seek the mechanism that "causes a rotor to go around and turn a crank," Berg says.

Berg and his colleagues first "tethered" the tails of Escherichia colicells to a sapphire base, then spun the cell bodies around in two directions, at various speeds, with a rotating electric field. Finally, they calculated the twisting power, or torque, of the bacterium's tiny motor.

Two new findings emerged, Berg reports. First, when spun forward, the engines produced a steady force at a wide range of speeds. "This finding is very unusual," Berg says. "Most engines don't behave that way" Second, when spun backward, the driveshafts first resisted, then slipped and broke. "This, too, was interesting," Berg adds. "It's like a ratchet mechanism."

While many theoretical models seek to explain how bacterial motors turn, these results point strongly to a "tightly coupled" model, notes Berg. That model suggests that a fixed number of protons, moving through the bacterial membrane, causes each rotation.

"These ion-driven machines are a marvel of nanotechnology," says Berg. "That nature could invent such an engine at all is utterly fascinating. People are amazed by little nanotechnology gears, but these engines are so small that 1,000 could fit on a man-made motor."

Details of Berg's experiment, carried out with Linda Turner, a biologist at the Rowland Institute for Science in Cambridge, Mass., appear in the November BIOPHYSICAL JOURNAL.
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Title Annotation:research indicates that the rotation of the helical flagella that propels bacteria forward is caused by a fixed number of protons that move through the bacterial membrane
Author:Lipkin, Richard
Publication:Science News
Article Type:Brief Article
Date:Dec 11, 1993
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