A team of scientists led by Igor Aronson at the U.S. Department of Energy's (DOE) Argonne National Laboratory placed Bacillus subtilis bacteria in a solution containing microgears which were a million times larger than the bacteria. The microgears, manufactured in collaboration with Northwestern University, contained slanted spokes. Although bacteria normally swim randomly through solution, when enough of them collide with the spokes, the gears begin turning. When two gears are connected, the bacteria spin the gears together.
Like all obligate aerobic organisms, Bacillus subtilis requires oxygen in order to function. The less oxygen, the slower they go. If you remove all oxygen, they completely stop moving, but they can be revived by adding back oxygen. In this way, the speed of gear turning can be carefully controlled.
"Our discovery demonstrates how microscopic swimming agents, such as bacteria or man-made nanorobots, in combination with hard materials can constitute a 'smart material' which can dynamically alter its microstructures, repair damage, or power microdevices."