Researchers have discovered that common bacteria suspended in a solution can be made to turn microgears. This opens up the possibility of building hybrid biological machines at the microscopic scale. The researchers say the 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.

Scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory and Northwestern University produced microgears just 380 microns (0.38 mm) long with slanted spokes and placed them in a solution along with the common aerobic bacteria Bacillus subtilis. The researchers observed that the bacteria appeared to swim at random—but occasionally the organisms collided with the spokes of the gear and began turning it in a definite direction.

A few hundred bacteria work together in order to turn the gear. When multiple gears are placed in the solution with the spokes connected as in a clock, the bacteria will turn both gears in opposite directions, causing the gears to rotate in synchrony—even for long stretches of time.

The researchers were also able to control the speed at which the gears turn through the manipulation of oxygen in the suspended liquid. Since the bacteria need oxygen to swim they were able to slow down the gears’ movement by decreasing the amount of oxygen available. Eliminating the oxygen completely halted the movement entirely and, once the oxygen is reintroduced into the system, the bacteria “wake up” and begin swimming again.

“The ability to harness and control the power of bacterial motion is an important requirement for further development of hybrid biomechanical systems driven by microorganisms," said Argonne physicist and principal investigator Igor Aronson. “In this system, the gears are a million times more massive than the bacteria."

A paper on the discovery appears in Proceedings of the National Academy of Sciences.