There's a good chance that you've seen a horse pulling a carriage or dogs hauling a sled. For the latest use of animal power, however, you'd need a microscope to see the critters in action.

Researchers in Japan have found a way to use crawling bacteria to power a micromotor.

Like many simple motors, the micromachines devised by the researchers include a tiny rotor—a part that can turn. In this case, the rotor is shaped like a star with six arms. Tabs, which sit in a ring-shaped groove, support the rotor. The rotor is made from a material called silicon dioxide.

To get the rotor to rotate, the scientists use a strain of bacteria called Mycoplasma mobile, which move quickly—for bacteria. These pear-shaped bacteria are just 1 micrometer (one millionth of a meter) long. They crawl when placed on a mat made of certain types of proteins.

The scientists coat the groove beneath the rotor with one of these proteins. They then cover the rotor with another type of protein and give the bacteria a coat of a substance that's attracted to the rotor's protein.

The researchers let loose these sticky bacteria into the grooves and encourage them to all move in one direction around the circle. As the coated bacteria pass the tabs supporting the rotor, they brush against them but keep moving. These brief tugs make the rotor turn.

The movement is relatively slow—in normal machine terms. The rotor spins only about twice the rate of the second hand on a watch. The scientists estimate, however, that with more bacteria, they could make the rotor spin 100 times faster.

Using bacteria to power machines is appealing because bacteria can replicate and repair themselves. And they run on a sugar called glucose. With this new discovery, the future of "living machines" is looking brighter.—E. Sohn