"It was theoretically predictable that a microrotary motor driven by bacteria works," Yuichi Hiratsuka of Japan's National Institute of Advanced Industrial Science and Technology (AIST) told nanotechweb.org. "We were extremely excited when we first saw the motor rotate because its rotation was smoother than we ever imagined and it did not look like an uncertain device driven by living materials."

Hiratsuka and colleagues at the AIST, Osaka City University, and Japan Science and Technology Agency used the bacterium Mycoplasma mobile, which has been found in freshwater fish and is known for its gliding motion.

The researchers employed the bacteria in conjunction with a microstructure consisting of a 20 µm diameter silicon dioxide rotor sitting in a circular silicon track. By introducing the bacteria to a central square chamber with a system of asymmetric channels leading to the track, the researchers ensured that most of the bacteria entering the track were moving in a clockwise direction.

The team promoted motion of the bacteria by coating the bottom of the silicon structure's channels and tracks with molecules of fetuin, a sialic protein. The gliding bacteria were able to move the rotor as biotin molecules chemically added to their cell walls linked to molecules of streptavidin coating the rotor. As a result, the bacteria pulled the rotor with them as they glided along.

"We believe that this work will stimulate and encourage a number of researchers from broad disciplines, especially in the field of nanotechnology," said Hiratsuka. "I hope that nanotechnologists would be interested in our approach to integrate biological materials with inorganic microstructures."

Typically, the rotor began to move within a few minutes while rotations in some cases lasted more than one minute. The rotation rate was 1.5–2.6 rpm.

The team believes that it may be useful to genetically modify the bacteria's surface proteins either to aid biotin linking to cargo or to cause the cells to migrate in a particular direction in response to a chemical. In order to avoid potential biohazard issues, the researchers propose the use of "ghost" bacteria, i.e. dead versions of the cells in which the motor units are still active as long as adenosine triphosphate is available externally.

"We can suggest use of the device as a micropump in microTAS [micro total analysis systems, also known as labs-on-a-chip], so that external pumps and pipes would no longer be necessary, and they become real on-chip devices," said Hiratsuka. "Alternatively, we may be able to construct electronic generator systems, which generate electric energy from abundant chemical energy – glucose – in the body."

In the long term, the team would like to make microrobots driven by biological motors. "We will make such sophisticated micro devices by further developing this work," said Hiratsuka. "Before realizing them, we need to improve the stability and lifetime of the motor. Although in this case we used living bacteria as driving units, we will develop micromechanical devices using purified motor proteins, such as myosin or kinesin, as well as living bacteria."

The researchers reported their work in PNAS.