Cited research: Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0910426107 (2010)

Nanotechnology is still far from producing anything as efficient and compact as self-propelling bacteria. But Roberto Di Leonardo at the National Research Council in Rome and his colleagues have managed to harness Escherichia coli to power a small ratchet motor.

They made a variety of symmetrical and asymmetrical glass-based gears (pictured), 48 or 80 micrometres wide. The shape of the asymmetrical gears means that bacteria swimming into them either slide off the end of a cog tooth or become stuck in a corner. Bacteria that stick exert a force that drives the gear around until they free themselves.

When the researchers placed their cogs in a liquid bacterial suspension, they observed about one rotation per minute for the asymmetrical gears, showing that geometry can be used to convert chaotic bacterial motion into predictable movement. D.P.C.

R. DI LEONARDO ET AL.