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We humans have been putting lesser organisms to work for us since the dawn of civilization. But whereas a workhorse might have powered a grist mill in the olden days, scientists are now harnessing a bacterium to form a tiny hybrid micromachine. It is an exploitation that probably will not bother even the most stalwart animal-rights activist.

Yuichi Hiratsuka, of the Japan Advanced Institute of Science and Technology, and his colleagues at the National Institute of Advanced Industrial Science and Technology in Japan have for some time now been interested in making tiny hybrid devices combining biological elements, such as motor proteins, with inorganic materials. Recently they were inspired by a presentation by Makoto Miyata from Osaka City University, now a close collaborator, who showed a movie of M. mobile gliding unidirectionally on a glass surface. “It immediately occurred to us that we should be able to make microrotary motors using these bacterial cells,” says Hiratsuka.

Using photolithography, they created a sunken, circular track coated with sialic proteins to restrict the movement of the bacteria. To yoke the bugs to a rotor designed to move along the track, they covered the surface of the rotor with streptavidin molecules and chemically biotinylated cell-surface proteins on M. mobile (Fig. 1). They captured movies of the bugs turning the rotor with a rotation rate of ∼1.5–2.6 r.p.m.

Figure 1: Biotinylated M. mobile bacteria turn a streptavidin-coated rotor along a circular track.
figure 1

Copyright 2006, National Academy of Sciences, USA.

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Hiratsuka and colleagues hope to put their hybrid motor to work, for example, as a micropump in lab-on-a-chip systems. In the future, “we would like to make microrobots driven by biological motors, which would move around and do mechanical work in a micrometer world,” says Hiratsuka. Though this is the first description of a bacteria-driven microdevice, he believes that various micro-organisms with interesting motility properties could be exploited to create other exciting hybrid devices.