From the archive, originally posted by: [ spectre ]

“When bacteria crawl clockwise in the circular groove underlying this
motor, they brush past the tabs that support the motor’s star-shaped
rotor. Molecular bonds between the microbes and a coating on the rotor
tug the device around.”

Published online before print September 1, 2006
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0604122103

Yuichi Hiratsuka *, Makoto Miyata ¶, Tetsuya Tada ||, and Taro Q. P.
Uyeda *,**
*Gene Function Research Center, ||Advanced Semiconductor Research
Center, National Institute of Advanced Industrial Science and
Technology, Tsukuba, Ibaraki 305-8562, Japan; Department of Biology,
Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka
558-8585, Japan; and ¶Precursory Research for Embryonic Science and
Technology, Japan Science and Technology Agency, Sumiyoshi-ku, Osaka
558-8585, Japan

Edited by James A. Spudich, Stanford University School of Medicine,
Stanford, CA, and approved July 21, 2006 (received for review May 21,

Biological molecular motors have a number of unique advantages over
artificial motors, including efficient conversion of chemical energy
into mechanical work and the potential for self-assembly into larger
structures, as is seen in muscle sarcomeres and bacterial and
eukaryotic flagella. The development of an appropriate interface
between such biological materials and synthetic devices should enable
us to realize useful hybrid micromachines. Here we describe a
microrotary motor composed of a 20-µm-diameter silicon dioxide rotor
driven on a silicon track by the gliding bacterium Mycoplasma mobile.
This motor is fueled by glucose and inherits some of the properties
normally attributed to living systems.


Author contributions: Y.H. designed research; Y.H. performed research;
M.M. and T.T. contributed new reagents/analytic tools; Y.H. analyzed
data; and Y.H. and T.Q.P.U. wrote the paper.

Conflict of interest statement: No conflicts declared.

Present address: Center for International Research on
MicroMechatronics, Institute of Industrial Science, University of
Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.

To whom correspondence should be addressed.

**Present address: Research Institute for Cell Engineering, National
Institute of Advanced Industrial Science and Technology, Tsukuba,
Ibaraki, 305-8562, Japan.

Yuichi Hiratsuka, E-mail: yhira [at] iis [dot]

Wheel of Life: Bacteria provide horsepower for tiny motor
Peter Weiss

For millennia, people have hitched beasts to plows to exploit the
animals’ strength and energy. In a modern variant of that practice,
scientists have chemically harnessed bacteria to a micromotor so that
they can make the device’s rotor slowly turn.

The new work might lead to improved lab-on-a-chip devices and engines
to propel microrobots, says Yuichi Hiratsuka, now of the University of
Tokyo, who codeveloped the bacteria-powered micromotor. He and his
colleagues describe the research in an upcoming Proceedings of the
National Academy of Sciences.

The novel micromachine “is an important step in integrating biological
components into microengineered systems,” comments bioengineer William
O. Hancock of Pennsylvania State University in University Park.

To make the motors, Hiratsuka’s team, led by Taro Q.P. Uyeda of the
National Institute for Advanced Industrial Science and Technology in
Tsukuba, Japan, borrowed fabrication techniques from the
microelectronics industry.

The machinery of each motor consists of two parts: a ring-shaped groove
etched into a silicon surface, and a star-shaped, six-armed rotor
fabricated from silicon dioxide that’s placed on top of the circular
groove. Tabs beneath the rotor arms fit loosely into the groove.

To prepare the bacterial-propulsion units, the team used a strain of
the fast-crawling bacterium Mycoplasma mobile that was genetically
engineered to crawl only on a carpet of certain proteins, including one
called fetuin. The researchers laid down fetuin within the circular
groove and coated the rotor with a protein called streptavidin.

The scientists then coated the micrometer-long, pear-shaped bacteria
with a solution containing biotin, a vitamin that readily binds to

The team released the treated bacteria into the grooves in a way that
sent them mostly in one direction around the circle. As the microbes
passed each of a rotor’s supporting ridges, their biotin-treated cell
membranes clung to the streptavidin coating, causing tugs on the tabs
and thereby turning the rotor.

Slow and weak, the rotors circle at about twice the speed of the second
hand on a watch and generate only a ten-thousandth as much torque as
typical electrically powered micromachines do. By using more bacteria,
the scientists could boost the torque 100-fold, Hiratsuka predicts.

In earlier work, many specialists in biologically inspired
micromotors-including Uyeda’s group-used components of cells, such
as filaments called microtubules (SN: 10/27/01, p. 268: Available to
subscribers at, to devise
microscale systems that transport objects.

Other teams have also used complete, living microbial cells to drag
tiny loads (SN: 8/20/05, p. 117: or to move

By using whole microbes as machine components, the Japanese team “adds
a new direction to our field,” comments biomolecular-motor specialist
Henry Hess of the University of Florida in Gainesville.

“The micromotor system points the way to self-sustaining and
self-repairing machines, since the active units … can multiply and
replace each other,” he adds. “Living machines rock!”

Researchers at the National Institute of Advanced Industrial Science
and Technology near Tokyo have created the first micromechanical device
with living components incorporated into them.

Nanobiotechnologist Yuichi Hiratsuka, now at the University of Tokyo,
and his colleagues, have built a microscopic motor powered by bacteria.

The bacterium used in the device, Mycoplasma mobile is one of
nature’s fastest moving microbes; it is able to glide over surfaces
at speeds of up to seven-tenths of an inch per hour, the equivalent of
a person moving at 20 miles per hour.

Hiratsuka and his team etched circular tracks, coated with
glycoproteins, into tiny cogs. M. mobile needs these sugary proteins to
adhere to a surface. The bacteria were genetically engineered, and
coated with vitamin B7, to make them more adhesive. A rotor (left) was
then added to the device, so that it moved when the bacteria slid along
the pathways on the cog, which can hold 100 bacteria. The researchers
were able to place 20,000 such rotors onto the surface of a silicon
chip, with each cog rotating at an average of 2 revolutions per minute.

The system can repair itself and needs only glucose as a source of
fuel. It contains no wires and, unlike electronic motors,  can work in
a wet environment. The system could be improved by adding more bacteria
to the cogs.

“We would like to make micro-robots driven by biological motors,”
says Hiratsuka, adding that “we may be able to construct electronic
generator systems, which generate electric energy from an abundant
chemical source – glucose in the body”.

The microbe-powered motor may possibly be used to propel micropumps,
perhaps like the one developed by researchers at the University of

Alexander Mamishev, an associate professor of electrical engineering,
led a team which has developed a microscopic ion pump small enough to
fit on a silicon chip. The device uses an electrical charge to produce
a jet of air on the surface of the chip.

The ion pump consists of two basic components, an emitter and a
collector. The emitter, which has a diameter of 2 micrometers,
generates ions, which travel along an electrical field to the
collector, creating a cool jet of air that cools the chip surface. The
infrared images on the right show the changes in surface temerature of
a chip when the pump is switched off (top) and on (bottom).

“With this pump, we are able to integrate the entire cooling system
right onto a chip,” says Mamishev. “That allows for cooling in
applications and spaces where it just wasn’t realistic to do

The University of Washington researchers, together with collaborators
from Kronos Advanced Technologies and Intel, have received a $100,000
grant from the Washington Technology Center to take the project into
the second phase.

The ultimate aim of the project is to develop cooling systems which can
be built into the next generation of microchips and
microelectromechanical devices. Researchers involved in the work are
looking into incorporating carbon nanotubes and other nano-structures
to improve the performance of the ion pumps.