Protozoan power for nano-scale devices
18 December 2005
A single-celled animal first observed 300 years ago could hold the key to
powering tiny medical devices. Researchers have come a step closer to
understanding how a powerful microscopic spring in the protozoan Vorticella
Researchers have known for some time that a long, fibrous coil grown by
the single-cell protozoan is, gram for gram, more powerful than a car
engine. Now, researchers at the Whitehead Institute in Cambridge,
Massachusetts, USA — together with colleagues at MIT, Marine Biological
Laboratory in Woods Hole, MA, and University of Illinois, Chicago — have
found that this coil is far stronger than previously thought. In addition,
the researchers have discovered new clues into the mechanism behind this
"These findings are twofold," says Danielle France, a graduate student in
the lab of Whitehead Member Paul Matsudaira, and, along with Matsudaira, a
member of MIT's Division of Biological Engineering. "First, they give us an
idea of how a cell can manage to generate such enormous force; and second,
they provide clues for how engineers might reconstruct these mechanisms for
Scientists have known about this nano-spring for roughly 300 years, ever
since Anton van Leeuwenhoek first observed the protozoan, Vorticella
convallaria, through a hand-made microscope. The spring in the unicellular
Vorticella is a contractile bundle of fibre, called the spasmoneme, which
runs the length of the stalk of protozoan. At rest, the stalk is elongated
like a stretched telephone cord. When it contracts, the spasmoneme winds
back in a flash, forming a tight coil.
To find out how strongly Vorticella's spring recoils, France and
colleagues used a unique microscope to apply an extra load to the spring.
The microscope, developed by Shinya Inoue and colleagues at the Marine
Biological Laboratory in Woods Hole, MA, uses a spinning platform to
increase the centrifugal force exerted against the protozoan.
In the past, researchers have measured Vorticella's ability to recoil its
spring at 40 nano newtons of force and at a speed of eight centimeters per
second, units of measurement that are typically too large to be relevant for
biological processes. However, when France used the centrifuge microscope,
she discovered that the spring was able to recoil against as much as 300
nano newtons of force. "This is the maximum amount of power we can currently
test," says France. "We suspect the coil is even more powerful."
France and colleagues also made an important link between the engine's
fuel, calcium, and a major protein component of the stalk. This protein,
centrin, belongs to a class of proteins that can be found in organisms
ranging from green algae to humans. When the researchers introduced an
antibody for the Vorticella centrin into the cell, the spring was no longer
able to contract, indicating that the cell uses a powerful centrin-based
mechanism, one that is unlike other known cellular engines.
"When it comes to creating nano devices, this is a great mechanism for
movement," says France. "Rather than requiring electricity, this is a way to
generate movement simply from a change in the chemical environment. Here, a
simple change in calcium would power this spring." France and colleagues are
now developing methods for replicating this mechanism in the lab.
France presented her findings at the 45th Annual Meeting of the American
Society for Cell Biology in San Francisco 10-14 December.
News from The American Society for Cell Biology 45th Annual Meeting San
Francisco, CA December 10-14, 2005.
“A Centrin-based Cellular Spring that Generates nNs of Force."
The Whitehead Institute
Pictures and video of Vorticella convallaria