E. coli bacteria spin microscopic discs without physical contact
Researchers at the Institute of Science and Technology Austria have demonstrated that Escherichia coli bacteria can rotate tiny disc-shaped objects without touching them, using only the fluid forces generated by their motion. The findings, published in Nature Physics, reveal a previously unknown mechanism that could support the development of bio-hybrid micromachines powered by living organisms.
The study builds on earlier work from 2023, when scientists observed that dense suspensions of bacteria, known as active baths, could drive rotating clusters of particles. At the time, the origin of this rotation remained unclear.
The new research identifies the physical mechanism behind the phenomenon. As E. coli moves, its body rotates in one direction while its corkscrew-like flagella spin in the opposite direction. This counter-rotation creates what physicists describe as a hydrodynamic torque dipole, a pair of opposing rotational forces separated along the length of the bacterium.
When these bacteria are confined beneath a microscopic disc inside a narrow channel, the forces no longer cancel each other out. Instead, they generate a net torque that drives continuous clockwise rotation of the disc. The result is a stable, contact-free transfer of motion from living cells to an external object.
According to the research team, the system behaves like a microscopic engine. Each bacterium contributes to the overall torque, meaning that increasing the number of cells leads to faster rotation. The effect is purely hydrodynamic and does not rely on direct mechanical interaction.
This approach differs from earlier bacterial micromachine designs, which often depended on asymmetrical gears or surfaces to convert random motion into directed movement. In contrast, the discs used in this study are perfectly symmetrical. The rotation emerges from confinement and fluid dynamics alone.
The findings also provide insight into how bacteria behave in confined environments such as biofilms or porous materials. In these settings, hydrodynamic interactions with nearby surfaces play a critical role in collective motion and organization.
Beyond fundamental physics, the research opens new possibilities for engineering applications. Bio-hybrid micromachines could use living microorganisms to generate controlled motion at microscopic scales. Potential uses include targeted drug delivery, micro-scale fluid control, and advanced material systems.
The study highlights how biological activity can be harnessed through physical principles to produce mechanical work, linking nanoscale motion to larger functional systems without traditional components such as gears or motors.
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