The hydrodynamic torque dipole from rotary bacterial flagella powers symmetric discs
Grober DB, Dhar T, Saintillan D, Palacci JA. 2026. The hydrodynamic torque dipole from rotary bacterial flagella powers symmetric discs. Nature Physics.
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Abstract
Swimming bacteria move through a fluid by actuating their moving body parts. They are force-free and can be described as hydrodynamic force dipoles: pushers or pullers. This modelling description is broadly used in biological physics and active matter research, and it has successfully predicted, for example, the superfluid behaviour of suspensions of pushers or the bend instability and emergence of turbulent flows in active nematics. However, this description accounts only for the translational motion of the swimming body and neglects the effects of hydrodynamic torque dipoles, which are relevant to bacteria with rotary motor-driven flagella, such as swimming Escherichia coli. Here we show that the torque dipole of confined swimming E. coli can power the persistent rotation of symmetric discs. The torque dipole leads to a traction force on the discs, an additive mechanism that is both contactless and independent of the orientation of the bacteria. Our results indicate that the torque dipole of swimming E. coli is notable in confined geometries, which is relevant to bacterial transport through porous materials, biofilms and the development of chiral fluids.
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2026-03-27
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Nature Physics
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Springer Nature
Acknowledgement
We thank E. Krasnopeeva for help with the bacterial culture, motility and genetic engineering. We thank Q. Martinet for help with the experimental design, F. Pertl for atomic force microscopy measurements and S. Hajek for the scanning electron microscopy imaging. This project has received funding from the European Research Council under the European Union’s Horizon Europe research and innovation programme (VULCAN, 101086998). The views and opinions expressed are, however, those of the authors only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. Neither the European Union nor the granting authority can be held responsible for them. J.P. thanks the Nanofabrication and Electron Microscopy Shared Scientific Units of ISTA for support. Open access funding provided by Institute of Science and Technology (IST Austria).
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Cite this
Grober DB, Dhar T, Saintillan D, Palacci JA. The hydrodynamic torque dipole from rotary bacterial flagella powers symmetric discs. Nature Physics. 2026. doi:10.1038/s41567-026-03189-4
Grober, D. B., Dhar, T., Saintillan, D., & Palacci, J. A. (2026). The hydrodynamic torque dipole from rotary bacterial flagella powers symmetric discs. Nature Physics. Springer Nature. https://doi.org/10.1038/s41567-026-03189-4
Grober, Daniel B, Tanumoy Dhar, David Saintillan, and Jérémie A Palacci. “The Hydrodynamic Torque Dipole from Rotary Bacterial Flagella Powers Symmetric Discs.” Nature Physics. Springer Nature, 2026. https://doi.org/10.1038/s41567-026-03189-4.
D. B. Grober, T. Dhar, D. Saintillan, and J. A. Palacci, “The hydrodynamic torque dipole from rotary bacterial flagella powers symmetric discs,” Nature Physics. Springer Nature, 2026.
Grober DB, Dhar T, Saintillan D, Palacci JA. 2026. The hydrodynamic torque dipole from rotary bacterial flagella powers symmetric discs. Nature Physics.
Grober, Daniel B., et al. “The Hydrodynamic Torque Dipole from Rotary Bacterial Flagella Powers Symmetric Discs.” Nature Physics, Springer Nature, 2026, doi:10.1038/s41567-026-03189-4.
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