Mechanical origin for non-equilibrium ultrasensitivity in the bacterial flagellar motor

Nature Physics (2026)Cite this article Flagellar motors enable bacteria to navigate their environments by switching rotation direction in response to external cues with high sensitivity. Previous work indicated that the ultrasensitivity of the flagellar motor originates from conformational spread, in which subunits of the switching complex are strongly coupled to their neighbours as in an equilibrium Ising model. However, dynamic single-motor measurements indicated that rotation switching is driven out of equilibrium, and the mechanism for this dissipative driving remains unknown. Here we propose that local mechanical torques on motor subunits can affect their conformation dynamics, based on recent structures observed with cryo-electron microscopy. This gives rise to a tug of war between stator-associated subunits that produces cooperative, non-equilibrium switching responses without requiring nearest-neighbour interactions. Our model predicts that the motor response cooperativity grows with the number of stators driving rotation, which is consistent with published experimental results. Finally, we show that operating out of equilibrium enables motors to achieve high cooperativity with faster responses compared with equilibrium motors. Our results indicate a general role for mechanics in sensitive chemical regulation.This is a preview of subscription content, access via your institution Access Nature and 54 other Nature Portfolio journals Get Nature+, our best-value online-access subscription $32.99 / 30 days cancel any timeSubscribe to this journal Receive 12 print issues and online access $259.00 per yearonly $21.58 per issueBuy this articleUSD 39.95Prices may be subject to local taxes which are calculated during checkoutSource data are provided with this paper.Code that can be used to reproduce the main text figures is included as Supplementary Code. 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Hanson for help visualizing the motor structures and the Biophysical Modeling Group at the Flatiron Institute for feedback. We also thank J. Yuan and R. He for the experimental measurements of CW bias in Fig. 4.

The Flatiron Institute is a division of the Simons Foundation.Center for Computational Biology, Flatiron Institute, New York, NY, USAHenry H. Mattingly & Yuhai TuCenter for Computational Neuroscience, Flatiron Institute, New York, NY, USAYuhai TuSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarH.M. and Y.T. conceived the project, developed the models and wrote the paper. H.M. performed the simulations.Correspondence to Henry H. Mattingly or Yuhai Tu.The authors declare no competing interests.Nature Physics thanks the anonymous reviewers for their contribution to the peer review of this work.Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.Supplementary information, derivations and simulation details.Code to reproduce Fig. 2.Code to reproduce Fig. 3.Code to reproduce Fig. 4.Code to reproduce Fig. 5.Code to reproduce Fig. 6. This zip file contains data for all main text figures. Data plotted in Fig. 2 are contained in subfolder Fig. 2.

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Source Data Fig. 6 This zip file contains data for all main text figures. Data plotted in Fig. 6 are contained in subfolder Fig. 6.Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.Reprints and permissionsMattingly, H.H., Tu, Y. Mechanical origin for non-equilibrium ultrasensitivity in the bacterial flagellar motor. Nat. Phys. (2026). https://doi.org/10.1038/s41567-025-03105-2Download citationReceived: 04 February 2025Accepted: 21 October 2025Published: 07 January 2026Version of record: 07 January 2026DOI: https://doi.org/10.1038/s41567-025-03105-2Anyone you share the following link with will be able to read this content:Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative