DATE2025.03.18 #Press Releases
Unraveling the Pathway to Chaotic Flow in Swimming Bacterial Collective Motion
Disclaimer: machine translated by DeepL which may contain errors.
— Contributing to the Design of Active Fluid Devices through Collective Motion Control —
Summary of Presentation
Associate Professor Daiki Nishiguchi from the Department of Physics, School of Science, Science Tokyo (formerly Assistant Professor at the Department of Physics, Graduate School of Science, The University of Tokyo, and currently a Visiting Researcher at the same institution), along with graduate student Sora Shiratani and Associate Professor Kazumasa Takeuchi from the Graduate School of Science, The University of Tokyo, as well as Professor Igor S. Aranson from Pennsylvania State University (formerly a GSGC Professor at the Graduate School of Science, The University of Tokyo), and their research team, have elucidated the pathway leading to an active turbulence state—a collective motion exhibiting chaotic spatiotemporal flow—in highly dense suspensions of swimming bacteria.
In such dense bacterial suspensions, bacteria exhibit chaotic collective motion accompanying numerous vortices, known by the name of active turbulence. When confined within a small circular region, these bacterial suspensions develop a steady vortex that rotates in a single direction. In this study, the researchers discovered that as the radius of the circular confinement increases, the steady vortex becomes unstable, and its rotation periodically reverses before transitioning into active turbulence. Furthermore, they validated their findings through numerical simulations and analytical theory, obtaining consistent results.
This study reveals a method to transform chaotic collective motion into a stable vortex structure by imposing geometric constraints and further converting this vortex structure into a periodically reversing state. Since this theory is universally applicable not only to bacterial populations but also to other systems including cultured cells and self-propelled colloidal systems, it is expected to serve as a design principle for novel active fluid devices.
These findings were published in the Proceedings of the National Academy of Sciences (PNAS) on March 14 (local time).
Figure: A high-density suspension of swimming bacteria exhibiting disordered collective motion (left) was confined within circular regions of different radii (right). By comparing their behavior, the researchers elucidated the pathway in which a stable single vortex gradually becomes unstable and transitions into spatiotemporal chaos as the radius increases.
Related Links
Science Tokyo, Japan Science and Technology Agency (JST)
Published Journals
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Journal name Proceedings of National Academy of Science USATitle of paper Vortex reversal is a precursor of confined bacterial turbulence