“Emergence of Large-Scale Mechanical Spiral Waves in Bacterial Living Matter”, Shiqi Liu, Ye Li, Yuhao Wang, Yilin Wu2024-04-10 (cellular automata, microbiome)⁠:

Propagating spiral waves have been discovered in various chemical, biological, and physical systems. Spiral waves in multicellular organisms are often associated with essential living functions. Although certain eukaryotic microorganisms have long been known to generate spiral waves, evidence of spiral wave pattern has been lacking in the bacterial world.

Here we report the discovery of a unique form of propagating spiral waves in dense bacterial populations where cells engage in cyclic force-generating processes driven by type-IV pilus motility. Specifically, we discovered that synchronization of pilus activity in the bacterial living matter leads to large-scale spatiotemporal regulation of tension force in the form of propagating spiral waves. Theoretical modeling reveals that the spiral tension waves result from non-reciprocity in cell-cell interactions.

Our findings reveal a novel mechanism of large-scale force regulation in the bacterial world and may shed light on the emergent mechanics of biofilms and microbiomes. Pilus-driven bacterial living matter also provides a mechanical active medium for studying electrical or chemical spiral waves in living systems.