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 a grappling-hook-like motile organelle called type-IV pilus motor. 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 modelling reveals that the spiral tension waves result from non-reciprocity in cell–cell interactions. Our findings reveal a mechanism of large-scale force regulation in 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.

人们在各种化学、生物和物理系统中都发现了传播的螺旋波。多细胞生物中的螺旋波通常与基本的生命功能相关。尽管长期以来已知某些真核微生物会产生螺旋波，但细菌世界中一直缺乏螺旋波模式的证据。在这里，我们报告在密集的细菌群体中发现了一种独特形式的螺旋波传播，其中细胞参与由称为 IV 型菌毛马达的抓钩状运动细胞器驱动的循环力生成过程。具体来说，我们发现细菌生命物质中菌毛活动的同步导致以传播螺旋波的形式对张力进行大规模时空调节。理论模型表明，螺旋张力波是由细胞间相互作用的非互易性引起的。我们的研究结果揭示了细菌世界中大规模力调节的机制，并可能揭示生物膜和微生物组的新兴机制。菌毛驱动的细菌活物质还为研究生命系统中的电或化学螺旋波提供了机械活性介质。