Active matter consists of units that generate mechanical work by consuming energy¹. Examples include living systems (such as assemblies of bacteria^2,3,4,5 and biological tissues^6,7), biopolymers driven by molecular motors^8,9,10,11 and suspensions of synthetic self-propelled particles^12,13,14. A central goal is to understand and control the self-organization of active assemblies in space and time. Most active systems exhibit either spatial order mediated by interactions that coordinate the spatial structure and the motion of active agents^12,14,15 or the temporal synchronization of individual oscillatory dynamics². The simultaneous control of spatial and temporal organization is more challenging and generally requires complex interactions, such as reaction–diffusion hierarchies¹⁶ or genetically engineered cellular circuits². Here we report a simple technique to simultaneously control the spatial and temporal self-organization of bacterial active matter. We confine dense active suspensions of Escherichia coli cells and manipulate a single macroscopic parameter—namely, the viscoelasticity of the suspending fluid— through the addition of purified genomic DNA. This reveals self-driven spatial and temporal organization in the form of a millimetre-scale rotating vortex with periodically oscillating global chirality of tunable frequency, reminiscent of a torsional pendulum. By combining experiments with an active-matter model, we explain this behaviour in terms of the interplay between active forcing and viscoelastic stress relaxation. Our findings provide insight into the influence of bacterial motile behaviour in complex fluids, which may be of interest in health- and ecology-related research, and demonstrate experimentally that rheological properties can be harnessed to control active-matter flows^17,18. We envisage that our millimetre-scale, tunable, self-oscillating bacterial vortex may be coupled to actuation systems to act a ‘clock generator’ capable of providing timing signals for rhythmic locomotion of soft robots and for programmed microfluidic pumping¹⁹, for example, by triggering the action of a shift register in soft-robotic logic devices²⁰.

活性物质由通过消耗能量¹产生机械功的单元组成。例子包括生命系统（例如细菌^2,3,4,5和生物组织^6,7的组装），由分子马达驱动的生物聚合物^8,9,10,11和合成自推进粒子的悬浮液^12,13,14 . 一个中心目标是理解和控制活动组件在空间和时间上的自组织。^{大多数活性系统要么表现出由协调空间结构和活性剂12、14、15}运动的相互作用介导的空间顺序，要么表现出单个振荡动力学的时间同步². 同时控制空间和时间组织更具挑战性，通常需要复杂的相互作用，例如反应-扩散层次¹⁶或基因工程细胞电路²。在这里，我们报告了一种简单的技术，可以同时控制细菌活性物质的空间和时间自组织。我们限制了大肠杆菌的密集活性悬浮液细胞并通过添加纯化的基因组 DNA 来操纵单个宏观参数，即悬浮液的粘弹性。这揭示了毫米级旋转涡旋形式的自驱动时空组织，具有可调谐频率的周期性振荡全局手性，让人联想到扭转钟摆。通过将实验与活性物质模型相结合，我们根据主动强迫和粘弹性应力松弛之间的相互作用来解释这种行为。我们的研究结果提供了对复杂流体中细菌运动行为的影响的洞察，这可能对健康和生态相关的研究感兴趣，并通过实验证明可以利用流变特性来控制活性物质流动^17,18. 我们设想，我们的毫米级、可调谐、自振荡细菌涡流可以耦合到驱动系统，以充当“时钟发生器”，该“时钟发生器”能够为软机器人的有节奏运动和程序化微流体泵送¹⁹提供定时信号，例如，通过触发软机器人逻辑设备²⁰中的移位寄存器的动作。