Viscoelastic control of spatiotemporal order in bacterial active matter

Active matter consists of units that generate mechanical work by consuming energy. Examples include living systems, such as assemblies bacteria and biological tissues, biopolymers driven molecular motors, suspensions synthetic self-propelled particles. A central question in the field is to understand control self-organization active space time. Most systems exhibit either spatial order mediated interactions coordinate structure motion agents or temporal synchronization individual oscillatory dynamics. The simultaneous organization more challenging generally requires complex interactions, reaction-diffusion hierarchies genetically engineered cellular circuits. Here, we report a novel simple means simultaneously bacterial matter. By confining an suspension manipulating single macroscopic parameter, namely viscoelasticity suspending fluid, have found fluid first self-organizes into millimeter-scale rotating vortex; then displays giant vortex switches its global chirality periodically with tunable frequency, reminiscent torsional pendulum - self-driven one. Combining experiments model, explain this striking behavior terms interplay between forcing viscoelastic stress relaxation. Our findings advance understanding fluids, demonstrate experimentally for time rheological properties can be harnessed flows. Coupled actuation, our self-oscillating may used "clock" locomotion soft robots microfluidic pumping.