Extended Data Fig. 9: Coexistence of two global motion modes in bacterial active solids under isotropic lateral confinement.

(a,b) Temporal dynamics of spatially averaged collective velocity in circular disk-shaped bacterial active solids where the oscillatory translation and oscillatory rotation modes co-existed with identical frequencies (\({f}_{t}={f}_{r}=0.15\) Hz; panel a) or with the frequency of the oscillatory translation mode doubled (\({f}_{t}=0.14\) Hz, \({f}_{r}=0.07\) Hz; panel b). The velocity was decomposed as Cartesian (yellow and blue traces) and polar-coordinate components (red: tangential component; green: radial component). (c,d) Panels c and d display representative trajectories of mass elements in bacterial active solids analysed in panels a and b, respectively. In each panel the trajectories were obtained by integrating the spatially averaged collective velocity over a \(50\,\mu m\times 50\,\mu m\) domain located ~ 500 µm from the centre of the disk-shaped bacterial active solid (black dot) at different polar angles. The trajectories were brought close to the centre for better visualization, and thus the scale bars (panel c, 10 μm; panel d, 20 μm) apply to the trajectories only. Colour map indicates time (unit: s).