Ordered protrusions and bacterial self-organization near the interface of an active drop

Upper: Phase-contrast image of a P. mirabilis active suspension drop's interface with ordered interfacial protrusions. Lower: Colormap showing the averaged velocity field at the region shown in the Upper panel computed by optical flow analysis on phase-contrast images. The collective velocity field was averaged over a duration of 10 s. Arrows in the figure represent velocity direction while the colormap at the right indicates the radial velocity component (unit: µm/s). A positive value indicates moving outward toward the interface, while a negative value indicates moving inward away from the interface.The active drop was prepared by colony growth. This video is played at 50 frames per second with the real elapsed time indicated in the time stamp. Scale bar, 50 μm. See: Xu et al., Proc. Natl. Acad. Sci. U.S.A. 120.30 (2023): e2219708120.