Ordered vortex lattice in quasi-2D dense bacterial active fluids

Ordered vortex lattice in quasi-2D dense bacterial active fluids consisting of S. marcescens cells. Left, phase-contrast video. Middle, spatial distribution of instantaneous collective velocity associated with the phase-contrast video. Arrows represent velocity direction; the colour map at right indicates velocity magnitude (μm s−1). Right, spatial distribution of instantaneous vorticity associated with the phase-contrast video. Vorticity value indicated on the colour bar to the right is normalized by the mean of absolute vorticity over the entire field. Positive and negative values of vorticity correspond to counterclockwise and clockwise rotation, respectively. This video is played at 50 frames s−1 with real elapsed time indicated in the time stamp. All panels share the same scale bar, 500 μm. See: Xu et al., Nature 627, 553–558 (2024).