Extended Data Fig. 7: Rosettes drive convergent flow in a mixed WT/∆pilH subsurface colony and have a topological charge of +1.
From: Bacteria solve the problem of crowding by moving slowly
a, We used particle image velocimetry (PIV) to quantify collective cell movement in a monolayer of cells over a period of 60 min. The divergence and streamlines of the temporally averaged velocity field reveal that cells locally accumulate (indicated by negative divergence) at rosettes (purple stars). b, A timeseries of brightfield images during rosette formation illustrates this process (also shown in Fig. 4d–f and the first part of Supplementary Video 9), with increasing numbers of cells becoming verticalized and trapped within the boundary of the rosette core (white circles) over time. By calculating the director field of these images (Methods), we can calculate the topological charge n around the core of the rosette (c, white circular arrows). At all timepoints, the charge of the rosette is equal to +1. In a, the region shown in the second part of Supplementary Video 9 is indicated with a white dashed box.
