Formation, collective motion, and merging of macroscopic bacterial aggregates
Fig 4
Single cell motility and aggregate movement.
High magnification imaging of cells in an aggregate. Aggregates were formed within a coverslip bottom chamber to enable 100X imaging of cells within the aggregate. (A) Motile cells exist in the vicinity of the aggregate and a subset consolidates with the aggregate and becomes immotile. Representative trajectories of individual cells that are motile at t = 0. Yellow lines denote cells that swim towards the spot and become immotile within 0.24 s. Green lines denote cells that remain motile for 0.24 s. (B) Immotile cells within the aggregate. Shown in blue are representative cells within the aggregate that do not change position over 10 seconds. In A and B, trajectories are labeled with respective cellular velocities in μm/sec, and the scale bar is 40 μm. (C) Aggregate movement on the microscale. Progression of the boundary of a typical aggregate over 80 mins. The yellow solid line marks the periphery of the spot in real time, whereas the cyan solid line indicates the position of the spot front at t = 0 mins. Direction of the spot movement is shown with the white arrow. (D) Distribution of aggregate front speeds. By tracking the position of an aggregate boundary over time, the front speed is calculated for n = 40 aggregates. The histogram shows the measured distribution of front speeds with an average value of 0.023 mm/hr.