Dynamics of pattern formation in bacterial swarms

To gain a more thorough understanding of the dynamics of swarming bacteria, a nonlabeled cell tracking algorithm was used to study the velocity field of flagellated bacteria, Serratia marcescens, swarming on a soft agar plate. The average velocities for local regions regularly arranged over the entire flow field were investigated. The velocity field of the bacteria typically featured the combination of curvilinear translation and vortex modes. They repeated these patterns for short periods of time, forming several groups and dissipating. To further investigate the flow patterns generated by the collective motion of the swarming bacteria, the velocity field on the swarm was spatially correlated. The highest velocities and correlation lengths have been found to occur in the region from 0.5 to 1 mm from the swarm edge, followed by a steady decline as distance from the edge increases, and a sudden decrease in motion typically occurs between 2 and 4 mm from the swarm edge. © 2008 American Institute of Physics. DOI: 10.1063/1.2953245