Collective motion in bacterial colonies

Hepeng Zhang

Center for Nonlinear Dynamics and Department of Physics

The University of Texas at Austin, Austin

    We study collective motion in two species of swarming bacteria. In colonies of Paenibacillus dendritiformis, the characteristic correlation length of collective motion is essentially independent of the mean bacterial speed, while the correlation time is linearly proportional to the ratio of the correlation length to the mean speed. In experiments with Bacillus subtilis, we observe that bacteria swim cooperatively in dynamic clusters, whose size exhibits a power-law distribution truncated by an exponential tail. Large mobile clusters lead to anomalous fluctuations in bacterial density; the standard deviation (N) grows with the mean (N) of the number of bacteria as N ~ N^3/4 rather than N ~ N^1/2.