Collective dynamics and model verification: Connecting kinetic modeling to data

Underlying physics of collective motion in bacterial suspensions

Andrey Sokolov

Argonne National Lab

We present the experimental study of physical properties of self-organized behavior in suspensions of swimming bacteria Bacillus Subtilis. Hydrodynamics interaction and physical collisions between swimming bacteria lead to collective motion at high concentration. We probe the physical properties of emerged collective motion via direct measurements of bacterial flow and its correlation length and time for a various swimming speeds and concentrations. Our measurements have shown puzzling result: while the energy injection rate is proportional to the swimming speed and concentration, the correlation length remains practically constant upon small speeds where random tumbling of bacteria dominates. We suggested a physical mechanism for emergence of collective motion in suspension of swimming bacteria and demonstrated a good agreement with the experiments.