Swarming Proteus Colony Advancing over Agar

A dense group of E. coli swims in the roughly two dimensional space at an air water interface. Their collective motion is significantly different from their motion as single cells. Under these conditions they behave more like an active fluid, hence changing the way that nutrients are shared within the group. Notice the appearance of vortices and turbulence-like flow fields. The advancing front in this active bacterial colony moves significantly faster than the rate determined strictly by colony growth.