Collective motion, superdiffusion, and non-thermal noise in active bacterial baths

We present experimental studies of the dynamics of concentrated bacterial colonies in three-dimensions. The bacteria we use is e. coli at varying densities. By analyzing the trajectories of colloidal spheres embedded in these bacterial bath suspensions, we extract one- and two-point mean square displacements which exhibit superdiffusion crossing over to a diffusive regime. When combined with independent measurements of the response function of the suspension, the data enable us to extract the noise spectrum of the bath. This work was supported by NSF DMR02-03378 and NASA NAG3-2172