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Enhanced diffusion of nonswimmers in a three-dimensional bath of motile bacteria

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Original languageEnglish
Article number041002
Number of pages5
JournalPhysical Review E - Statistical, Nonlinear and Soft Matter Physics
Issue number4
Publication statusPublished - 28 Oct 2013


We show, using differential dynamic microscopy, that the diffusivity of nonmotile cells in a three-dimensional (3D) population of motile E. coli is enhanced by an amount proportional to the active cell flux. While nonmotile mutants without flagella and mutants with paralyzed flagella have quite different thermal diffusivities and therefore hydrodynamic radii, their diffusivities are enhanced to the same extent by swimmers in the regime of cell densities explored here. Integrating the advective motion of nonswimmers caused by swimmers with finite persistence-length trajectories predicts our observations to within 2%, indicating that fluid entrainment is not relevant for diffusion enhancement in 3D.

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