Filling an emulsion drop with motile bacteria

Authors :: Vladescu, I. D.
Marsden, E. J.
Schwarz-Linek, J.
Martinez, V. A.
Arlt, J.
Morozov, A. N.
Marenduzzo, D.
Cates, M. E.
Poon, W. C. K.
Publication Year :: 2014
Abstract: We have measured the spatial distribution of motile Escherichia coli inside spherical water droplets emulsified in oil. At low cell concentrations, the cell density peaks at the water-oil interface; at increasing concentration, the bulk of each droplet fills up uniformly while the surface peak remains. Simulations and theory show that the bulk density results from a `traffic' of cells leaving the surface layer, increasingly due to cell-cell scattering as the surface coverage rises above $\sim 10\%$. Our findings show similarities with the physics of a rarefied gas in a spherical cavity with attractive walls.<br />Comment: 5 pages, 4 figures, Supporting Information (5 pages, 5 figures)