Migration of chemotactic bacteria in soft agar: role of gel concentration

Details Migration of chemotactic bacteria in soft agar: role of gel concentration Migration of chemotactic bacteria in soft agar: role of gel concentration

2011-01-26

arxiv.org/abs/1101.5063v2

Biophys. J. Volume 101, Issue 3, 3 August 2011, Pages 525-534

Physics

Condensed Matter

Soft Condensed Matter

28 pages, 5 figures. Published online at http://www.sciencedirect.com/science/article/pii/S0006349511007211

Scientific paper

10.1016/j.bpj.2011.06.023

We study the migration of chemotactic wild-type Escherichia coli populations in semisolid (soft) agar in the concentration range C = 0.15-0.5% (w/v). For C < 0.35%, expanding bacterial colonies display characteristic chemotactic rings. At C = 0.35%, however, bacteria migrate as broad circular bands rather than sharp rings. These are growth/diffusion waves arising because of suppression of chemotaxis by the agar and have not been previously reported experimentally to our knowledge. For C = 0.4-0.5%, expanding colonies do not span the depth of the agar and develop pronounced front instabilities. The migration front speed is weakly dependent on agar concentration at C < 0.25%, but decreases sharply above this value. We discuss these observations in terms of an extended Keller-Segel model for which we derived novel transport parameter expressions accounting for perturbations of the chemotactic response by collisions with the agar. The model makes it possible to fit the observed front speed decay in the range C = 0.15-0.35%, and its solutions qualitatively reproduce the observed transition from chemotactic to growth/diffusion bands. We discuss the implications of our results for the study of bacteria in porous media and for the design of improved bacteriological chemotaxis assays.

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