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

Lookup NU author(s): Dr Otti CrozeORCiD


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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 C0.35%, 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. © 2011 Biophysical Society.

Publication metadata

Author(s): Croze OA, Ferguson GP, Cates ME, Poon WCK

Publication type: Article

Publication status: Published

Journal: Biophysical Journal

Year: 2011

Volume: 101

Issue: 3

Pages: 525-534

Online publication date: 03/08/2011

ISSN (print): 0006-3495

ISSN (electronic): 1542-0086

Publisher: Cell Press


DOI: 10.1016/j.bpj.2011.06.023

PubMed id: 21806920


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