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

Abstract

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.

arXiv comment28 pages, 5 figures. Published online at http://www.sciencedirect.com/science/article/pii/S0006349511007211

References in corpus (3)

• Statistical Mechanics of Interacting Run-and-Tumble Bacteria
• The Bacterial Chemotactic Response Reflects a Compromise Between Transient and Steady State Behavior
• Persistence of direction increases the drift velocity of run and tumble chemotaxis

Cited by in corpus (19)

• Diffusive transport without detailed balance in motile bacteria: Does microbiology need statistical physics?
• Bacterial hopping and trapping in porous media
• Confinement and activity regulate bacterial motion in porous media
• Optimized Diffusion of Run-and-Tumble Particles in Crowded Environments
• Dynamics of active filaments in porous media
• Growth of bacteria in 3-d colonies
• Mechanisms for bacterial gliding motility on soft substrates
• Enhanced propagation of motile bacteria on surfaces due to forward scattering
• Chemotactic smoothing of collective migration
• A Traveling-Wave Solution for Bacterial Chemotaxis with Growth
• Invariance properties of bacterial random walks in complex structures
• From Clarkia to Escherichia and Janus: the physics of natural and synthetic active colloids
• Microscopic theory for the diffusion of an active particle in a crowded environment
• Influence of confinement on the spreading of bacterial populations
• Stirring by swimmers in confined microenvironments
• Migration and accumulation of bacteria with chemotaxis and chemokinesis
• Motile bacteria in a critical fluid mixture
• Escherichia coli as a model active colloid: a practical introduction
• Mathematical models for chemotaxis and their applications in self-organisation phenomena