A two-sphere model for bacteria swimming near solid surfaces

JOCELYN DUNSTAN; GASTON MIÑO; ERIC CLEMENT; RODRIGO SOTO

PHYSICS OF FLUIDS

AMER INST PHYSICS

Lugar: American Institute of Physics; Año: 2012 vol. 24 p. 119011 - 1190114

1070-6631

We present a simple model for bacteria like Escherichia coli swimming near solid surfaces. It consists of two spheres of different radii connected by a dragless rod. The effect of the flagella is taken into account by imposing a force on the tail sphere and opposite torques exerted by the rod over the spheres. The hydrodynamic forces and torques on the spheres are computed by considering separately the interaction of a single sphere with the surface and with the flow produced by the other sphere. Numerically, we solve the linear system which contains the geometrical constraints and the force-free and torque-free conditions. The dynamics of this swimmer near a solid boundary is very rich, showing three different behaviors depending on the initial conditions: (1) swimming in circles in contact with the wall, (2) swimming in circles at a finite distance from the wall, and (3) swimming away from it. Furthermore, the order of magnitude of the radius of curvature for the circular motion is in the range 8-50μm, close to values observed experimentally.