Continuum model of actin-mediated bacterial propulsion

The mechanism of propulsion of host bacteria under the action of actin gel networks is examined by means of a continuum model of the dynamics of the F-actin concentration. The model includes the elasticity of the network, its attachment to the host and the polymerization at the interface with it. A formula for the cruise velocity is derived wherefrom the respective contributions of elasticity and polymerization are made explicit. The velocity tends to elongate the gel in the direction opposite to motion, and in turn is proportional to the size of its active portion. It is shown that the motion can start only past a finite latency time: the condition for the onset of motion is explicitly given.It is numerically found that at steady state the motion has a pulsating behavior, with sudden decelerations and subsequent recoveries.