Figure 1.

Idealized schematic model of migration through the motility agar matrix. Although straight-swimming cells can be trapped in the agar matrix and idle, tumbles generated via a variety of mechanisms that alter flagellar bundling enable the unjamming of cells at internal boundaries and net migration through the porous medium. In wild-type cells, tumbles are under the control of the chemotaxis sensory network, whereas in the cms mutants lacking the chemotactic response, erratic swimming motion and random directional changes are caused by mutations in the motility apparatus. The panels schematically illustrate how a straight-swimming cell (A) can encounter an agar matrix barrier and idle (B), until a tumble occurs (C) causing reorientation (D), and allowing the cell to become unjammed and swim away (E). The arrows denote the run direction.