Cell Shape and Population Migration Are Distinct Steps of Swarming That Are Decoupled on High-Percentage Agar.

Swarming on rigid surfaces requires movement of cells as individuals and as a group of cells. For the bacterium , an individual cell can respond to a rigid surface by elongating and migrating over micrometer-scale distances. Cells can form groups of transiently aligned cells, and the collective population is capable of migrating over centimeter-scale distances.