Extracellular slime associated with Proteus mirabilis during swarming

Light microscopy, transmission electron microscopy, and scanning electron microscopy were used to visualize the extracellular slime of Proteus mirabilis swarm cells. Slime was observed with phase-contrast microscopy after fixation in hot sulfuric acid-sodium borate. Ruthenium red was used to stain slime for transmission electron microscopy. Copious quantities of extracellular slime were observed surrounding swarm cells; the slime appeared to provide a matrix through which the cells could migrate. Swarm cells were always found embedded in slime. These observations support the argument that swarming of P. mirabilis is associated with the production of large quantities of extracellular slime. Examination of nonswarming mutants of P. mirabilis revealed that a number of morphological changes, including cell elongation and increased flagellum synthesis, were required for swarm cell migration. It is still unclear whether extracellular slime production also is required for migration.