Swarming Salmonella typhimurium
When grown on soft agar (0.5-0.8%) and a rich medium, cells of Salmonella typhimurium (and other Gram-negative bacteria) elongate, produce more flagella, and move over the surface of the agar in a coordinated manner. Lipopolysaccharide (slime) appears to be important as a wetting agent. The chemotaxis system is required, but the cells need not respond to specific attractants or repellents. As you will see in the movies, the cells swirl about in rafts or packs. At the edge of the swarm they form a monolayer. At the very edge, cells are nearly stationary. Farther back, closer to the point of inoculation, cells pile up in multilayers and are very active. The videos were made in phase contrast.
Harshey, R. M. Bees aren't the only ones: swarming in Gram-negative bacteria. Mol. Microbiol. 13, 389-394 (1994).
We would like to thank for her help in creating these movies.