Cover photograph (Copyright © 2005, American Society for Microbiology. All Rights Reserved.): A swarm of Myxococcus xanthus, strain DK1622, on agar. A total of 2.5 × 10⁷ cells were spotted on a 0.5× CTT-0.4% agar plate, and the photo was taken after several days of incubation at 32°C. The center of the swarm has several layers of cells. At the edge of the swarm, a single layer of single cells and lateral clusters of cells are spreading outward. The rings and spokes are areas of high cell density. M. xanthus cells have pigments in their outer membrane that give them a golden color. (See related article on page 2105.)