Cover photograph (Copyright © 2007, American Society for Microbiology. All Rights Reserved.): Wild-type Myxococcus xanthus cells foraging for prey bacteria on low nutrient agar medium. As M. xanthus migrates into new territory, large groups of cells organize and are visible at the colony edge, while individual cells can also be seen among the groups. The organization of groups of cells is altered when they encounter prey. The photo was taken at a magnification of ×400. (See related article on page 5675.)