Cover photograph (Copyright © 2004, American Society for Microbiology. All Rights Reserved.): Swarming motility of Pseudomonas aeruginosa wild-type and flagellar motor mutant strains on the surface of solified agar medium. The flagellar motor of P. aeruginosa is more complex than previously studied flagellar motors and enables the organism to function very effectively as an “all-terrain” bacterium. (See related article on page 6341.)