Cover photograph (Copyright © 2005, American Society for Microbiology. All Rights Reserved.): Transmission electron micrograph of the Lactococcus lactis bacteriophage TP901-1 mutated in a nonessential gene (orf50). The phage are negatively stained with uranyl acetate, and the picture was taken at a magnification of ×400,000. (See related article on page 4187.)