Cover photograph (Copyright © 2005, American Society for Microbiology. All Rights Reserved.): False-color scanning electron micrograph (magnification, ×) of bacterial cells of a Mycobacterium smegmatis conditional kasA mutant. The chromosomal copy of kasA, an essential gene encoding a mycolic acid biosynthesis enzyme, has been deleted, and a second integrated copy is expressed from an acetamide-inducible promoter. Conditional depletion of KasA after 24 h of growth in medium without acetamide causes "crumpling" of bacterial cells prior to lysis. (See related article on page 7596.)