Cover photograph (Copyright © 2003, American Society for Microbiology. All Rights Reserved.): Streptomyces coelicolor displays one of the most dramatic examples of prokaryotic morphological development. Colonies growing on an agar surface produce red and blue pigments associated with the production of two different antibiotics as well as aerial hyphae (the white covering on the colony surface) and spores which appear grey. (See related article on page 6147.)