Cover photograph (Copyright © 2000, American Society for Microbiology. All rights reserved.): Deconvolved images of an optical section through an Escherichia coli cell stained with 10-N-nonyl acridine orange (NAO). The yellow is the result of superposition of green and red fluorescence characteristic of a complex between cardiolipin and NAO. Distinct fluorescent spots are consistent with the existence of cardiolipin-enriched domains in the membrane of a mutant of E. coli lacking phosphatidylethanolamine that displays filamentous growth. A similar distribution of fluorescence is seen in wild-type cells. (See related article on page 1172.)