Cover photograph (Copyright © 2008, American Society for Microbiology. All Rights Reserved.): High-resolution scanning electron micrograph of “Chlorochromatium aggregatum.” This phototrophic consortium represents a highly developed interspecific association of bacteria and consists of green sulfur bacteria, so-called epibionts, surrounding a central, motile, chemotrophic bacterium. Phototrophic consortia occur in numerous stratified lakes worldwide, where they can account for up to two-thirds of the total bacterial biomass in the chemocline. Secondary electron and back-scattered electron images are combined in different color channels for better visualization of topographic contrast. (See related article on page 3721.)