Cover photograph (Copyright © 2007, American Society for Microbiology. All Rights Reserved.): Scanning electron micrograph of the purple phototrophic bacterium Rhodopseudomonas palustris, showing the rosettes of cells that this species typically forms as it divides and multiplies. R. palustris catalyzes a remarkable range of metabolic processes and holds promise as a biocatalyst for the production of hydrogen gas as a biofuel. (Electron micrograph courtesy of Yasuhiro Oda.) (See related article on page 1665.)