Cover photograph (Copyright © 2007, American Society for Microbiology. All Rights Reserved.): Scanning electron micrograph of crystalline Fe(III) oxides produced by Fe(II)-oxidizing phototrophs. Minerals such as these can be found in banded iron formations, an enigmatic class of ancient sedimentary deposits. Whether Fe(II)-oxidizing phototrophs were involved in their deposition is an intriguing open question. (Photo courtesy of Andreas Kappler.) (See related articles on pages 1765 and 1774.)