Cover photograph (Copyright © 2003, American Society for Microbiology. All Rights Reserved.): Geobacter sulfurreducens is representative of the Geobacter species that predominate in many subsurface environments, in which microbial reduction of insoluble Fe(III) and Mn(IV) oxides is an important process. G. sulfurreducens must attach to the insoluble oxides, as illustrated here, in order to carry out this novel electron transfer to an extracellular electron acceptor. (Photomicrograph courtesy of Susan Childers, University of Massachusetts-Amherst.) (See related article on page 2096.)