Cover photograph (Copyright © 2000, American Society for Microbiology. All rights reserved.): A DNA microarray showing the genome-wide expression profile of Bacillus subtilis grown under anaerobic conditions. The DNA microarray contained 4,020 open reading frames and was hybridized with fluorescence-labeled probes generated from total RNA of aerobic and anaerobic cultures supplemented with nitrate. The RNA sample from the anaerobic culture was labeled with Cy-3 (green), while the sample from the aerobic culture was labeled with Cy-5 (red). (See related article on page 4458.)