Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): sirA orthologs are known to regulate horizontally acquired virulence genes in several species of the  subdivision of proteobacteria. A more ancient physiological function for sirA orthologs may be the control of flagellar regulons. Consistent with this hypothesis, sirA of Salmonella enterica serovar Typhimurium represses the flagellar regulon and has its greatest regulatory effects while the cells are growing in motility agar. Shown are two serovar Typhimurium strains encoding a fliA::luxCDABE fusion photographed while swimming through a motility agar plate. Light intensity emanating from the cells is color coded, with red being the most intense. (See related article on page 2249.)