Genome-Wide Screening of Genes Required for Swarming Motility in Escherichia coli K-12†

Escherichia coli K-12 has the ability to migrate on semisolid media by means of swarming motility. A systematic and comprehensive collection of gene-disrupted E. coli K-12 mutants (the Keio collection) was used to identify the genes involved in the swarming motility of this bacterium. Of the 3,985 nonessential gene mutants, 294 were found to exhibit a strongly repressed-swarming phenotype. Further, 216 of the 294 mutants displayed no significant defects in swimming motility; therefore, the 216 genes were considered to be specifi-cally associated with the swarming phenotype. The swarming-associated genes were classified into various functional categories, indicating that swarming is a specialized form of motility that requires a wide variety of cellular activities. These genes include genes for tricarboxylic acid cycle and glucose metabolism, iron acqui-sition, chaperones and protein-folding catalysts, signal transduction, and biosynthesis of cell surface compo-nents, such as lipopolysaccharide, the enterobacterial common antigen, and type 1 fimbriae. Lipopolysaccha-ride and the enterobacterial common antigen may be important surface-acting components that contribute to the reduction of surface tension, thereby facilitating the swarm migration in the E. coli K-12 strain. Swarming is a flagellum-dependent form of bacterial motil-ity that facilitates migration of bacteria on viscous substrates, such as semisolid agar surfaces, which has been observed for