Gliding motility (the active movement of cells over surfaces without the aid of flagella) is a trait shared by diverse bacteria. Gliding motility was first observed nearly 200 years ago, yet the mechanisms responsible for cell movement are still largely unknown. Flavobacterium johnsoniae is a convenient model organism for studies of bacterial gliding motility. Techniques to genetically manipulate F. johnsoniae have recently been developed and used to characterize a number of genes that are required for gliding (gld genes). The proteins encoded by these genes appear to localize to the cell envelope, where the motility apparatus is expected to reside. GldA, GldF, and GldG are thought to interact to form an ATP-binding cassette (ABC) transporter. Most of the other Gld proteins do not exhibit significant similarity to proteins of known function. The role of the Gld ABC transporter in gliding is not known and will be investigated. Wild-type and mutant cells are being biochemically characterized to identify the cargo of the transporter and determine the role of the transporter in gliding. Additional genes required for gliding will also be identified by cosmid complementation and transposon mutagenesis. These genes will be cloned, sequenced, and analyzed to determine possible functions for the individual components of the gliding machinery. Mutations will be created in individual gld genes and the effects on cell motility will be assessed. The genes will also be cloned into expression vectors to allow overproduction of Gld proteins. These proteins will be used to raise antibodies, which will allow localization of the Gld proteins by cell fractionation and by immuno-electron microscopy. This may allow visualization of the motility machinery at high resolution for the first time, and will be an important step toward determining the mechanism of gliding. Bacteriophages that infect only motile cells will also be used as tools to aid in identification of the outermost components of the motility machinery. These studies will lead to a better understanding of the mechanism of Flavobacterium gliding motility. In addition to expanding our knowledge on this common but little understood means of bacterial locomotion, these studies could have more practical value since gliding bacteria related to F. johnsoniae are important as pathogens of plants, animals, and humans, as agents of biodegradation, and as producers of enzymes, antibiotics and other secondary metabolites.
