Galactose transport in Salmonella typhimurium.

We have studied the various systems by which galactose can be transported in Salmonella typhimurium, in particular the specific galactose permease (GP). Mutants that contain GP as the sole galactose transport system have been isolated, and starting from these mutants we have been able to select point mutants that lack GP. The galP mutation maps close to another mutation, which results in the constitutive synthesis of GP, but is not linked to galR. Growth of wild-type strains on glaactose induces GP but not the beta-methylgalactoside permease (MGP). Strains lacking GP are able to grow slowly on galactose, and MGP is induced; however, D-fucose is a much better inducer of MGP. Induction of GP or MGP is not prevented by a pts mutation, although this mutation changes the apparent Km of MGP for galactose. pts mutations have no effect on GP. GP has a rather broad specificity: galactose, glucose, mannose, fucose, 2-deoxygalactose, and 2-deoxyglucose are substrates, but only galactose and fucose can induce this transport system.