title: Lactobacillus casei 64H contains a phosphoenolpyruvate-dependent phosphotransferase system for uptake of galactose, as confirmed by analysis of ptsH and different gal mutants.
abstract: Galactose metabolism in Lactobacillus casei 64H was analyzed by genetic and biochemical methods. Mutants with defects in ptsH, galK, or the tagatose 6-phosphate pathway were isolated either by positive selection using 2-deoxyglucose or 2-deoxygalactose or by an enrichment procedure with streptozotocin. ptsH mutations abolish growth on lactose, cellobiose, N-acetylglucosamine, mannose, fructose, mannitol, glucitol, and ribitol, while growth on galactose continues at a reduced rate. Growth on galactose is also reduced, but not abolished, in galK mutants. A mutation in galK in combination with a mutation in the tagatose 6-phosphate pathway results in sensitivity to galactose and lactose, while a galK mutation in combination with a mutation in ptsH completely abolishes galactose metabolism. Transport assays, in vitro phosphorylation assays, and thin-layer chromatography of intermediates of galactose metabolism also indicate the functioning of a permease/Leloir pathway and a phosphoenolpyruvate-dependent phosphotransferase system (PTS)/tagatose 6-phosphate pathway. The galactose-PTS is induced by growth on either galactose or lactose, but the induction kinetics for the two substrates are different.
authors.affiliation: Universität Osnabrück, Fachbereich Biologie/Chemie, AG Genetik, 49076 Osnabrück, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Bettenbrock
authors.forename: U
authors.initials: U
authors.lastname: Siebers
authors.forename: P
authors.initials: P
authors.lastname: Ehrenreich
authors.forename: C A
authors.initials: CA
authors.lastname: Alpert
mesh_terms: D001426:Bacterial Proteins; D001693:Biological Transport, Active; D005690:Galactose / Q000378:metabolism*; D005798:Genes, Bacterial; D007700:Kinetics; D007780:Lacticaseibacillus casei / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D007785:Lactose / Q000378:metabolism; D009154:Mutation; D010641:Phenotype; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000235:genetics* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C030182:phosphocarrier protein HPr; D007785:Lactose; D005690:Galactose