title: A unique gene cluster for the utilization of the mucosal and human milk-associated glycans galacto-N-biose and lacto-N-biose in Lactobacillus casei.
abstract: The probiotic Lactobacillus casei catabolizes galacto-N-biose (GNB) and lacto-N-biose (LNB) by using a transport system and metabolic routes different from those of Bifidobacterium. L. casei contains a gene cluster, gnbREFGBCDA, involved in the metabolism of GNB, LNB and also N-acetylgalactosamine. Inactivation of gnbC (EIIC) or ptsI (Enzyme I) of the phosphoenolpyruvate : sugar phosphotransferase system (PTS) prevented the growth on those three carbohydrates, indicating that they are transported and phosphorylated by the same PTS(Gnb) . Enzyme activities and growth analysis with knockout mutants showed that GnbG (phospho-β-galactosidase) hydrolyses both disaccharides. However, GnbF (N-acetylgalactosamine-6P deacetylase) and GnbE (galactosamine-6P isomerase/deaminase) are involved in GNB but not in LNB fermentation. The utilization of LNB depends on nagA (N-acetylglucosamine-6P deacetylase), showing that the N-acetylhexosamine moieties of GNB and LNB follow different catabolic routes. A lacAB mutant (galactose-6P isomerase) was impaired in GNB and LNB utilization, indicating that their galactose moiety is channelled through the tagatose-6P pathway. Transcriptional analysis showed that the gnb operon is regulated by substrate-specific induction mediated by the transcriptional repressor GnbR, which binds to a 26 bp DNA region containing inverted repeats exhibiting a 2T/2A conserved core. The data represent the first characterization of novel metabolic pathways for human milk oligosaccharides and glycoconjugate structures in Firmicutes.
authors.affiliation: Laboratorio de Bacterias Lácticas y Probióticos, Departamento de Biotecnología de Alimentos, IATA-CSIC, Valencia, Spain; Instituto de Investigaciones Biotecnológicas 'Dr. Rodolfo A. Ugalde', Universidad Nacional de San Martín, Buenos Aires, Argentina.
authors.forename: Gonzalo N
authors.initials: GN
authors.lastname: Bidart
authors.forename: Jesús
authors.initials: J
authors.lastname: Rodríguez-Díaz
authors.forename: Vicente
authors.initials: V
authors.lastname: Monedero
authors.forename: María J
authors.initials: MJ
authors.lastname: Yebra
mesh_terms: D000117:Acetylglucosamine / Q000031:analogs & derivatives* / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D004187:Disaccharides / Q000378:metabolism*; D005690:Galactose / Q000378:metabolism; D020869:Gene Expression Profiling; D055786:Gene Knockout Techniques; D005798:Genes, Bacterial; D006801:Humans; D007780:Lacticaseibacillus casei / Q000235:genetics* / Q000378:metabolism*; D008895:Milk, Human / Q000737:chemistry*; D009092:Mucous Membrane / Q000737:chemistry*; D005810:Multigene Family; D009154:Mutation; D009876:Operon; D010728:Phosphoenolpyruvate / Q000378:metabolism*; D011134:Polysaccharides; D060888:Real-Time Polymerase Chain Reaction; D001616:beta-Galactosidase / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004187:Disaccharides; D011134:Polysaccharides; C056853:6-O-galactopyranosylgalactose; C033398:galactosyl-1,3-N-acetylglucosamine; D010728:Phosphoenolpyruvate; D001616:beta-Galactosidase; D000117:Acetylglucosamine; D005690:Galactose