An l-Fucose Operon in the Probiotic Lactobacillus rhamnosus GG Is Involved in Adaptation to Gastrointestinal Conditions

摘要

l-Fucose is a sugar present in human secretions as part of human milk oligosaccharides, mucins, and other glycoconjugates in the intestinal epithelium. The genome of the probiotic Lactobacillus rhamnosus GG (LGG) carries a gene cluster encoding a putative l-fucose permease ( fucP ), l-fucose catabolic pathway ( fucI , fucK , fucU , and fucA ), and a transcriptional regulator ( fucR ). The metabolism of l-fucose in LGG results in 1,2-propanediol production, and their fucI and fucP mutants displayed a severe and mild growth defect on l-fucose, respectively. Transcriptional analysis revealed that the fuc genes are induced by l-fucose and subject to a strong carbon catabolite repression effect. This induction was triggered by FucR, which acted as a transcriptional activator necessary for growth on l-fucose. LGG utilized fucosyl-α1,3- N -acetylglucosamine and contrarily to other lactobacilli, the presence of fuc genes allowed this strain to use the l-fucose moiety. In fucI and fucR mutants, but not in fucP mutant, l-fucose was not metabolized and it was excreted to the medium during growth on fucosyl-α1,3- N -acetylglucosamine. The fuc genes were induced by this fucosyl-disaccharide in the wild type and the fucP mutant but not in a fucI mutant, showing that FucP does not participate in the regulation of fuc genes and that l-fucose metabolism is needed for FucR activation. The l-fucose operon characterized here constitutes a new example of the many factors found in LGG that allow this strain to adapt to the gastrointestinal conditions.