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

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 probioticLactobacillus rhamnosus GG (LGG) carries a gene cluster encoding a putativel -fucose permease (fucP ),l -fucose catabolic pathway (fucI ,fucK ,fucU , andfucA ), and a transcriptional regulator (fucR ). The metabolism ofl -fucose in LGG results in 1,2-propanediol production, and theirfucI andfucP mutants displayed a severe and mild growth defect onl -fucose, respectively. Transcriptional analysis revealed that thefuc genes are induced byl -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 onl -fucose. LGG utilized fucosyl-α1,3-N -acetylglucosamine and contrarily to other lactobacilli, the presence offuc genes allowed this strain to use thel -fucose moiety. InfucI andfucR mutants, but not infucP mutant,l -fucose was not metabolized and it was excreted to the medium during growth on fucosyl-α1,3-N -acetylglucosamine. Thefuc genes were induced by this fucosyl-disaccharide in the wild type and thefucP mutant but not in afucI mutant, showing that FucP does not participate in the regulation offuc genes and thatl -fucose metabolism is needed for FucR activation. Thel -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.