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 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.This study was supported by the Spanish Ministry of Economy and Competitiveness (MINECO)/FEDER through projects AGL2010-18696 and AGL2013-40657-R and by the Valencian Government through project ACOMP/2012/030. J.E.B. received a Santiago Grisolía Fellowship from the Generalitat Valenciana.Peer reviewe