Identification of a Gene Cluster for the Biosynthesis of a Long, Galactose-Rich Exopolysaccharide in Lactobacillus rhamnosus GG and Functional Analysis of the Priming Glycosyltransferase

• Published in: Applied and Environmental Microbiology Vol. 75; no. 11; pp. 3554 - 3563
• Main Authors: Lebeer, Sarah, Verhoeven, Tine L.A, Francius, Grégory, Schoofs, Geert, Lambrichts, Ivo, Dufrêne, Yves, Vanderleyden, Jos, De Keersmaecker, Sigrid C.J
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.06.2009; American Society for Microbiology (ASM)
• Subjects: Adhesins; Bacteria; Bacterial Adhesion; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Biofilms - growth & development; Biological and medical sciences; Biosynthetic Pathways - genetics; Caco-2 Cells; Carbohydrates; Cells; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; Fundamental and applied biological sciences. Psychology; Galactose - analysis; Gene Knockout Techniques; Gene Order; Genes; Genetic Complementation Test; Genetics and Molecular Biology; Glycosyltransferases - genetics; Glycosyltransferases - metabolism; Humans; Lacticaseibacillus rhamnosus - enzymology; Lacticaseibacillus rhamnosus - genetics; Lacticaseibacillus rhamnosus - physiology; Lactobacillus rhamnosus; Microbiology; Models, Biological; Molecular Sequence Data; Molecular weight; Multigene Family; Mutagenesis, Insertional; Mutation; Polysaccharides, Bacterial - biosynthesis; Polysaccharides, Bacterial - chemistry; Sequence Analysis, DNA; Gene cluster; Lactic acid bacteria; Enzyme; Transferases; Glycosyltransferases; Functional analysis; Biosynthesis; Identification; Extracellular; Bacteria; Lactobacillaceae; Galactose; Polysaccharide; Lactobacillus rhamnosus
• ISSN: 0099-2240; 1098-5336; 1098-6596
• DOI: 10.1128/AEM.02919-08

Cell surface polysaccharides have an established role as virulence factors in human bacterial pathogens. Less documented are the biosynthesis and biological functions of surface polysaccharides in beneficial bacteria. We identified a gene cluster that encodes the enzymes and regulatory and transporter proteins for the different steps in the biosynthesis of extracellular polysaccharides (EPS) of the well-documented probiotic strain Lactobacillus rhamnosus GG. Subsequent mutation of the welE gene, encoding the priming glycosyltransferase within this cluster, and comparative phenotypic analyses of wild-type versus mutant strains confirmed the specific function of this gene cluster in the biosynthesis of high-molecular-weight, galactose-rich heteropolymeric EPS molecules. The phenotypic analyses included monomer composition determination, estimation of the polymer length of the isolated EPS molecules, and single-molecule force spectroscopy of the surface polysaccharides. Further characterization of the welE mutant also showed that deprivation of these long, galactose-rich EPS molecules results in an increased adherence and biofilm formation capacity of L. rhamnosus GG, possibly because of less shielding of adhesins such as fimbria-like structures.