Lebeer Sarah, Verhoeven Tine L A, Francius Grégory, Schoofs Geert, Lambrichts Ivo, Dufrêne Yves, Vanderleyden Jos, De Keersmaecker Sigrid C J
Centre of Microbial and Plant Genetics, K.U. Leuven, Kasteelpark Arenberg, Belgium.
Appl Environ Microbiol. 2009 Jun;75(11):3554-63. doi: 10.1128/AEM.02919-08. Epub 2009 Apr 3.
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.
细胞表面多糖作为人类细菌病原体的毒力因子已有明确作用。关于有益细菌中表面多糖的生物合成和生物学功能的文献较少。我们鉴定了一个基因簇，该基因簇编码了在充分研究的益生菌鼠李糖乳杆菌GG胞外多糖（EPS）生物合成不同步骤中的酶、调节蛋白和转运蛋白。随后对编码该基因簇内起始糖基转移酶的welE基因进行突变，并对野生型菌株和突变菌株进行比较表型分析，证实了该基因簇在高分子量、富含半乳糖的杂聚EPS分子生物合成中的特定功能。表型分析包括单体组成测定、分离的EPS分子聚合物长度估计以及表面多糖的单分子力谱分析。对welE突变体的进一步表征还表明，缺乏这些长的、富含半乳糖的EPS分子会导致鼠李糖乳杆菌GG的黏附能力和生物膜形成能力增强，这可能是因为诸如菌毛样结构等黏附素的屏蔽作用减弱。
