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A gene cluster is identified that has encoded the enzymes and regulatory and transporter proteins for the different steps in the biosynthesis of extracellular polysaccharides (EPS) of the probiotic strain Lactobacillus rhamnosus GG. The characterization of the welE mutant has shown that deprivation of the long, galactose-rich EPS molecules has resulted in an increased adherence and biofilm formation capacity of Lactobacillus rhamnosus GG, because of less shielding of adhesins such as fimbria-like structures.

The comparative study of genuine luxS mutant and luxS mutant containing unknown suppressor mutations of the probiotic strain Lactobacillus rhamnosus GG with the wild type was conducted to examine the survival and persistence in the murine gastrointestinal tract. The results showed that shorter residence time of suppressor mutant luxS in the murine gastrointestinal tract contributes significantly to the biofilm formation and exopolysaccharides in the persistence capacity of L. rhamnosus GG.

The study presents a functional analysis of D-alanylation of lipoteichoic acid (LTA) in the probiotic strain Lactobacillus rhamnosus GG, which leads to several modifications in the bacterial cell surface properties. The results show that lack of such anylation highly affects the cell morphology, while it has no effect on the important probiotic characteristics.

Lipoteichoic acid (LTA) is a macroamphiphile molecule which performs several functions in gram-positive bacteria, such as maintenance of cell wall homeostasis. D-alanylation of LTA requires the proteins encoded by the dlt operon, and this process is directly related to the charge properties of this polymer strongly contributing to its function. The insertional inactivation of dltD of the probiotic strain Lactobacillus rhamnosus GG (ATCC 53103) resulted in the complete absence of D-alanyl esters in the LTA as confirmed by nuclear magnetic resonance analysis. This was reflected in modifications of the bacterial cell surface properties. The dltD strain showed 2.4-fold-increased cell length, a low survival capacity in response to gastric juice challenge, an increased sensitivity to human beta-defensin-2, an increased rate of autolysis, an increased capacity to initiate growth in the presence of an anionic detergent, and a decreased capacity to initiate growth in the presence of cationic peptides compared to wild-type results. However, in vitro experiments revealed no major differences for adhesion to human intestinal epithelial cells, biofilm formation, and immunomodulation. These properties are considered to be important for probiotics. The role of the dlt operon in lactobacilli is discussed in view of these results.