Pili of Lactobacillus rhamnosus GG mediate interaction with β-lactoglobulin

• Interactions between a probiotic strain and milk food matrices were studied.
• Use of AFM to study interaction between Lactobacillus rhamnosus GG and isolated whey proteins.
• Specific interactions between L. rhamnosus GG and β-lactoglobulin.
• Key role of pili in interaction with β-lactoglobulin.
• No specific interaction with α-lactalbumin and bovine serum albumin.

Recently dairy products like cheese, yogurt or milk proteins are increasingly used to encapsulate probiotic bacteria to promote their survival. The knowledge of interactions occurring between bacteria and milk matrices is essential for the formulation of efficient new products. In this work, Atomic Force Microscopy was used to study interactions between Lactobacillus rhamnosus GG and isolated whey proteins: β-lactoglobulin (β-LG), α-lactalbumin (α-LA) and bovine serum albumin (BSA). For the first time, it was clearly demonstrated that L. rhamnosus GG is able to interact with the β-LG but not with α-LA and BSA. To identify the bacterial surface biomolecules involved in interaction with β-LG, two of its surface mutants were used: a pili depleted strain (L. rhamnosus GG spaCBA) and an exopolysaccharides (EPS) depleted strain (L. rhamnosus GG welE). Two predictive models, FJC and WLC, were used to describe behaviors of the molecule stretched by providing parameters like contour length (Lc), adhesion force (Fadh), Kuhn length (lk) and Persistence length (lp). The absence of adhesion events between β-LG and mutants having no pili reflects the crucial role of this biomolecule for interactions with the protein.

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