Pili of Lactobacillus rhamnosus GG mediate interaction with β-lactoglobulin

Abstract

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.