Exopolysaccharide production and degradation by lactic acid and probiotic bacteria: a functional approach to improve their applications in food and health

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Exopolysaccharides can improve food texture and influence intestinal colonisation by probiotic bacteria. The aim of this research program is to understand how EPS structural characteristics determine their functional properties. By manipulating the attachment, composition and molecular mass of polysaccharides, we will be able to investigate the effect of these parameters on the functional properties of exopolysaccharides in food and in interactions with human mucosal cells. Genetic engineering can thus be used as a tool for advancing our understanding of the mechanisms of exopolymer biosynthesis, the biological activities of polysaccharides as well as of the development of food texture and structure. However, EPS yield varies greatly among the strains we have studied, indicating possible differences in regulation and degradation. The effect of oxygen and bile on gene expression will first be examined, as this will help determine the optimal conditions necessary in food processes, while suggesting how EPS production may change through the digestive system. The second objective is to elucidate the role of the regulator gene wzr in controlling EPS biosynthesis to understand how exopolysaccharide production is coordinated by environmental signals and metabolism. The third objective is to investigate the role of the priming glycosyltransferase enzyme in determining EPS molecular mass. The fourth objective is to explore the unique aspects of polysaccharide elongation in lactic acid and probiotic bacteria. The EPS polymerisation complex of Lactobacillus rhamnosus shows intriguing differences from other model systems studied to date. This may lead to means of manipulating EPS size for testing in dairy food systems and in adhesion to human mucosal cells. The fifth objective is to produce EPS with lower molecular mass using glycosylhydrolases. This will contribute to the development of viscosifying ingredients that can influence the rheological properties of fermented milk products. Understanding gene function and regulation in probiotic and lactic acid bacteria is essential for improving yogurt and cheese starter microorganisms, as well as for preventing food spoilage and improving human health.