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

胞外多糖可以改善食物的质地，并影响益生菌在肠道的定植。本研究计划的目的是了解EPS的结构特征如何决定其功能特性。通过控制多糖的附着、组成和分子质量，我们将能够研究这些参数对食品中胞外多糖的功能性质以及与人类粘膜细胞相互作用的影响。因此，基因工程可以作为一种工具来促进我们对胞外聚合物生物合成机制、多糖的生物活性以及食物质构和结构发展的了解。然而，EPS的产量在我们所研究的菌株中差异很大，这表明可能在调节和降解方面存在差异。我们将首先研究氧气和胆汁对基因表达的影响，因为这将有助于确定食品加工过程中所需的最佳条件，同时暗示EPS的产生可能通过消化系统发生变化。第二个目标是阐明调控基因wzr在控制EPS生物合成中的作用，以了解胞外多糖的产生如何与环境信号和代谢相协调。第三个目的是研究启动糖基转移酶在测定EPS分子质量中的作用。第四个目标是探索乳酸菌和益生菌中多糖伸长的独特方面。鼠李糖乳杆菌的EPS聚合复合体显示出与迄今为止研究的其他模型系统的有趣的不同。这可能会导致操纵EPS大小的方法，以在乳制品食品系统中进行测试，并粘连到人类粘膜细胞上。第五个目标是利用糖基水解酶生产低相对分子质量的EPS。这将有助于增粘成分的开发，这些成分可以影响发酵乳制品的流变性。了解益生菌和乳酸菌的基因功能和调控，对于改良酸奶和奶酪发酵剂微生物，防止食品变质和改善人类健康至关重要。

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.