Supplementary materials for "The key quorum sensing gene <i>luxS</i> in <i>Lactobacillus acidophilus</i> CICC6074 and <i>Lactobacillus helveticus</i> R0052 mediates organic acid production and promotes protein hydrolysis in yogurt"

In this study, the effect of <i>luxS</i>, a key gene for QS, on the characteristic flavor of yogurt and its molecular mechanism in the co-fermentation of yogurt with Lactobacillus acidophilus CICC6074 and <i>Lactobacillus helveticus</i> R0052 engineered probiotics was investigated. Using the pMG36e plasmid as a vector and employing gene editing technology, we have initially constructed the <i>luxS</i> gene overexpression strains <i>L. acidophilus</i> CICC6074-pMG36e-<i>luxS</i> and<i> L. helveticus </i>R0052-pMG36e-<i>luxS</i>. Their effects on yogurt quality, including pH, titratable acidity, viable bacterial count, texture, water-holding capacity, and protein hydrolysis, were further explored. In addition, HS-SPME-GC-MS and UHPLC-MS, combined with metabolomics, were used to elucidate its effects and molecular mechanisms on the production of volatile and non-volatile flavor substances. By enhancing AI-2 signal transmission, we improved the flavor of yogurt, increased the survival rate and metabolic efficiency of probiotics, thereby enhancing the overall quality and functionality of the yogurt. This study provides a theoretical foundation and technical support for manipulating the LuxS/AI-2 system in yogurt production and probiotic engineering, offering a new approach for developing probiotic strains with enhanced health benefits, and holds broad application prospects.