Roles of luxS in regulation of probiotic characteristics and inhibition of pathogens in Lacticaseibacillus paracasei S-NB

Lactic acid bacteria (LAB) have excellent tolerance to the gastrointestinal environment and high adhesion ability to intestinal epithelial cells, which could be closely related to the LuxS/AI-2 Quorum sensing (QS) system. Here, the crucial enzymes involved in the synthesis of AI-2 was analyzed in Lacticaseibacillus paracasei S-NB, and the luxS deletion mutant was constructed by homologous recombination based on the Cre-lox system. Afterwards, the effect of luxS gene on the probiotic activities in L. paracasei S-NB was investigated. Notably, the tolerance of simulated gastrointestinal digestion, AI-2 production, ability of auto-aggregation and biofilm formation significantly decreased (p < 0.05 for all) in the S-NB triangle luxS mutant. Compared to the wild-type S-NB, the degree of reduction in the relative transcriptional level of the biofilm -related genes in Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923 was diminished when co-cultured with S-NB triangle luxS. Furthermore, the inhibitory effect of S-NB triangle luxS on the adhesion (competition, exclusion and displacement) of E. coli ATCC 25922 and S. aureus ATCC 25923 to Caco-2 cells markedly decreased. Therefore, comprehensive analysis of the role by luxS provides an insight into the LuxS/AI-2 QS system of L. paracasei S-NB in the regulation of strain characteristics and inhibition of pathogens.