Exploration of the mechanism by which quorum sensing signals AI-2 and AIP enhance ethanol tolerance of Lacticaseibacillus paracasei 5

Lacticaseibacillus paracasei (L. paracasei) plays an indispensable role in food fermentation and probiotic formulations. Nonetheless, its industrial utilization is frequently limited by its low tolerance to ethanol. Given that biofilm formation constitutes a critical survival mechanism for bacteria under stress conditions, this study sought to examine the impact of exogenous autoinducer-2 (AI-2) and autoinducing peptides (AIP) on the biofilm formation of L. paracasei in the presence of ethanol stress. The findings revealed that both AI-2 and AIP substantially enhanced biofilm formation, increased membrane fluidity, and augmented exopolysaccharide (EPS) production under ethanol stress conditions. Transcriptomic analysis further revealed distinct regulatory mechanisms: AI-2 primarily upregulated genes encoding ABC transporters (e.g., potABCD, phnCDE, oppABCDF), which support ATP-driven uptake of compounds essential for cellular homeostasis under ethanol stress. In contrast, AIP mainly activated genes involved in the phosphotransferase system (PTS) (e.g., BglF, MtlA, CelB, CelC), facilitating carbohydrate uptake and central carbon metabolism to meet the biosynthetic demands of EPS and biofilm matrix assembly. This work would provide important insights into the stress adaptation mechanisms mediated by quorum sensing (QS) in L. paracasei 5.