Mechanism insights into the regulation of the LuxS/AI-2 quorum sensing system on the formation of viable but nonculturable state in biofilm cells of beer-spoilage Lactiplantibacillus plantarum

Lactiplantibacillus plantarum is a major beer spoilage bacterium that poses significant challenges to industrial brewing processes. This study investigated the function of the luxS gene in regulating the transformation of biofilm cells to a viable but non-culturable (VBNC) state induced by iso-α-acids from hops. Scanning electron microscopy revealed increased cell adhesion in biofilms versus planktonic cells, with VBNC cells exhibiting surface protrusions and reduced volume. Temporal analysis showed synchronized upregulation of luxS expression and AI-2 levels during VBNC induction, peaking at 4 hours before declining. Exogenous AI-2 facilitated biofilm-to-VBNC transition and revival, whereas luxS manipulation disrupted these processes, indicating luxS regulates VBNC dynamics via AI-2 biosynthesis in the quorum sensing (QS) system. A luxS -overexpressing strain was engineered to explore molecular mechanisms. Multi-omics analyses (transcriptomics, proteomics, ChIP-seq) demonstrated that luxS directly activates genes involved in carbohydrate metabolism and stress responses, promoting energy homeostasis and stress resilience in the VBNC state. Differential gene enrichment analysis identified luxS -regulated genes upregulated during VBNC entry, forming a regulatory network linked to QS and biofilm formation. This study integrates the multi-omics data, systematically elucidating the LuxS-AI-2 axis in VBNC-state establishment, providing a molecular framework for understanding beer spoilage and controlling biofilm-associated industrial contamination.