This study systematically investigated the effect of interfering with autoinducer-2 (AI-2) signaling system on controlling initial fouling attachment and irreversible components. Exposure of bacteria to the inhibitor significantly reduced the expression of the luxS gene, which resulted in a 37.3% reduction of AI-2 signaling molecule synthesis. Expression of flagellin and kinesin, which determine bacteria adhesion properties, and virulence genes was significantly down-regulated. AI-2 quorum quenching (QQ) significantly suppressed the initial biofilm growth and inhibition efficiency was positively correlated with bacteria concentration. Extracellular polymeric substances accumulation decreased by 40.8% in QQ experiment relative to the control, thus mitigating the flux decline. Polysaccharides, which constitute irreversible components, were significantly reduced by 69.3% with presence of inhibitor. AI-2 QQ altered protein and peptide structure of fouling layer, which converted irreversible fouling into reversible fouling. These findings contributed to the understanding of QQ susceptibility to initial fouling, providing a theoretical basis for engineering applications.
Xueqi Lu,Mengying Sun,Yuqing Chen,Dashuai He,Yanfeng Tuo,Guangqing Mu,Yinglong Song
Fermented milk is a typically product of co-fermentation by a variety of lactic acid bacteria (LAB). Quorum sensing (QS), as an intercellular communication mechanism of bacteria, may serve as a key factor influencing the quality of fermented milk. In this study, the fermentation performance of Lactobacillus delbrueckii subsp . bulgaricus DPUL-F36 were evaluated after supplementation with auto-inducer-2 (AI-2). The protein-protein interaction network (PPIN) was used to retrieve the interactions between QS genes and four major metabolic pathway genes. The expression of luxS gene in DPUL-F36 may affect amino acid metabolism, carbohydrate metabolism and cell wall formation. The key differential metabolites were identified by metabolomics analysis. A variety of amino acids including L-Glutamic, L-Tryptophan, L-Threonine, L-Histidine and L-Glutamine were found to be up-regulated in response to the addition of AI-2. Malic acid and succinate gradually accumulate in the tricarboxylic acid cycle. The consumption of citric acid increased with the fermentation process. In terms of rheological and texture characteristics of fermented milk, addition of AI-2 could effectively improve its shear stress resistance, firmness and index of viscosity. Our research provided a theoretical basis for improving the fermentation performance of DPUL-F36 strains, and support for the screening of excellent composite starter culture.
Lactobacillus plantarum R is the predominant bacterium widely used in food fermentation. However, it has a low tolerance to ethanol during fermentation, which restricts its broader application in the food industry. Although biofilm formation enhances bacterial resistance to various stresses, regulating biofilm formation in L. plantarum R remains challenging. In this study, we established a pathway for producing autoinducer 2 (AI-2), a quorum-sensing (QS) signaling molecule, by heterologously expressing pfs and LuxS in L. plantarum R. This approach aimed to modulate cell membrane structure and improve bacterial ethanol resistance. The findings showed that exogenous AI-2 significantly enhanced the growth of L. plantarum R under high-ethanol concentration and improved its biofilm formation at different ethanol concentrations. Furthermore, a multi-omics analysis revealed potential mechanisms by which AI-2 improved the tolerance of L. plantarum R to ethanol. Notably, the upregulation of the crr gene, a component of the phosphotransferase system (PTS), enhanced biofilm formation in response to ethanol stress. In addition, differential metabolites enriched in cysteine and methionine metabolic pathways further supported the role of QS in enhancing the tolerance of L. plantarum R to ethanol. These findings lay the groundwork for enhancing the fermentation performance of strains applied in the food fermentation industry, presenting a novel method for expanding the utilization of L. plantarum R in high-ethanol fermentation.
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