| Lactic acid bacteria are a group of gram-positive bacteria that are facultatively anaerobic and capable of fermenting carbohydrates to produce lactic acid and have the potential to be developed as probiotics and starter cultures.The quorum sensing phenomenon is ubiquitous in lactic acid bacteria and is involved in regulating a variety of physiological behaviors of lactic acid bacteria.Existing studies have shown that lactic acid bacteria use AI-2 quorum sensing signal molecules to exchange information with other bacteria in the surrounding environment,and from the signals fed back by AI-2 molecules to regulate the expression of corresponding genes in the bacteria,so that the bacteria are more suitable for the surrounding environment.However,at present,AI-2 mediated quorum sensing systems mostly focus on the study of pathogenic bacteria,and related research involving lactic acid bacteria has just started.In recent years,lactic acid bacteria has become a research hot spot as a kind of probiotic with great potential.With the deepening of research,researchers turn to focus on the resistance mechanism of lactic acid bacteria,and expect to breed the strain with a strong ecological footprint in the intestine and resistance to stomach acid and bile salts.Based on the important role of Lactobacillus AI-2 in regulating the anti-stress of bacteria,it is of great significance to study the AI-2 mediated quorum sensing system of lactic acid bacteria.In this study,2 strains of AI-2 high-producing strains were screened out from laboratory-preserved lactic acid bacteria strains,and the expression of luxS,a key gene for AI-2 signal synthesis,was detected.By constructing luxS overexpression strains and screening AI-2 Signal inhibitors,We study the relationship between the luxS/AI-2 QS system and the physiological characteristics of lactic acid bacteria.The specific research content and main results are as follows:Through the optimization of fluorescence detection methods,two strains of Lactobacillus strains producing high AI-2 signal were screened from the strains of laboratory strains.The luxS expression of the high-yield AI-2 signal lactic acid bacteria was found to be strong by the RT-PCR assay,indicating that the lactic acid bacteria are Contains luxS gene and is a key gene for AI-2 signal synthesisBy screening AI-2 signal inhibitors and constructing luxS overexpression strains,the survival rate of lactic acid bacteria after treatment under different stress environment treatment was tested,and the effect of luxS/AI-2 QS on the stress tolerance of lactic acid bacteria was analyzed.The results showed that AI-2 signal inhibitors weakened the anti-stress ability of lactic acid bacteria,luxS over-expression strains increased the anti-stress ability of lactic acid bacteria to stresses,which was conducive to the lactic acid bacteria regulating intestinal acid-base balance and bacterial population balance through quorum sensing signals.Through the analysis of the biofilm formation of lactic acid bacteria,the results showed that luxS overexpression strains had strong biofilm formation,indicating that luxS/AI-2 participated in the biofilm formation of lactic acid bacteria,and luxS mainly affected transport and membrane-associated proteins,indicating luxS overexpression may be through regulation of cell membrane-associated proteins and membrane transporters,thereby regulating the adaptation and response of the cells to the extracellular environment,helping the cells to resist external environmental stress.After co-cultivation of lactic acid bacteria and E.coli,the survival rate of Escherichia coli was examined.The results showed that lactic acid bacteria and luxS over-expression strains with high AI-2 production have a strong growth inhibitory effect on E.coli,and also have a certain inhibitory effect on the film formation of E.coli organisms.This study was the first to investigate the relationship between luxS/AI-2 QS system and lactic acid bacteria's resistance to stresses and biofilm formation.The study results have important theoretical significance and reference value for further studying on the anti-stress mechanism of lactic acid bacteria and selectively breeding of lactic acid bacteria with anti-stress ability. |
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