Effects Of Different Physiological And Environmental Stresses On The Production Of Signal Molecules AI-2 In Lactic Acid Bacteria

In this study, Vibrio harveyi BB170 were used as bio luminescent control to test the AI-2 production from eight lactic acid bacteria(LAB),which were isolated from koumiss, then screened and identified high-yield strains with AI-2,the signaling molecules.The results showed that eight LAB could produce AI-2,1-3-2、2-1 and 8-3 strains produced the relatively more quantity of AI-2. Identified with molecular identification method, the mentioned strains were Pediococcus acidilactici, Lactobacillus fermentum, Enterococcus faecium respectively.The co-cultureeffect on AI-2 production of L.fermentum 2-land E. faecium 8-3 was analyzed under two conditions,which was added metabolites of yeast or co-cultured with yeast,the yeast strain number were J6,J8 and J14.Within a certain time, the metabolites of yeast J8 and J14 had significantly promotional effect on the L.fermentum 2-1 and E. faecium 8-3. The promoting effect was obviously observed at 19h during J8 and J14 co-cultured with L.fermentum 2-1(P< 0.01),while yeast J6 had inhibitory effect on Lfermentum 2-1 after co-cultured 25h, a period of time the AI-2 production was inhibited when yeast J8,J14 and E. faecium 8-3 were co-cultured.Changed the culture condition such as pH,osmotic pressure,temperature, nutrient concentration to study the AI-2 production of tested strains when subjected to environmental stress.(1)In low pH cultivation, bacteria density was not the primary Factor of inducing AI-2. AI-2 could produced more when L.fermentum 2-1 and E. faecium 8-3 encountered acid stress.While the densities of L.fermentum 2-1 and E. faecium 8-3 were both positively correlated with fluorescence intensity under alkaline conditions,which indicates the primary factorof inducing AI-2 production of L.fermentum 2-1 and E. faecium 8-3,was bacteria density under alkaline environment.(2)When subjected to osmotic pressure,the AI-2 production of L.fermentum 2-land E. faecium 8-3 were mainly promoted or inhibited by bacteria densities.(3)When L.fermentum 2-1 and E.faecium 8-3 were under temperature stress, the AI-2 production was mainly influenced by bacteria densities.(4)AI-2 production of L.fermentum 2-1 were induced by low nutritional conditon,especially could excrete large amount of AI-2 when the medium concentration was down to 40%,at this exactlypoint was the threshold value of AI-2 induction.