Study On Symbiotic Screening And Signaling Molecular AI-2 Between Lactic Acid Bacteria And Yeasts

There are many reasons and mechanisms in symbiotic microoganisms. Most researchers study the symbiosis on trophic interactions or cooperative metabolism, they barely from the aspect of quorum sensing (QS) to investigate. In this experiment, QS was examined to lay the foundation for the further study of symbiotic mechanisms.Nine lactic acid bacteria (LAB) strains and eight yeast strains isolated from koumiss were screened twice to select the symbiotic strains. Metabolites were added to the culture mediums with the addition of the same amount of saline as control groups. Turbidity values and dry weight values were measured in the stationary phase. Better symbiotic combinations in the first sceening were chosen to rescreen within the viable count as an indicator, then detected influence on producing signaling molecule AI-2 by symbiotic strains. Influences on producing signaling molecule AI-2 by monoxenie, monoxenie with metabilites and co-cultivaton were detected within Vibrio harveyi BB170 as an indicator.The results showed that there were twelve combinations that LAB metabolites benefited the yeasts. There were thirty-four yeasts metabolites benefited the growth of LAB during seventy-two potential symbiotic combinations. While seven combinations showed mutual positive interactions. Three pairs of symbiotic strains were selected in the rescreening, which were LAB4 and YST2, LAB7 and YST2, LAB9 and YST2. They were picked out to do further researches. All of LAB4 LAB7 and LAB9 could produce signaling molecule AI-2 and LAB4, LAB7 could produce more. Moreover, relative fluorescence intensity positively correlated with cell desity in intial growth. The strains peaked the relative fluorescence intensity at stationary phase (18h). YST2 didn’t produce signaling molecule AI-2. While the metabolites of YST2 could promote LAB’s producing signaling molecule AI-2, especially LAB4 and LAB7 (P<0.01). The reason maybe was the yeast stimulated the growth of LAB. Co-cultured YST2 and LAB4, YST2 and LAB9 significantly promoting LAB’s producing signaling molecule AI-2 (P<0.01). While co-cultured YST2 and LAB7 had both promotions and suppressions, the reason need to be further studied.