Study On The Relationship Between Signal Molecule AI-2 And Exopolysaccharides Production By Lactic Acid Bacteria

Quorum-sensing(QS)is a mechanism used for bacterial cell communication.It has been found that QS system could regulate various metabolic processes of bacteria,and the signal molecule AI-2 is one of the important signal molecules in the QS system.Exopolysaccharide(EPS)is an important metabolite of lactic acid bacteria(LAB)with good prebiotic and food processing properties.Whether the QS system can regulate the production of EPS in LAB is still unknown,so it is of certain significance to explore the specific regulation mechanism.In this research,62 strains of LAB isolated from traditional fermented dairy products were used as the research objects,and EPS production and activity of signal molecule AI-2 were used as indicators to screen,and 4 strains with different characteristics were determined for subsequent experiments.Firstly,the correlation between EPS production,related gene expression and signal molecule AI-2 activity under different culture time were explored.Secondly,Quorum-sensing Inhibitors(QSIs)and exogenous signal molecule AI-2 were used to regulate the signal molecule AI-2 activity of strains.The effects on EPS production,the activity of signal molecule AI-2,cell morphology,expression of EPS synthesis-related genes and EPS biological activity were studied,and the effect of signal molecule AI-2 on EPS synthesis of LAB was explored.The main results are as follows:(1)By measuring the activity of signal molecule AI-2 and EPS production of 62 strains of LAB,4 strains of LAB were screened.L.plantarum RM3-1-3 was a strain with high yield of signal molecule AI-2 and EPS,L.fermentum TZ1-1-9 was a strain with high yield of signal molecule AI-2 but low yield of EPS,L.fermentum TG4-1-1was a strain with yield of signal molecule AI-2 but high yield of EPS,P.acidilactici11-3 was a strain with low yield of signal molecule AI-2 and EPS.(2)The relationship between the activity of signal molecule AI-2 and EPS production at different culture times showed that L.plantarum RM3-1-3 、 L.fermentum TZ1-1-9、L.fermentum TG4-1-1 and P.acidilactici 11-3 had the highest signal molecule AI-2 activity and EPS production at 10 h and 22 h respectively,EPS production reaching 186.389 mg/m L,195.863 mg/m L and 125.179mg/m L.L.fermentum TZ1-1-9 showed the highest signal molecule AI-2 activity and EPS production at 13 h and 19 h,EPS production reaching 126.171mg/m L.The expression of EPS synthesis-related genes with culture time was measured,and the results showed that L.plantarum RM3-1-3 and L.fermentum TG4-1-1with high EPS production had relatively higher levels of eps A,eps B,eps E and gt genes within 4～7h.The expression of L.fermentum TZ1-1-9 and P.acidilactici 11-3 with low EPS production had higher expression of eps B,eps E and gt genes in 4～7h.(3)The effects of different concentrations of QSIs on the high-producing signal molecule AI-2 of strain showed that furanone,D-ribose and D-galactose had no significant effect on the growth of L.plantarum RM3-1-3 and L.fermentum TZ1-1-9.It had an effect on the highest activity of signal molecule AI-2 and EPS production of L.plantarum RM3-1-3 and L.fermentum TZ1-1-9,but the effect was different.Among them,300μmol/L and 150μmol/L D-galactose had the most significant inhibitory effect on the highest activity of signal molecule AI-2 and EPS production of L.plantarum RM3-1-3 and L.fermentum TZ1-1-9(p<0.05),respectively.(4)The addition of exogenous signal molecule AI-2 had a certain effect on the activity of signal molecule AI-2 at 10 h and the EPS production at 22 h in L.fermentum TG4-1-1 and P.acidilactici 11-3,which produced signal molecule AI-2.Among them,100μmol/L of exogenous signal molecule AI-2 had the most significant promoting effect on the activity of signal molecule AI-2 and EPS production in the both strains(p<0.05).(5)The addition of D-galactose had no effect on the morphology of L.plantarum RM3-1-3 and L.fermentum TZ1-1-9,but reduced the adhesion between the bacteria.The expression of eps A,eps C,eps D and gt of EPS synthesis genes had been affected by D-galactose.The adhesion between L.fermentum TG4-1-1 and P.acidilactici 11-3was enhanced by the addition of exogenous signaling molecule AI-2.The expressions of eps A,eps B,eps E and gt of EPS synthesis genes had been up-regulated.The addition of QS inhibitors or exogenous signal molecule AI-2 had no significant effect on the growth of strains.