The Effects Of Environmental Stress On The Production Of Biofilm,Signal Molecule AI-2 And EPS In Lactic Acid Bacteria

Lactic Acid Bacteria(LAB)has many probiotic functions,but its growth is easily changed by environmental stresses.The biofilm of LAB can effectively protect the cells of strain to resist the adverse environment and keep probiotic functions.Signal molecule Autoinducer-2(AI-2),an important signaling substance for quorum sensing,is involved in regulating various physiological functions including bacterial biofilm formation.In this research,Lactobacillus plantarum 5-4-1 and Pediococcus acidilactici TG1-1-10 isolated from fermented dairy products were used for investigating the changes of biofilm formation,exopolysaccharide(EPS)production and AI-2 activity under different environmental conditions.Meanwhile,the maximum amount of biofilm was used as an indicator to obtain the best environmental condition through a four-factor three-level orthogonal optimization test.The tested factors included pH value,temperature,NaCl mass fraction and nutrient concentration.The main results are as follows:Different pH value and culture temperature stress had no significant effect on the biofilm formation of the two tested strains;At pH 4.5,pH 5.5 and temperature stress,the bacterial density,extracellular polysaccharide and the secretion of signal molecule ai-2 of the two strains were correspondingly reduced.The biofilms of L.plantarum 5-4-1 and P.acidilactici TG1-1-10 were induced to form more under the NaCl mass fraction was 3.0%and 4.5%respectively;The bacterial density was inhibited with the increase of NaCl mass fraction;Under certain NaCl mass fraction stress,the secretion rate of AI-2 and EPS was increased.With the increase of NaCl mass fraction,the secretion of EPS and AI-2 was inhibited.There was no significant effect on biofilm formation under different nutrient stresses;Both the bacterial density and the planktonic cells EPS were inhibited with the decrease of nutrient concentration;The biofilm cells EPS production increased under the condition of the nutrient concentration was 80%.With the increase of nutrient concentration,the secretion of EPS was inhibited;The strains secreted more AI-2 in nutrient mass fraction was 20%and 40%.Through orthogonal optimization experiments,the optimal environmental condition for the formation of L.plantarum 5-4-1 biofilms was obtained.The optimum conditions for biofilm formation were pH value of 7.5,culture temperature of 44?,NaCl mass fraction of 1.5%and nutrient concentration of 100%.The optimal condition for P.acidilactici TG1-1-10 biofilm formation were pH value of 7.5,culture temperature of 30?,NaCl mass fraction of 4.5%,and nutrient concentration of 80%.