Optimization Of Fermentation Conditions And Research Of Induction Regulation For Bacteriocin Production By Lactobacillus Plantarum B23

At present, bacteriocins of lactic acid bacteria are the most popular natural food preservative in the food industry. They are ribosomally synthesized bioactive peptides or proteins with antimicrobial activity against many Gram-positive species, which have lots of advantages including non-toxic, no residue, non-resistance, high stability, etc. Therefore bacteriocins of lactic acid bacteria have became very important in the research and development of the field of microbial food preservative. However, the commercial application of bacteriocins can be hampered by low production. Thus, the development of low-cost culture medium and the research approach of increasing of bacteriocins production by lactic acid bacteria is always the focus in the lactic acid bacteria bacteriocins research field.In our laboratory, a bacterial strain producing bacteriocin Lac-B23 had been isolated from fermented milk and the strain had been named Lactobacillus plantarum B23 after bacterial identification. But bacteriocin Lac-B23 production was low. So one variable at a time(OVAT) approach, Plackett-Burman, Steepest ascent and Central Composite Design were used to obtain a best culture media for bacteriocins production. Results of the experiment indicated that we got a novel modify MRS(m MRS): glucose 20 g/L, yeast extract 10 g/L, dipotassium phosphate 5 g/L, manganese sulfate 0.1 g/L, Tween 80 1.88 m L/L, Sodium acetate anhydrous 9.9 g/L. On this condition, bacteriocin Lac-B23 production increased from 280 AU/m L to 2560 AU/m L, and the cost drastically reduced from 12. 26 RMB of MRS broth to 5.16 RMB of m MRS. After that, we researched the effect of initial p H, temperature and initial inoculum size on bacteriocin production. Results showed that bacteriocin production reached the maximum when initial p H=7, 37℃and 109 CFU/m L.We researched the effect of exogenous inducer on bacteriocin production. We found that tyrosine, arginine, phenylalanine, glutamine and leucine were favored for the synthesis of bacteriocin; glutamate, aspartate, cysteine, glycine, aspartyl and methionine inhibited bacteriocin production. In addition, glycerinum and pyruvic acid had no effect on bacteriocin production. We also found that we could not detect bacteriocin activity when initial inoculum size < 106 CFU/m L, which illustrated synthesis of bacteriocin depended on initial cell concentration. After that, signal molecule(autoinducing peptide) was added to m MRS, results showed that adding 5% and 10% signal molecule could increase bacteriocin production. Moreover, protease E and protease K could degrade signal molecule, which indicated signal molecule was a kind of polypeptide or protein.At last, we researched influence of co-culture on bacteriocin production. We found bacteriocin production could be increased when lactobacillus plantarum was cocultivated with Listeria monocytogenes and Staphylococcus aureus, and initial induction bacteria concentration strongly affected bacteriocin production. In addition, we proved that inducers were no released into medium, and only live induction bacteria could improve bancteriocin production.