Study On The Optimization Of Phenyllactate Production By Lactobacillus Plantarum And The Function Of Key Genes For Synthesis

PLA is a new type of natural biological preservative discovered in recent years.It has a wide range of antibacterial properties.It not only inhibits gram-negative bacteria,but also inhibits the growth of Gram-positive bacteria and fungi.In this thesis,Lactobacillus plantarum YM-4-3 was used as the research object.The effect of different glucose concentration on the production of Lactobacillus plantarum PLA in MRS medium was determined by HPLC.The results showed that with the increase of glucose concentration in the medium,PLA production increased first and then decreased.When the glucose concentration was 30 g/L,the highest PLA production was 74.5391 mg/L.In order to explore the molecular mechanism for the synthesis of PLA from glucose,in this study,we selected two genes whose expression levels are positively regulated by glucose—prephenate dehydrogenase gene(Pdh)and citrate transporter protein gene(Citp).Expression and knockout studies.The results of heterologous expression showed that Pdh could be induced in L.lactis NZ9000.When the concentration of inducer Nisin was 20 ng/m L,the concentration of substrate prephenate barium salt was 0.1 mg/m L,and the concentration of chloramphenicol was 10 ?g/m L,the heterologous expression effect of the engineering bacterium NZ9000/p NZ8048-Pdh was the best.The contents of PLA and OH-PLA were 37.7707 and 19.548 mg/L,which were 2.6 and 2.4 times of the host strain NZ9000 respectively.The antibacterial effect of pathogenic bacteria showed that was significantly improved after induction.The citric acid transporter knockout results showed that there was no significant difference in the growth characteristics of the knockout strains,but the production of PLA and OH-PLA was far lower than that of the wild strain.In addition,the results of scanning electron microscopy and transmission electron microscopy showed that the knockout strains had a certain amount of plasmolysis,outflow of internal dissolution,and cell membrane folds.This paper studied the effect of external conditions on the production of PLA by L.plantarum YM-4-3,and the role of two key genes in the biosynthesis of PLA were researched,which provided a theoretical basis for future industrial production of PLA.