Study On Genome And Carbohydrate Metabolism Of Lactiplantibacillus Plantarum LP-F1 And Its Application In Fermented Milk

Lactiplantibacillus plantarum is recognized as a probiotic,which can maintain the balance of human intestinal flora,regulate immunity,lower blood lipids,regulate blood pressure.At present,L.plantarum has been widely used in the food industry,which endows the product with excellent quality,unique flavor and probiotic properties.Therefore,to obtain L.plantarum strains with excellent production characteristics is of great significance and application value for the development of food industry and functional products.L.plantarum LP-F1 with good properties was isolated from fermented milk in our laboratory.In this study,the strain was deeply studied for laying a foundation for its further application.In order to understand the genetic characteristics of the strain at the whole genome level,the whole genome of the strain was sequenced,and its CRISPR-Cas system,prophage,potential virulence factors,drug resistance genes and bacteriocin biosynthesis ability were analyzed.The results showed that the strain has not complete CRISPR-Cas system,bacteriophage fragments and potential virulence factors.The strain contains the bacteriocin biosynthesis genes.Compared with other lactic acid bacteria,L.plantarum has a strong carbohydrate utilization ability.This characteristic plays an important role in its colonization in the gastrointestinal tract and its probiotic effect.In this study,the carbohydrate utilization ability of six L.plantarum strains LP-F1,LP-E1,LP-A4,LP-I5,LP-1 and LP-4 was evaluated.The results showed that LP-F1 had a strong carbohydrate utilization ability,and can utilize efficiently glucose,fructose and sucrose,and prebiotic fructooligosaccharides.The growth ability analysis showed that LP-F1 entered the logarithmic phase at about 4 h and the stable phase at about 10 h.Under the condition of using glucose or sucrose as a carbon source,the growth ability of this strain is the most active.In order to determine the expression of key sugar metabolism genes of LP-F1 strain under different carbon source fermentation conditions,real-time fluorescent quantitative PCR technology was used to analyze the gene expression.Compared with the condition of the sugar-free medium,the expression of most sugar metabolism genes were upregulated in the sugar-containing medium at 4 h.With the extension of fermentation time,the expression of most genes in sugar-containing medium decreased significantly.The correlation analysis of sugar metabolism gene expression showed that pts11 BC was negatively correlated with most genes,but only positively correlated with agl4,while agl4 was negatively correlated with most genes,indicating that the expressions of pts11 BC and agl4 are different from those of other genes.Fructooligosaccharides metabolism related genes sac A,sac R1,sac K1,pts1 BCA and mal Z were positively correlated with each other,indicating that the expressions of these genes have the same trend in the process of metabolism.At the same time,the expression of two-component signal transduction system under different sugar fermentation conditions were analyzed.The results showed that compared with the sugar-free fermentation medium,the expressions of most two-component signal transduction systems encoding genes were up-regualted in the sugar-containing fermentation media,such as hpk2/rr2,pln BCD and rr3/hpk3.Furthermore,the expression trend of hpk and rr was consistent in most two-component signal transduction systems.The correlation analysis between regulatory genes and sugar metabolism genes indicated that rr1/hpk1,rr2/hpk2,pln BCD and rr3/hpk3 were positively correlated with most sugar metabolism genes,while rr6/hpk6,hpk7,lam R/lam K,hpk11 and yes N/yes M were negatively correlated with most sugar metabolism genes.It is speculated that the twocomponent signal transduction system might be involved in the regulation of sugar metabolism.The above results demonstrated that the utilization of sugar in the strain is a complex process,which is closely related to the sugar transport,decomposition,metabolism and regulatory related genes.The application possibility of L.plantarum LP-F1 in fermented milk was studied.In this study,skim milk was fermented with Streptococcus thermophilus CS6,Lactobacillus bulgaricus LDB-C1 and L.plantarum LP-F1.The results show that the addition of LPF1 can effectively reduce the hardness and viscosity of fermented milk and improve its cohesion.It is speculated that L.plantarum LP-F1 has a certain application potential.