Optimization Of Exopolysaccharide Biosynthesis Conditions Of Lactic Acid Bacteria And The Analysis Of Eps Gene Clusters

Exopolysaccharides(EPSs)produced by Lactobacillus delbrueckii subsp.bulgaricus(L.delbrueckii subsp.bulgaricus)and Lactobacillus paracasei(L.paracasei)have a wide variety of application.They can not only improve the quality of dairy products,but also have antioxidant activity,anticancer,hypoglycemic and other prebiotic effects.In this study,the fermentation conditions of EPS production of L.delbrueckii subsp.bulgaricus LDB-C1 and L.paracasei LC-C2 were optimized,and the bioinformatics analysis of eps gene cluster was analyzed in order to lay a theoretical basis for the directed synthesis of EPS of the above strains.In this experiment,the EPS biosynthesis ability of six strains of L.delbrueckii subsp.bulgaricus and 18 strains of L.paracasei was evaluated.The high EPS-producing strains L.delbrueckii subsp.bulgaricus LDB-C1 and L.paracasei LC-C2 were selected and used as the experimental strains for the optimization of EPS production.In this study,EPS production conditions of strains LDB-C1 and LC-C2 were optimized under the conditions of MRS medium and skimmed milk medium.In MRS medium,the optimal inoculation amount of LDB-C1 and LC-C2 was 3%,the optimal p H was 6.5 and 7.0 respectively,the optimal carbon source was galactose,and the optimal concentration of carbon source was 4%.Under the condition of skimmed milk medium,the best carbon source of LDB-C1 and LC-C2 were sucrose and fructose,the best carbon source concentration was 4% and 1%,the best nitrogen source was soybean peptone and tryptone,the best nitrogen source concentration was 9%.The optimal conditions are determined by means of central composite design method,as flowed: the sucrose content is 4.0%,the soybean peptone 9.0%,the inoculum amount content is 5.00 %.Under the optimal condition,the EPS yield of LBD-C1 reaches the highest,which is 0.802 mg / m L.In this study,the eps gene clusters of L.delbrueckii subsp.bulgaricus strains(DSM 20080,LJJ,KCTC 13731,ATCC 11842,and 2038)and L.casei strains(LC5,W56,IIA,BL23,and DSM 20080)were analyzed.The results indicated that these eps gene clusters are various in different strains in the same species.In the eps clusters of five L.delbrueckii subsp.bulgaricus strains,the transcriptional regulator genes involved in the regulation of EPS production are conversed.A flippase gene located at the 3'-end of these five eps gene clusters.Interestingly,the strains 2038 and ATCC 11842 have an additional flippase gene.In the eps clusters of five L.casei strains,a tyrosine protein phosphatase gene and a transcriptional regulator gene also are conversed.The phylogenetic tree analysis of glycosyltransferases showed that there is abundant diversity in eps gene clusters of L.delbrueckii subsp.bulgaricus and L.casei.A special glycosyltransferase will facilitate the biosynthesis of EPS with unique structure.To clarify the glycosyltransferase in eps gene cluster will be helpful to direct the directed synthesis of EPS.