Effects Of Metabolites On ?-polylysine Synthesis And Construction Of High-yield Strains

?-polylysine(?-polylysine,?-PL)has high safety,a broad antibacterial spectrum,good water solubility and good thermal stability.Because of its above advantages,many countries will ?-PL is approved as a food preservative for the food industry.In order to meet market demand,it is necessary to improve the production efficiency of ?-PL and reduce production costs.In the early stage of the laboratory,the ?-PL producing strain S.Diastatochromogenes TUST was used as the starting strain,and a high-yield mutant strain S.Diastatochromogenes 6#-7 was induced by ARTP technology and NTG complex.Through multi-omics technology,high-yield mutant cells were found.The content of internal metabolites such as sugar,arabinose,trehalose,and citric acid is higher than that of the original strain during the fermentation process;in the fermentation process,The expression level of the key enzymes of the diaminopimelate pathway aspartokinase(ASK)and diaminopimelate synthase(DHDPS)was higher than that of the original strain.In this paper,Streptomyces diastatochromogenes TUST,the original strain of ?-polylysine,was used as the experimental strain.First,4 kinds of metabolites(D-fructose,L-arabinose,trehalose,and citric acid)were added exogenously to study the production of ?-The impact of PL;then the strain was subjected to aspartokinase gene(ask)and dihydropyridine dicarboxylic acid synthase Genes(dhdps)were overexpressed to enhance the diaminopimelate pathway.The following research results were obtained:1.By optimizing the concentration and time of the four metabolites,an effective method for increasing ?-PL was obtained:based on M3G medium,shake flask fermentation for 72 hours,and add 2.5 g/L at 0 hours of fermentation.Citric acid and 3 g/L trehalose,1 g/L D-fructose was added at 12 h,and 1 g/L L-arabinose was added at 36 h.The final yield reached 1.1 g/L,which was an increase of 110%compared with 0.52 g/L in the control group.2.Overexpression of ask and dhdps,respectively,to enhance the metabolic intensity of the diaminopimelate pathway producing ?-PL.The test results show that both overexpression of ask and dhdps can promote the production of ?-PL.Among them,a dhdps overexpression strain Streptomyces diastatochromogenes D-4 yields 0.72 g/L after 72 h shake flask fennentation,and the control group 0.58 g/L,an increase of 24%.3.The strain Streptomyces diastatochromogenes D-4 was subjected to 5 L fermenter fed-batch fermentation,and the maximum ?-PL yield was 21.40 g/L at 132 h.The conversion rate of sugar acid was 8.46%,and the conversion rate of nitrogen acid was 82.90%.Compared with the control group,it increased by 31%,40%and 51%respectively.