Study On The Breeding Of High-yielding Strain And Intrinsic Kinetics For Ascomycin

Ascomycin (FK-520) is a twenty-three-ring macrolide compound as well asimmunosuppressant biosynthesized by Streptomyces hygroscopicus var.ascomyceticus.The ascomycin will be widely used in the treatment of atopicdermatitis, allergic contact dermatitis, psoriasis, lupus erythematosus, lichen planus,vitiligo and other autoimmune diseases. However, the research on ascomycin is in theprimary stage in our country and there is a considerable gap in fermentation yieldcomparing with foreign study. There is little report on the selection of ascomycinoverproducing strain, optimization of fermentation process and model description ofascomycin fermentation. So, it is important that breeding high-yield strains and thephenotype studies of strain characteristics and fermentation behavior. Also, it has animportant scientific value for guiding the rational transformation of follow-up strains.First, a titanium-sapphire laser system with center wavelength of800nm,frequency76MHz, pulse duration150fs was employed for the first time to improvethe ascomycin (FK520) yield of Streptomyces hygroscopicus var. ascomyceticusNT2-11. The mutant FS35with high and stable (ten generations) FK520productioncapacity was then obtained in the optimal irradiation conditions (25mW for6min)under which the death rate is80%and the mutation rate is15%. The FK520production capacity of FS35was45%higher than that of the parental strain NT2-11and reached240mg/L.Second, the optimized fermentation medium was harvested by optimizing theaddition of exogenous precursors and metal inorganic salt. In the optimizedfermentation medium, the ascomycin fermentation titer of FS35was300mg/L，25%higher than before optimization and the fermentation period is shortened to six days.Third, a comprehensive intrinsic kinetics of mutant FS35and parental strainNT2-11were studied and the mathematical models were established, which were usedto describe quantitatively the difference of fermentation behavior of both strains. Thecorrelation coefficients of models of cell growth, FK520formation, and substrateconsumption of FS35(NT2-11) were0.915(0.893),0.975(0.980),0.989(0.985),respectively, which demonstrated that there was good correspondence between the experimental results and model prediction.