Study On Mutagenic Breeding Of High-yield Nuclease Producing Strain And Fermentation Dynamic

Nucleotides and its derivatives, playing significant roles in restoring central nervous system, circulatory system and urinary system, were widely used in foodstuff, pharmaceutical, agricultural industry, cosmetics manufacture and could be used in synthesizing antivirus and anticancer medicaments. Therefore, it had been the focus to develop 5’-nucleotides production economically. Comparing with fermentation and chemical synthesis, the enzymolysis method had the advantages that the others were beyond comparison and had been the focus of research recently.Strain PJ5 was isolated from fermentation broth. This strain’s enzyme activity stably reached 140U after culturing in the original fermentation medium for 72 hours. Molecular identification show that the strain and Penicillium decumbens have high homologous sequence.Five strains had been screened from the strain PJ5’s spore suspending-liquid, which was treated by ultraviolet rays, microwave induced and LiCl. Their enzyme activitys were 1.28 time as higher as the starting strain.The medium components of the Penicillium citrinum A51 were optimized through orthogonal experiment and single factor experiments in the flasks. The components of the optimized medium suitable for the growth of A51 consisted of 50 g/L glucose,6 g/L peptone,3 g/L steeping,3% Bran leaching juice,0.3 g/L MgSO4·7H2O,0.5 g/L K2HPO4, 0.5 g/L KH2PO4·3H2O,0.2 g/L ZnSO4·7H2O,0.6 g/L CaCl2,1.5 g/L TW80. In this medium condition, the flasks’ nuclease enzyme activitys were raised from 280U to about 439U with the increase of 56.8 percentage points.The dynamic model to describe the nuclease P1 fermented by Penicillium citrinum in 30L Bio-stat automatic fermenter was builted. According to the Logistic equation and the Luedeking-Piret equation, different mathematic models describing cell growth, aim metabolites production and substrate consumption over time in Penicillium citrinum fermentation were proposed. Logistic model for growth, the Luedeking-Piret model for the enzyme production can perfectly describle the fermentation of nuclease P1. The results indicated that there was a coincidence between models calculated values and experimental data. Therefore, the fermentation process of the Penicillium citrinum batch fermentation in 30L Bio-stat fermenter can be reflected by the model equations well. It is significant to guide large-scale industrial production of the nuclease P1. Then the filtering amplification experiment was carried out. In flasks,30L、500L、5m3 and 10m3 fermenters, the nuclease enzyme activity could be keeped in 400U above through fermentation process control.