| Nemadectin is a kind of 16-membered ring polyene macrolide antibiotics, and it is maily produced by Streptomyces cyaneogriseus subspecies noncyanogenus. In this paper, we attempt to improve their production through screening the high nemadectin-producing strains and optimizing of the fermentation conditions and put to use in production large scale having provided the reliable technological parameter.First, through purification,a stable yield strain was obtained. Based on the biosynthetic pathway and metabolic regulation of Streptomyces cyaneogriseus subspecies noncyanogenus, sodium acetate, valine, valinehudroxamate and 2-deoxy-D-glucose chose as screening agents, a rational selection procedure with UV mutation was performed to obtain a higher nemadectin-producing strain. Finally a high producing strain N-09-20 was obtained and produced 77 mg/L nemadectin, which was four times higher than the original strain. Then the strain N-09-20 was treated with UV and streptomycin, after self-metabolic regulation for 4 times, the production of N-16-19 was 172 mg/L, 10 times higher than N-01-31. Subculture test indicated that the hereditary character of strain N-16-19 was of stability.The optimization of the fermentation progress for higher nemadectin-producing strain N-16-19 was studied. On the optimal fermentation medium, the production of N-16-19 is 236 mg/L, which was 67% higher than primary medium. At the same time, the effects of strain age, inoculums, seed age, inoculum level, temperature and dissolved oxygen on nemadectin fermentation were studied in the shaking flasks. Short-chain fatty acid precursor and amine acid precursor were invested in fermentation, additional time and additional volumes were determined.Furthermore, the tablism of nemadecctin including living things amounts, pH value, general sugar contents, deoxidize sugar and amino nitrogen contents were studies during the fermentation. These messages would be useful for large scale production.
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