Improvement Of Natamycin-producing Strain And The Optimization Of Its Fermentation Process

Natamycin is a kind of 26-membered ring polyene macrolide antibiotics, and it is mainly produced by Streptomyces chattanovgensis, Streptomyces natulonso and Streptomyces gilvosporeus. Natamycin serves as a broad-spectrum antifungal (fungistatic and fungicid) agent. It can effectively inhibit mold and yeast growth, and has no toxic effects even at high levels of ingestion on mammalian species. Therefore natamycin is effective in the therapy of fungus infections of eyes and in protection of foods from mold and yeast growth. In this paper, the determination of natamycin by HPLC, the strain improvement by rational selection, the optimization of the natamycin fermentation process and the kinetic model of natamycin fermentation were studied.A RP-HPLC method for the analysis of natamycin in fermentation broth was developed. The fermentation broth was extracted by methanol and the extraction was analysed by HPLC. The within-day RSD (Relative standard deviation) and inter-day RSD were 0.15% ( n=6 ) and 0.90 % ( n=6 ), respectively. The mean recoveries were 99.84%, 101.18% and 101.41% verse the added authentic sample at the concentrations of 92, 184 and 368 ug/ml respectively. This method is simple, rapid, accurate and reliable for determination of natamycin.Based on the biosynthetic pathway and metabolic regulation of S. gilvosporeus, a rational selection procedure was performed to obtain a higher natamycin-producing strain. The higher productive strain S. gilvosporeus was selected, which, after UV mutation, could grow well on the medium with corresponding concentration of sodium propionate. The productivity reached 1.055g/L, which is increased by 68% in comparison with that of the parent strain 1-12.The optimization of the fermentation progress was studied. The effects of seed age, inoculum level, medium volume, the initial pH value, temperature, precursors on natamycin fermentation were studied in the shaking flasks. The slant medium and seed medium were optimized systematically. A set of culturing medium compositionsand conditions to make the strain grow better and obtain higher productivity were obtained.Based on the results in shaking flasks' fermentation, natamycin fermentation was scaled up in a 5L fermentor, and a productivity of 2.856 g/L was obtained. A simplified morphologically structured model was proposed to describe the batch fermentation process of natamycin according to the growth mechanism of filamentous microorganisms and the kinetic character of natamycin formation.