Study On Fermentation Process Of Streptomyces Lydicus A02

Streptomyces lydicus A02 has strong effective inhibitiory on plant diseases.The main active substance of its metabolites is Natamycin which has effective inhibitiory action against a variety of plant pathogenic Fungi. The fermatation process of natamycin produced by S.lydicus A02 was systematically studed in this paper, including optimization of medium composition and fermentation proeess and increase of natamycin yield. Results are as followings:(1) The optimum conditions for fermentation in shake-flask were defined as follows:seed culture time, 24~28 h;rotational speed, 240 r/min;initiativefermentation(0~48 h)temperature, 30℃, middle and late period fermentation(48 h~end)temperature, 28℃; fermentation period, 144 h.(2) Fermentation medium for strain A02 was optimized with methods of fractional factorial design, path of steepest ascent and central composite design. Results showed that corn starch, cotton seed flour and glucose were the major factors affecting natamycin production. According to the evaluation by the response surface model established in this study, the optimum mass concentrations of the three components in fermentation medium were 52.7, 31.7 and 11.7 g/L, with the highest natamycin yield of 1735.3 mg/L. Fermentation experiments with shake flasks and 30 L fermentor verified that there was no statistical difference between the yield value forecasted by the model and that obtained in the tests, and the capacity of the optimized medium was increased by 32.9%~34.8% in comparison with basic fermentation medium.(3)The most positive precursor was n-propanol for natamycin synthesis. The addition of 0.2% n-propanol can increase natamycin yield (1.84 g/L) at cultivation time of 24 h.(4)The batch fermentatlon was performed in a 30 liter fermenter with S. lydicus A02. The best fermentation conditions were inoculation volume 9%, Pack material coefficient 65%, fermentation period 120h, fermentation temperature 30℃(0~48 h) and 28℃(48~120 h), ventilation volume 600~800 L/h, stirring rate 200~500 r/min, initiative fermentation DO 40%~80%, middle and late period fermentation DO 20%~30%. Natamycin yield in fermentation broth and the supernatant of the fermentation broth reached 6.91 g/L and 2.02 g/L respectively when fermentation broth pH was 6.0 by feeding glucose.(5)Batch fermentation of S. lydicus A02 for natamycin production was carried out in the study. Mathematical kinetic model describing the time-course of biomass, products and substrates were obtained based on the unstructured model of biochemical process. The results showed that these models fit for the experimental data quiet well during the batch fermentation process of S. lydicus A02 for natamycin.(6)Fermentation was successively scaled up by controlling dissolved oxygen. The batch fermentation in 300 L fermenter,the natamycin yield of fermentation broth and the supernatant of the fermentation broth reached 6.78 g/L and 1.65 g/L respectively.