| The spiramycin producing strain Streptomyces spiramyceticus XCH1-23 was treated with UV irradiation. The 2-deoxy-D-glucose tolerant mutants, valine tolerant mutants, soybean oil tolerant mutants and SPM resistant mutants were screened by means of rational selection and natural selection, respectively. By above methods, a high-titer strain XCH9-15 was obtained, its potency was increased by 65.9% over the parent strain XCH1-23. Subculture test indicated that the hereditary character of stain XCH9-15 was stable.By the fermentative experiments of the strain XCH9-15, it was found that the optimum proportion of soybean oil in the production medium was 2.0% and the optimum feeding time of soybean oil was in the initial stages (0-12h) of fermentation process. Feeding propyl alcohol as precursors in the fermentation process, the productivity was further increased by 21%, and the optimum feeding time was 24 h for shake culture and 20 h for 50M3 fermentor. The suitable amount of NP^NOa and KH2PO4 for spiramycin fermentation was 0.8% and 0.1%, respectively. Compared with the parent strain, the potency and fermentation index of S. spiramyceticus XCH9-15 was increased by 52.2% and 42.7% respectively. The quality of product was improved a little by using improved fermentation conditions. The cheaper mixed fatty acid was adopted instead of partial soybean oil, the productivity was not declined obviously.The effects of temperature on spiramycin production were studied both in shaking flask and in 50M3 fermentor. It was found that the optimum temperature for spiramycin biosynthesis was 25 癈. Fed-batch fermentation with continuous feeding can avoid sudden change of environment in fed-batch fermentation. Comparing with fed-batch fermentation with batch feeding, the potency and fermentation index of fed-batch fermentation with continuous feeding was increased by 13.5% and 12.5%, respectively. The highest potency of fed-batch fermentation with continuous feeding in 50M3 fermentor reached 5700u/ml.
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