| Steroid drugs, including Adrennocroticosteroids, Anabolicsteroids and Sex Hormone, are useful to improve body metabolization. Using plant sterols from the low-cost oil as the substrate, the key intermediate of steroidal drug could be biotransformed by microbe, which can not only raise the utilization rate of the foot of industry materials, but also reduce the cost of steroid drugs. In our previous works, a starin (Mycobacterium sp.) which can transformed plant sterols into ADD as well as a certain percentage of AD was screened. So in this work, we mainly focus on the mutation and breeding a mutants which can biotransform phytosterol into single product ADD. Moreover, the fermentation conditions to improve the convertion rates and production of ADD was optimized and the methods of purification of the product from the broth was explored.The main work includes the following three steps:1. A mutant Mycobacterium sp.-11-12, which could stably transform phytosterol into Androst-1, 4-dione-3, 17-dione as the single product, was obtained by UV and UV -NTG mutation and plate screening from a parent strain Mycobacterium sp.. The productivity of ADD was superior to that of the parental strain. The highest lever (0.87g/L) was found in the 7th fematation day, about 40% exceeding to the original strain. Meanwhile the AD in the fermentation could not be detected in the 5th day.2. Parameters of the biotransformation medium we optimized, such as(%) : Phytosterol 1.0, glucose 1.0, peptone 1.0, K2HPO4 0.3, MgSO4 0.02, MnCl2,510-5, lecithin 0.4. The obtained optimal culture conditions were: inoculum 12%, rotation speed 200 r / min , initial pH 7.0. After fermentation 7 days, the concentration of ADD reached 1.44 mg/L, which impoving about 72%. The yield of ADD was 21.73%.3. The separation and purification of ADD from the broth by Amberlite xad-7 was prelimily established. The purity of crude products ADD was 66.6%, almost no AD detected.
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