Studies On Optimization Of The Fermentation Condition With Streptomyces Aureofaciens And Novel Method For Selection Of High-yielding Chlortetracycline Strain

Based on the Fermentation results of Streptomyces aureofaciens named 5.11-3, 3-119-3 and H-CTC-5. We selected study the optimal condition for Chlortetracycline(CTC) fermentation of strain 5.11-3 and found a novel method for selection of high-yielding CTC strain. Studies on the molecular mechanism of the novel method were carried out. The effect of inorganic phosphate , amylum and yeast flour on CTC biosynthesis were also studied.In order to improve the antibiotic-producing trait of strain 5.11-3, we exposed its protoplasts and spores to UV and isolated mutant strains. The antibiotic's titer of the mutant's fermented broth was 4 times as high as the parent strain through OD₄₄₀ data. And its high capacity for producing antibiotic remained stable after 4 times of subcultures. It was also found that the effect of protoplasts' UV mutagenic breeding was better than spores'.UV irradiated spores of strain 5.11-3 were incubated at 33℃, 36℃ and close to inhibiting growth temperature 30 ℃ and 39 ℃. Results showed that among the offspring from UV irradiated spores grown at 30 ℃, the amount of forward mutants whose antibiotics-producing ability were over the original strain's were many more than that at the others temperatures. The percentage of the forward mutants was 29.85% at 36℃ and 47.69% at 30℃ respectively. The isozyme electrophoresis analysis of the progeny strain was carried out, it was concluded that the diversity of the progeny strain's titer were caused by the mutation of strain's DNA. Total DNA of the progeny strain and the original strain was tested by RAPD with 10 primers. It was demonstrated that the variations occurred in the chromosomal DNA of the progeny strains grown at 30℃ were more than that at the others temperatures. This method improved the efficiency of UV mutagenic breeding and put forward a new way in researching into the mechanisms of mutation formation in Streptomyces aureofaciens cells irradiated by UV.