Mutagenesis And Screening Of Streptomyces Avermitilis Producing Avermectins And The Fermentation Condition Optimization

Avermectins produced by Streptomyces avermitilis are a group of natural antiphrastic macroliders, reactive and significant biological compounds. Its fermentation products have eight components, and B1 component has the most effective antiphrastic acting. In medicine , agriculture and animal husbandry , avermectins have fine application value and the vast marketplace prospect. In this paper, we attempt to improve their production through breeding the high averment-producing strains and optimizing of the fermentation conditions and put to use in production large scale having provided the reliable technological parameter.First, through purification a stable high-yielding strain was obtained. It was regarded as an original strain, which was treated with ultraviolet radiation(UV) or nitro guanidine (NTG) respectively, or firstly with UV and then with NTG .The results showed, the UV was more sensitive to Streptomyces avermitilis. But NTG method was better, and NTG joint compound mutagenic effects were more obvious than those of a single mutagenic .In addition, a new means was used that which Streptomyces avermitilis were exposured by the 80.55Mev/u 12C+ particle beam. Compared with the original strain it was found the growth of bacterium was quicker,the form and size changed obviously,the bacterial colony was bigger obviously; abrupt change extent was broader , the abrupt change rate was exactly higher, abrupt change plant kind was more; compared the front bacterial colony. The B1a titer improved by 50%. After generation test, the stability of the high-yielding mutant was tested. Above all ultraviolet ray and the sub nitro group guanidine induce an ability to change , the heavy ion beam irradiation induces to be changed into the vegetable sifting the bacterial strain arriving at being able to improve the product testing bacterial strain's to varying degrees without exception, heavy ion beam irradiation effect was best among them , the title rised obviously, the kind wielding ion beam mutagenesis having many ions and the biological material limitation being small, can yet be regarded as one kind of fairly good mutagenesis breeding method.Besides, the fermentation conditions of avermectins were studied in shaking flask. First, we explored the influence of different carbon source, nitrogen source, inorganic salt, trace elements and precursor on avermectins production. On single-factor experimental basis through statistical analysis,the optimum medium was determined,and the B1a titer improved again. What was more,we researched the temperature, pH value, fermentation time, the volume of vaccination,and found that the container of 40ml, pH value of 7.2, the vaccination of 4%, 28℃, fermentation of 10 days, avermectins B1a titer was the highest. Furthermore, the tablism of avermectins including living things amounts, pH value, general candy contents, amino nitrogen contents was studied during the fermentation.