Genetic Modification Of Enramycin Producing Strain And Breeding Selection Of Excellent Strains

Adding moderate amounts of enramycin in feed can not only prevent the common animal digestive tract diseases,but also improve the balance of community in animal’s tract,which is good for the digestion and absorption of feed nutrients and the gain of animal’s weight.In addition,enramycin has the advantages of broad-spectrum,low toxicity,no residue and hard to engender drug and crossed resistance,which makes enramycin become one of some antibiotics that can be used as feed additives.Enramycin,as present,is obtained mainly through the method of fermentation of Streptomyces fungicidicus which has eumycetin resistance,but S.fungicidicus’s fermentation period is long,and few enramycin can be obtained through the above method,so the mass production of enramycin and further application is restricted.For improving the production level and performance of eumycetin producing strain of Streptomyces fungicidicus F1,the study constructed a set of complete system of genetic operation for Streptomyces fungicidicus F1 at first,and then the ribosomal S12 protein encoding gene rpsl which affects the secondary metabolism and biosynthesis of antibiotics was changed through the method of site-directed mutagenesis,during which the Lys43 was substituted for Arg and Asn respectively,and Lys88 was substituted for Glu;and then the growth characteristics,production level and fermentation performance of three modified strains LM1(Arg43),LM2(Asn43)and LM3(Glu88)was studied.The results showed that the growth,physiological and biochemical characteristics of the modified strains were changed greatly compared with wild type stain.(1)The resistance to eumycetin was changed,the minimum inhibitory concentration of the antibiotics(MIC)for the wild type strain was 3μg/mL,and 30 times increased for LM1(Arg43)and LM2(Asn43),3 times increased for LM3(Glu88).(2)Sporulation cycle was shorten,spore was produced from wild type strain using MS medium under the condition of 28℃ for 5～7 days,and modified strain can produced large amounts of spore only after 3 days.(3)Enramycin’s producing level was increased,the activity of enramycin of 3 modified strain was dectected,the enramycin producing level of LM1(Arg43)and LM2(Asn43)was increased by 19.6%and 11.3%compared by wild type strain F1,and LM3(Glu88)had no significant changes in the production of enramycin.