Study On Mutation Breeding And Protoplasts Fusion Of Mildiomycin-producing Strains

Mildiomycin, a new nucleoside antibiotic, showed remarkable biological activity against powdery mildews of many plants with low toxicity. A systematic investigation was carried out to improve the mildiomycin-producing strain by using of mutation breeding, protoplast fusion technique, in which, mutation breeding, prescreening and rescreening methods, protoplast preparation and regenerationprotoplast fusion and protoplast mutation were adopted for high mildiomycin-producing strains breeding.1) Prescreening and rescreening methods of mildiomycin were developed. The rapid determination method called agar-block was adopted with Rhodotorula sp. as the test microorganism and the comparisons of this method with conventional HPLC method showed the consistent results.2) A mutant breeding procedure of mildiomycin-produicng strain was developed according to the suggested biosynthesis pathway of mildiomycin. High producing mutants were selected with the rational breeding technoque after physical and chemical mutation. Two strains, D-62-2 and ZD519, were obtained which could produce 1034 mg/L and 698 mg/L mildiomycin, which were four and two times higher than that of the origin strain ZD615, respectively.3) Protoplast separation and regeneration technique was established. And protoplast formation concentration was reached to 1×10~8/ml and 57.4% protoplast regeneration was obtained.4) The fusion of biparental inactivated protoplasts was studied. And 5.2% fusion ratio was achieved. One highest producer, 51-19, could produce 1035 mg/L mildiomycin, about 45% higher than that of the origin strain.5) With preliminary study on protoplast mutation breeding of mildiomycin-producing strain, one highest producer, 51-19* was obtained the mildiomycin productivity of 1395 mg/L .