Screening Of High-Producing Strain Of Avermectin B1a And Optimization Of Its Fermentation Process

Avermectins is one of highly potent anthelmintic and insecticidal agents discovered so far. The key to enhance avermectins production lies in screening of high-producing mutant and optimizing of culture conditions.In the experiment, the method of semi-rational screening was applied. The original strain named as R-V-22 was treated with UV, NTG and MMS, and Aza-leucine, sodium-chloroacetate and 2-deoxy glucose were used as screening cribbles, respectively. Finally, the high-producing avermectin Bla resistant strain AV-4-56 was obtained, which produced 60% more avermectin Bla than R-V-22 did.The influences of different culture conditions were investigated. As a result, the growth speed of AV-4-56 was higher than that of R-V-22. At the same time, the strain AV-4-56 requested higher aeration, and had lower hyposensitivity of shearing force and higher tolerance of 0.1% K2HPO4. When 0.1% Mg3(PO4)2, 5.0ppm Zn2+ and 40ppm Co2+ were added in the fermentation medium, the avermectin Bla yield was improved. Also orthogonal design was carried out to determine the best ratio of carbon source and nitrogen source. Based on the optimization of fermentation proceed, the seed age and crossing volume were examined. At last, the strain AV-4-56 produced 1.7 times of avermectin Bla as the original strain R-V-22 did under flask culture condition.The metabolism characteristic of the strain AV-4-56 and R-V-22 in 2 ton seed tank and 80 ton fermentation tank were researched, respectively. The result showed the metabolism ability of AV-4-56 was more active than that of R-V-22. In the process of the AV-4-56 fermentation, when pH dropped to 6.0 quickly within 48hr, amino nitrogen was used up to the lowest level, and PCV increased to the highest level, the growth period changed to the product period. But AV-4-56 requested 10% more antifoam and motive force than R-V-22. While the speed of glucose consumer was 1% higher than that of R-V-22, AV-4-56 produced 60% more avermectin Bla in 80 ton fermentation tank after 10 days culture than R-V-22, reached to 2500ug/ml.