[Selection of high avermectins producing strain and identification of avermectin B1].
Three types of colony, powdery gray, white and bald, were isolated from Streptomyces avermitilis ATCC31272. Among them, only the powdery grey one produces avermectins. Sa-76 strain was selected from the powdery grey strain by mutation with high energy electric flow, and its avermectins titer attainde 100 micrograms/mL in shaking flask. Avermectin B1 was extracted and purified from the mycelia of Sa-76, and identified by UV, IR, 1H-NMR, 13C-NMR and mass spectra. After Sa-76 strain was treated twice with NTG, a strain named Sa-76-8 was selected with avermectins titer over 2000 micrograms/mL. The Sa-76-8 strain was treated with NTG once again, and a high avermectins producing strain named as Sa-76-9 with avermectins titer up to 3500-4000 micrograms/mL was selected.