De-worming Streptomyces (streptomyces Avermitilis) Genetically Engineered

Avermectins (AVM) produced by Streptomyces avermitilis are composed ofeight compounds of sixteen-membered macrocylic lactones resulting from structuraldifferences at three positions, C-5, C22-23, C26. Among these components, B1fraction, especially B1a, has the most effective antiparasitic activity. The discovery ofavermectins has had a great impact on animal husbandry because of its broad-spectrum activity against nematode and arthropod parasites.Firstly, optimum methods for introducing genes into Streptomyces avermitilisMMR630 and NRRL 8165 have been established. We decided to introduced genesinto MMR630 and NRRL 8165 with the conjugal plasmid pSET152. aveR, orfX ,genes of Streptomyces avermitilis, which are putative regulatory genes for antibioticproduction in Streptomyces avermitilis were cloned by PCR amplification. BecauseStreptomyces avermitilis is homologous to coelicolor A3(2), afsR, a putativepleiotropic regulatory gene for antibiotic production in Streptomyces coelicolorA3(2),was also cloned by PCR amplification. We introduced these genes intoMMR630 with conjugation. And these strains also resulted in an increase of B1a ofavermectin production by 2.5, 2.0and 2.9-fold, respectively.A set of ordered cosmids for Streptomyces avermitilis NRRL8165 chromosome isconstructing now. High-molecular-weigh DNA of Streptomyces avermitilisNRRL8165 was partially digested with sau3AI ,treated with sucrose gradientcentrifugation. Now we are constructing the suitable vector to finish the constructionof the cosmid library.