Isolation and Characterization of New 16-Membered Macrolides from the aveA3Gene Replacement Mutant Strain Streptomyces avermitilisTM24 with Acaricidal and Nematicidal Activities

Polyketides represent an important class of biologically active and structurally diverse compounds found in nature. They are biosynthesized from acyl CoA precursors by polyketide synthases (PKSs). The use of combinatorial biosynthesis to form hybrid PKSs is considered to be an excellent approach for the development of novel polyketides. Here, 10 new 16-membered macrolide compounds were isolated from the broth of the genetically engineered strain Streptomyces avermitilisTM24, in which the PKS gene aveA3was seamlessly replaced by the milbemycin PKS gene milA3. Their structures were elucidated on the basis of NMR and MS spectroscopic analyses. The acaricidal and nematicidal activities of them against Tetranychus cinnabarinusand Bursaphelenchus xylophiluswere tested. The results indicated that compound 1had potent acaricidal activity against adult mites with an LC50value of 0.0022 mg L–1, while compounds 5and 7possessed potent nematicidal activity with LC50values of 4.56 and 4.30 mg L–1, respectively.