Improved doramectin production based on high-throughput screening and medium optimization in <i>Streptomyces avermitilis</i>

Doramectin, a 16-membered macrocyclic lactone that is widely used in the treatment of mammalian parasitic diseases. Doramectin was produced by mutant <i>Streptomyces avermitilis</i> using cyclohexanecarboxylic acid as a precursor. As a semi-synthetic insecticidal agent produced, the production of doramectin was low, which could not be satisfy the demands of industrial fermentation. In this study, a high-yield mutant strain <i>S. avermitilis</i> DA-137 was screened from the starting strain <i>S. avermitilis</i> D-11 through a high-throughput screening strategy. <i>S. avermitilis</i> D-11 was treated with iterative atmospheric and room temperature plasma mutagenesis to induce mutations. Mutation strains were prescreened by spreading on enhanced doramectin-tolerance plates and were rescreened in 24-deep microtiter plates and via microplate readers to obtain high-producing strains. The resulting mutant strain <i>S. avermitilis</i> DA-137 produced 431.5 mg/L doramectin, a 187% increase compared to that of D-11, revealing mutagenesis and doramectin-tolerance screening is an efficient method to enhance doramectin production. Then, fermentation medium was optimized using the response surface method to improve doramectin production. In the optimized fermentation medium, the yield of doramectin was increased to 934.5 mg/L in shake flask. Furthermore, batch culture was carried out in a 50 L fermenter, and the yields of doramectin reached 1217 mg/L at 216 h, which was the highest yield reported to date. This study demonstrates a successful approach for enhancing doramectin production through high-throughput screening strategy and medium optimization, serving as a reference for increasing the yield of other macrocyclic lactone antibiotics.