Spinosyns are natural broad-spectrum biological insecticides with a double glycosylated polyketide structure that are produced by aerobic fermentation of the actinomycete, Saccharopolyspora spinosa. However, their large-scale overproduction is hindered by poorly understood bottlenecks in optimizing the original strain, and poor adaptability of the heterologous strain to the production of spinosyn. In this study, we genetically engineered heterologous spinosyn-producer Streptomyces albus J1074 and optimized the fermentation to improve the production of spinosad (spinosyn A and spinosyn D) based on our previous work. We systematically investigated the result of overexpressing polyketide synthase genes ( spnA , B , C , D , E ) using a constitutive promoter on the spinosad titer in S. albus J1074. The supply of polyketide synthase precursors was then increased to further improve spinosad production. Finally, increasing or replacing the carbon source of the culture medium resulted in a final spinosad titer of ∼70 mg/L, which is the highest titer of spinosad achieved in heterologous Streptomyces species . This research provides useful strategies for efficient heterologous production of natural products.

Maduramicin is the most efficient and possesses the largest market share of all anti-coccidiosis polyether antibiotics (ionophore); however, its biosynthetic gene cluster (BGC) has yet to been identified, and the associated strains have not been genetically engineered. Herein, we performed whole-genome sequencing of a maduramicin-producing industrial strain of Actinomadura sp. J1-007 and identified its BGC. Additionally, we analyzed the identified BGCs in silico to predict the biosynthetic pathway of maduramicin. We then developed a conjugation method for the non-spore-forming Actinomadura sp. J1-007, consisting of a site-specific integration method for gene overexpression. The maduramicin titer increased by 30% to 7.16 g/L in shake-flask fermentation following overexpression of type II thioesterase MadTE that is the highest titer at present. Our findings provide insights into the biosynthetic mechanism of polyethers and provide a platform for the metabolic engineering of maduramicin-producing microorganisms for overproduction and development of maduramicin analogs in the future.

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