Metabolic engineering of Streptomyces cinnamonensis enhances biosynthesis of monensin

Abstract:

[Objective] Monensin is a polyether antibiotic produced by Streptomyces cinnamonensis. To enhance the production of monensin by microbial fermentation, we employed metabolic engineering to strengthen the synthesis pathway of the key precursor methylmalonyl-CoA in S. cinnamonensis 2110. [Methods] Firstly, crotonyl-CoA reductase (CCR) was overexpressed to strengthen the acetoacetyl-CoA pathway. Subsequently, methylmalonyl-CoA mutase (MCM) was overexpressed to improve the succinyl-CoA pathway. Finally, an engineered strain with tandem overexpression of CCR and MCM was constructed and evaluated for the fermentation performance. [Results] The overexpression of CCR increased the strain biomass and monensin titer by 10.4% and 19.0%, respectively, after 10 days of shake-flask fermentation. The overexpression of MCM increased the monensin titer by 9.9%, whereas it did not increase the strain biomass after 10 days of shake-flask fermentation. The tandem overexpression of CCR and MCM increased the biomass and monensin titer by 9.4% and 26.8%, respectively, after 10 days of shake-flask fermentation. In a 5 L bioreactor, the engineered strain 2110-CCR-MCM reached the highest biomass of 54.6 g/L and monensin titer of 11.3 kU/mL, which increased by 12.7% and 36.2%, respectively, compared with those of the starting strain 2110. [Conclusion] CCR and MCM mediated the key metabolic pathway of monensin biosynthesis in S. cinnamonensis, and the overexpression of CCR and MCM was highly favorable for monensin synthesis. This study provides technical reference for the engineering of strains with high yields of other polyketides.