[Enhancement of monensin production by metabolic engineering of the redox cofactor supply in <i>Streptomyces cinnamonensis</i>].

Monensin, a polyether ionophore antibiotic produced by <i>Streptomyces cinnamonensis</i>, is widely used in the livestock industry. To address the yield bottleneck caused by insufficient intracellular reducing power (NADPH/NADH) during industrial fermentation, we employed a multi-pathway collaborative metabolic engineering strategy. We fused the genes <i>zwf</i> (encoding glucose-6-phosphate dehydrogenase) and <i>gnd</i> (encoding 6-phosphogluconate dehydrogenase) from the pentose phosphate pathway with <i>fadB</i> (encoding 3-hydroxyacyl-ACP dehydratase) from the fatty acid β-oxidation pathway to construct a synthetic expression cassette. This cassette was cloned into the integrative vector pSET152 under the control of the strong <i>ermE</i> promoter and <i>fd</i> terminator and then introduced into <i>S</i>. <i>cinnamonensis</i> SDSL6002 (WT) <i>via</i> intergeneric conjugation, yielding the recombinant strain S-<i>zwf</i>-<i>gnd</i>-<i>fadB</i>. Shake-flask fermentation demonstrated that the engineered strain achieved the intracellular NADPH/NADH level 1.8 folds of that in the wild type, with a monensin titer of 22.6 g/L (a 51.7% increase). The yield remained stable after five generations of antibiotic-free subculturing. Further scale-up validation in 50 L and 5 m³ industrial fermenters demonstrated that the engineered strain achieved monensin titers of 37.2 g/L and 40.4 g/L, which represented 16.3% and 18.8% improvements, respectively, over that of the control strain. These results highlight the exceptional scalability and industrial production potential of the engineered strain. This study establishes a multi-gene co-expression system to reinforce the reducing power network, providing a high yield engineered strain and a feasible metabolic engineering approach for industrial biosynthesis of monensin.