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Background  Polyketides, such as spinosad, are mainly synthesized in the stationary phase of the fermentation. The synthesis of these compounds requires many primary metabolites, such as acetyl-CoA, propinyl-CoA, NADPH, and succinyl-CoA. Their synthesis is also significantly influenced by NADH/NAD + .  Rex  is the sensor of NADH/NAD +  redox state, whose structure is under the control of NADH/NAD +  ratio. The structure of  rex  controls the expression of many NADH dehydrogenases genes and cytochrome  bd  genes. Intracellular redox state can be influenced by adding extracellular electron acceptor H 2 O 2 . The effect of extracellular oxidoreduction potential on spinosad production has not been studied. Although extracellular oxidoreduction potential is an important environment effect in polyketides production, it has always been overlooked. Thus, it is important to study the effect of extracellular oxidoreduction potential on  Saccharopolyspora spinosa  growth and spinosad production.    Results  During stationary phase,  S. spinosa  was cultured under oxidative (H 2 O 2 ) and reductive (dithiothreitol) conditions. The results show that the yield of spinosad and pseudoaglycone increased 3.11 fold under oxidative condition. As H 2 O 2  can be served as extracellular electron acceptor, the ratios of NADH/NAD +  were measured. We found that the ratio of NADH/NAD +  under oxidative condition was much lower than that in the control group. The expression of  cytA  and  cytB  in the  rex  mutant indicated that the expression of these two genes was controlled by  rex , and it was not activated under oxidative condition. Enzyme activities of PFK, ICDH, and G6PDH and metabolites results indicated that more metabolic flux flow through spinosad synthesis.    Conclusion  The regulation function of rex was inhibited by adding extracellular electron acceptor-H 2 O 2  in the stationary phase. Under this condition, many NADH dehydrogenases which were used to balance NADH/NAD +  by converting useful metabolites to useless metabolites and unefficient terminal oxidases (cytochrome  bd ) were not expressed. So lots of metabolites were not waste to balance. As a result, un-wasted metabolites related to spinosad and PSA synthesis resulted in a high production of spinosad and PSA under oxidative condition.    Electronic supplementary material  The online version of this article (doi:10.1186/s12934-014-0098-z) contains supplementary material, which is available to authorized users.

Suitable extracellular oxidoreduction potential inhibit rex regulation and effect central carbon and energy metabolism in Saccharopolyspora spinosa