Effect of precise control of flux ratio between the glycolytic pathways on mevalonate production in Escherichia coli

Mevalonate is a useful metabolite synthesized from three molecules of acetyl-CoA, consuming two molecules of NADPH. Escherichia coli (E. coli) catabolizes glucose to acetyl-CoA via several routes, such as the Embden-Meyerhof-Parnas (EMP) and the oxidative pentose phosphate (oxPP) pathways. Although the oxPP pathway supplies NADPH, it is disadvantageous in terms of acetyl-CoA supply, compared with the EMP pathway. In this study, the optimal flux ratio between the EMP and oxPP pathways on the mevalonate yield was investigated. Expression level of pgi was controlled by isopropyl beta-D-1-thiogalactopyranoside (IPTG) inducible promoter in an engineered mevalonate-producing E. coli strain. The relationship between the flux ratio and mevalonate yield was evaluated by changing the flux ratio by varying IPTG concentration. At the stationary phase, the mevalonate yield was maximum at an EMP flux of 39.7%, and was increased by 25% compared with that with no flux control (EMP flux of 70.4%). The optimal flux ratio was consistent with the theoretical value based on the mass balance of NADPH. The flux ratio between EMP and oxPP pathways affects the synthesis fluxes of mevalonate and acetate from acetyl-CoA. Fine tuning of the flux ratio would be necessary to achieve an optimized production of metabolites that require NADPH.