Fig. 4

Tuning the glucose uptake rate to improve the yield of n-butanol. a Schematic metabolic pathway for n-butanol fermentation. The dotted black outer lines and red and blue arrows indicate controlled glycolytic flux and the corresponding flux change for pyruvate, respectively. b Result of fermentation for ptsG UTR variants (Biomass, consumed glucose, n-butanol, and pyruvate). c Leaking of pyruvate as a function of the glucose consumption rate. d Relative yield (blue) and productivity (red) of n-butanol depending on the glucose consumption rate. Relative yield represents the ratio compared to the theoretical maximum yield. From left, the open circle represents ∆ptsG, UTR1, UTR2, UTR3, UTR4, UTR_WT, and UTR5. All data were obtained after fermentation for 24 h in TB medium. It should be noted that the components in the TB medium also contributed to biomass yield; therefore, glycolytic flux was represented as the glucose consumption rate during the initial exponential phase, rather than the specific glucose uptake rate. The error bars indicate standard deviations of measurements from two independent cultures