Figure 4

Flux solution spaces and batch fermentation results of wild-type and mutant ( ΔldhA ) strains of K. oxytoca . (A) 3D mesh plot graph as a continuous surface for in silico flux solution space of K. oxytoca wild-type strain correlated with cell growth rate, byproducts formation rate, and 2,3-BD production rate and its corresponding contour graph. (B) 3D mesh plot graph as a continuous surface for in silico flux solution space of ldhA gene knockout mutant of K. oxytoca correlated with cell growth rate, byproducts formation rate, and 2,3-BD production rate and its corresponding contour graph. The colors changed by gradation in graph indicate the value of cell growth rate. The red color means larger value of cell growth rate than other colors. (C) Batch fermentation result of K. oxytoca wild-type strain. (D) Batch fermentation result of ldhA gene knockout mutant of K. oxytoca. The arrow indicates the position of in silico optimal cell growth rate. Based on the flux solution space of wild-type strain, the large amount of byproducts were produced during 2,3-BD production. After in silico knockout of ldhA gene, byproducts formation rate was decreased, while 2,3-BD production rate was increased in comparison with wild-type strain. The fermentation was performed at 150 rpm, pH 6.5, and 37°C in 3 L working volume. The symbols in fermentation profiles indicates the concentration of glucose (○), 2,3-BD (●), OD₆₀₀ (■), ethanol (▲), succinic acid (♦), lactic acid (*), formic acid (◊), and acetic acid (∆).