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Fig. 4 | Biotechnology for Biofuels

Fig. 4

From: Engineering of E. coli inherent fatty acid biosynthesis capacity to increase octanoic acid production

Fig. 4

Optimization of culture conditions for free octanoic acid production in the ZEFA (TE10) strain. a Effects of different IPTG dosages on octanoic acid production. ZEFA (TE10) strain produced the highest titer of octanoic acid (430 mg/L) when induced with 200 μM IPTG for increasing expression of thioesterase TE10 gene. Cultures were performed in 40 mL M9+ 1.5% (wt/v) dextrose with the C/N ratio of 18.8 in 250-mL shake flasks at 250 rpm 30 °C with an initial pH of 7.0 and the IPTG was added when the OD550 reached 0.4–0.5. b Effects of different initial C/N ratios on octanoic acid production under 200 μM IPTG. ZEFA (TE10) strain has the highest C8 production at the C/N ratio of 18.8. For changing the C/N ratio, the glucose (carbon source) concentration is fixed at 15 g/L and the amount of NH4Cl (carbon source) added was varied accordingly. (C) Maintenance of culture broth pH at neutral range (pH = 7.0) increased octanoic acid production under 200 μM IPTG and C/N ratio of 18.8. Culture was performed in 300 mL M9+ 1.5% (wt/v) dextrose in a 500-mL bioreactor. Cultures were grown at 30 °C, and the pH was maintained at 7.0 by adding 2.0 M potassium hydroxide (KOH). Air flow rate was controlled at 0.3 L/min with 300 rpm as the initial stirring speed. The dissolved oxygen (DO) level was set over 40% and controlled by changing the stirring speed with the maximum of 600 rpm. Titers are the average of at least three replicates with error bars indicating one standard deviation. ZEFA, +fadZ ΔfadE ΔfumAC ΔackA

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