Effect of flue gas components on succinate production and CO2 fixation by metabolically engineered Escherichia coli
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Escherichia coli pfl ldhA ptsG (AFP111) was studied for succinate production in defined medium using trace gases typically found in flue gas; i.e. oxygen (O2), nitrogen dioxide (NO2), sulfur dioxide (SO2) and carbon monoxide (CO). Following aerobic cell growth, cells were exposed to 50% CO2 and 3–10% O2, or 50–300 ppm NO2, SO2 or CO during the succinate production phase. Although 3% O2 did not significantly affect succinate formation, 10% O2 reduced the final succinate concentration from 33 to 17 g/L, specific productivity from 1.90 to 1.13 mmol/g h and yield from 1.15 to 0.81 mol/mol glucose. The effect of O2 correlated with the culture redox potential (ORP) with more reducing conditions favoring succinate production. The trace gases NO2 and SO2 also reduced the rate of succinate formation by as much as 50%, and led to a greater than twofold increase in pyruvate formation. Similar concentrations of CO showed no effect on succinate production rate or yield. Using synthetic flue gas AFP111 generated 12 g/L succinate with a specific productivity of 0.73 mmol/g h and a yield of 0.65 mol/mol.