pH and base counterion affect succinate production in dual-phase Escherichia coli fermentations
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Succinate production was studied in Escherichia coli AFP111, which contains mutations in pyruvate formate lyase (pfl), lactate dehydrogenase (ldhA) and the phosphotransferase system glucosephosphotransferase enzyme II (ptsG). Two-phase fermentations using a defined medium at several controlled levels of pH were conducted in which an aerobic cell growth phase was followed by an anaerobic succinate production phase using 100% (v/v) CO2. A pH of 6.4 yielded the highest specific succinate productivity. A metabolic flux analysis at a pH of 6.4 using 13C-labeled glucose showed that 61% of the PEP partitioned to oxaloacetate and 39% partitioned to pyruvate, while 93% of the succinate was formed via the reductive arm of the TCA cycle. The flux distribution at a pH of 6.8 was also analyzed and was not significantly different compared to that at a pH of 6.4. Ca(OH)2 was superior to NaOH or KOH as the base for controlling the pH. By maintaining the pH at 6.4 using 25% (w/v) Ca(OH)2, the process achieved an average succinate productivity of 1.42 g/l h with a yield of 0.61 g/g.
KeywordsSuccinic acid CO2 Calcium
Financial support from the US Department of Energy (DE-FG26-04NT42126) is gratefully acknowledged. We acknowledge Drs. G.P. Wylie, T.M. Andacht and D.R. Phillips for NMR and MS analyses. We also acknowledge S.A. Lee for technical assistance and Y. Zhu for helpful discussion.
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