Effect of flue gas components on succinate production and CO2 fixation by metabolically engineered Escherichia coli

Succinic acid production and CO2 fixation using a metabolically engineered Escherichia coli in a bioreactor equipped with a self-inducing agitator

A 5-L bioreactor equipped with a self-induction agitator was applied to a two-stage culture of Escherichia coli NZN111 for succinic acid production in a mineral salts medium. CO(2) was cycled inside this reactor and a sufficient CO(2) transfer rate was maintained with the elimination of CO(2) wasted by ventilation. In the anaerobic stage, much less supplemental CO(2) was required at pH6.3 compared to that at pH7.0, and the succinate yield increased. The performances of succinate production were little changed when compared to a process with CO(2) sparging indicating that use of the self-inducing agitator reduced CO(2) waste. The succinate production process was further coupled with ethanol fermentation by using the CO(2) produced from ethanol fermentation. This integrated system demonstrated that both succinate and bioethanol can be effectively produced while the emission of the CO(2) formed during ethanol fermentation can be greatly reduced.

Significance of CO2 donor on the production of succinic acid by Actinobacillus succinogenes ATCC 55618

Background

Succinic acid is a building-block chemical which could be used as the precursor of many industrial products. The dissolved CO₂ concentration in the fermentation broth could strongly regulate the metabolic flux of carbon and the activity of phosphoenolpyruvate (PEP) carboxykinase, which are the important committed steps for the biosynthesis of succinic acid by Actinobacillus succinogenes. Previous reports showed that succinic acid production could be promoted by regulating the supply of CO₂ donor in the fermentation broth. Therefore, the effects of dissolved CO₂ concentration and MgCO₃ on the fermentation process should be investigated. In this article, we studied the impacts of gaseous CO₂ partial pressure, dissolved CO₂ concentration, and the addition amount of MgCO₃ on succinic acid production by Actinobacillus succinogenes ATCC 55618. We also demonstrated that gaseous CO₂ could be removed when MgCO₃ was fully supplied.

Results

An effective CO₂ quantitative mathematical model was developed to calculate the dissolved CO₂ concentration in the fermentation broth. The highest succinic acid production of 61.92 g/L was obtained at 159.22 mM dissolved CO₂ concentration, which was supplied by 40 g/L MgCO₃ at the CO₂ partial pressure of 101.33 kPa. When MgCO₃ was used as the only CO₂ donor, a maximal succinic acid production of 56.1 g/L was obtained, which was just decreased by 7.03% compared with that obtained under the supply of gaseous CO₂ and MgCO₃.

Conclusions

Besides the high dissolved CO₂ concentration, the excessive addition of MgCO₃ was beneficial to promote the succinic acid synthesis. This was the first report investigating the replaceable of gaseous CO2 in the fermentation of succinic acid. The results obtained in this study may be useful for reducing the cost of succinic acid fermentation process.