Abstract
BackgroundSuccinic 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.ResultsAn 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.ConclusionsBesides 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.
Highlights
Succinic acid is a building-block chemical which could be used as the precursor of many industrial products
The succinic acid productions were 8.84, 10.21, 10.44, and 10.97 g/L as obtained on 48 hour at the CO2 partial pressure of 25.33, 50.66, 75.99, and 101.33 kPa, respectively, and its corresponding productivities were 0.18, 0.21, 0.22, and 0.23 g/L per hour. This indicated that when gaseous CO2 was used as the sole CO2 donor, CO2 partial pressure showed no significant effect on the succinic acid accumulation
As reported by Lu et al [22] and Samuelov et al [23], a higher available CO2 concentration could cause higher succinic acid production by increasing the activity of PEP carboxykinase. These indicated that when gaseous CO2 was used as the sole CO2 donor, the available dissolved CO2 concentration was not high enough to increase the production of succinic acid in the fermentation of A. succinogenes
Summary
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. 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. As the end-product of the energy metabolism, succinic acid could be produced by many anaerobic microbes, such as Actinobacillus succinogenes, Anaerobiospirillum succiniciproducens, Mannheimia succiniciproducens, Escherichia coli, and other microbes [2,4,6,7]. When A. succinogenes and A. succiniciproducens were used for the production of succinic acid, as a kind of co-substrate of phosphoenolpyruvate (PEP)-carboxykinase in the TCA cycle, CO2 could promote carbon flow toward the production of succinic acid [10,11]. For the other succinic acid production microorganisms such as E. coli and Mannheimia succiniciproducens, CO2 was incorporated into the backbone of threecarbon compound to generate four-carbon oxaloacetate via PEP carboxylase to enhance the production of succinic acid [12,13]
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