9
the end. Among the advantages of using microalgae, there is the opportunity to
produce succinic acid in a large-scale system and achieve an elevated conversion
efficiency (1 CO 2 : 1 succinic acid). Drawbacks of using microalgae are often the
contamination of the culture medium and the cost of nutrients into liquid media
(Chen et al. 2015).
Not only algae but also cyanobacteria represent an opportunity to reduce CO 2
while producing value-added products as succinic acid. Synechocystis sp. PCC
6803 produced succinic acid under anaerobic dark fermentation in absence of sugar
(Hasunuma et al. 2016). Indeed, under phototrophic conditions, cyanobacteria
assimilate CO 2 and synthesize glycogen, which is catabolized to organic acids (i.e.,
acetate, malate, succinate, ketoglutarate) under dark anoxic conditions. Hasunuma,
Matsuda, and Kondo (2016) enhanced succinic acid production up to 192 mg/L by
the overexpression of phosphoenolpyruvate (PEP) carboxylase enzyme and 10 mM
bicarbonate amendment into the medium. Lan and Wei (2016) modified genetically
the model cyanobacterium Synechocystis elongatus PCC 7942 to enable direct succinic acid secretion in photosynthetic conditions. Among the four branches of the
TCA cycle, the one based on ketoglutarate decarboxylase (KGD) and succinatesemialdehyde dehydrogenase (SSD) enzymes is the most energetically favored.
Thus, they inserted the recombinant genes encoding the KGD and SSD enzymes.
The modified cyanobacterium showed a productivity of 120 mg/L. A more elevated
production rate corresponding to 430 mg/L was reached when α-ketoglutarate was
replenished introducing the recombinant genes holding PEP decarboxylase and
citrate synthase belonging to Corynebacterium glutamicum (Lan and Wei 2016).
A noteworthy example of CO 2 fixation and conversion to succinic acid in bacteria domain is represented by Actinobacillus succinogenes ATCC 55618. This Gramnegative organism, isolated from bovine rumen, presents interesting titers, yields,
and productivities, and it shows high organic acid tolerance (Herselman et al. 2017;
Cao et al. 2018). However, the process requires MgCO 3 to maintain a neutral pH
and to avoid cell flocculation. When using MgCO 3 together with CO 2 , the former is
favored as a supplier of carbon (CO 3
2−
). Moreover, the elevated cost for MgCO 3 and
its poor solubility in water discourage the willing to scale up this system.
Another case is the one in Wang et al. (2008), which has enhanced succinic acid
productivity from 1.624 to 3.486 g/L, when using Escherichia coli carrying a plasmid containing the carbonic anhydrase (CA) gene from cyanobacterium Anabaena
sp. 7120. The activity of PEP decarboxylase was also augmented due to the higher
amount of HCO 3
−
available in the liquid phase as a consequence of CA overexpression induced by CO 2 .
Adipic Acid
The global adipic acid market revenue amounted to USD 5.56 billion in 2016 and is
forecast to develop at an annual growth rate of 4.7% up to 2024. Growth in nylon-6,6
demand, which is mainly driven by the interest into durable and lightweight products in the automotive industry, accounts for 70–80% of the adipic acid demand.
1 Use of Carbon Dioxide in Polymer Synthesis
the end. Among the advantages of using microalgae, there is the opportunity to
produce succinic acid in a large-scale system and achieve an elevated conversion
efficiency (1 CO 2 : 1 succinic acid). Drawbacks of using microalgae are often the
contamination of the culture medium and the cost of nutrients into liquid media
(Chen et al. 2015).
Not only algae but also cyanobacteria represent an opportunity to reduce CO 2
while producing value-added products as succinic acid. Synechocystis sp. PCC
6803 produced succinic acid under anaerobic dark fermentation in absence of sugar
(Hasunuma et al. 2016). Indeed, under phototrophic conditions, cyanobacteria
assimilate CO 2 and synthesize glycogen, which is catabolized to organic acids (i.e.,
acetate, malate, succinate, ketoglutarate) under dark anoxic conditions. Hasunuma,
Matsuda, and Kondo (2016) enhanced succinic acid production up to 192 mg/L by
the overexpression of phosphoenolpyruvate (PEP) carboxylase enzyme and 10 mM
bicarbonate amendment into the medium. Lan and Wei (2016) modified genetically
the model cyanobacterium Synechocystis elongatus PCC 7942 to enable direct succinic acid secretion in photosynthetic conditions. Among the four branches of the
TCA cycle, the one based on ketoglutarate decarboxylase (KGD) and succinatesemialdehyde dehydrogenase (SSD) enzymes is the most energetically favored.
Thus, they inserted the recombinant genes encoding the KGD and SSD enzymes.
The modified cyanobacterium showed a productivity of 120 mg/L. A more elevated
production rate corresponding to 430 mg/L was reached when α-ketoglutarate was
replenished introducing the recombinant genes holding PEP decarboxylase and
citrate synthase belonging to Corynebacterium glutamicum (Lan and Wei 2016).
A noteworthy example of CO 2 fixation and conversion to succinic acid in bacteria domain is represented by Actinobacillus succinogenes ATCC 55618. This Gramnegative organism, isolated from bovine rumen, presents interesting titers, yields,
and productivities, and it shows high organic acid tolerance (Herselman et al. 2017;
Cao et al. 2018). However, the process requires MgCO 3 to maintain a neutral pH
and to avoid cell flocculation. When using MgCO 3 together with CO 2 , the former is
favored as a supplier of carbon (CO 3
2−
). Moreover, the elevated cost for MgCO 3 and
its poor solubility in water discourage the willing to scale up this system.
Another case is the one in Wang et al. (2008), which has enhanced succinic acid
productivity from 1.624 to 3.486 g/L, when using Escherichia coli carrying a plasmid containing the carbonic anhydrase (CA) gene from cyanobacterium Anabaena
sp. 7120. The activity of PEP decarboxylase was also augmented due to the higher
amount of HCO 3
−
available in the liquid phase as a consequence of CA overexpression induced by CO 2 .
Adipic Acid
The global adipic acid market revenue amounted to USD 5.56 billion in 2016 and is
forecast to develop at an annual growth rate of 4.7% up to 2024. Growth in nylon-6,6
demand, which is mainly driven by the interest into durable and lightweight products in the automotive industry, accounts for 70–80% of the adipic acid demand.
1 Use of Carbon Dioxide in Polymer Synthesis