7
fixing pathways (rPP, also known as the Calvin–Benson Cycle; rTCA, reductive
tricarboxylic acid cycle (Evans et al. 1966); rAcCoA, oxygen-sensitive reductive
acetyl-CoA pathway (Ragsdale and Pierce 2008); the 3-hydroxypropionate cycle
(Herter et al. 2002); the 3-hydroxypropionate/4-hydroxybutyrate cycle (Berg et al.
2007); and the recently discovered dicarboxylate/4-hydroxybutyrate cycle (Huber
et al. 2008)) in nature prompted the conception of artificial pathways fixing CO 2
based on superior kinetics, energetic efficiency, favorable thermodynamics, and
topological compatibility criteria. Nonetheless, implementing these synthetic pathways has not been achieved yet in autotrophic microorganisms owing to the daunting challenges to genetically modify these hosts.
Significant achievements have been obtained in the attempt to enhance the supply
of energy which is required in CO 2 -fixation pathways. Main ways include optimizing natural photosystems, modifying photosynthetic reaction centers or widening the
spectrum of light wavelengths, introducing artificial photosystems in microorganisms not provided with light-harvesting capability (Sakimoto et al. 2016), and developing electrical CO 2 fixation where sunlight is transformed into electricity which in
turn drives CO 2 fixation (Rabaey and Rozendal 2010) (Claassens et al. 2016).
Another approach to enhance the efficiency of CO 2 -fixing pathways includes
carbon supplementation from organic substrates (Zhang et al. 2017) and the induction of the CO 2 assimilation by reinforcing the product synthetic pathway or acting
on the CO 2 -concentrating mechanisms.
As aforementioned, different strategies can be utilized to reduce the amount of
CO 2 released from microorganisms, which mainly consist in improving the redox
balance, e.g., through substrate selection and co- generation of products, designing
a CO 2 -fixing synthetic photorespiratory bypass (Shih et al. 2014), and decreasing
the respiratory ATP production, for instance, by artificial systems producing ATP.
1.3 Aliphatic Monomers
Polyesters are among the most promising families of renewable polymers because the
building blocks needed for their synthesis, both diols and diacids, are relatively easily
accessible. Although aromatic polyesters are predominant at the industrial scale, aliphatic polyesters are rapidly gaining relevance due to their unique ability to combine
a satisfactory performance with significant biocompatibility and biodegradability.
1.3.1 Production of Dicarboxylic Acids in Engineered
Microorganisms
Organic acids, such as dicarboxylic acids (HO 2 C−R−CO 2 H), represent an interesting platform of polymer precursors which can be applied to food, pharmaceutical,
material, and textile industries (Jang et al. 2012) (Le Yu et al. 2018). From dicarbox1 Use of Carbon Dioxide in Polymer Synthesis
fixing pathways (rPP, also known as the Calvin–Benson Cycle; rTCA, reductive
tricarboxylic acid cycle (Evans et al. 1966); rAcCoA, oxygen-sensitive reductive
acetyl-CoA pathway (Ragsdale and Pierce 2008); the 3-hydroxypropionate cycle
(Herter et al. 2002); the 3-hydroxypropionate/4-hydroxybutyrate cycle (Berg et al.
2007); and the recently discovered dicarboxylate/4-hydroxybutyrate cycle (Huber
et al. 2008)) in nature prompted the conception of artificial pathways fixing CO 2
based on superior kinetics, energetic efficiency, favorable thermodynamics, and
topological compatibility criteria. Nonetheless, implementing these synthetic pathways has not been achieved yet in autotrophic microorganisms owing to the daunting challenges to genetically modify these hosts.
Significant achievements have been obtained in the attempt to enhance the supply
of energy which is required in CO 2 -fixation pathways. Main ways include optimizing natural photosystems, modifying photosynthetic reaction centers or widening the
spectrum of light wavelengths, introducing artificial photosystems in microorganisms not provided with light-harvesting capability (Sakimoto et al. 2016), and developing electrical CO 2 fixation where sunlight is transformed into electricity which in
turn drives CO 2 fixation (Rabaey and Rozendal 2010) (Claassens et al. 2016).
Another approach to enhance the efficiency of CO 2 -fixing pathways includes
carbon supplementation from organic substrates (Zhang et al. 2017) and the induction of the CO 2 assimilation by reinforcing the product synthetic pathway or acting
on the CO 2 -concentrating mechanisms.
As aforementioned, different strategies can be utilized to reduce the amount of
CO 2 released from microorganisms, which mainly consist in improving the redox
balance, e.g., through substrate selection and co- generation of products, designing
a CO 2 -fixing synthetic photorespiratory bypass (Shih et al. 2014), and decreasing
the respiratory ATP production, for instance, by artificial systems producing ATP.
1.3 Aliphatic Monomers
Polyesters are among the most promising families of renewable polymers because the
building blocks needed for their synthesis, both diols and diacids, are relatively easily
accessible. Although aromatic polyesters are predominant at the industrial scale, aliphatic polyesters are rapidly gaining relevance due to their unique ability to combine
a satisfactory performance with significant biocompatibility and biodegradability.
1.3.1 Production of Dicarboxylic Acids in Engineered
Microorganisms
Organic acids, such as dicarboxylic acids (HO 2 C−R−CO 2 H), represent an interesting platform of polymer precursors which can be applied to food, pharmaceutical,
material, and textile industries (Jang et al. 2012) (Le Yu et al. 2018). From dicarbox1 Use of Carbon Dioxide in Polymer Synthesis