21
conditions. These results are comparable to the 2.38 g/L of 2,3-BDO achieved after
21 days in Synechococcus sp. PCC 7942 in Oliver et al. (2013). Under natural light,
chemical production from a photo-dependent chemical platform is necessarily confined to 8–14 h of exposure to optimal natural lightening. However, industrial workability would derive substantial benefit from operating 2,3-BDO production in light
and dark conditions. Furthermore, high cell density conditions, which are desirable
for efficient production in a large-scale platform, are troublesome for photoautotrophic microorganisms owing to the consequent decrease in light penetration into the
culture and to the increased mutual cell shading. Economic analysis of 2,3-BDO
production demonstrated that engineering photomixotrophy, namely, enhancing the
flux of carbon towards chemical production by simultaneously exploiting optimized
CO 2 fixation and glucose catabolism, allows to surmount the limitations related to
the increase in cell density which would be typical of purely phototrophic conditions. To pursue photomixotrophy, a line of studies sought to engineer the carbon
metabolism of photosynthetic microorganisms to afford consumption of externally
supplied sugars. McEwen, Kanno, and Atsumi (2016) demonstrated that the supply
of sugar in conjunction with sodium bicarbonate allowed the Synechococcus elongatus strain engineered by heterologous sugar importers and 2,3-BDO biosynthetic
pathway to achieve a maximum titer of 3.0 g/L 2,3-BDO, which is comparable to
that achieved under continuous light conditions. Kanno, Carroll, and Atsumi (2017)
engineered the carbon metabolism of Synechococcus elongatus PCC 7942 by coupling glucose metabolism with the Calvin–Benson cycle to enhance CO 2 fixation
and 2,3-BDO chemical production up to 12.6 g/L of 2,3-BDO with a rate of 1.1 g/L/
day under continuous light conditions.
More recently, a synthetic and syntrophic co-culture of the solventogen
Clostridium acetobutylicum and the acetogen Clostridium ljungdahlii, mimicking
naturally occurring microbial consortia, was found to metabolically couple the glycolytic glucose breakdown in C. acetobutylicum and the Wood–Ljungdahl pathwaybased CO 2 fixation in C. ljungdahlii, thus expanding the metabolic capabilities of
the individual strains to include 2,3-BDO (Charubin and Papoutsakis 2019). Indeed,
although neither strain produces any 2,3-BDO—exception made for around 2 mM
of 2,3-BDO in C. ljungdahlii—the co-culture managed to produce 23 mM of 2,3BDO. The nontrivial production of unexpected metabolites shown by this co-culture
is likely due to the upregulated expression of the native 2,3-BDO dehydrogenase in
C. ljungdahlii caused by the presence of ketones—acetone and acetoin—generated
by C. acetobutylicum.
1.4 Aromatic Monomers
Herein we describe the biotransformation of carbon dioxide into aromatic monomers
potentially relevant to produce high-performance electronics and fabrics that possess
appealing properties like ultraviolet absorbance, higher resistance to
temperature, and higher mechanical strength relative to aliphatic polymers. Owing to
1 Use of Carbon Dioxide in Polymer Synthesis
conditions. These results are comparable to the 2.38 g/L of 2,3-BDO achieved after
21 days in Synechococcus sp. PCC 7942 in Oliver et al. (2013). Under natural light,
chemical production from a photo-dependent chemical platform is necessarily confined to 8–14 h of exposure to optimal natural lightening. However, industrial workability would derive substantial benefit from operating 2,3-BDO production in light
and dark conditions. Furthermore, high cell density conditions, which are desirable
for efficient production in a large-scale platform, are troublesome for photoautotrophic microorganisms owing to the consequent decrease in light penetration into the
culture and to the increased mutual cell shading. Economic analysis of 2,3-BDO
production demonstrated that engineering photomixotrophy, namely, enhancing the
flux of carbon towards chemical production by simultaneously exploiting optimized
CO 2 fixation and glucose catabolism, allows to surmount the limitations related to
the increase in cell density which would be typical of purely phototrophic conditions. To pursue photomixotrophy, a line of studies sought to engineer the carbon
metabolism of photosynthetic microorganisms to afford consumption of externally
supplied sugars. McEwen, Kanno, and Atsumi (2016) demonstrated that the supply
of sugar in conjunction with sodium bicarbonate allowed the Synechococcus elongatus strain engineered by heterologous sugar importers and 2,3-BDO biosynthetic
pathway to achieve a maximum titer of 3.0 g/L 2,3-BDO, which is comparable to
that achieved under continuous light conditions. Kanno, Carroll, and Atsumi (2017)
engineered the carbon metabolism of Synechococcus elongatus PCC 7942 by coupling glucose metabolism with the Calvin–Benson cycle to enhance CO 2 fixation
and 2,3-BDO chemical production up to 12.6 g/L of 2,3-BDO with a rate of 1.1 g/L/
day under continuous light conditions.
More recently, a synthetic and syntrophic co-culture of the solventogen
Clostridium acetobutylicum and the acetogen Clostridium ljungdahlii, mimicking
naturally occurring microbial consortia, was found to metabolically couple the glycolytic glucose breakdown in C. acetobutylicum and the Wood–Ljungdahl pathwaybased CO 2 fixation in C. ljungdahlii, thus expanding the metabolic capabilities of
the individual strains to include 2,3-BDO (Charubin and Papoutsakis 2019). Indeed,
although neither strain produces any 2,3-BDO—exception made for around 2 mM
of 2,3-BDO in C. ljungdahlii—the co-culture managed to produce 23 mM of 2,3BDO. The nontrivial production of unexpected metabolites shown by this co-culture
is likely due to the upregulated expression of the native 2,3-BDO dehydrogenase in
C. ljungdahlii caused by the presence of ketones—acetone and acetoin—generated
by C. acetobutylicum.
1.4 Aromatic Monomers
Herein we describe the biotransformation of carbon dioxide into aromatic monomers
potentially relevant to produce high-performance electronics and fabrics that possess
appealing properties like ultraviolet absorbance, higher resistance to
temperature, and higher mechanical strength relative to aliphatic polymers. Owing to
1 Use of Carbon Dioxide in Polymer Synthesis