29
tailor-made products to be used in the agricultural, pharmacological, and medical
fields (Kynadi and Suchithra 2014). The first evidence of microbial PHAs was
reported in 1925 by the French scientist Lemoigne which found poly(3-hydroxybutyrate) (PHB) in Bacillus megaterium (Raza et al. 2018). Since then, the number of
PHA producers accounts for more than 90 genera among Gram-positive and Gramnegative bacteria, with aerobic and anaerobic metabolism. These bacteria can store
PHAs within the cytoplasm as granules (0.2–0.5 μm) covered by phospholipids or
protein layers. In the Archaea domain, PHA production concerns only haloarchaeal
species (Han et al. 2010).
PHA general structure consists of a monomer of 3-hydroxy fatty acids, where the
residual group R length can vary between C 1 and C 14 (Kynadi and Suchithra 2014).
Biopolymer properties and chemical composition change on the basis of the monomer types. Depending on the structure of the PHA, they can be short-chain length
(PHAscl), medium-chain length (PHAmcl), and long-chain length (PHAlcl). The
type of PHA which is mainly produced depends on the nature of substrate that is
provided to the microorganisms.
Many different carbon sources can be used as substrates for PHA production.
Examples include sugarcane molasses, starch (Haas et al. 2008), whey (Kim 2000),
wheat and rice bran, waste vegetable oils and plant oils (Haba et al. 2007), and
wastewater rich in organic acids. However, also gaseous molecules can be recycled
as feedstock for PHAs production. Industrial exhaust gases and syngas from gasification and pyrolysis process of organic wastes represent an opportunity to base the
industrial manufacture on carbon-reducing process.
Short-Chain Length Polyhydroxyalkanoates
Short-chain length polyhydroxyalkanoates (PHAscl) contain 3 to 5 C-atoms, own
high crystallinity level, and are more frequently generated during syngas fermentation. Common PHAscl examples are represented by polyhydroxybutyrate (PHB)
and polyhydroxyvalerate (PHV). Among the most promising producers of poly3-hydroxybutyrate P(3HB), there is the aerobic bacterium Cupriavidus necator.
This microorganism fixes CO 2 via the Calvin–Benson–Bassham (CBB) with hydrogen as the sole source of energy and reducing equivalents (Yu 2018). Volova et al.
(2013) performed an interesting study on macronutrients influence on the growth
and PHAs productivity of Cupriavidus eutrophus B-10646 cultivated in continuous
mode. They found out that the highest (about 40%) PHA content was obtained under
nitrogen deficiency, whereas the lowest (about 15%) PHA content was obtained
under potassium or magnesium deficiency. T synthesized PHA consisted of over
99 mol% P(3HB) and of 0.3–0.9 mol% 3 HV. In Garcia-Gonzalez et al. (2015), the
autotrophic growth of Cupriavidus necator on a mixture of CO 2 /O 2 /H 2 combined
with the heterotrophic growth on glucose or waste glycerol has been studied. Indeed,
this model microorganism owns a very versatile metabolism, which enables PHB
1 Use of Carbon Dioxide in Polymer Synthesis
tailor-made products to be used in the agricultural, pharmacological, and medical
fields (Kynadi and Suchithra 2014). The first evidence of microbial PHAs was
reported in 1925 by the French scientist Lemoigne which found poly(3-hydroxybutyrate) (PHB) in Bacillus megaterium (Raza et al. 2018). Since then, the number of
PHA producers accounts for more than 90 genera among Gram-positive and Gramnegative bacteria, with aerobic and anaerobic metabolism. These bacteria can store
PHAs within the cytoplasm as granules (0.2–0.5 μm) covered by phospholipids or
protein layers. In the Archaea domain, PHA production concerns only haloarchaeal
species (Han et al. 2010).
PHA general structure consists of a monomer of 3-hydroxy fatty acids, where the
residual group R length can vary between C 1 and C 14 (Kynadi and Suchithra 2014).
Biopolymer properties and chemical composition change on the basis of the monomer types. Depending on the structure of the PHA, they can be short-chain length
(PHAscl), medium-chain length (PHAmcl), and long-chain length (PHAlcl). The
type of PHA which is mainly produced depends on the nature of substrate that is
provided to the microorganisms.
Many different carbon sources can be used as substrates for PHA production.
Examples include sugarcane molasses, starch (Haas et al. 2008), whey (Kim 2000),
wheat and rice bran, waste vegetable oils and plant oils (Haba et al. 2007), and
wastewater rich in organic acids. However, also gaseous molecules can be recycled
as feedstock for PHAs production. Industrial exhaust gases and syngas from gasification and pyrolysis process of organic wastes represent an opportunity to base the
industrial manufacture on carbon-reducing process.
Short-Chain Length Polyhydroxyalkanoates
Short-chain length polyhydroxyalkanoates (PHAscl) contain 3 to 5 C-atoms, own
high crystallinity level, and are more frequently generated during syngas fermentation. Common PHAscl examples are represented by polyhydroxybutyrate (PHB)
and polyhydroxyvalerate (PHV). Among the most promising producers of poly3-hydroxybutyrate P(3HB), there is the aerobic bacterium Cupriavidus necator.
This microorganism fixes CO 2 via the Calvin–Benson–Bassham (CBB) with hydrogen as the sole source of energy and reducing equivalents (Yu 2018). Volova et al.
(2013) performed an interesting study on macronutrients influence on the growth
and PHAs productivity of Cupriavidus eutrophus B-10646 cultivated in continuous
mode. They found out that the highest (about 40%) PHA content was obtained under
nitrogen deficiency, whereas the lowest (about 15%) PHA content was obtained
under potassium or magnesium deficiency. T synthesized PHA consisted of over
99 mol% P(3HB) and of 0.3–0.9 mol% 3 HV. In Garcia-Gonzalez et al. (2015), the
autotrophic growth of Cupriavidus necator on a mixture of CO 2 /O 2 /H 2 combined
with the heterotrophic growth on glucose or waste glycerol has been studied. Indeed,
this model microorganism owns a very versatile metabolism, which enables PHB
1 Use of Carbon Dioxide in Polymer Synthesis