116
can be the result of the combination of one molecule of propionyl-CoA and one
molecule of acetyl-CoA (Serafim et al. 2008). This production route is usually
known as pathway I for polyhydroxyalkanoates production.
The two other polyhydroxyalkanoates pathways are associated with the accumulation of mcl-polyhydroxyalkanoates because longer-chain volatile fatty acids are
implicated in the process. In the second known pathway, the carbon source, typically fatty acids, is oxidized to 3-hydroxyacyl-CoA as summarized in Fig. 5.4. This
reaction is conducted by enoyl-CoA hydratase (PhaJ) and PhaC enzymes. The conversion of fatty acids to polyhydroxyalkanoates involves a few steps and results in
high yields (Kourmentza et al. 2017). The last known pathway is a chain elongation
from simple carbons, and a regulatory protein (PhaG) and PhaC are the main
enzymes, as explained in Fig. 5.5 (Możejko-Ciesielska and Kiewisz 2016).
Additionally, random copolymers of polyhydroxyalkanoates are usually produced
when mixed substrates are employed, which occurs during pathway II and III
(Verlinden et al. 2007).
Genetic engineering is also used to modify the pathway of polyhydroxyalkanoates production and to increase the yield and simultaneously decrease the expenses
(Lutke-Eversloh and Steinbuchel 2004). Experiments conducted on Escherichia
coli revealed that a production of 90% of polyhydroxybutyrate was reached via this
method, where the PhaC enzyme was added to the Escherichia coli from Cupriavidus
necator (Możejko-Ciesielska and Kiewisz 2016; Koller et al. 2017). While the
results of genetically modified bacteria are great, the costs are high for their development and for maintaining the pure culture during production, making them typically not suitable for wastewater treatment applications.
Fig. 5.3 Pathway I for short-chain-length polyhydroxyalkanoates production (Modified after
Serafim et al. 2008). Scl, short chain length
S. Sali and H. R. Mackey
can be the result of the combination of one molecule of propionyl-CoA and one
molecule of acetyl-CoA (Serafim et al. 2008). This production route is usually
known as pathway I for polyhydroxyalkanoates production.
The two other polyhydroxyalkanoates pathways are associated with the accumulation of mcl-polyhydroxyalkanoates because longer-chain volatile fatty acids are
implicated in the process. In the second known pathway, the carbon source, typically fatty acids, is oxidized to 3-hydroxyacyl-CoA as summarized in Fig. 5.4. This
reaction is conducted by enoyl-CoA hydratase (PhaJ) and PhaC enzymes. The conversion of fatty acids to polyhydroxyalkanoates involves a few steps and results in
high yields (Kourmentza et al. 2017). The last known pathway is a chain elongation
from simple carbons, and a regulatory protein (PhaG) and PhaC are the main
enzymes, as explained in Fig. 5.5 (Możejko-Ciesielska and Kiewisz 2016).
Additionally, random copolymers of polyhydroxyalkanoates are usually produced
when mixed substrates are employed, which occurs during pathway II and III
(Verlinden et al. 2007).
Genetic engineering is also used to modify the pathway of polyhydroxyalkanoates production and to increase the yield and simultaneously decrease the expenses
(Lutke-Eversloh and Steinbuchel 2004). Experiments conducted on Escherichia
coli revealed that a production of 90% of polyhydroxybutyrate was reached via this
method, where the PhaC enzyme was added to the Escherichia coli from Cupriavidus
necator (Możejko-Ciesielska and Kiewisz 2016; Koller et al. 2017). While the
results of genetically modified bacteria are great, the costs are high for their development and for maintaining the pure culture during production, making them typically not suitable for wastewater treatment applications.
Fig. 5.3 Pathway I for short-chain-length polyhydroxyalkanoates production (Modified after
Serafim et al. 2008). Scl, short chain length
S. Sali and H. R. Mackey