25
PQ-9 (Sadre et al. 2012) (Pfaff et al. 2013). Recently, p-HBA production has witnessed an increasing demand for sustainable biological processes from renewable
feedstocks, including carbon dioxide.
A possible way for the production of p-HBA from CO 2 concerns the combinatory production of p-CA from cyanobacteria with its further conversion in p-HBA
by soil bacteria (Fig. 1.9).
Jung et al. (2016) sought to produce p-HBA in Burkholderia glumae strain BGR1
which can grow on the sole p-CA carbonaceous source via a CoA-dependent non-βoxidation pathway. To enhance the production of p-HBA, the strain was modified by
overexpressing the rate-limiting enzyme in p-HBA synthesis, which turned out to be
the p-hydroxcinnmaoyl-CoA synthetase II, upon promoter optimization. Furthermore,
to prevent the synthesized p-HBA from natural degradation, the strain was optimized
by knocking out the p-hydroxybenzoate-3-hydroxylase and benzoyl-CoA ligase
genes, which catalyze the transformation of p-HBA into intermediates employed in
central metabolism. The resulting Burkholderia glumae mutant resulted in 19.8 mM
of p-HBA with the 99% of conversion at 20 mM p-CA. Aresta and Dibenedetto
(2002) tested an alternative route to produce p-HBA based on the application of a
phenol carboxylase enzyme for the functionalization of phenolic organic substrates
with carbon dioxide at room temperature under atmospheric pressure. The phenol
carboxylase enzyme extracted from the bacterium Thauera aromatica and supported
on a low-melting agar showed a turnover number of around 16,000 with an enzyme
activity that lasts from a few days to weeks. In alternative, a reversible carboxylation
of the phenols with CO 2 to produce p-hydroxybenzoate could be also performed
from 4-hydroxybenzoate decarboxylases from Chlamydophila pneumoniae AR39
and Enterobacter cloacae P240109 (Liu et al. 2007) (Matsui et al. 2006).
1.5 In Vivo Synthetic Polymers
1.5.1 Cyanophycin
Cyanophycin (CP) is a non-ribosomally synthesized amino acid polymer consisting
of a polyaspartate backbone with arginine side chains attached with their α-amino
group to the β-carboxylic group of each aspartate (Simon 1976; Berg et al. 2000).
Cyanophycin is naturally produced in many cyanobacteria though their autotrophic
metabolism by the cyanophycin synthetase, which catalyzes an ATP-dependent
polymerization of arginine and aspartate. Cyanophycin, with a molecular weight
Fig. 1.9 Oxidation of p-coumaric acid (p-CA) to p-hydroxybenzoate (p-HBA)
1 Use of Carbon Dioxide in Polymer Synthesis
PQ-9 (Sadre et al. 2012) (Pfaff et al. 2013). Recently, p-HBA production has witnessed an increasing demand for sustainable biological processes from renewable
feedstocks, including carbon dioxide.
A possible way for the production of p-HBA from CO 2 concerns the combinatory production of p-CA from cyanobacteria with its further conversion in p-HBA
by soil bacteria (Fig. 1.9).
Jung et al. (2016) sought to produce p-HBA in Burkholderia glumae strain BGR1
which can grow on the sole p-CA carbonaceous source via a CoA-dependent non-βoxidation pathway. To enhance the production of p-HBA, the strain was modified by
overexpressing the rate-limiting enzyme in p-HBA synthesis, which turned out to be
the p-hydroxcinnmaoyl-CoA synthetase II, upon promoter optimization. Furthermore,
to prevent the synthesized p-HBA from natural degradation, the strain was optimized
by knocking out the p-hydroxybenzoate-3-hydroxylase and benzoyl-CoA ligase
genes, which catalyze the transformation of p-HBA into intermediates employed in
central metabolism. The resulting Burkholderia glumae mutant resulted in 19.8 mM
of p-HBA with the 99% of conversion at 20 mM p-CA. Aresta and Dibenedetto
(2002) tested an alternative route to produce p-HBA based on the application of a
phenol carboxylase enzyme for the functionalization of phenolic organic substrates
with carbon dioxide at room temperature under atmospheric pressure. The phenol
carboxylase enzyme extracted from the bacterium Thauera aromatica and supported
on a low-melting agar showed a turnover number of around 16,000 with an enzyme
activity that lasts from a few days to weeks. In alternative, a reversible carboxylation
of the phenols with CO 2 to produce p-hydroxybenzoate could be also performed
from 4-hydroxybenzoate decarboxylases from Chlamydophila pneumoniae AR39
and Enterobacter cloacae P240109 (Liu et al. 2007) (Matsui et al. 2006).
1.5 In Vivo Synthetic Polymers
1.5.1 Cyanophycin
Cyanophycin (CP) is a non-ribosomally synthesized amino acid polymer consisting
of a polyaspartate backbone with arginine side chains attached with their α-amino
group to the β-carboxylic group of each aspartate (Simon 1976; Berg et al. 2000).
Cyanophycin is naturally produced in many cyanobacteria though their autotrophic
metabolism by the cyanophycin synthetase, which catalyzes an ATP-dependent
polymerization of arginine and aspartate. Cyanophycin, with a molecular weight
Fig. 1.9 Oxidation of p-coumaric acid (p-CA) to p-hydroxybenzoate (p-HBA)
1 Use of Carbon Dioxide in Polymer Synthesis