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the progress accomplished in metabolic engineering approaches, the production of
aromatic monomers from renewable feedstocks through bacterial cell factories has
recently attracted growing interest. Aromatic compounds are usually biochemically
produced by the shikimate pathway. The branching points mainly exploited in industrially relevant biochemical processes are aromatic amino acids, which have been the
preferential targets in the past, and chorismate. Among several derivatives of aromatic
amino acids, the phenylpropanoid acids and their derivatives have been the focus of
growing attention (Maeda and Dudareva 2012). Chorismate is the precursor mainly
for benzoate derivatives such as salicylic acid, p-aminobenzoic acid, p-hydroxybenzoic acid, cis,cis-muconic acid, and phenyllactic acid. However, most of the aforementioned benzoates are biochemically obtained using fermentation from sugar
rather than carbon dioxide feedstocks. Indeed, the most widely employed bacteria for
production of aromatics are engineered Escherichia coli, Pseudomonas Putida,
Saccharomyces cerevisiae, and Corynebacterium glutamicum (Noda and Kondo
2017). Here we focus in particular on p-hydroxybenzoate since we limit to highlight
the biotechnological processes implying microorganisms that directly transform carbon dioxide into aromatic compounds or microorganisms that transform carbon dioxide into intermediates to aromatic compounds valuable in polymer synthesis.
1.4.1 Production of Phenylpropanoid Acids in Engineered
Microorganisms
Phenylpropanoid acids are precursors for the synthesis of thermoplastics besides
flavoring, cosmetic, and health products. Plants are usually able to accumulate only
small amounts of these secondary metabolites; furthermore, the metabolites of
interest are often contaminated by other structurally similar compounds making difficult their extraction and purification (Hamilton 2004). For these reasons, alternative production strategies were explored. The recent advances in synthetic biology
and metabolic engineering prompted the exploitation of alternative microorganisms
for the production of these plant natural products. Cyanobacteria represent the best
choice for the green synthesis of phenylpropanoid acid derivatives from CO 2 .
Among the phenylpropanoid acid-based compounds, we discuss p-coumaric acid
(p-CA), 3,4-dihydroxycinnamic acid (DHCA), p-hydroxybenzene (p-HBA), and
p-hydroxystyrene (p-HS), which showed potential characteristics for the production
of biopolymers (Thi et al. 2008).
P-Coumaric Acid
Xue et al. (2014a) engineered a strain of CO 2 -fixing cyanobacterium Synechocystis
PCC6803 to produce p-coumaric acid (p-CA) from the precursor tyrosine through
the shikimate pathway. Synechocystis was genetically engineered to express the
tyrosine ammonia lyase (encoded by sam8) from Saccharothrix espanaensis and to
A. A. Azim et al.
the progress accomplished in metabolic engineering approaches, the production of
aromatic monomers from renewable feedstocks through bacterial cell factories has
recently attracted growing interest. Aromatic compounds are usually biochemically
produced by the shikimate pathway. The branching points mainly exploited in industrially relevant biochemical processes are aromatic amino acids, which have been the
preferential targets in the past, and chorismate. Among several derivatives of aromatic
amino acids, the phenylpropanoid acids and their derivatives have been the focus of
growing attention (Maeda and Dudareva 2012). Chorismate is the precursor mainly
for benzoate derivatives such as salicylic acid, p-aminobenzoic acid, p-hydroxybenzoic acid, cis,cis-muconic acid, and phenyllactic acid. However, most of the aforementioned benzoates are biochemically obtained using fermentation from sugar
rather than carbon dioxide feedstocks. Indeed, the most widely employed bacteria for
production of aromatics are engineered Escherichia coli, Pseudomonas Putida,
Saccharomyces cerevisiae, and Corynebacterium glutamicum (Noda and Kondo
2017). Here we focus in particular on p-hydroxybenzoate since we limit to highlight
the biotechnological processes implying microorganisms that directly transform carbon dioxide into aromatic compounds or microorganisms that transform carbon dioxide into intermediates to aromatic compounds valuable in polymer synthesis.
1.4.1 Production of Phenylpropanoid Acids in Engineered
Microorganisms
Phenylpropanoid acids are precursors for the synthesis of thermoplastics besides
flavoring, cosmetic, and health products. Plants are usually able to accumulate only
small amounts of these secondary metabolites; furthermore, the metabolites of
interest are often contaminated by other structurally similar compounds making difficult their extraction and purification (Hamilton 2004). For these reasons, alternative production strategies were explored. The recent advances in synthetic biology
and metabolic engineering prompted the exploitation of alternative microorganisms
for the production of these plant natural products. Cyanobacteria represent the best
choice for the green synthesis of phenylpropanoid acid derivatives from CO 2 .
Among the phenylpropanoid acid-based compounds, we discuss p-coumaric acid
(p-CA), 3,4-dihydroxycinnamic acid (DHCA), p-hydroxybenzene (p-HBA), and
p-hydroxystyrene (p-HS), which showed potential characteristics for the production
of biopolymers (Thi et al. 2008).
P-Coumaric Acid
Xue et al. (2014a) engineered a strain of CO 2 -fixing cyanobacterium Synechocystis
PCC6803 to produce p-coumaric acid (p-CA) from the precursor tyrosine through
the shikimate pathway. Synechocystis was genetically engineered to express the
tyrosine ammonia lyase (encoded by sam8) from Saccharothrix espanaensis and to
A. A. Azim et al.