18
ces useful in tissue engineering (Moon et al. 2012). Amino acid-derived polymers
have been proven highly valuable in anti-infective applications (Gontsarik et al.
2019) and wound healing activities (Durão et al. 2018). The zwitterionic nature of
amino acids has been demonstrated to be important in the application of amino
acid polymers as antifouling materials (Zheng et al. 2017). Amino acid-derived
polymers are therefore well positioned to boost the spectrum of available means to
address a number of problems of enormous significance.
ω-Amino Acid-Based Lactams
Besides the proteinogenic α-amino acids, several ω-amino acids such as
γ-aminobutyric acid (GABA), δ-aminovaleric acid (5-AVA), ε-aminocaproic acid
(6-ACA), and β-alanine occur as intermediates of cellular metabolism and have
been employed as precursors of industrially relevant polyamides in their cyclized
form. For instance, the ring cyclization of 5-AVA and 6-ACA produces the lactams
δ-valerolactam and ε-caprolactam which are employed in bio-based renewable
manufacturing of nylon-5, nylon-6, and nylon-6,5. δ-Aminovaleric acid is a common product of the anaerobic degradation of protein hydrolysates by several
Clostridium species, and γ-aminobutyric acid, which is produced by the decarboxylation of glutamic acid (Buckel 2001), is widespread in nature. By reason of the
ever-increasing industrial demand for lactams, microorganisms have been metabolically engineered for enhancing the production of the ω-amino acid precursors
γ-aminobutyric acid (Choi et al. 2015b), δ-aminovaleric acid (Shin et al. 2016), and
ε-aminocaproic acid (Turk et al. 2016). However, the identification and engineering
of biocatalysts, in particular, enzymes or pathways, for the industrial synthesis of
ω-amino acids does not rely on gas fermentation or photosynthetic microorganisms
(Yeom et al. 2018). A study examined growth characteristics and intracellular components of Chlorella zofingiensis G1 cultivated under pH regulations using CO 2 in
bench-scale outdoor ponds using diluted dairy wastewater as medium for algal
growth. Results showed that the content of cell-free γ-aminobutyric acid was
284.1 mg/g under CO 2 -based regulation (Huo et al. 2012). Nonetheless, no previous
report designed biosynthetic pathways finalized towards the photosynthetic or gas
fermentative production of ω-amino acids.
1.3.4 Production of Diols in Engineered Microorganisms
1,3-Propanediol
1,3-Propanediol (1,3-PDO) is the organic compound with the formula CH 2 (CH 2 OH) 2 .
The global 1,3-PDO market is estimated to register a CAGR of 10.4% between
2014 and 2021, and the market value is estimated to reach $621.2 million by 2021.
1,3-PDO is utilized for manufacturing a number of chemicals and materials. Among
A. A. Azim et al.
ces useful in tissue engineering (Moon et al. 2012). Amino acid-derived polymers
have been proven highly valuable in anti-infective applications (Gontsarik et al.
2019) and wound healing activities (Durão et al. 2018). The zwitterionic nature of
amino acids has been demonstrated to be important in the application of amino
acid polymers as antifouling materials (Zheng et al. 2017). Amino acid-derived
polymers are therefore well positioned to boost the spectrum of available means to
address a number of problems of enormous significance.
ω-Amino Acid-Based Lactams
Besides the proteinogenic α-amino acids, several ω-amino acids such as
γ-aminobutyric acid (GABA), δ-aminovaleric acid (5-AVA), ε-aminocaproic acid
(6-ACA), and β-alanine occur as intermediates of cellular metabolism and have
been employed as precursors of industrially relevant polyamides in their cyclized
form. For instance, the ring cyclization of 5-AVA and 6-ACA produces the lactams
δ-valerolactam and ε-caprolactam which are employed in bio-based renewable
manufacturing of nylon-5, nylon-6, and nylon-6,5. δ-Aminovaleric acid is a common product of the anaerobic degradation of protein hydrolysates by several
Clostridium species, and γ-aminobutyric acid, which is produced by the decarboxylation of glutamic acid (Buckel 2001), is widespread in nature. By reason of the
ever-increasing industrial demand for lactams, microorganisms have been metabolically engineered for enhancing the production of the ω-amino acid precursors
γ-aminobutyric acid (Choi et al. 2015b), δ-aminovaleric acid (Shin et al. 2016), and
ε-aminocaproic acid (Turk et al. 2016). However, the identification and engineering
of biocatalysts, in particular, enzymes or pathways, for the industrial synthesis of
ω-amino acids does not rely on gas fermentation or photosynthetic microorganisms
(Yeom et al. 2018). A study examined growth characteristics and intracellular components of Chlorella zofingiensis G1 cultivated under pH regulations using CO 2 in
bench-scale outdoor ponds using diluted dairy wastewater as medium for algal
growth. Results showed that the content of cell-free γ-aminobutyric acid was
284.1 mg/g under CO 2 -based regulation (Huo et al. 2012). Nonetheless, no previous
report designed biosynthetic pathways finalized towards the photosynthetic or gas
fermentative production of ω-amino acids.
1.3.4 Production of Diols in Engineered Microorganisms
1,3-Propanediol
1,3-Propanediol (1,3-PDO) is the organic compound with the formula CH 2 (CH 2 OH) 2 .
The global 1,3-PDO market is estimated to register a CAGR of 10.4% between
2014 and 2021, and the market value is estimated to reach $621.2 million by 2021.
1,3-PDO is utilized for manufacturing a number of chemicals and materials. Among
A. A. Azim et al.