244
M. M. Maroneze et al.
and is frequently used for human and animal nutrition, food coloring, and cosmetics
due to its provitamin A and antioxidant claims (Sui and Vlaeminck 2020).
The phycobiliproteins, in turn, are of a protein nature, hydrophilic, and highly
fluorescent. These molecules are classified into phycoerythrin, phycoerythrocyanin,
phycocyanin, and allophycocyanin according to their absorption spectra. Besides,
based on their colors are classified into two major groups, to know: phycocyanin
(blue) and phycoerythrin (red). Phycocyanin, especially C-phycocyanin, is found
mainly in cyanobacteria and phycoerythrin in cyanobacteria, cryptophyte, and red
microalgae (Pan-utai and Iamtham 2019). Phycocyanin is widely used as a natural
dye for various purposes, in the food and cosmetic industry, due to its intense blue
pigmentation and its excellent stability. Besides, interest in the use of phycocyanin in
healthy foods and as a nutraceutical has grown thanks to its functional properties, such
as antioxidant, anti-inflammatory, anti-viral, and anti-cancer (Vernès et al. 2015).
11.3 Biosynthesis of Carotenoids and Phycobiliproteins
The exploration of the microalgae photosynthetic machinery has led to the production
of valuable biochemicals. In photoautotrophic metabolism, microalgae convert solar
energy into chemical energy by fixing CO 2 . From this metabolic pathway, biosynthetic precursors of carotenoid and phycobiliproteins are generated. Both accessory pigments are of commercial interest. The molecular basis of the microalgae
pigments biosynthetic pathway is under investigation. The current understanding of
metabolism and the regulatory mechanism of synthesis in microalgae is limited and
inferred, mainly based on the knowledge obtained for plant cells (Sathasivam and Ki
2018). Figure 11.2 presents the biosynthetic pathways of carotenoids and phycobilins
in microalgae.
The carotenoids are lipophilic isoprenoids biosynthesized from isopentenyl
diphosphate (IPP) or its isomer dimethylallyl diphosphate (DMAPP) (Fernandes
et al. 2017). There are two distinct routes for IPP biosynthesis: the mevalonic acid
(MVA) route in the cytosol and the methylerythritol 4-phosphate (MEP) route in the
chloroplast. Fungi and animals perform the MVA route. In microalgae, it is suggested
that isoprenoid biosynthesis is derived from the MEP route (Paniagua-Michel et al.
2012).
The biosynthesis of IPP by the route MEP utilizes glyceraldehyde 3-phosphate and
pyruvate as substrates to form deoxy-D-xylulose-5-phosphate (DXP); through the
enzyme DXS (Huang et al. 2017). Subsequently, DXP is reduced by the enzyme DXR
to yields to MEP. In the following, IPP and DMAPP are formed and pass a series
of condensation and elongation reactions to produce geranylgeranyl diphosphate
(GGPP, C20), the precursor of carotenoid biosynthesis. Head-to-head condensation
of two GGPP molecules by the enzyme PSY gives origin to the C40 carotenoid,
the phytoene (Gong and Bassi 2016). The phytoene is converted to lycopene and
then cyclized by β-LCY, and ε-LCY followed by β-LCY to produce β-carotene and
α-carotene, respectively.
M. M. Maroneze et al.
and is frequently used for human and animal nutrition, food coloring, and cosmetics
due to its provitamin A and antioxidant claims (Sui and Vlaeminck 2020).
The phycobiliproteins, in turn, are of a protein nature, hydrophilic, and highly
fluorescent. These molecules are classified into phycoerythrin, phycoerythrocyanin,
phycocyanin, and allophycocyanin according to their absorption spectra. Besides,
based on their colors are classified into two major groups, to know: phycocyanin
(blue) and phycoerythrin (red). Phycocyanin, especially C-phycocyanin, is found
mainly in cyanobacteria and phycoerythrin in cyanobacteria, cryptophyte, and red
microalgae (Pan-utai and Iamtham 2019). Phycocyanin is widely used as a natural
dye for various purposes, in the food and cosmetic industry, due to its intense blue
pigmentation and its excellent stability. Besides, interest in the use of phycocyanin in
healthy foods and as a nutraceutical has grown thanks to its functional properties, such
as antioxidant, anti-inflammatory, anti-viral, and anti-cancer (Vernès et al. 2015).
11.3 Biosynthesis of Carotenoids and Phycobiliproteins
The exploration of the microalgae photosynthetic machinery has led to the production
of valuable biochemicals. In photoautotrophic metabolism, microalgae convert solar
energy into chemical energy by fixing CO 2 . From this metabolic pathway, biosynthetic precursors of carotenoid and phycobiliproteins are generated. Both accessory pigments are of commercial interest. The molecular basis of the microalgae
pigments biosynthetic pathway is under investigation. The current understanding of
metabolism and the regulatory mechanism of synthesis in microalgae is limited and
inferred, mainly based on the knowledge obtained for plant cells (Sathasivam and Ki
2018). Figure 11.2 presents the biosynthetic pathways of carotenoids and phycobilins
in microalgae.
The carotenoids are lipophilic isoprenoids biosynthesized from isopentenyl
diphosphate (IPP) or its isomer dimethylallyl diphosphate (DMAPP) (Fernandes
et al. 2017). There are two distinct routes for IPP biosynthesis: the mevalonic acid
(MVA) route in the cytosol and the methylerythritol 4-phosphate (MEP) route in the
chloroplast. Fungi and animals perform the MVA route. In microalgae, it is suggested
that isoprenoid biosynthesis is derived from the MEP route (Paniagua-Michel et al.
2012).
The biosynthesis of IPP by the route MEP utilizes glyceraldehyde 3-phosphate and
pyruvate as substrates to form deoxy-D-xylulose-5-phosphate (DXP); through the
enzyme DXS (Huang et al. 2017). Subsequently, DXP is reduced by the enzyme DXR
to yields to MEP. In the following, IPP and DMAPP are formed and pass a series
of condensation and elongation reactions to produce geranylgeranyl diphosphate
(GGPP, C20), the precursor of carotenoid biosynthesis. Head-to-head condensation
of two GGPP molecules by the enzyme PSY gives origin to the C40 carotenoid,
the phytoene (Gong and Bassi 2016). The phytoene is converted to lycopene and
then cyclized by β-LCY, and ε-LCY followed by β-LCY to produce β-carotene and
α-carotene, respectively.