102
M. Scarsini et al.
(Ben Amor-Ben Ayed et al. 2015), that are thought to act as a cell stress signalling
way involved in the carotenoid production.
Salinity occupies a particular place in the biology of living organisms because
sodium are highly toxic to organisms that are not adapted to it (Masmoudi et al. 2013).
Therefore, increasing the sodium concentration in the growth medium may constitute a stress able to trigger the accumulation of secondary carotenoids (astaxanthinHaematococcus pluvialis: Gao et al. (2015), β-carotene-Dunaliella: Raja et al. (2007),
Zarandi-Miandoab et al. (2019), lutein-Chlorella sorokiniana: Cordero et al. (2011)).
Altogether, a careful look at the ionic composition of the growth medium is required
when optimizing carotenoid production by microalgae.
5.4.1.2 The Nitrate and Phosphate Availability
Nitrogen availability is among the crucial component of the growth medium because
it stimulates cell division. When the growth medium is depleted partially or totally
in bioavailable nitrogen, cell replication is slowed down and the accumulation of
secondary carotenoid is stimulated (Lemoine and Schoefs 2010). The gene coding
the acetyl-CoA carboxylase, the enzyme catalysing the limiting step of fatty acid
synthesis, is especially upregulated (Zhao et al. 2019). Actually, all the genes coding
enzymes catalysing the transformation of IPI/DMAPP to astaxanthin were upregulated, the highest regulation being observed for psy, zds, chyB and bkt genes (Zhao
et al. 2019). Geranylgeraniol diphosphate is at the crossroad of the chlorophyll
(Schoefs and Bertrand 2000) and carotenoid biosynthetic pathways (Heydarizadeh
et al. 2013). Nitrogen deprivation down-regulates the expression of genes coding
enzymes involved in phytol production suggesting that the flux of IPP is oriented
toward secondary carotenoid production. This is correlated with the overexpression
of the PSY encoding genes (Zhao et al. 2019) and consistent with the disorganization
of the photosynthetic apparatus (Tan et al. 1995; Lemoine et al. 2008). Interestingly,
the genes involved in lutein biosynthesis were also upregulated. The genes coding for
the enzymes involved in zeaxanthin and canthaxanthin pathways both reported to end
with astaxanthin were upregulated. A similar upregulation was observed in Haematococcus pluvialis exposed to blue light (Gu et al. 2014) and exogenous phytohormone
applications.
Recent data suggest that the level of nitrogen is probably not the sole factor
acting on the activity of the secondary carotenoid pathway. Actually, it would be the
C/N ratio that would regulate the secondary carotenoid production and not the actual
carbon or nitrogen cellular quota. High C/N ratio would favour the production of these
compounds (astaxanthin-Haematococcus pluvialis: Kang et al. (2007), Kakizono
et al. (1992), astaxanthin-Chromochloris zofingiensis: Sun et al. (2008), cantaxanthinChlorosarcinopsis sp.: Cherdchukeattisak et al. (2018).
As nitrate starvation, phosphate starvation triggers astaxanthin accumulation in
Haematococcus pluvialis (Fan et al. 1998).
M. Scarsini et al.
(Ben Amor-Ben Ayed et al. 2015), that are thought to act as a cell stress signalling
way involved in the carotenoid production.
Salinity occupies a particular place in the biology of living organisms because
sodium are highly toxic to organisms that are not adapted to it (Masmoudi et al. 2013).
Therefore, increasing the sodium concentration in the growth medium may constitute a stress able to trigger the accumulation of secondary carotenoids (astaxanthinHaematococcus pluvialis: Gao et al. (2015), β-carotene-Dunaliella: Raja et al. (2007),
Zarandi-Miandoab et al. (2019), lutein-Chlorella sorokiniana: Cordero et al. (2011)).
Altogether, a careful look at the ionic composition of the growth medium is required
when optimizing carotenoid production by microalgae.
5.4.1.2 The Nitrate and Phosphate Availability
Nitrogen availability is among the crucial component of the growth medium because
it stimulates cell division. When the growth medium is depleted partially or totally
in bioavailable nitrogen, cell replication is slowed down and the accumulation of
secondary carotenoid is stimulated (Lemoine and Schoefs 2010). The gene coding
the acetyl-CoA carboxylase, the enzyme catalysing the limiting step of fatty acid
synthesis, is especially upregulated (Zhao et al. 2019). Actually, all the genes coding
enzymes catalysing the transformation of IPI/DMAPP to astaxanthin were upregulated, the highest regulation being observed for psy, zds, chyB and bkt genes (Zhao
et al. 2019). Geranylgeraniol diphosphate is at the crossroad of the chlorophyll
(Schoefs and Bertrand 2000) and carotenoid biosynthetic pathways (Heydarizadeh
et al. 2013). Nitrogen deprivation down-regulates the expression of genes coding
enzymes involved in phytol production suggesting that the flux of IPP is oriented
toward secondary carotenoid production. This is correlated with the overexpression
of the PSY encoding genes (Zhao et al. 2019) and consistent with the disorganization
of the photosynthetic apparatus (Tan et al. 1995; Lemoine et al. 2008). Interestingly,
the genes involved in lutein biosynthesis were also upregulated. The genes coding for
the enzymes involved in zeaxanthin and canthaxanthin pathways both reported to end
with astaxanthin were upregulated. A similar upregulation was observed in Haematococcus pluvialis exposed to blue light (Gu et al. 2014) and exogenous phytohormone
applications.
Recent data suggest that the level of nitrogen is probably not the sole factor
acting on the activity of the secondary carotenoid pathway. Actually, it would be the
C/N ratio that would regulate the secondary carotenoid production and not the actual
carbon or nitrogen cellular quota. High C/N ratio would favour the production of these
compounds (astaxanthin-Haematococcus pluvialis: Kang et al. (2007), Kakizono
et al. (1992), astaxanthin-Chromochloris zofingiensis: Sun et al. (2008), cantaxanthinChlorosarcinopsis sp.: Cherdchukeattisak et al. (2018).
As nitrate starvation, phosphate starvation triggers astaxanthin accumulation in
Haematococcus pluvialis (Fan et al. 1998).