261
El-Baky et al. (2009) studied the effect of H 2 O 2 stress on carotenoid content
and cellular antioxidants response of Spirulina platensis. The contents of hydrophilic antioxidants ascorbic acid and glutathione and lipophilic antioxidant
tocopherol increased with the increase in the concentration of H 2 O 2 . The activities
of enzymatic antioxidants CAT, POX and SOD also increased consistently.
Carotenoid profiling showed increase in the accumulation of β-carotene, astaxanthin, lutein, zeaxanthin and cryptoxanthin with the increase in the concentration of
H 2 O 2 . This suggests the role of different carotenoids and their derivatives as protectors in the dissipation of chloroplastic ROS (Bennoun 1998). Wei et al. (2008)
studied the effects of oxidative stress on lutein production in heterotrophic
Chlorella protothecoides. The addition of 0.1 mM H 2 O 2 and 0.01 mM NaClO plus
0.5 mM Fe
2+
into the culture led to the generation of OH
•
radicals and enhanced
the lutein content from 1.75 to 1.90 and 1.95 mg/g, respectively. The higher lutein
content of 1.98 mg/g was observed when 0.01 mM H 2 O 2 and 0.5 mM NaClO were
used to generate
1
O 2 .
Oxidative stress caused by intense light illumination is also effective for inducing carotenoid accumulation in microalgae. The underlying mechanism is that
excess photo-oxidation under high-light irradiance generates various ROS like
O 2
•− , OH
•
and
1
O 2 . In the presence of ROS, the antioxidative carotenoids are produced, which could forestall damage of excessive irradiance by directly quenching triplet chlorophyll (
3
Chl) or
1
O 2 produced from photodynamic reactions
(Krinsky 1979) and thus protect the cells against oxidative damage (Ip and Chen
2005). Hu et al. (2008) observed enhanced protection against photo-oxidative
stress in an astaxanthin- overproduction mutant of Haematococcus MT 2877.
After 3 days of high-light induction from 20 to 250 μmol m
−2
s
−1 , the astaxanthin
content of mutant cells increased by twofolds compared to wild-type cells,
whereas the lutein and β-carotene content remained almost constant. Regulation
of astaxanthin biosynthesis might be most likely attributed to the ‘secondary messengers’’ role of ROS to transduce signalling pathways and altered expression of
certain genes and antioxidant enzymes involved in carotenogenesis (Kullik and
Storz 1994; Bouvier et al. 1998). Another mechanism of carotenoid photoprotection was described by Ben- Amotz et al. (1989) who concluded that large amount
of β-carotene accumulate in the inter-thylakoid space of the green algae Dunaliella
bardawil. This carotenoid could protect the cells from high irradiance injury by
acting as a screen preventing excessive irradiance of blue light from reaching the
antenna chlorophylls. This ‘filter effect’ of β-carotene is attributed to the large
overlap between the absorption spectra of β-carotene and chlorophyll in the blue
light regime (Boussiba 2000). Shaish et al. (1993) observed that addition of promoters of oxygen radicals greatly enhanced β-carotene synthesis, photodegradation of chlorophyll and inhibition of photosynthesis in D. bardawil under high
irradiance and suggested that D. bardawil adapts to the oxidative stress caused by
high irradiance by accumulation of β-carotene along with increasing the activities
of CAT and SOD.
13 Oxidative Stress-Induced Bioprospecting of Microalgae
El-Baky et al. (2009) studied the effect of H 2 O 2 stress on carotenoid content
and cellular antioxidants response of Spirulina platensis. The contents of hydrophilic antioxidants ascorbic acid and glutathione and lipophilic antioxidant
tocopherol increased with the increase in the concentration of H 2 O 2 . The activities
of enzymatic antioxidants CAT, POX and SOD also increased consistently.
Carotenoid profiling showed increase in the accumulation of β-carotene, astaxanthin, lutein, zeaxanthin and cryptoxanthin with the increase in the concentration of
H 2 O 2 . This suggests the role of different carotenoids and their derivatives as protectors in the dissipation of chloroplastic ROS (Bennoun 1998). Wei et al. (2008)
studied the effects of oxidative stress on lutein production in heterotrophic
Chlorella protothecoides. The addition of 0.1 mM H 2 O 2 and 0.01 mM NaClO plus
0.5 mM Fe
2+
into the culture led to the generation of OH
•
radicals and enhanced
the lutein content from 1.75 to 1.90 and 1.95 mg/g, respectively. The higher lutein
content of 1.98 mg/g was observed when 0.01 mM H 2 O 2 and 0.5 mM NaClO were
used to generate
1
O 2 .
Oxidative stress caused by intense light illumination is also effective for inducing carotenoid accumulation in microalgae. The underlying mechanism is that
excess photo-oxidation under high-light irradiance generates various ROS like
O 2
•− , OH
•
and
1
O 2 . In the presence of ROS, the antioxidative carotenoids are produced, which could forestall damage of excessive irradiance by directly quenching triplet chlorophyll (
3
Chl) or
1
O 2 produced from photodynamic reactions
(Krinsky 1979) and thus protect the cells against oxidative damage (Ip and Chen
2005). Hu et al. (2008) observed enhanced protection against photo-oxidative
stress in an astaxanthin- overproduction mutant of Haematococcus MT 2877.
After 3 days of high-light induction from 20 to 250 μmol m
−2
s
−1 , the astaxanthin
content of mutant cells increased by twofolds compared to wild-type cells,
whereas the lutein and β-carotene content remained almost constant. Regulation
of astaxanthin biosynthesis might be most likely attributed to the ‘secondary messengers’’ role of ROS to transduce signalling pathways and altered expression of
certain genes and antioxidant enzymes involved in carotenogenesis (Kullik and
Storz 1994; Bouvier et al. 1998). Another mechanism of carotenoid photoprotection was described by Ben- Amotz et al. (1989) who concluded that large amount
of β-carotene accumulate in the inter-thylakoid space of the green algae Dunaliella
bardawil. This carotenoid could protect the cells from high irradiance injury by
acting as a screen preventing excessive irradiance of blue light from reaching the
antenna chlorophylls. This ‘filter effect’ of β-carotene is attributed to the large
overlap between the absorption spectra of β-carotene and chlorophyll in the blue
light regime (Boussiba 2000). Shaish et al. (1993) observed that addition of promoters of oxygen radicals greatly enhanced β-carotene synthesis, photodegradation of chlorophyll and inhibition of photosynthesis in D. bardawil under high
irradiance and suggested that D. bardawil adapts to the oxidative stress caused by
high irradiance by accumulation of β-carotene along with increasing the activities
of CAT and SOD.
13 Oxidative Stress-Induced Bioprospecting of Microalgae