265
The MDA content also exhibited a positive correlation with the ROS production. The
activities of SOD, CAT and POX increased by 1.66-, 3.6- and 2.98-folds, respectively than those of control. In another study (Pancha et al. 2015a), increase in the
salinity of culture medium resulted into simultaneous increase in the lipid and carbohydrate accumulation by Scenedesmus sp. Addition of 400 mM NaCl increased the
lipid and carbohydrate contents by 1.8- and 2-folds, respectively. There was over 9and 1.5-folds increase in the H 2 O 2 content and APX activity, respectively. The lipid
peroxidation increased by 2-folds, while the proline content increased by 4.5-folds.
When the microalgal cells are subjected to high light, the excess electrons in
photosynthetic electron transport chain generate numerous ROS. Lipids, especially
neutral lipids, and carbohydrates are the preferred storage products in microalgae
under various stress conditions as they have highly reduced states and could be used
during adverse conditions for the survival of cells (Li et al. 2011). Along with various enzymatic and non-enzymatic antioxidants, synthesis of lipid could also serve
as a receptor to dissipate excess electrons to overcome the oxidative damage. He
et al. (2015) studied the effect of different light intensities (40, 200 and 400 μmol
m
−2
s
−1
) on neutral lipid accumulation and changes in the activity of ROS scavenging enzymes in Chlorella sp. and Monoraphidium dybowskii. After 10 days of cultivation in high light of 400 μmol m
−2
s
−1
, there was about 3- and 5-folds increase in
SOD activity, 4- and 4.6-folds increase in POD activity and 2.53- and 2.43-folds
increase in CAT activity of Chlorella sp. and M. dybowskii, respectively. The protein and carbohydrate contents of the cells decreased and the chlorophyll degraded.
The accumulation of total lipid and neutral lipid increased with the increase in light
intensity. The transcriptomic differentiation of antioxidant defence of H. pluvialis
revealed that an increase in ROS scavenging activity, a decrease in ROS production
and the relaxation of over-reduction of photosynthetic electron transport chain work
together to protect the cells against photo-oxidative stress (Gwak et al. 2014). Under
high irradiance, accumulation of TAG was attributed to moderate upregulation of de
novo fatty acid biosynthesis at the gene level as well as moderate elevation of the
TAG assembly pathways. It is known that carbohydrate and lipid synthesis is a parallel phenomenon in microalgae, and reduced energy is first stored as carbohydrate
and excess is converted into lipids (Fan et al. 2012). Under stress conditions, the
ROS production might divert the provisions of carbon skeleton for amino acids and
protein synthesis to TAG biosynthesis to resist the cell damage (Msanne et al. 2012).
Osundeko et al. (2013) studied oxidative stress tolerance of five different microalgal strains in raw municipal wastewater secondary effluent for their biofuel application. The ROS generation in all strains was about 130–170% higher relative to
non-stressed conditions. There was significant reduction in cell density of nonadapted strains Chlamydomonas debaryana, Hindakia tetrachotoma and
Desmodesmus subspicatus at 15 and 20 mol/m
3
H 2 O 2 , while Chlorella luteoviridis
and Parachlorella hussii could completely survive and grow very well due to their
substantial tolerance to oxidative stress generated by wastewater. These strains also
exhibited high APX activity. In another study (Osundeko et al. 2014), 8 weeks of
acclimation of various microalgae to wastewater resulted in significantly higher
growth rate and biomass productivity. The acclimation to wastewater tolerance was
13 Oxidative Stress-Induced Bioprospecting of Microalgae
The MDA content also exhibited a positive correlation with the ROS production. The
activities of SOD, CAT and POX increased by 1.66-, 3.6- and 2.98-folds, respectively than those of control. In another study (Pancha et al. 2015a), increase in the
salinity of culture medium resulted into simultaneous increase in the lipid and carbohydrate accumulation by Scenedesmus sp. Addition of 400 mM NaCl increased the
lipid and carbohydrate contents by 1.8- and 2-folds, respectively. There was over 9and 1.5-folds increase in the H 2 O 2 content and APX activity, respectively. The lipid
peroxidation increased by 2-folds, while the proline content increased by 4.5-folds.
When the microalgal cells are subjected to high light, the excess electrons in
photosynthetic electron transport chain generate numerous ROS. Lipids, especially
neutral lipids, and carbohydrates are the preferred storage products in microalgae
under various stress conditions as they have highly reduced states and could be used
during adverse conditions for the survival of cells (Li et al. 2011). Along with various enzymatic and non-enzymatic antioxidants, synthesis of lipid could also serve
as a receptor to dissipate excess electrons to overcome the oxidative damage. He
et al. (2015) studied the effect of different light intensities (40, 200 and 400 μmol
m
−2
s
−1
) on neutral lipid accumulation and changes in the activity of ROS scavenging enzymes in Chlorella sp. and Monoraphidium dybowskii. After 10 days of cultivation in high light of 400 μmol m
−2
s
−1
, there was about 3- and 5-folds increase in
SOD activity, 4- and 4.6-folds increase in POD activity and 2.53- and 2.43-folds
increase in CAT activity of Chlorella sp. and M. dybowskii, respectively. The protein and carbohydrate contents of the cells decreased and the chlorophyll degraded.
The accumulation of total lipid and neutral lipid increased with the increase in light
intensity. The transcriptomic differentiation of antioxidant defence of H. pluvialis
revealed that an increase in ROS scavenging activity, a decrease in ROS production
and the relaxation of over-reduction of photosynthetic electron transport chain work
together to protect the cells against photo-oxidative stress (Gwak et al. 2014). Under
high irradiance, accumulation of TAG was attributed to moderate upregulation of de
novo fatty acid biosynthesis at the gene level as well as moderate elevation of the
TAG assembly pathways. It is known that carbohydrate and lipid synthesis is a parallel phenomenon in microalgae, and reduced energy is first stored as carbohydrate
and excess is converted into lipids (Fan et al. 2012). Under stress conditions, the
ROS production might divert the provisions of carbon skeleton for amino acids and
protein synthesis to TAG biosynthesis to resist the cell damage (Msanne et al. 2012).
Osundeko et al. (2013) studied oxidative stress tolerance of five different microalgal strains in raw municipal wastewater secondary effluent for their biofuel application. The ROS generation in all strains was about 130–170% higher relative to
non-stressed conditions. There was significant reduction in cell density of nonadapted strains Chlamydomonas debaryana, Hindakia tetrachotoma and
Desmodesmus subspicatus at 15 and 20 mol/m
3
H 2 O 2 , while Chlorella luteoviridis
and Parachlorella hussii could completely survive and grow very well due to their
substantial tolerance to oxidative stress generated by wastewater. These strains also
exhibited high APX activity. In another study (Osundeko et al. 2014), 8 weeks of
acclimation of various microalgae to wastewater resulted in significantly higher
growth rate and biomass productivity. The acclimation to wastewater tolerance was
13 Oxidative Stress-Induced Bioprospecting of Microalgae