transport, nitrite/nitrate and sulfate reduction, nitrogen fixation, and/or detoxification of reactive oxygen species (ROS). Sulfur involves the formation of sulfolipids,
polysaccharides, and proteins, as well as in the electron transport chain. When
sulfur is present at limiting concentrations, it inhibits cell division, whereas high
concentrations inhibit the photosynthetic assimilation of carbon-rich compounds,
such as carbohydrates. CO 2 is the most common source of carbon (autotrophic
condition), and under nitrogen depletion conditions, the supplementation of CO 2 in
conjunction with light intensity causes the carbon to be absorbed and converted into
carbohydrates more efficiently.
According to Dragone et al. (2011), increasing microalgal starch content by
nutrient limitation has been regarded as an affordable approach for the production of
the third-generation bioethanol. Thus, these authors have evaluated starch accumulation in C. vulgaris P12 under different initial concentrations of nitrogen
(0–2.2 g urea /L) and iron (0–0.08 g FeNa-EDTA /L) sources, using an experimental
design. Starch accumulation occurred at nitrogen depletion conditions. Cell growth
was much slower than that observed during nitrogen-supplemented cultivations.
The authors proposed a two-stage cultivation process for high starch accumulation:
Table 2 Microalgae carbohydrate content in different growth conditions (adapted from Dragone
et al. 2011; de Farias Silva and Bertucco 2016; Rizza et al. 2017)
Microalgae
Growth conditions
Carbohydrate
(%)
Arthrospira platensis
150 µmol/(m
2
s), 30 °C, bubbling air
58.0
Chlamydomonas reinhardtii
UTEX 90
450 µmol/(m
2
s), 23 °C, 4 days, and
130 rpm
59.7
Chlorella vulgaris KMMCC-9
UTEX26
150 µmol/(m
2
/s), 20–22 °C, bubbling air
22.4
Chlorella sp. KR-1
80 µmol/(m
2
s), 30 °C, and 10% CO 2
49.7
Chlorella sp. TISTR 8485
BG11 medium for 20 days
27.0
Chlorococcum sp. TISTR 8583
BG11 medium for 20 days
25.9
Scenedesmus obliquus
150 µmol/(m
2
s), 25 °C, bubbling air
30.0
Scenedesmus obliquus CNW-N
210–230 µmol/(m
2
s), 28 °C, 300 rpm, and
2.5% CO 2
51.8
Synechococcus elongatus PCC
7942
200 µmol/(m
2
s), 28 °C, and 5% CO 2
28.0
Synechococcus sp. PCC 7002
250 µmol/(m
2
s) and 1% CO 2
59.0
Tetraselmis subcordiformis
FACHB-1751
150 µmol/(m
2
s), 25 °C, and 3% CO 2
40.0
Ankistrodesmus sp. strain LP1
BG11 medium supplemented with 1 mM
NaNO 3
51.3
Desmodesmus sp. strain FG
BG11 medium with 1 mM NaNO 3
53.5
Pseudokirchneriella sp. strain
C1D
BG11 medium with 1 mM NaNO 3
40.5
Scenedesmus obliquus strain C1S BG11 medium with 1 mM NaNO 3
29.9
11 Biofuels from Microalgae: Bioethanol
235
polysaccharides, and proteins, as well as in the electron transport chain. When
sulfur is present at limiting concentrations, it inhibits cell division, whereas high
concentrations inhibit the photosynthetic assimilation of carbon-rich compounds,
such as carbohydrates. CO 2 is the most common source of carbon (autotrophic
condition), and under nitrogen depletion conditions, the supplementation of CO 2 in
conjunction with light intensity causes the carbon to be absorbed and converted into
carbohydrates more efficiently.
According to Dragone et al. (2011), increasing microalgal starch content by
nutrient limitation has been regarded as an affordable approach for the production of
the third-generation bioethanol. Thus, these authors have evaluated starch accumulation in C. vulgaris P12 under different initial concentrations of nitrogen
(0–2.2 g urea /L) and iron (0–0.08 g FeNa-EDTA /L) sources, using an experimental
design. Starch accumulation occurred at nitrogen depletion conditions. Cell growth
was much slower than that observed during nitrogen-supplemented cultivations.
The authors proposed a two-stage cultivation process for high starch accumulation:
Table 2 Microalgae carbohydrate content in different growth conditions (adapted from Dragone
et al. 2011; de Farias Silva and Bertucco 2016; Rizza et al. 2017)
Microalgae
Growth conditions
Carbohydrate
(%)
Arthrospira platensis
150 µmol/(m
2
s), 30 °C, bubbling air
58.0
Chlamydomonas reinhardtii
UTEX 90
450 µmol/(m
2
s), 23 °C, 4 days, and
130 rpm
59.7
Chlorella vulgaris KMMCC-9
UTEX26
150 µmol/(m
2
/s), 20–22 °C, bubbling air
22.4
Chlorella sp. KR-1
80 µmol/(m
2
s), 30 °C, and 10% CO 2
49.7
Chlorella sp. TISTR 8485
BG11 medium for 20 days
27.0
Chlorococcum sp. TISTR 8583
BG11 medium for 20 days
25.9
Scenedesmus obliquus
150 µmol/(m
2
s), 25 °C, bubbling air
30.0
Scenedesmus obliquus CNW-N
210–230 µmol/(m
2
s), 28 °C, 300 rpm, and
2.5% CO 2
51.8
Synechococcus elongatus PCC
7942
200 µmol/(m
2
s), 28 °C, and 5% CO 2
28.0
Synechococcus sp. PCC 7002
250 µmol/(m
2
s) and 1% CO 2
59.0
Tetraselmis subcordiformis
FACHB-1751
150 µmol/(m
2
s), 25 °C, and 3% CO 2
40.0
Ankistrodesmus sp. strain LP1
BG11 medium supplemented with 1 mM
NaNO 3
51.3
Desmodesmus sp. strain FG
BG11 medium with 1 mM NaNO 3
53.5
Pseudokirchneriella sp. strain
C1D
BG11 medium with 1 mM NaNO 3
40.5
Scenedesmus obliquus strain C1S BG11 medium with 1 mM NaNO 3
29.9
11 Biofuels from Microalgae: Bioethanol
235