The oils produced by microalgae are similar to those obtained from plants. In
that sense, biodiesel fuel can fundamentally be produced with the neutral lipids
obtained from microalgae. In addition, many species of microalgae are known to be
capable of accumulating neutral lipids, which can account for 50% or more of dry
algal bodies. Biodiesel fuel can also be produced with hydrocarbon raw materials
(Miao and Wu 2006).
The freshwater microalga Botryococcus braunii is considered highly promising
for its ability to produce large amounts of hydrocarbons. At the same time, its
growth rate is also slow, which makes its culturing (growth) difficult to control. As
no other microalgae species besides B. braunii have be found to produce hydrocarbons accounting for double-digit percentages of dry weight, other species cannot
be used in producing hydrocarbon with microalgae at the present time. For now, we
must rely entirely on the success or failure of B. braunii.
For this reason, neutral lipids, which are accumulated universally by various
species of microalgae, can be viewed as a future target material in terms of biodiesel
fuel production with microalgae. We therefore need to obtain marine microalgae
that are characterized by their ability to accumulate neutral lipids with the greatest
efficiency.
The search among the more than 10,000 species of marine organisms for
microalgae that produce oils containing neutral lipids has led to the discovery of
Navicula sp. JPCC DA0580, a marine diatom that produces large amounts of oil.
While the marine green algae strain Scenedesmus rubescens JPCC GA0024 was
previously found to produce large amounts of oil, DA0580 has both a faster growth
rate and higher oil content than GA0024 (Matsunaga et al. 2009; Takeyama and
Matsumoto 2010).
(a) Optical observation
(b) Fluorescence observation (white portions are oil droplets)
Peak growth for DA0580 is achieved within one week, with oil stores reaching
40–60 wt% per dry algal body cultured over a one-week period. Oil accumulation
was also found to occur from the middle to end period of culturing (Fig. 9.12).
Typically, the accumulation of oil in microalgae has required a two-stage culturing process, in which growth is induced and culturing is performed in a medium
from with nitrogen nutrient salt components have been removed. In the case of
DA0580, however, oils can be accumulated during growth. Since this does not
entail the starvation required with other microalgae, its characteristics are superior
to those of previous species: equal or greater amounts of oils can be produced with
a shorter culturing period, allowing for reduced culturing costs.
The oils produced by DA0580 are meaningless if they are not suited for use in
biodiesel fuel. As shown in Table 9.10, the oil components produced by DA0580
are distinctive even in comparison with Chlorella. While Chlorella possesses a
broad scope of fatty acid ingredients, the oils in DA0580 consisted of 90% C 16 fatty
acids (C 16:0 : palmitic acid, C 16:1 palmitoleic acid), although EPA (C 18 fatty acid),
which is typically present in diatoms, was absent.
9.6 Developing Microalgae with High Oil Concentrations
339
that sense, biodiesel fuel can fundamentally be produced with the neutral lipids
obtained from microalgae. In addition, many species of microalgae are known to be
capable of accumulating neutral lipids, which can account for 50% or more of dry
algal bodies. Biodiesel fuel can also be produced with hydrocarbon raw materials
(Miao and Wu 2006).
The freshwater microalga Botryococcus braunii is considered highly promising
for its ability to produce large amounts of hydrocarbons. At the same time, its
growth rate is also slow, which makes its culturing (growth) difficult to control. As
no other microalgae species besides B. braunii have be found to produce hydrocarbons accounting for double-digit percentages of dry weight, other species cannot
be used in producing hydrocarbon with microalgae at the present time. For now, we
must rely entirely on the success or failure of B. braunii.
For this reason, neutral lipids, which are accumulated universally by various
species of microalgae, can be viewed as a future target material in terms of biodiesel
fuel production with microalgae. We therefore need to obtain marine microalgae
that are characterized by their ability to accumulate neutral lipids with the greatest
efficiency.
The search among the more than 10,000 species of marine organisms for
microalgae that produce oils containing neutral lipids has led to the discovery of
Navicula sp. JPCC DA0580, a marine diatom that produces large amounts of oil.
While the marine green algae strain Scenedesmus rubescens JPCC GA0024 was
previously found to produce large amounts of oil, DA0580 has both a faster growth
rate and higher oil content than GA0024 (Matsunaga et al. 2009; Takeyama and
Matsumoto 2010).
(a) Optical observation
(b) Fluorescence observation (white portions are oil droplets)
Peak growth for DA0580 is achieved within one week, with oil stores reaching
40–60 wt% per dry algal body cultured over a one-week period. Oil accumulation
was also found to occur from the middle to end period of culturing (Fig. 9.12).
Typically, the accumulation of oil in microalgae has required a two-stage culturing process, in which growth is induced and culturing is performed in a medium
from with nitrogen nutrient salt components have been removed. In the case of
DA0580, however, oils can be accumulated during growth. Since this does not
entail the starvation required with other microalgae, its characteristics are superior
to those of previous species: equal or greater amounts of oils can be produced with
a shorter culturing period, allowing for reduced culturing costs.
The oils produced by DA0580 are meaningless if they are not suited for use in
biodiesel fuel. As shown in Table 9.10, the oil components produced by DA0580
are distinctive even in comparison with Chlorella. While Chlorella possesses a
broad scope of fatty acid ingredients, the oils in DA0580 consisted of 90% C 16 fatty
acids (C 16:0 : palmitic acid, C 16:1 palmitoleic acid), although EPA (C 18 fatty acid),
which is typically present in diatoms, was absent.
9.6 Developing Microalgae with High Oil Concentrations
339