Basic HTML Version
International Journal of Marine Science 2013, Vol.3, No.17, 135-144
http://ijms.sophiapublisher.com
142
Figure 4 Lipid concentration based on Gravimetric method in
response to varying nutrient and temperature condition.
Gravimetric lipid reading of (A)
Dunaliella tertiolecta
, (B)
Scenedesmus
sp. and (C)
Nannochloropsis
sp.
to the depletion of nutrients from the medium. The
result is confirmed by previous report by Chen et al (2011)
who recorded that cells incubated in nitrogen-deficient
medium accumulated substantial amounts of lipid by
day 3, but this had declined by day 7. Rossler (1988)
reported that the nutrient deficiency induced an
increase in the rate of lipid synthesis in a diatom,
Cyclotella cryptica
, and resulted in lipid accumulation
in the cells.
3.2.3 Lipid detection by FTIR spectroscopy
FTIR spectroscopy can be used to monitor the
biochemical content of phytoplankton cells in very
short time intervals of less than one hour (Wagner et
al., 2010). In this study, FTIR spectroscopy was used
to determine relative neutral lipid content in three
selected microalgae (
Dunaliella tertiolecta, Scenedesmus
sp. and
Nannochloropsis
sp.) (Figure 5).
Neutral lipid content was measured using this method
for the end of algal cultivation period, such as day 9
and day 10 for
Scenedesmus
sp. and
Dunaliella
tertiolecta
and
Nannochloropsis
sp., respectively. At
FTIR spectroscopy, the bands were assigned to
specific molecular groups on the basis of biochemical
standards and published studies, as described
previously (Stehfest et al., 2005). Bands were
attributed to
Ʋ
(C=O) stretching of amides from
proteins (amide I,~1655 cm
-1
); δ(N–H) bending for
amides from proteins (amide II, ~1545 cm
-1
); δ
as
(CH
2
)
and δ
as
(CH
3
) bending of methyl from protein (
͂
1455
cm
-1
); and δ
s
(CH
2
) and δ
s
(CH
3
) bending of methyl and
Ʋ
s
(C–O) stretching of COO-groups (~1380 cm
-1
)
and
Ʋ
as
(>P=O) stretching, associated with phosphorus
compounds (~1260 cm
-1
). Two bands were of particular
interst, the band at 1740 cm
-1
which was associated
with
Ʋ
(C=O) of ester groups, primarily from lipid and
fatty acids and the region from 950~1200 cm
-1
associated with
Ʋ
(C
-
O
-
C) stretching of poly-
saccharides.
Relative lipid content was determined by calculating
the ratio of the lipid (1740 cm
-1
) band to the protein
band (amide I) (Figure 5). The range of lipid:protein
ration for all microalgal culture from 0.67 to 3.77.
The highest lipid:protein ration was recorded at
Scenedesmus
sp. for
-
N nutrient treatment at 25
℃
cultivation temperature account for 3.78. Interestingly,
Dunaliella tertiolecta
showed the highest lipid:protein
ratio at replete nutrient treatment for 18
℃
cultivation
temperature. However, there was no significant
different of lipid:protein ratio between temperature
condition for all nutrient treatments except for
Scenedesmus
sp. This result indicated that
Scenedesmus
sp.
had higher lipid production at N limitation condition
than others two species (
Dunaliella tertiolecta
and
Nannochloropsis
sp.) based on FTIR spectroscopy
reading. Recent study of
Scenedesmus subspicatus
found lipid production reduced markedly in the low-N
culture by over 50% compare to high
-
N culture
(Dean et al., 2010). These experiments indicated that
optimization of nutrient limitation conditions rather
than complete starvation offers the potential to
increase lipid productivity.