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International Journal of Marine Science 2013, Vol.3, No.17, 135-144
http://ijms.sophiapublisher.com
139
Figure 1 Cell growth in response to varying nutrient and
temperature condition. Cell count of
Dunaliella tertiolecta
(A),
Scenedesmus
sp. (B) and
Nannochloropsis
sp. (C)
The response of
Dunaliella tertiolecta
to nutrient
limitation on cell growth was also investigated. The
growth curve in terms of cell density of three
microalgal cultured for different nutrient condition are
shown at Figure 1. Reasonably, the maximum algal
density increased with deplete nitrogen and
phosphorus condition. Range of cell density of
Dunaliella tertiolecta
were 7.3×10
4
to 182×10
4
,
5.7×10
4
to 106.7×10
4
and 10.3×10
4
to 109.7×10
4
cell/mL for replete,
-
N and
-
P culture medium,
respectively (Figure 1A). Similar with temperature
stress condition, the highest growth of cell was
occurred at replete nutrient condition for both
temperature treatment. The highest number of cell
account for 182×10
4
cell/mL at replete nutrient
treatment with the temperature cultured was 18
℃
at
day 10 of cultivation. Statistically, there was a
significant different of cell density over cultivation
period between nutrient treatments (p<0.05).
The growth curves of
Scenedesmus
sp. in the growth
medium for different cultivation temperature and
nutrient condition are shown in Figure 1 (B). After 9
days of cultivation
Scenedesmus
sp. grew into the
decreasing phase and reached a maximum cell density
at day 6 of cultivation for all temperature and nutrient
treatments. The study found that the optimal
temperature for
Scenedesmus
sp. growth was 25
℃
.
Through Paired-samples t-test, microalgal densities in
the cultivation process at the temperature of 25
℃
was
significantly higher than at 18
℃
(p < 0.001). At 18
℃
Scenedesmus
sp. grew very slowly at the beginning till
the end of cultivation. The peak of cell density at low
temperature was one day later than higher temperature.
The result was supported by previous study by Xin et
al (2010) who found that at 25
℃
Scenedesmus
sp.
LX1 got the maximum specific growth rate and at 30
℃
it had the maximum carrying capacity K and
population growth rate Rmax. Cell density of
Scenedesmus
sp. was lower at deplete nutrient condition
than replete nutrient condition not only at 18
℃
but
also at 25
℃
.
Nannochloropsis
sp. growth appeared to be affected at
temperatures above 18
℃
(Figure 1C). At 25
℃
, this
microalgae exhibited a very low and almost no grow in
terms of cell density, this temperature led to an abrupt
interruption of microalgal growth and later the cell dead
on further period of cultivation. Previous studies by
Sayegh and Montagnes (2010); James et al (1989) and
Brown and Jeffrey (1992) found that
Nannochloropsis
sp.
grown optimally at temperature around 20
℃
.
In
nutrient
deplete,
exponential
phase
of
Nannochloropsis
sp. are similar to those in the
literature, under comparable conditions (Figure 1C).
Nannochloropsis
sp have maximum cell growth in
terms of cell density of 792×10
4
cell/mL at day 7 of
cultivation.
The effect of temperature on microalgal growth was
species-dependent. Previous studies by Converti et al