biomass production was stopped in the second stage as shown in
Fig. 4a due to the low salt conditions.
As shown in Fig. 4b, oil accumulation with low-salt stress
differed significantly with culture time and microalgae species. The
oil content of I. galbana increased from 24.0% to 47.0% and reached a
maximum in 2 days with 10 psu. I. galbana increased the production
of oil in two-stage culture with low salt stress of second stage.
Therefore, two-stage culture of I. galbana can be appropriate for the
large scale oil production to produce biodiesel due to high cell and
oil productivities. The oil content of N. oculata increased with time
of low-salt stress and reached a maximum oil content of 29.0% at 3
days with zero psu. The oil content of D. salina decreased with time
of low-salt stress and reached a maximum oil content of 43.0% on
day 1 with 10 psu. The oil content of D. tertiolecta increased from
23% to 40.0% and reached a maximum in 2 days with zero psu.
These results indicate that the time required to reach the maximum
oil content was 2 days except for N. oculata. The two-stage culture
of microalgae achieved maximum biomass production in nutrientsufficient
conditions and then oil accumulation with low-salt
stress. The two-stage culture system enhanced overall cell mass
and oil productions as summarized in Table 1.