Yeast extract is one of the most suitable nitrogen sources to promote
growth of C. protothecoides [9]. In order to confirm the optimal
yeast extract amount in culture medium, a series of
experiments using ESJ supplemented with 1–3 g L1 yeast extract
were carried out. As shown in Fig. 4, when the initial yeast extract
was 1, 2 and 3 g L1, the biomass achieved 5.30, 5.85, 6.00 g L1,
respectively. However, the lipid content was 50.2%, 49.2% and
48.9%. With the increase of yeast extract from 2 to 3 g L1, the biomass
increased slightly and the lipid content seldom changed. The
highest lipid mass 586.8 mg L1 day1 (6.00 g L1 48.9%/5 day)
was achieved with the yeast extract concentration of 3 g L1,
8.5% higher than that before adding yeast extract.