After 15 days of growth (cells at the stationary phase),
cells were collected and the production of fatty acids was
measured as described in Section 2. As shown in Fig. 3, fatty
acid production of Chlorella sp. was enhanced by adding
glucose to the culture medium. As compared with the
control, both 2.5 mM and 5.0 mM of glucose added initially
to medium enhanced in fatty acid production by 38%.
However, the increase of fatty acid production induced by
low concentration of glucose was not the cause of enhancing
accumulation of fatty acids in cells, but the results of
enhancement of cell growth, since nearly the same percentage
of cell density was enhanced by initially adding glucose
(Fig. 2).
Since sodium thiosulphate heavily inhibited cell growth
(Fig. 2), the fatty acid production of Chlorella sp. cultured in
the medium containing 5.0 mM of sodium thiosulphate
decreased only about 8.1% as compared with that of control
and there was no difference in fatty acid production between
cells grown in medium containing 2.5 mM of sodium thiosulphate
and in the control (Fig. 3). These results suggest
that sodium thiosulphate enhanced accumulation of lipids in
the cells. When cells were grown in a medium containing
both glucose and sodium thiosulphate, the production of
fatty acid apparently depended on concentrations of both
compounds. When the glucose concentration was fixed at
2.5 mM, an increase in sodium thiosulphate concentration
from 2.5 mM to 5.0 mM induced an augmentation of fatty
acid production from 72.5 mg/ml to 80.6 mg/ml. Similar
results were also obtained in cells grown in the presence
of 5.0 mM glucose plus sodium thiosulphate. In contrast,
when the concentration of sodium thiosulphate was fixed, an
increase in glucose concentration from 2.5 mM to 5 mM
resulted in a decrease in fatty acid production (Fig. 3).