Lipid production by rhodotorula gracilis grown in continuous culture

Abstract

There has been persistent progress in the study on the applications of microorganism as a potential lipid producer as well as in the fermentation technology ever since the microbial lipid may be expected for a contribution to coping with the world food crisis. Microbial lipids were produced by $\underline{Rhodotorula}$ $\underline{gracillis}$ grown in continuous culture at dilution rate from 0.02 to 0.09 $hr^{-1}$ under nitrogen limitation. Maximum lipid content was 49.8% (W/W) at a dilution rate of 0.02 $hr^{-1}$. In batch culture, which was performed under slight excess of nitrogen source in order to increase biomass, lipid content of 54%(W/W) was obtained after 70 hr. As this strain was obligate aerobe, not only biomass but also lipid contents were increased with increasing dissolved oxygen concentration in the range of 45 to 234 μM/liter. At low pH values, cell growth was found to be retarded. On the other hand, with increasing pH from 5.5 to 7.5 biomass was also decreased, and lipid content was somewhat increased. However, the overall lipid productivity at pH 7.5 was shown to be lower. The result of HPLC analysis showed that main fatty acids were palmitic, stearic, oleic, linoleic and linolenic acid. The variation of fatty acids with changes of dissolved oxygen concentration was not occurred enough to affect the degree of unsaturation. The change in fatty acid compositions was occurred very considerably by slight changes in growth rate. It seems that the amount of oxygen required for desaturation of fatty acids is much smaller and most of the oxygen is consumed first for the proliferation and lipid synthesis including fatty acid synthesis. Addition to this assumption, the effect of growth rate on the desaturation of fatty acids may be explained by the consideration of growth pattern, that is nongrowth-associated product formation.