Lipid formation by Cryptococcus albidus in nitrogen-limited and in carbon-limited chemostat cultures

Abstract

Cryptococcus albidus var. Albidus CBS 4517 was grown in nitrogen-limited and in carbon-limited chemostat cultures. The effect of growth rate and limiting nutrient on lipid accumulation and fatty acid composition was investigated. The maximum lipid content in the biomass was, in both cultivation systems, observed at the lowest dilution rate (growth rate) tested. At this dilution rate, D=0.31 h-1, cells from the nitrogen-limited culture contained 41% (w/w) lipid and cells from the carbon-limited culture 37%. These results indicate the ability of C. albidus, unlike other oleaginous yeasts, to accumulate lipid also in carbon-limited chemostats. The yield of lipid from carbon source was about the same at D=0.031 h-1 in nitrogen-limited (Y L/S=0.16 g/g) as in carbon-limited (Y L/S=0.17 g/g) cultures and decreased with increasing growth rates. In the nitrogen-limited culture, the lipid productivity was about constant at low growth rates (0.031–0.056 h-1) and a slight decrease was observed at D=0.08 h-1, while the specific lipid productivity, q L, increased to 27.5 mg/g per hour. In the carbon-limited culture, however, lipid productivity increased with increasing growth rates and reached its maximum value near μmax, whereas q L was about constant at 20 mg/g per hour. The fatty acid composition was influenced by the specific growth rate in nitrogen-limited as well as in carbon-limited cultures, although the changes were more pronounced during carbonlimitation. A decrease in the degree of unsaturation (Δ/mole) was also observed with increasing lipid content in the cells.