Lipid biosynthesis in Cunninghamella bainieri 2A1 in N-limited and N-excess media

Lipid biosynthesis and fatty acids composition of oleaginous zygomycetes, namely Cunninghamella bainieri 2A1, cultured in media with excess or limited nitrogen were quantitatively determined at different times of culture growth. Accumulation of lipids occurred even when the activity of NAD(+)-ICDH (β-Nicotinamide adenine dinucleotide-isocitrate dehydrogenase) was still detectable in both media. In C. bainieri 2A1, under nitrogen limitation, the ratio of lipids was around 35%, whereas in nitrogen excess medium (feeding media supplemented with ammonium tartarate), the lipid ratio decreased. The amount of this decrease depended on the level of ammonium tartarate in the media. The main findings in this paper were that C. bainieri 2A1 has the ability to accumulate lipid although nitrogen concentration detected inside the media and that NAD-ICDH was active in all culture periods. These results proved that the strain C. bainieri 2A1 has an alternative behavior in lipid biosynthesis that differs from yeast. According to the old hypotheses, yeasts could not accumulate lipid more than 10% when nitrogen was detected inside the media. Nitrogen-limited and excess media both contained the same fatty acids (palmitic acid, stearic acid, olic acid, linoleic acid and γ-linolenic acid), but at different concentrations. The C:N ratio was also studied and showed no effects on total lipid accumulation, but a significant effect on γ-linolenic acid concentration.