Nitrogen limitation, oxygen limitation, and lipid accumulation in Lipomyces starkeyi

Lipid production by oleaginous yeasts is optimal at high carbon-to-nitrogen ratios. In the current study, nitrogen and carbon consumption by Lipomyces starkeyi were directly measured in defined minimal media with nitrogen content and agitation rates as variables. Shake flask cultures with an initial C:N ratio of 72:1 cultivated at 200 rpm resulted in a lipid output of 10 g/L, content of 55%, yield of 0.170 g/g, and productivity of 0.06 g/L/h. All of these values decreased by ≈50-60% when the agitation rate was raised to 300 rpm or when the C:N ratio was lowered to 24:1, demonstrating the importance of these parameters. Under all conditions, L. starkeyi cultures tolerated acidified media (pH ≈ 2.6) without difficulty, and produced considerable amounts of alcohols; including ethanol, mannitol, arabitol, and 2,3-butanediol. L. starkeyi also produced lipids from a corn stover hydrolysate, showing its potential to produce biofuels from renewable agricultural feedstocks.