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 200rpm resulted in a lipid output of 10g/L, content of 55%, yield of 0.170g/g, and productivity of 0.06g/L/h. All of these values decreased by ≈50-60% when the agitation rate was raised to 300rpm 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.

Effect of feeding strategies on lipid production by Lipomyces starkeyi.

The aim of this study was to produce microbial oil from Lipomyces starkeyi DSM 70296 grown in hemicellulose hydrolysate (H-H). Glucose and xylose were used for batch, fed-batch, repeated fed-batch, and continuous cultures, and H-H was tested at continuous culture. The highest cell and lipid concentrations of 85.4 and 41.8g/L, respectively, were obtained using repeated fed-batch strategy. Continuous culture with dilution rate of 0.03h(-1) presented the highest overall cell (0.443g/g) and lipid yields (0.236g/g). At 0.06h(-1) were obtained the highest cell and lipid productivities. Continuous cultivation using H-H at 0.03h(-1) resulted in higher cell productivity than that obtained using glucose:xylose. Gas chromatography analysis of the esterified lipids indicated that the major constituents of this complex are palmitic acid, stearic acid, oleic acid, and linoleic acid with an estimated cetane number (approximately 61) similar to that of palm biodiesel, which is important for biofuel production.

Co-fermentation of cellobiose and xylose by Lipomyces starkeyi for lipid production.

Hydrolysates of lignocellulosic biomass contain glucose, xylose, arabinose, cellobiose, among other sugars. Effective utilization of these sugars remains challenging for microbial conversion, because most microorganisms consume such sugars sequentially with a strong preference for glucose. In the present study, the oleaginous yeast, Lipomyces starkeyi, was shown to consume cellobiose and xylose simultaneously and to produce intracellular lipids from cellobiose, xylose and glucose. In flask cultures with glucose, cellobiose or a mixture of cellobiose/xylose as carbon sources, overall substrate consumption rates were close to 0.6 g/L/h, and lipid coefficients were 0.19 g lipid/g sugar, respectively. This cellobiose/xylose co-fermentation strategy provides an opportunity to efficiently utilize lignocellulosic biomass for microbial lipid production, which is important for biorefinery and biofuel production.

Microbial treatment of the monosodium glutamate wastewater by Lipomyces starkeyi to produce microbial lipid.

The monosodium glutamate (MSG) wastewater as a medium was treated by Lipomyces starkeyi to produce microbial lipid in the study. The effect of related factors (initial glucose concentration, inoculation concentration, initial culture pH, and cultivation time) on biomass, lipid production and lipid content was discussed, respectively. According to the experiments, the optimal fermentation conditions were determined: addition of 80g/L glucose, 10% inoculation concentration, initial pH about 5.0, incubation time 96h. Under this condition, the biomass production reached up to 4.61g/L, lipid production and lipid content was 1.14g/L and 24.73%, respectively. Simultaneously, protein and COD removal rate was 78.60% and 74.96%, respectively. The main composition of fatty acid in the resultant lipid was analyzed by gas chromatography-mass spectrometry, which showed: oleic acid (C18:1) 35.85%, palmitic acid (C16:0) 19.91%, palmitoleic acid (C16:1) 17.65%, and myristic acid (C14:0) 16.03%.