15-18: Lipid accumulation in Lipomyces starkeyi with xylose and glucose in single stage continuous culture

As the need to replace fossil fuels increases, lipids accumulated in oleaginous organisms come into view for the production of biodiesel. Besides oleaginous microalgae, oleaginous yeasts and may be a promising option. Microbial lipids produced by Lipomyces starkeyi grown in continuous culture with xylose and glucose were evaluated and the effects of dilution rate (D) in lipid accumulation were studied. As the D decreased, cell biomass, lipid content and lipid yield gradually increased. The maximum lipid content recorded was 49% (w/w) of dry cell biomass (14.8 g/L) at a dilution rate of 0.03 h^-1. At a D of 0.06 h^-1, increase amount of sugars were detected in the culture medium and a decrease of lipid accumulation was observed, in accordance with literature data. Dilution rate of less than 0.06 h^-1 were normally required for optimum conversion, since the microbial cells need to remain within the chemostat for at least 12–24 h in order to consume the available nitrogen and then convert the remaining sugar to oil and ‘‘fatten’’. Lipid-free material and lipid yields were critically influenced by the change of D. At low D, increased amounts of substrate were disposed for lipid synthesis whereas at higher ones substrate was consumed mainly for non-lipid material synthesis. Changes of these yields as a function of D have been already observed in other oleaginous yeasts growing in continuous cultures.