Medium optimization for lipid production through co-fermentation of glucose and xylose by the oleaginous yeast Lipomyces starkeyi

Co-fermentation of lignocellulose-based carbohydrates is a potential solution to improve the economics of microbial lipid production. In the present paper, experiments were performed to optimize the media composition for lipid production by the oleaginous yeast Lipomyces starkeyi AS 2.1560 through co-fermentation of glucose and xylose (2 : 1 wt/wt). Statistical screening of nine media variables was performed by a Plackett-Burman design. Three factors, namely mixed sugar, yeast extract and FeSO4, were found as significant components influencing cellular lipid accumulation. Further optimization was carried out using a Box-Behnken factorial design to study the effects of these three variables on lipid production. A mathematical model with the R-2 value at 96.66% was developed to show the effect of each medium composition and their interactions on the lipid production. The model estimated that a maximal lipid content of 61.0 wt-% could be obtained when the concentrations of mixed sugar, yeast extract and FeSO4 were at 73.3 g/L (glucose 48.9 g/L, xylose 24.4 g/L), 7.9 g/L and 4.0 mg/L, respectively. The predicted value was in good accordance with the experimental data of 61.5%. Compared with the initial media, the optimized media gave 1.59-fold and 2.03-fold increases for lipid content and lipid productivity, respectively.