Culture Strategies for Lipid Production Using Low-cost Carbon Sources by Rhodosporidium Toruloides

Abstract

The development of sustainable biofuels is inserted in the biorefinery concept through the use and valorization of raw material. Volatile fatty acids (VFAs) and rich-carbon wastes, present in different raw materials, have gradually been used as the carbon source for lipid production by oleaginous yeasts. In this context, it is essential to develop practical culture strategies for oleaginous yeast to use these wastes, acetic acid and the carob industry by-product. In this study, new approaches in the cultivation of the yeast Rhodosporidium toruloides were tested, in order to maximize the accumulation of biomass and lipids. Different concentrations of carob kibbles sugar rich extract and acetic acid waste were used, as low-cost carbon sources, to select the best culture strategy for the bioconversion of these wastes into microbial oils. Microbial oils were produced by R. toruloides using 3–18 g/l acetic acid and 9–70 g/l carob extract, with different carbon-to-nitrogen ratios (C/Ns). Batch and fed-batch cultures were compared in terms of biomass and lipid production and lipid productivity. The highest biomass of 19.14 ± 0.54 g/l was obtained in batch cultures with 70 g/l of carob extract. A lipid content of 20% (w/w) was achieved using 15 g/l of acetic acid as the carbon source in a fed-batch mode. To improve biomass production as well as lipid accumulation, the strategy used was the combination of both residues in fed-batch sequential mode of the cultures in a 2L STR bioreactor. This strategy improved the lipid yield to 40% (w/w). These results provide viable culture strategies for lipid accumulation by R. toruloides using diverse waste-derived VFA’s and sugars.