Characterization and optimization of Rhodosporidium toruloides for production of lipids

Abstract: Oleaginous microorganisms provide an opportunity to produce oils without the use of arable land for cultivation of oil-containing plants. Oleaginous microorganisms are also capable of storing products of pharmaceutical interest alongside storing polymers, which could open new opportunities in the bioplastic industry. Oily yeasts have several advantages in comparison to alternatives; their doubling times are shorter than that of plant cells; their resistance to environmental changes is than those of bacteria, and they grow as single cells as opposed to (other) fungi. In this study, Rhodosporidium toruloides strain BOT A-2 was characterized to select the best carbon source, temperature, and pH requirements for maximal lipid accumulation. Specific growth rates of ~0.2 h-1 were measured at optimal growth conditions of 30°C temperature, pH of 5.5, and glucose as the carbon source. Different C:N ratios were evaluated (20, 40, 80, and 100) to determine the value giving the highest titer of lipids. Of the process parameters tested, a C:N ratio of 80 and glucose concentration of 50 g/L was selected for batch experiments and 20 g/L of glucose for the fed-batch experiment. Batch and fed-batch mode resulted in a lipid accumulation of about 40 %(w/w) of the cell dry weight. The lipid profile showed a dominance of unsaturated C-16:0 fatty acids at higher C:N ratios. Further investigation of lipid accumulation was done using flow cytometry, and it was clearly shown that cells grow in size in the later stages of fermentation due to lipid accumulation. The experimental results were compared to predictions made using the flux balance analysis software OptFlux, to assess the capability of the model in predicting results.