Improving lipid and biomass production by Rhodosporidium toruloides

The production of renewable fuels that can act as drop-in replacements for diesel, jet fuel, and gasoline has gained significant recent attention. Lipid production using oleaginous yeasts represents an alternative for the production of diesel-range hydrocarbons, as many of these microorganisms are natural C16-C20 lipid producers, and lipid production using oleaginous yeasts can often be improved when media with low nitrogen content is used during cultivation. However, nitrogen is also required to generate biomass. In this work, we tested a modified fed-batch strategy using Rhodosporidium toruloides where two different media were used: during the batch phase, complex media was used to favor biomass production; and in the second phase, minimal media was used to favor lipid production. Moreover, the effect on lipid production when different molar C/N ratios were used in the second phase was compared to the fermentation performance obtained in batch mode. A 39% increase FAME titer and a 27% increase FAME volumetric productivity were obtained when using the modified fed-batch compared to the batch mode when no nitrogen source was used during the lipid production phase. In addition, the search for cost-effective N-sources as alternative to the use of yeast extract and peptone during the biomass production phase was further pursued. Corn steep liquor is an effective N-source alternative to increase biomass production during the biomass production phase when using R. toruloides.