8-04: Comparative Lipid Production on Hydrolyzates of Pretreated Lignocellulosic Biomass Using Oleaginous Yeasts

Oleaginous yeasts can accumulate up to 70% of cell biomass as lipid, predominantly as triacylglycerides.   Yeast lipid fatty acid profiles have been reported to be similar to that of vegetable oils and consist primarily of oleic, palmitic, stearic and linoleic acids.  This capability provides the opportunity to use yeasts to produce bio-based fuels and chemicals from agricultural residues and bioenergy crops, such as corn stover and switchgrass, respectively.   Successful cultivation of these yeasts on lignocellulosic hydrolyzates is uncertain because little has been published on their tolerance to fermentation inhibitors associated with pretreated biomass.  For this study, selected yeasts of several genera were obtained from the ARS Culture Collection (NCAUR, Peoria, IL) and were screened for their abilities to produce oil on one of the more benign hydrolyzates, AFEX-pretreated corn stover, and one of the more toxic hydrolyzates, dilute acid-pretreated switchgrass, respectively.  Hydrolyzates were prepared at 20% solids loading to provide over 100 g/L sugars (at ~60:40 mass ratio glucose:xylose).    Nitrogen from amino acids and ammonia was controlled to > 95:1 C:N ratio to trigger oil production, and cultures were assessed for relative growth and oil yield, composition and productivity.  Stress on yeasts was increased by decreasing culture pH to further distinguish more robust strains.   Depending upon plant biomass yields, we estimated that oleaginous yeasts have the capability of producing ~48 and 190 gal oil per acre from corn stover and switchgrass, respectively.  As a frame of reference, ~68 gallons of oil per acre are produced from processing soybeans.