(567b) Process Strategies for High Titers of Lipid Production By Oleaginous Yeasts in Undetoxified Hydrolyzates of Lignocellulosic Biomass
Oleaginous yeasts can accumulate up to 70% of cell biomass as lipid, predominantly as triacylglycerols. 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 inhibitory lignocellulosic hydrolyzates is uncertain because little has been published regarding their application to bioconversion of plant biomass. Several novel yeasts producing promising lipid concentrations (>10 g/L) from enzyme hydrolyzates of acid and base pre-treated lignocellulosic biomass were discovered in a prior screening of the ARS Culture Collection (NCAUR, Peoria, IL). Three of the top strains have not previously been reported for the bioconversion of lignocellulose to lipids. Process strategies for maximizing lipid production in one of the more benign hydrolyzates, AFEX-pretreated corn stover, and one of the more toxic hydrolyzates, dilute acid-pretreated switchgrass, respectively, were employed. Hydrolyzates were prepared at up to 20% solids loading to provide over 100 g/L sugars (at ~56:39:5 mass ratio glucose:xylose:arabinose). A two stage process boosting the molar C:N ratio from 60 to well above 400 in undetoxified switchgrass hydrolyzate was optimized with respect to nitrogen source, C:N, carbon loading and pH. Using this process three strains were able to consume acetic acid and nearly all available sugars to accumulate 50-65% of cell biomass as lipid (w/w), to produce 25-30 g/L lipid at 0.12-0.22 g/L/h and 0.13-0.15 g/g (or 39-45% of the theoretical yield) at pH 6 and 7, a performance unprecedented in lignocellulosic hydrolyzates. 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, ~48 gallons of oil per acre are produced from processing soybeans. The successful application of top-performing lipid-producing yeast in undetoxified lignocellulose hydrolyzates is expected to advance the economic feasibility of high quality biodiesel and jet fuels from renewable biomass, expanding the market potential for lignocellulose-derived fuels beyond ethanol for automobiles to the entire U.S. transportation market.