17-23: Identification and Characterization of Limit Products in High Solids Saccharification of Dilute-Acid Pretreated Corn Stover by Cellic Ctec2

Monday, April 29, 2013
Exhibit Hall
Sarah E. Hobdey1, William E. Michener2, Michael E. Himmel3 and Larry E. Taylor II3, (1)Biosciences Center, National Renewable Energy Laboratory and EERE Biomass Program, Golden, CO, (2)National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, (3)Biosciences Center, National Renewable Energy Laboratory, Golden, CO
Increasing the efficiency of biomass hydrolysis is essential for lowering the cost of biofuel production. In the current study we investigated the digestion of pretreated corn stover by the Cellic Ctec2 (Novozymes) enzyme cocktail with an emphasis on characterizing and identifying the sources of oligosaccharides that we have previously shown to have a negative effect on enzymatic digestion.  In a high solids (>20%) digestion of washed pretreated corn stover with Ctec2 we found significant amounts of oxidized cello- and xylo-oligomers, verified by LC-MS-MS. Interestingly, with increasing oxidized products, we also saw a decrease in glucan conversion and an increase in cellobiose accumulation. The addition of supplemental beta-glucosidase eliminated the accumulation of cellobiose but had little effect on the overall glucan conversion, suggesting that oxidized oligomers are inhibiting enzymes other than beta-glucosidase. Soluble cello-oligomers from Avicel have been generated, purified, chemically oxidized and added back to the cocktail digestions to determine the inhibitory concentrations of the relevant oxidized oligomers. We are also performing assays using individual proteins and simplified enzyme mixtures to identify which enzymes are most significantly inhibited by oxidized cello-oligomers. Our ultimate goal is to identify which enzymes are being inhibited by oxidized oligomers and determine how to overcome the inhibition, i.e. supplemental enzymes and/or protein engineering.