5-3 Multiple levers to overcome the recalcitrance of cellulosic biomass for conversion to biofuels
Tuesday, April 26, 2016: 8:50 AM
Key Ballroom 8-11-12 2nd Fl (Hilton Baltimore)
E. Holwerda*, D.G. Olson and L.R. Lynd, Dartmouth College, Hanover, NH, USA; M. Davis, National Renewable Energy Laboratory, Golden, CO, USA; B.H. Davison, G. Tuskan and P. Gilna, Oak Ridge National Laboratory, Oak Ridge, TN, USA; M.E. Himmel, National Renewable Energy Laboratory, Biosciences Center, Golden, CO, USA; D. Mohnen, University of Georgia, Athens, GA, USA; C.E. Wyman, Center for Environmental Research and Technology, Bourns College of Engineering,University of California Riverside, Riverside, CA, USA
The primary barrier to economically competitive cellulosic biofuels is the resistance of plant cell walls to deconstruction – termed recalcitrance.  Overcoming this barrier may be accomplished via multiple recalcitrance “levers” including: 
  1. Starting with nature’s best with respect to feedstocks and biocatalysts; 
  2. Biotechnology to improve plants, enzymes, and microbes
  3. Non-biological processing prior to or during solubilization and fermentation;

Here we will report progress at applying and evaluating these levers.  Studies aimed at individual levers include:

• Comparison of the amenability of various feedstocks to solubilization, including natural variation within the same species;

• Comparison of the effectiveness of various biocatalysts at mediating plant cell wall solubilization; 

• Targeted modification of plants to decrease recalcitrance without sacrificing growth;

• Targeted modification of unfractionated saccharolytic enzyme preparations to improve their effectiveness at plant cell wall solubilization;

• Targeted modification of thermophilic anaerobes to improve ethanol yield and titer without sacrificing cellulose fermentation capability; 

• Co-solvent enhanced lignocellulosic fractionation (CELF) using tetrahydrofuran to greatly enhance biomass deconstruction by dilute acid pretreatment;

• Mechanical milling during fermentation, termed cotreatment.

We also report studies aimed at combinations of these levers – including the impact of various targeted plant modifications on fermentation by various biocatalysts and the effectiveness of modified plants in conjunction with cotreatment or pretreatment. Based on our results, we conclude that there are powerful, emergent strategies to overcoming plant cell wall recalcitrance, and that systematically exploring combinations of these levers is a promising approach to enabling the cost-effective production of cellulosic biofuels.

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