Currently available commercial enzymes for biomass depolymerization are complex and poorly defined mixtures of activities and proportions. The Walton team's long-term goal is to construct enzyme mixtures of optimized composition. To do so, they are building synthetic mixtures starting with pure, individual enzymes. Mixtures are optimized using statistical Design of Experiment and robotic liquid handling in an integrated system called GENPLAT. To date, they have constructed optimized cocktails containing up to 15 components. Some contribute to glucose (Glc) yield, others to xylose (Xyl) yield, and some enhance yield of both sugars from various pretreated biomass materials (Banerjee et al., 2010a). The required enzymes and their optimized proportions depend on the pretreatment conditions and biomass composition (Banerjee et al., 2010b).
The team is also identifying novel biomass deconstruction enzymes and testing their contribution to Glc and Xyl yield when combined with synthetic mixtures and with commercial enzymes. For example, secreted α-xylosidase (AXL) is predicted to be important for release of Glc and Xyl from plant cell walls, especially from dicots, which have high levels of xyloglucan. However, secreted AXL’s are rare in nature and this activity is absent from T. reesei. They identified and purifed a secreted AXL from Aspergillus niger. In combination with β‑glucosidase, AXL depolymerizes pea xyloglucan to free Xyl and Glc and in combination with commercial enzymes enhances Glc yields from corn stover (Scott-Craig et al., 2011; Jabbour et al., 2013).
Pretreatment research in the Great Lakes Bioenergy Research Center (GLBRC) focuses on alkaline methods. Alkaline hydrogen peroxide (AHP) is effective and performs at room temperature and atmospheric pressure (i.e., low capital cost demands). The high cost of hydrogen peroxide is currently the limiting factor in the economic implementation of AHP (Banerjee et al., 2012).
The use of mixed plant species as biomass feedstock has potential economic and environmental advantages over monocultures. The “Sustainability” research area of the GLBRC is investigating the potential of mixed prairie and marginal lands to provide biomass for renewable energy. Such landscapes contain a high percentage of herbaceous dicots (forbs). The cell wall composition of forbs is different from grasses, and little is known about what pretreatments and enzymes will be effective on forbs. Walton's lab has developed a model set of forbs for fundamental studies on the factors that limit the digestibility of this group of plants and hence their potential as biofuel “crops.” The results indicate that the apparent recalcitrance of forbs is due to a combination of lower Glc content and enzyme imbalance -- i.e., current commercial mixtures do not have the right enzymes to work effectively on forbs.
JONATHAN D. WALTON
DOE-Plant Research Laboratory
Michigan State University
East Lansing, MI 48824
Ph.D., Biological Sciences, 1982, Stanford Univ. Advisor: Peter M. Ray.
M.S., Plant Pathology, 1978, Cornell Univ. Advisor: Olen C. Yoder.
A.B., Biology, 1975, University of California, Santa Cruz.
Professor, Department of Energy Plant Research Laboratory, Michigan State
University. 1997‑present. (Joint appointment in Department of Plant Biology.)
Associate Professor, Michigan State University, 1992-1997.
Assistant Professor, Michigan State University, 1987‑1992.
Postdoctoral Associate, ARCO Plant Cell Research Institute, Dublin, CA, 1984‑1987.
NATO Postdoctoral Fellow, University of Rome, Italy, 1983‑1984.
Postdoctoral Associate, Department of Plant Breeding, Cornell University, 1981‑1983.
Honors and Professional Activities:
Thomas J. Watson Memorial National Merit Scholarship, 1971‑1975.
Honors in the Major, UC Santa Cruz, 1975.
Biology Teaching Fellowship, Stanford, 1979‑1981.
National Science Foundation Predoctoral Fellowship, 1976‑1979.
Sabbatical leave, Department of Environmental Science, Policy, and Management, University of California, Berkeley. Laboratory of John Casida. 1993-1994.
Senior Editor, Molecular Plant-Microbe Interactions, 1994-1997.
Editor-in-Chief, Intl. Society for Molecular Plant-Microbe Interactions (IS-MPMI);
Reporter (Newsletter), 2000-2003.
Editorial Board, Eukaryotic Cell, 2001-2006.
Board of Directors, IS-MPMI, 2001-2008.
President, IS-MPMI, 2003-2005.
Editorial Committee, Annual Review of Phytopathology, 2003-2006.
MSU Distinguished Faculty Award, 2002.
MSU College of Natural Sciences Distinguished Faculty Award, 2002.
Editor-in-Chief, Molecular Plant-Microbe Interactions, 2007-2010
Member of Publications Board, American Phytopathological Society (APS), 2007-2010.
Director of the Great Lakes Bioenergy Research Center (GLBRC) for MSU, 2007-2012
Fellow of the American Phytopathological Society, 2008