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Structural Characterization of Biomass using Chemical, Enzymic, Spectroscopic, and Immunological Techniques |
Senior personnel: William York (CCRC), Michael Hahn (CCRC), Malcolm O'Neill (CCRC), Alan Darvill (CCRC) Return to "Research Groups" main page
Background The difficulty of converting the polysaccharides present in biomass to fermentable sugars results in large part from the chemical and ultrastructural properties of plant secondary cell walls: Chemical features - hemicellulose structure, pectin structure, lignin-carbohydrate linkages, polysaccharide-polysaccharide interactions Ultrastructural features - cellulose crystallinity, ratio of cellulose polymorphs, and spatial distribution of polymers that limit enzyme access to plant cell walls |
Understanding the relationships between biomass structure and recalcitrance requires knowledge of: the chemical and physical properties of biomass that influence recalcitrance how biomass properties can be altered by modifying plant cell wall biosynthetic pathways how biomass properties change during pretreatment how pretreatment affects biomass deconstruction by enzymes and microorganisms Such information will allow the BESC biomass formation group to rationally modify biomass properties by altering wall composition and will provide the BESC bioconversion groups (Dartmouth, NREL) the information required to design and implement improved bioprocessing technologies.
The BESC-CCRC plant cell wall structure group will structurally characterize biomass with altered recalcitrance using a combination of chemical and enzymic methods together with NMR spectroscopy, mass spectrometry and immunological techniques Other researchers within the BESC biomass structure and modeling focus area will: Develop high-throughput screening pipelines to assay large numbers of Populus and switchgrass biomass for differences in cell wall Determine biomass surface chemistry using atomic force microscopy (AFM) and imaging mass spectrometry (GaTech, NREL) Characterize cellulose crystallinity and morpholgy using solid-state NMR spectroscopy (GaTech) and neutron scattering (ORNL) Characterize at the molecular level the interactions between biocatalysts and biomass (Ga Tech, NREL, ORNL)
Structural characterization of biomass with altered recalcitrance Changes in cell wall structure that result from modifying cell wall biosynthetic pathways may lead to major changes in recalcitrance. However, the chemical nature of such changes may only become apparent after detailed structural analysis. Current state-of-the-art methodology requires labor-intensive processing of biomass to isolate and purify cellulose, hemicellulose, lignin and lignin-carbohydrate complexes that can then be characterized chemically and by 1 and 2D NMR spectroscopy. Developments in the use of ionic liquids together with high-resolution NMR spectroscopy provide a opportunity to chemically characterize plant cell walls much more rapidly. Ionic liquids have been developed as solvents for starch, cellulose, xylan, and lignin (Fort et al., 2007), and for wood (Xie and Shi, 2006). Derivatized walls that are soluble in chloroform and thus amendable to NMR analysis are obtained by acetylating walls solubilized in dimethylsulfoxide containing N-methylimidazole (Lu and Ralph, 2003). We will develop protocols to solubilize plant cell walls, with minimal degradation of the constituent polymers, using ionic liquids. The solubilized wall materials will be analyzed using multidimensional NMR techniques to obtain correlations between the chemical shifts of diagnostic signals and the major chemical features of the biomass,including the abundances of hemicellulose, cellulose and lignin and the presence of lignin carbohydrate cross-links. We will also use chemical and enzymatic methods developed by the CCRC Plant Cell Wall Group to structurally characterize the major hemicellulosic and pectic polysaccharides present in switchgrass and Populus walls. A combination of tradtional chemical and enzymic analyses together with the use of solubilzed walls and NMR spectroscopy will allow us to develop a understanding of the fundamental relationships between recalcitrance and wall chemistry. |
Characterizing biomass with altered recalcitrance using monoclonal antibodies Monoclonal antibodies (MAbs) will be used to obtain information on changes in biomass surface composition that result from modifying plant cell walls and from chemical and enzymatic treatments of biomass. The CCRC, through its NSF-funded Monoconal Antibody Toolkit for Plant Cell Walls project, has generated a library of ~120 MAbs that selectively bind specific cell wall polysaccharides including hemicellulose (xyloglucan, xylan), pectins (homogalacturonan, rhamnogalacturonan I, rhamnogalacturonan II), and arabinogalactans (including arabinogalactan proteins). MAbs that bind to specific cell wall polymers will be used to develop protocols to detect polysaccharides on the surfaces of poplar and switchgrass biomass. Return to "Research Groups" main page
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