This project will investigate the multifaceted role that the non-covalent forces exerted by plant cell wall polymers within nanoscale cell wall pores have on a number of important phenomena influencing plant cell wall deconstruction for biofuel production, how these forces are impacted by plant cell wall properties and how these properties evolve during pretreatment and hydrolysis that lead to outcomes of improved polysaccharide conversion. Specifically this involves the role of surface properties in influencing: (1) water infiltration into the cell wall and cell wall swelling, (2) cellulolytic enzyme accessibility to binding sites within the cell wall, and (3) enzyme binding to chemically and physically modified surfaces within the cell wall. For this, the PIs will investigate a new paradigm for understanding plant cell wall recalcitrance, specifically that the limitations of cell wall porosity and inaccessible surface area to enzymes, can be best investigated in the context of understanding the plant cell wall matrix as a water-swellable hydrogel and understanding the porosity in the context of hydrogel swelling due to the opposing forces of water swelling versus the resistance of the plant cell wall matrix to swelling imparted by lignification. Additionally, the PIs propose that using a wider range of plant cell wall sources than have been explored in the past (graminaceous monocots and a woody dicot) and exploring a wider range of pretreatment/delignification conditions that result in a diverse range of cell wall properties (lignin contents, carboxylate contents) they will be able to significantly improve the understanding of how cell wall matrix properties impact water swelling and porosity and be able to link these differences to improved enzymatic conversion.
By comparing the diverse cell walls with the diverse properties, this project will address several important outstanding problems in cellulose hydrolysis: (1) untangle the complex relationship between cell wall rigidity, lignin content, cell wall swelling, and porosity in its impact on cell wall enzymatic digestibility, (2) understand the limiting factors controlling the penetration of charged and uncharged sets of polymer probes, enzymes, and non-catalytic glycan-binding protein modules into cell wall pores, and (3) develop an improved understanding of the fundamental differences in properties influencing recalcitrance in grasses versus woody dicots.
The project work will help enable the development of bioenergy technologies for displacing imported petroleum, and providing rural income and employment. The education of undergraduate engineering students by engaging them with hands-on experiences and examples of these bioenergy technologies is a logical development in the evolution of engineering education. The PIs will further develop an international bioenergy education program with the goal of enhancing student knowledge acquisition and increasing self-directed and life-long learning through the diverse experiences and perspectives that students gain in this international environment.
