SusChEM: Integrated Studies on Interactions between Lignocellulosic Fine Structure and Hydrolytic Enzymes toward Efficient Hydrolysis

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Lignocellulosic plant biomass such as grass straw and agricultural residues has been recognized a low-cost, abundant, and renewable source of fermentable sugars for production of fuel alcohol and other value-added chemicals. Current processes deployed in cellulosic biofuel facilities use a mixture of enzymes to convert the cellulosic fractions to fermentable sugars. However, this process is still fairly slow and is the most expensive step in cellulosic biofuels production, in part because lignocellulosic biomass is recalcitrant to enzymatic attack and breakdown. This recalcitrance is due to the complexity of lignocellulose structure at the molecular and microscopic levels. Therefore, before enzyme treatment, the lignocellulosic biomass is pretreated, typically with a combination of steam and chemicals, to open up the pores in the biomass so that the enzyme can be more effective. There is a need to develop a better, molecular level understanding of the biomass breakdown processes to identify new strategies optimize or eliminate pretreatment and improve the rate of conversion to realize cost reduction. The goal of this project is to develop a fundamental understanding of how lignocellulosic biomass is broken down, or deconstructed, during enzyme treatment so that these new cost-saving strategies can be identified. The innovative aspect of this study is the combination of molecular modeling and molecular chemical imaging to discover more about this complex process. The educational activities associated with this project feature the development of a workbook on the conversion of biomass to biofuels for use in summer youth programs.Lignocellulosic biomass is a three-dimensional biopolymer matrix of cellulose, hemicellulose, and lignin ordered at multiple scales ranging from the molecular scale to the microscale. The complexity of the lignocellulosic matrix has long been recognized as a key limiting factor in the efficiency of its enzymatic hydrolysis to fermentable sugars. This research will combine dynamic modeling and molecular imaging to gain new insights into the real-time dynamics of lignocellulosic molecular and fine structure changes during the conversion of lignocellulosic biomass to sugars using mixtures of hydrolytic enzymes. To accomplish this goal, the research has three objectives. The first objective is to gain a fundamental, quantitative understanding of the molecular mechanisms underlying the recalcitrance lignocellulosic biomass fine structure to enzymatic attack. The second objective is to establish relationships between cell wall component composition and molecular structural organization with hydrolysis processing conditions and correlate these relationships to biomass deconstruction efficiency. The third objective is to develop a mechanistic modeling framework capable of simulating biomass deconstruction under realistic hydrolysis conditions with comprehensive consideration of substrate morphology and component distribution. These objectives will be enabled through single-molecule imaging via Atomic Force Microscopy (AFM) and chemical imaging via Stimulated Raman Scattering (SRS) of the biomass deconstruction process during enzymatic treatment. Outcomes from the proposed research will enable the rational design of enzyme cocktails and processing conditions to overcome the factors that slow down the hydrolytic reactions, leading to optimal design of the hydrolysis bioreactor systems and cost reduction of cellulosic biofuel manufacturing systems.