Enzymatic hydrolysis of cellulosic biomass

Abstract

Biological conversion of cellulosic biomass to fuels and chemicals offers the high yields to products vital to economic success and the potential for very low costs. Enzymatic hydrolysis that converts lignocellulosic biomass to fermentable sugars may be the most complex step in this process due to substrate-related and enzyme-related effects and their interactions. Although enzymatic hydrolysis offers the potential for higher yields, higher selectivity, lower energy costs and milder operating conditions than chemical processes, the mechanism of enzymatic hydrolysis and the relationship between the substrate structure and function of various glycosyl hydrolase components is not well understood. Consequently, limited success has been realized in maximizing sugar yields at very low cost. This review highlights literature on the impact of key substrate and enzyme features that influence performance, to better understand fundamental strategies to advance enzymatic hydrolysis of cellulosic biomass for biological conversion to fuels and chemicals. Topics are summarized from a practical point of view including characteristics of cellulose (e.g., crystallinity, degree of polymerization and accessible surface area) and soluble and insoluble biomass components (e.g., oligomeric xylan and lignin) released in pretreatment, and their effects on the effectiveness of enzymatic hydrolysis. We further discuss the diversity, stability and activity of individual enzymes and their synergistic effects in deconstructing complex lignocellulosic biomass. Advanced technologies to discover and characterize novel enzymes and to improve enzyme characteristics by mutagenesis, post-translational modification and over-expression of selected enzymes and modifications in lignocellulosic biomass are also discussed.

Financial & competing interests disclosure

Bin Yang’s research is sponsored by the Center for Bioproducts and Bioenergy and Department of Biological Systems Engineering at Washington State University. Ziyu Dai’s research was funded by the Biomass Program of the US Department of Energy. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute, Pacific Northwest Division, for US Department of Energy under contract No: DE-AC05-76RL01830. Shi-You Ding is supported by the US Department of Energy, the Office of Science, Office of Biological and Environmental Research through the BioEnergy Science Center, a DOE Bioenergy Research Center. Charles Wyman is supported by the Ford Motor Company Chair in Environmental Engineering at the Center for Environmental Research and Technology of the Bourns College of Engineering at UCR; the BioEnergy Science Center, a DOE Bioenergy Research Center, supported by the Biological and Environmental Research Office in the DOE Office of Science, contract DE-AC05-00OR22725, and subcontract 4000063616; the University of California at Riverside; the USDA National Research Initiative Competitive Grants Program, contract 2008-35504-04596; the Defense Advanced Research Projects Agency through subcontract SUB-226-UCR1 from Logos Technologies supported by contract HR0011-09-C-0075; the Defense Advanced Research Projects Agency and Army Research Lab through Defense Science Office Cooperative Agreement W911NF-09-2-0010 and subcontract 09-005334-000 to the University of Massachusetts, Amherst; and the DOE Office of the Biomass Program, contract DE-FG36-07GO17102. Dr Wyman is also a co-founder, SAB chair, and Chief Development Officer of Mascoma Corporation. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.