Revealing the Differences Between Free and Complexed Enzyme Mechanisms and Factors Contributing to Cell Wall Recalcitrance
Enzymatic depolymerization of polysaccharides is a key step in the production of fuels and chemicals from lignocellulosic biomass, and discovery of synergistic biomass-degrading enzyme paradigms will enable improved conversion processes. Historically, revealing insights into enzymatic saccharification mechanisms on plant cell walls has been hindered by uncharacterized substrates and low resolution imaging techniques. Also, translating findings between model substrates to intact biomass is critical for evaluating enzyme performance. Here we employ a fungal free enzyme cocktail, a complexed cellulosomal system, and a combination of the two to investigate saccharification mechanisms on cellulose I, II and III along with corn stover from Clean Fractionation (CF), which is an Organosolv pretreatment. The insoluble Cellulose Enriched Fraction (CEF) from CF contains mainly cellulose with minor amounts of residual hemicellulose and lignin, the amount of which depends on the CF pretreatment severity. Enzymatic digestions at both low and high-solids loadings demonstrate that CF reduces the amount of enzyme required to depolymerize polysaccharides relative to deacetylated, dilute acid pretreated corn stover. Transmission and scanning electron microscopy of the biomass provides evidence for the different mechanisms of enzymatic deconstruction between free and complexed enzyme systems, and reveals the basis for the synergistic relationship between the two enzyme paradigms on a process-relevant substrate for the first time. These results also demonstrate that the presence of lignin, rather than cellulose morphology, is more detrimental to cellulosome action than to free cellulases. As enzyme costs are a major economic driver for biorefineries, this study provides key inputs for the evaluation of CF as a pretreatment method for biomass conversion.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); USDOE Office of Energy Efficiency and Renewable Energy (EERE)
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1215019
- Report Number(s):
- NREL/PR-5100-62724
- Resource Relation:
- Conference: 10th European Symposium on Biochemical Engineering Sciences (ESBES), 7-10 September 2014, Lille Grand Palais, Lille, France
- Country of Publication:
- United States
- Language:
- English
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