Abstract
Background: Populus natural variants have been shown to realize a broad range of sugar yields during sacchari-fication, however, the structural features responsible for higher sugar release from natural variants are not clear. In addition, the sugar release patterns resulting from digestion with two distinct biological systems, fungal enzymes and Clostridium thermocellum, have yet to be evaluated and compared. This study evaluates the effect of structural features of three natural variant Populus lines, which includes the line BESC standard, with respect to the overall process of sugar release for two different biological systems. Results: Populus natural variants, SKWE 24-2 and BESC 876, showed higher sugar release from hydrothermal pretreat-ment combined with either enzymatic hydrolysis or Clostridium thermocellum fermentation compared to the Populus natural variant, BESC standard. However, C. thermocellum outperformed the fungal cellulases yielding 96.0, 95.5, and 85.9% glucan plus xylan release from SKWE 24-2, BESC 876, and BESC standard, respectively. Among the feedstock properties evaluated, cellulose accessibility and glycome profiling provided insights into factors that govern differ-ences in sugar release between the low recalcitrant lines and the BESC standard line. However, because this distinc-tion was more apparent in the solids after pretreatment than in the untreated biomass, pretreatment was necessary to differentiate recalcitrance among Populus lines. Glycome profiling analysis showed that SKWE 24-2 contained the most loosely bound cell wall glycans, followed by BESC 876, and BESC standard. Additionally, lower molecular weight lignin may be favorable for effective hydrolysis, since C. thermocellum reduced lignin molecular weight more than fungal enzymes across all Populus lines. Conclusions: Low recalcitrant Populus natural variants, SKWE 24-2 and BESC 876, showed higher sugar yields than BESC standard when hydrothermal pretreatment was combined with biological digestion. However, C. thermocellum was determined to be a more robust and effective biological catalyst than a commercial fungal cellulase cocktail. As anticipated, recalcitrance was not readily predicted through analytical methods that determined structural properties alone. However, combining structural analysis with pretreatment enabled the identification of attributes that govern recalcitrance, namely cellulose accessibility, xylan content in the pretreated solids, and non-cellulosic glycan extractability.
Original language | English |
---|---|
Article number | 292 |
Pages (from-to) | 1-16 |
Number of pages | 16 |
Journal | Biotechnology for Biofuels |
Volume | 10 |
Issue number | 1 |
DOIs | |
State | Published - 2017 |
Funding
We gratefully acknowledge funding for this research by the Office of Biological and Environmental Research in the DOE Office of Science through the BioEnergy Science Center (BESC), a DOE Bioenergy Research Center (Contract DE-PS02-06ER64304). The generation of the CCRC series of plant cell wall glycan-directed monoclonal antibodies used in this work was supported by the US National Science Foundation Plant Genome Program (DBI-0421683 and IOS-0923992). We also recognize the Ford Motor Company Chair in Environmental Engineering at the University of California Riverside (UCR) for augmenting our ability to perform such research. NREL is a national laboratory of the US Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. This manuscript has been co-authored by UT-Battelle, LLC under contract no. DE-AC05-00OR22725 with the US Department of Energy. The publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). The valuable assistance of the team of Professor Lee R. Lynd at Dartmouth College in providing the C. thermocellum strain employed here and training in its use is also highly appreciated.
Keywords
- Clostridium thermocellum
- Consolidated bioprocessing
- Enzymatic hydrolysis
- Hydrothermal pretreatment
- Natural variants
- Populus
- Structural changes