Abstract
Background: Consolidated bioprocessing (CBP) by anaerobes, such as Clostridium thermocellum, which combine enzyme production, hydrolysis, and fermentation are promising alternatives to historical economic challenges of using fungal enzymes for biological conversion of lignocellulosic biomass. However, limited research has integrated CBP with real pretreated biomass, and understanding how pretreatment impacts subsequent deconstruction by CBP vs. fungal enzymes can provide valuable insights into CBP and suggest other novel biomass deconstruction strategies. This study focused on determining the effect of pretreatment by dilute sulfuric acid alone (DA) and with tetrahydrofuran (THF) addition via co-solvent-enhanced lignocellulosic fractionation (CELF) on deconstruction of corn stover and Populus with much different recalcitrance by C. thermocellum vs. fungal enzymes and changes in pretreated biomass related to these differences. Results: Coupling CELF fractionation of corn stover and Populus with subsequent CBP by the anaerobe C. thermocellum completely solubilized polysaccharides left in the pretreated solids within only 48 h without adding enzymes. These results were better than those from the conventional DA followed by either CBP or fungal enzymes or CELF followed by fungal enzyme hydrolysis, especially at viable enzyme loadings. Enzyme adsorption on CELF-pretreated corn stover and CELF-pretreated Populus solids were virtually equal, while DA improved the enzyme accessibility for corn stover more than Populus. Confocal scanning light microscopy (CSLM), transmission electron microscopy (TEM), and NMR characterization of solids from both pretreatments revealed differences in cell wall structure and lignin composition, location, coalescence, and migration-enhanced digestibility of CELF-pretreated solids. Conclusions: Adding THF to DA pretreatment (CELF) greatly enhanced deconstruction of corn stover and Populus by fungal enzymes and C. thermocellum CBP, and the CELF-CBP tandem was agnostic to feedstock recalcitrance. Composition measurements, material balances, cellulase adsorption, and CSLM and TEM imaging revealed adding THF enhanced the enzyme accessibility, cell wall fractures, and cellular dislocation and cell wall delamination. Overall, enhanced deconstruction of CELF solids by enzymes and particularly by C. thermocellum could be related to lignin removal and alteration, thereby pointing to these factors being key contributors to biomass recalcitrance as a barrier to low-cost biological conversion to sustainable fuels.
| Original language | English |
|---|---|
| Article number | 252 |
| Journal | Biotechnology for Biofuels |
| Volume | 10 |
| Issue number | 1 |
| DOIs | |
| State | Published - Nov 30 2017 |
Funding
We gratefully acknowledge funding 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 and support of a member of our team by a National Science Foundation grant (#2013142496). We also recognize the Ford Motor Company Chair in Environmental Engineering at the University of California Riverside (UCR). 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 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 the 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 Lynd at the Dartmouth College in providing the C. thermocellum strain and training in its use is highly appreciated. Funding for this research was provided 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. In addition, one author was supported by a National Science Foundation grant (#2013142496). We also recognize the Ford Motor Company Chair in Environmental Engineering at the University of California Riverside (UCR). None of these funding bodies designed the study, collected, analyzed, or interpreted data, or contributed to writing the manuscript.
| Funders | Funder number |
|---|---|
| BioEnergy Science Center | |
| DOE Bioenergy Research Center | |
| DOE Office of Science | |
| Office of Biological and Environmental Research | |
| US Department of Energy | |
| UT-Battelle | DE-AC05-00OR22725 |
| National Science Foundation | 2013142496 |
Keywords
- Consolidated bioprocessing
- Fractionation
- Recalcitrance
- Sugar
- Tetrahydrofuran
- Yield
