Abstract
The native recalcitrance of lignocellulosic biomass hinders its effective deconstruction for biological conversion to fuel ethanol. However, once cellulose is physically available to enzymes/microbes, i.e., macro-accessible, cellulose micro-accessibility, i.e., the accessibility as influenced by cellulose properties, further affects cellulose conversion. Here, we performed a comparative study of the effect of cellulose micro-accessibility on cellulose conversion by two biological approaches of potential commercial interest: Consolidated bioprocessing (CBP) using Clostridium thermocellum and cell-free saccharification mediated by fungal enzymes. Commercially available cellulosic substrates, Avicel® PH-101, Sigmacell Cellulose Type 50, cotton linters, Whatman™ 1 milled filter paper, and α-cellulose were employed to constitute different cellulose micro-accessibilities. Physiochemical characterization was performed on these substrates to determine key morphological and chemical differences. Biological conversion of these substrates showed that C. thermocellum was unaffected overall by cellulose structural properties, i.e., micro-accessibility, and achieved similar solids solubilization and metabolite production from these structurally different materials. However, fungal enzymes digested these substrates to different extents. Specifically, glucan conversion of these substrates diminished in the following order: Milled filter paper > Avicel > Sigmacell and α-cellulose > cotton linters. Here, we propose that C. thermocellum digestion of lignocellulosic biomass is primarily controlled by the physical availability of cellulose in the lignocellulosic matrix and largely unaffected by cellulose properties once cellulose is made macro-accessible. In contrast, fungal enzymes require cellulose to be physically accessible, i.e., macro-accessible, as well as have properties amenable to digestion, i.e., micro-accessible.
Original language | English |
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Pages (from-to) | 2810-2822 |
Number of pages | 13 |
Journal | Green Chemistry |
Volume | 21 |
Issue number | 10 |
DOIs | |
State | Published - 2019 |
Funding
We thank Dr Lee Lynd’s laboratory team at Dartmouth College, Hanover, NH, USA for providing the DSM 1313 strain of Clostridium thermocellum used in this work. We also acknowledge the Center for Environmental Research and Technology (CE-CERT) of the Bourns College of Engineering for providing the facilities and the Ford Motor Company for funding the Chair in Environmental Engineering that facilitates projects such as this one. We thank the Joint Institute of Advanced Materials (JIAM) at the University of Tennessee, Knoxville, for use of imaging facilities. We thank Dr Lee Lynd's laboratory teamat Dartmouth College, Hanover, NH, USA for providing the DSM 1313 strain of Clostridium thermocellum used in this work. We also acknowledge the Center for Environmental Research and Technology (CE-CERT) of the Bourns College of Engineering for providing the facilities and the Ford Motor Company for funding the Chair in Environmental Engineering that facilitates projects such as this one. We thank the Joint Institute of Advanced Materials (JIAM) at the University of Tennessee, Knoxville, for use of imaging facilities. This work was funded by the Office of Biological and Environmental Research in the Department of Energy (DOE) Office of Science through the BioEnergy Science Center (BESC) (Contract DE-PS02-06ER64304) and Center for Bioenergy Innovation (CBI) at Oak Ridge National Laboratory, and the Genomic Science Program (contract FWP ERKP752). Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U. S. Department of Energy under Contract DE-AC05-00OR22725. The United States Government and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide 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 views and opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.