Adding Tetrahydrofuran to Dilute Acid Pretreatment Provides New Insights into Substrate Changes that Greatly Enhance Biomass Deconstruction by Clostridium thermocellum and Fungal Enzymes

Bryon Donohoe, Vanessa Thomas, Mi Li, Yunqiao Pu, Arthur Ragauskas, Rajeev Kumar, Thanh Nguyen, Charles Cai, Charles Wyman

Research output: Contribution to journalArticlepeer-review

38 Scopus Citations

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 languageAmerican English
Article number252
Number of pages13
JournalBiotechnology for Biofuels
Volume10
Issue number1
DOIs
StatePublished - 2017

Bibliographical note

Publisher Copyright:
© 2017 The Author(s).

NREL Publication Number

  • NREL/JA-2700-70675

Keywords

  • Consolidated bioprocessing
  • Fractionation
  • Recalcitrance
  • Sugar
  • Tetrahydrofuran
  • Yield

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