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Title: Biomass Structure and Its Contributions to Recalcitrance During Consolidated Bioprocessing with Clostridium Thermocellum

Abstract

Each study provided compelling reasoning to strongly consider lignin’s part in limiting CBP efficiencies at the laboratory and eventually the industrial scale. To make cellulosic ethanol production feasible with CBP, lignin structure and content must be manipulated with genetic modifications or carefully selected in natural variants to combat these difficulties.

Authors:
 [1]
  1. Georgia Inst. of Technology, Atlanta, GA (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1376616
DOE Contract Number:
AC05-00OR22725
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
09 BIOMASS FUELS

Citation Formats

Akinosho, Hannah O. Biomass Structure and Its Contributions to Recalcitrance During Consolidated Bioprocessing with Clostridium Thermocellum. United States: N. p., 2017. Web. doi:10.2172/1376616.
Akinosho, Hannah O. Biomass Structure and Its Contributions to Recalcitrance During Consolidated Bioprocessing with Clostridium Thermocellum. United States. doi:10.2172/1376616.
Akinosho, Hannah O. 2017. "Biomass Structure and Its Contributions to Recalcitrance During Consolidated Bioprocessing with Clostridium Thermocellum". United States. doi:10.2172/1376616. https://www.osti.gov/servlets/purl/1376616.
@article{osti_1376616,
title = {Biomass Structure and Its Contributions to Recalcitrance During Consolidated Bioprocessing with Clostridium Thermocellum},
author = {Akinosho, Hannah O.},
abstractNote = {Each study provided compelling reasoning to strongly consider lignin’s part in limiting CBP efficiencies at the laboratory and eventually the industrial scale. To make cellulosic ethanol production feasible with CBP, lignin structure and content must be manipulated with genetic modifications or carefully selected in natural variants to combat these difficulties.},
doi = {10.2172/1376616},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 7
}

Thesis/Dissertation:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this thesis or dissertation.

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  • During consolidated bioprocessing (CBP), Clostridium thermocellum hydrolyzes several plant cell wall components. Cellulose hydrolysis, specifically, liberates sugars for fermentation, which generates ethanol, acetate, hydrogen, and other products. While several studies indicate that C. thermocellum hydrolyzes carbohydrates in biomass, the structural changes to lignin during CBP remain unclear. In this paper, the whole plant cell walls of untreated and C. thermocellum-treated Populus trichocarpa were characterized using NMR and FTIR. The results suggest that C. thermocellum reduces the β-O-4 linkage content and increases the lignin S/G ratio. Finally, this investigation indicates that C. thermocellum not only modifies lignin in order to accessmore » cellulose but also leaves behind a suitable lignin substrate for value-added applications in the cellulosic ethanol production scheme.« less
  • Background: Higher ratios of syringyl-to-guaiacyl (S/G) lignin components of Populus were shown to improve sugar release by enzymatic hydrolysis using commercial blends. Cellulolytic microbes are often robust biomass hydrolyzers and may offer cost advantages; however, it is unknown whether their activity can also be significantly influenced by the ratio of different monolignol types in Populus biomass. Hydrolysis and fermentation of autoclaved, but otherwise not pretreated Populus trichocarpa by Clostridium thermocellum ATCC 27405 was compared using feedstocks that had similar carbohydrate and total lignin contents but differed in S/G ratios. Results: Populus with an S/G ratio of 2.1 was converted moremore » rapidly and to a greater extent compared to similar biomass that had a ratio of 1.2. For either microbes or commercial enzymes, an approximate 50% relative difference in total solids solubilization was measured for both biomasses, which suggests that the differences and limitations in the microbial breakdown of lignocellulose may be largely from the enzymatic hydrolytic process. Unexpectedly, the reduction in glucan content per gram solid in the residual microbially processed biomass was similar (17–18%) irrespective of S/G ratio, pointing to a similar mechanism of solubilization that proceeded at different rates. Fermentation metabolome testing did not reveal the release of known biomass-derived alcohol and aldehyde inhibitors that could explain observed differences in microbial hydrolytic activity. Biomass-derived p-hydroxybenzoic acid was up to ninefold higher in low S/G ratio biomass fermentations, but was not found to be inhibitory in subsequent test fermentations. Cellulose crystallinity and degree of polymerization did not vary between Populus lines and had minor changes after fermentation. However, lignin molecular weights and cellulose accessibility determined by Simons’ staining were positively correlated to the S/G content. Conclusions: Higher S/G ratios in Populus biomass lead to longer and more linear lignin chains and greater access to surface cellulosic content by microbe-bound enzymatic complexes. Substrate access limitation is suggested as a primary bottleneck in solubilization of minimally processed Populus, which has important implications for microbial deconstruction of lignocellulose biomass. Our findings will allow others to examine different Populus lines and to test if similar observations are possible for other plant species.« less
  • Background: Higher ratios of syringyl-to-guaiacyl (S/G) lignin components of Populus were shown to improve sugar release by enzymatic hydrolysis using commercial blends. Cellulolytic microbes are often robust biomass hydrolyzers and may offer cost advantages, however, it is unknown whether their activity can also be significantly influenced by the ratio of different monolignol types in Populus biomass. Hydrolysis and fermentation of autoclaved but otherwise not pretreated Populus trichocarpa by Clostridium thermocellum ATCC 27405 was compared using feedstocks that had similar carbohydrate and total lignin contents but differed in S/G ratios. Results: Populus with an S/G ratio of 2.1 was converted moremore » rapidly and to a greater extent compared to similar biomass that had a ratio of 1.2. For either microbes or commercial enzymes, an approximate 50% relative difference in total solids solubilization was measured for both biomasses, which suggests that the differences and limitations in the microbial breakdown of lignocellulose may be largely from the enzymatic hydrolytic process. Unexpectedly, the reduction in glucan content per gram solid in the residual microbially processed biomass was similar (17 18 %) irrespective of S/G ratio, pointing to a similar mechanism of solubilization that proceeded at different rates. Fermentation metabolome testing did not reveal the release of known biomass-derived alcohol and aldehyde inhibitors that could explain observed differences in microbial hydrolytic activity. Biomass-derived p-hydroxybenzoic acid was up to nine-fold higher in low S/G ratio biomass fermentations, but was not found to be inhibitory in subsequent test fermentations. Cellulose crystallinity and degree of polymerization did not vary between Populus lines and had minor changes after fermentation. However, lignin molecular weights and cellulose accessibility determined by Simons staining were positively correlated to the S/G content. Conclusions: Higher S/G ratios in Populus biomass lead to longer and more linear lignin chains and greater access to surface cellulosic content by microbe-bound enzymatic complexes. Substrate access limitation is suggested as a primary bottleneck in solubilization of minimally processed Populus, which has important implications for microbial deconstruction of lignocellulose biomass. Our findings will allow others to examine different Populus lines and to test if similar observations are possible for other plant species.« less
  • First isolated in 1926, Clostridium thermocellum has recently received increased attention as a high utility candidate for use in consolidated bioprocessing (CBP) applications. These applications, which seek to process lignocellulosic biomass directly into useful products such as ethanol, are gaining traction as economically feasible routes toward the production of fuel and other high value chemical compounds as the shortcomings of fossil fuels become evident. This review evaluates C. thermocellum's role in this transitory process by highlighting recent discoveries relating to its genomic, transcriptomic, proteomic, and metabolomic responses to varying biomass sources, with a special emphasis placed on providing an overviewmore » of its unique, multivariate enzyme cellulosome complex and the role that this structure performs during biomass degradation. Both naturally evolved and genetically engineered strains are examined in light of their unique attributes and responses to various biomass treatment conditions, and the genetic tools that have been employed for their creation are presented. Several future routes for potential industrial usage are presented, and it is concluded that, although there have been many advances to significantly improve C. thermocellum's amenability to industrial use, several hurdles still remain to be overcome as this unique organism enjoys increased attention within the scientific community.« less
  • Background: Switchgrass is an abundant and dedicated bioenergy feedstock however its inherent recalcitrance is one of the economic hurdles for producing biofuels. The down-regulation of the caffeic acid O-methyl transferase (COMT) gene in the lignin pathway of switchgrass reduced lignin content and S/G ratio, and the transgenic lines showed improved fermentation yield with S. cerevisiae and C. thermocellum (ATCC 27405) in comparison to the wild-type switchgrass. Results: Here we examine the fermentation potential of the COMT transgenic switchgrass and its wild-type line, with an engineered and evolved Clostridium thermocellum (M1570) strain. The fermentation of the transgenic switchgrass had superior conversionmore » relative to the control line with an increase of 20% and ethanol was the primary metabolite accounting for 90% of the total metabolites measured by HPLC. Conclusions: The down-regulation of the COMT gene in switchgrass reduced recalcitrance and improved microbial bioconversion yield. Moreover, these results showed ethanol as the main fermentation metabolite produced by an engineered and evolved C. thermocellum strain grown on a transgenic switchgrass.« less