Citations available via the Publications page.
(taken from Gilna et al. 2017 Biotechnology for Biofuels, Special BESC Issue; in press)
Biomass Formation. Populus and switchgrass (Panicum virgatum) were the chosen feedstocks for studies of cell wall related genetic modifications that could impact recalcitrance and inform understanding. Both are high-yield perennials recognized as potential domestic biofeedstocks [U.S. DOE 2006; U.S. DOE 2011], Populus was the first sequenced woody feedstock [Tuskan 2006]. Switchgrass is a native herbaceous perennial that could grow on marginal land. Both were deemed tractable for studies aimed at determining the basis of, and ameliorating, recalcitrance. Key advances in biomass formation led by BESC include:
Biomass Conversion. One-step consolidated bioprocessing (CBP) without added enzymes [Lynd, 1996] was the central focus of BESC’s work in the conversion area, which featured both fundamental and applied components. BESC initially focused on two approaches: improving product-formation in thermophilic cellulolytic bacteria [primarily Clostridium thermocellum (C. thermocellum) and Caldicellulosiruptor bescii (C. bescii)] and conferring to yeasts the ability to ferment cellulose by virtue of heterologous expression of glycosyl hydrolases. Investigators came to regard the former approach as more promising and by the end of BESC were focused exclusively on this path. Key conversion advances led by BESC included:
Enabling Technology. Enabling technologies was organized to develop and apply cutting-edge analytical methodologies to characterize biomass as well as its conversion. There was also significant ’omic and computational biology of the modified plants and microbes to help improve metabolic models. The resulting data were used to create new insights into how biomass structure and chemistry affects recalcitrance during CBP or pretreatment. These efforts included analyses of partially digested solid residues from CBP.
Genome-Wide Association Study (GWAS) Dataset Released (Details)
Demonstrated further evidence that down-regulation of pectin biosynthetic genes has a major impact on recalcitrance in woody or grass feedstocks.
Reported results from multiple multi-year field trials of either genetically modified or natural variant Populus and switchgrass lines that continue to exhibit reduced recalcitrance and stable, or in some cases improved, agronomic performance.
Elucidated a third modality of cellulase action exhibited by C. thermocellum, contributing to its ultra-high performance on cellulose.
Achieved greater than 85% carbohydrate solubilization for some lines of Populus and switchgrass using consolidated bioprocessing with cotreatment in the absence of added enzymes or thermochemical pretreatment implying that C. thermocellum is able to attack all the major chemical linkages in representative woody and herbaceous lignocellulose crops given sufficient physical access.
Reported further evidence that lignin syringyl to guaiacyl (S/G) ratio impacts overall recalcitrance phenotype, effectiveness of microbial hydrolysis, and melt spinability in carbon fiber production.
Research Summaries from Genomic Science Program Awardee Meeting, March 2016. (see PDF page 75)
Engineered Clostridium thermocellum, a thermophilic, cellulolytic microbe, to produce isobutanol, an advanced biofuel.
BESC partner Mascoma, LLC, launched C5 FUEL™, a new yeast strain engineered for improved cellulosic biofuel production.
Study assessing the field performance of modified switchgrass demonstrated a doubling of biofuel production per hectare, the highest gain reported from any field-grown modified feedstock.
Molecular dynamics simulations performed on the TITAN supercomputer at Oak Ridge National Laboratory to determine the molecular basis of reduced recalcitrance.
Applied association genetics to rapidly identify specific genes best suited for producing biofuel from poplar trees planted in different environments.
Research Summaries from Genomic Science Program Awardee Meeting, February 2015. (see PDF page 23)
Discovered a unique form of lignin (i.e., C-lignin) in vanilla bean seed coats, which shows promise as a feedstock for carbon fiber.
Improved biofuel production from modified switchgrass when the feedstock was combined with an engineered C. thermocellum strain.
Outlined how more value can be derived from lignin within a biorefinery.
Demonstrated the biofuel potential of lignin-modified transgenic switchgrass in a field study.
Characterized Caldicellulosiruptor bescii; this microorganism secretes an enzyme, CelA, which can digest cellulose almost twice as fast as the current leading cellulase enzyme on the market.
Early BESC spinoff technology licensed to startup company Vertimass; technology directly converts ethanol into a hydrocarbon blend stock for use in transportation fuels. (Press Release)
Research Summaries from Genomic Science Program Awardee Meeting, February 2014. (see PDF page 329)
Demonstrated that fungal cellulases and complexed cellulosomal enzymes exhibit different, yet synergistic mechanisms in cellulose deconstruction; this finding highlights the potential for combining these two systems for enhanced performance.
Discovered a new plant structure (Arabinoxylan-Pectin-Arabinogalactan Protein 1 or APAP1) that may lead to improved biofuel processing.
Applied high-performance proteomics to identify important networks and pathways in Populus.
Developed hands-on "Farming for Fuels" lesson plans to educate fourth–sixth graders about a biobased fuel economy; educational outreach program has now reached 85,000 (27,000 in Year 6 alone) students, teachers, and parents nationwide. Also released a biofuel Road Trip Challenge game as a museum kiosk and as an iPad app.
Developed an integrated microscopy system for real-time imaging of pretreatment and enzyme digestion; findings show that biomass reactivity is determined by the nanoscale architecture of plant cell walls, in which lignin is the major factor impeding the access of chemical and enzymatic catalysts. (News Article; )
Research Summaries from Genomic Science Program Awardee Meeting, February 2013 (titles only; no abstracts available)
Developed the ability to genetically manipulate Caldicellulosiruptor, which are thermophilic cellulolytic microorganisms; this advance could enable the direct conversion of lignocellulose to biofuels.
Completed sequencing and analysis of a reference genome for Setaria; this advance enables the further development of Setaria as a model plant and improves understanding of cell wall composition, plant structure and development, and traits pertinent to the development of biofuel crops.
Discovered an unusual lignin polymer in certain plant seeds; constructed from catechyl (C) units, C-lignin demonstrates the natural capability of native plants to produce specific lignin polymers and supports the radical coupling polymerization hypothesis. C-lignin also may be a source for carbon fiber manufacturing.
Demonstrated that GAUT1 and GAUT7, proteins in the plant cell wall, are co-expressed not only in a plant's primary walls but also in the secondary walls and in many plant tissues; this discovery changes the way scientists think about how plant cell walls are made and opens a new door for converting plants to biofuels and other bioproducts.
Discovered a gene (GXMT1) that plays a major role in the cell wall development of Arabidopsis plants; this finding lays the groundwork for improved biofuel processing.
Genetically modified switchgrass to improve biofuel production; discovered that the down regulation of a single gene reduces recalcitrance with no apparent growth defects, increases ethanol production by more than 30%, and requires three- to four-fold less enzyme for processing, potentially reducing production costs by at least 20%. Modification to be field tested at large scale.
Demonstrated that Clostridium cellulolyticum, a cellulose-degrading microbe, can be metabolically engineered to produce isobutanol directly from cellulose, thereby demonstrating the ability to apply consolidated bioprocessing (CBP) technology to produce advanced biofuels.
Developed a set of hands-on "Farming for Fuels" lesson plans to educate fourth–sixth graders about the carbon cycle, use of lignocellulosic biomass for biofuels production, and technical and economic obstacles to a biobased fuel economy. This national outreach program, developed in partnership with the Creative Discovery Museum in Chattanooga, Tennessee, has reached over 35,000 students, teachers, and parents by partnering with museums and centers in Tennessee, Georgia, Texas, Michigan, Illinois, Florida, New York, and Arizona. (Lesson Plan PDF)
With BESC assistance, Mascoma, LLC, developed yeasts that express recombinant cellulases; these reagents are intended for use in Mascoma's commercial 20-million-gallon hardwood-to-ethanol plant in Kinross, Michigan.
Genomic Science Awardee Meeting IX and USDA-DOE Plant Feedstock Genomics for Bioenergy Awardee Meeting, Crystal City, Va., April 10-13 2011 (see extracted PDF page 2)
Completed a baseline analysis of reduced recalcitrance switchgrass lines, finding that the transgenic material had normal growth habit, but reduced lignin, improved sugar release, and 24% to 38% higher ethanol yields than the wild type after fermentation; demonstrated for the first time the direct impact of reduced biomass recalcitrance at the bioconversion process level. (Journal Article)
Developed new biocatalysts, demonstrating the feasibility of producing active, engineered cellulosomes; a key achievement was the successful production of an engineered, active minicellulosome in Escherichia coli.
Continued relationship with National Geographic's The JASON Project to film and generate an educational module on bioenergy; this module, Operation: Infinite Potential, won three 2010 CODiE awards for best instructional solution grades K–12. (Module)
Genomic Science 2010 Awardee Workshop VIII and Knowledgebase Workshop, Crystal City, Va., February 7-10 2010 (see extracted PDF page 32)
Established three Populus field trials with 1,100 genotypes at each location; variations among these diverse populations are being mined to identify key genes in biomass composition and sugar release.
Created yeasts that ferment an application-relevant cellulosic feedstock to recoverable ethanol at high conversion with no added cellulose.
Developed a Biofuels Outreach lesson with the Creative Discovery Museum in Chattanooga, Tennessee; this interactive educational lesson is targeted for third-eighth graders.
Genomics:GTL Contractor-Grantee Workshop VII, Bethesda, Md., February 8-11 2009 (see extracted PDF page 26)
Established and put in operation a large-scale gene transformation pipeline; pipeline targets plant cell wall mutants and aids the selection of high-priority, recalcitrance-associated genes. Screened multiple samples from 100 Populus plants and 50 switchgrass plants to identify native variants with modified composition.
Developed a preliminary functional model of the cellulosome, a multi-enzyme complex that breaks down cellulose and hemicellulose found in plant cell walls.
Implemented a high-throughput characterization pipeline (capable of screening more than 2,000 samples per month) to screen biomass composition and identify the most promising samples for more detailed characterization.
Completed omics analyses of initial wild type consolidated bioprocessing (CBP) microbes.
Genomics:GTL Contractor-Grantee Workshop VI, Bethesda, Md., February 10-13 2008 (see extracted PDF page 2, bottom)
Department of Energy selected three Bioenergy Research Centers; Centers are intended to accelerate basic research in the development of cellulosic ethanol and other biofuels. (Details)
BESC researchers received funding and began work.