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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Milligrams to kilograms: making microbes work at scale

Energy is one of the most complex fields of study and an issue that influences nearly every aspect of modern life. Over the past century, combustion of fossil fuels, particularly in the transportation sector, has been the dominant form of energy release. Refining of petroleum and natural gas into liquid transportation fuels is also the centerpiece of the modern chemical industry used to produce materials, solvents, and other consumer goods. In the face of global climate change, the world is searching for alternative, sustainable means of producing energy carriers and chemical building blocks. The use of biofuels in engines predates modern refinery optimization and today represents a small but significant fraction of liquid transportation fuels burnt each year. Similarly, white biotechnology has been used to produce many natural products through fermentation. The evolution of recombinant DNA technology into modern synthetic biology has expanded the scope of biofuels and bioproducts that can be made by biocatalysts. This opinion examines the current trends in this research space, highlighting the substantial growth in computational tools and the growing influence of renewable electricity in the design of metabolic engineering strategies. In short, advanced biofuel and bioproduct synthesis remains a vibrant and critically important field of study whose focus is shifting away from the conversion of lignocellulosic biomass towards a broader consideration of how to reduce carbon dioxide to fuels and chemical products.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Valorization of lignin from aqueous-based lignocellulosic biorefineries

An additional 100 million tons/year of lignin coproduct will result when lignocellulosic biomass is processed in biorefineries to fiber, sugars, biofuels, and bioproducts. This will double the amount of lignin already generated from pulping and paper production. Unlike pulping that results in lignosulphonate (88% of total) or Kraft lignin (9%), aqueous-based biorefining leaves behind non-sulfonated lignin and aromatic molecules. Furthermore, this new type of lignin provides opportunities for large volume agricultural uses such as controlled-release carriers and soil amendments as well as feedstocks for new chemistries that lead to molecular building blocks for the chemical industry and to precursors for sustainable aviation biofuels.

03 NATURAL GAS↗
DOE OSTI2020

Transgenic Poplar Designed for Biofuels

Members of the genus Populus (i.e., cottonwood, hybrid poplar) represent a promising source of lignocellulosic biomass for biofuels. However, one of the major factors negatively affecting poplar’s efficient conversion to biofuel is the inherent recalcitrance to enzymatic saccharification due to cell wall components such as lignin. To this effect, there have been efforts to modify gene expression to reduce biomass recalcitrance by changing cell wall properties. Furthermore, we review recent genetic modifications of poplar that led to change cell wall properties and the resulting effects on subsequent pretreatment efficacy and saccharification. Although genetic engineering’s impacts on cell wall properties are not fully predictable, recent studies have shown promising improvement in the biological conversion of transgenic poplar to biofuels.

09 BIOMASS FUELS↗
DOE OSTI2020

Metabolic engineering of β-oxidation to leverage thioesterases for production of 2-heptanone, 2-nonanone and 2-undecanone

Medium-chain length methyl ketones are potential blending fuels due to their cetane numbers and low melting temperatures. Biomanufacturing offers the potential to produce these molecules from renewable resources such as lignocellulosic biomass. Here, we designed and tested metabolic pathways in Escherichia coli to specifically produce 2-heptanone, 2-nonanone and 2-undecanone. We achieved substantial production of each ketone by introducing chain-length specific acyl-ACP thioesterases, blocking the β-oxidation cycle at an advantageous reaction, and introducing active β-ketoacyl-CoA thioesterases. Using a bioprospecting approach, we identified fifteen homologs of E. coli β-ketoacyl-CoA thioesterase (FadM) and evaluated the in vivo activity of each against various chain length substrates. The FadM variant from Providencia sneebia produced the most 2-heptanone, 2-nonanone, and 2-undecanone, suggesting it has the highest activity on the corresponding β-ketoacyl-CoA substrates. We further tested enzyme variants, including acyl-CoA oxidases, thiolases, and bi-functional 3-hydroxyacyl-CoA dehydratases to maximize conversion of fatty acids to β-keto acyl-CoAs for 2-heptanone, 2-nonanone, and 2-undecanone production. In order to address the issue of product loss during fermentation, we applied a 20% (v/v) dodecane layer in the bioreactor and built an external water cooling condenser connecting to the bioreactor heat-transferring condenser coupling to the condenser. Finally, using these modifications, we were able to generate up to 4.4 g/L total medium-chain length methyl ketones.

2-Heptanone↗
DOE OSTI2023

Deuterated water as a substrate-agnostic isotope tracer for investigating reversibility and thermodynamics of reactions in central carbon metabolism

Stable isotope tracers are a powerful tool for the quantitative analysis of microbial metabolism, enabling pathway elucidation, metabolic flux quantification, and assessment of reaction and pathway thermodynamics. 13 C and 2 H metabolic flux analysis commonly relies on isotopically labeled carbon substrates, such as glucose. However, the use of 2 H-labeled nutrient substrates faces limitations due to their high cost and limited availability in comparison to 13 C-tracers. Furthermore, isotope tracer studies in industrially relevant bacteria that metabolize complex substrates such as cellulose, hemicellulose, or lignocellulosic biomass, are challenging given the difficulty in obtaining these as isotopically labeled substrates. In this study, we examine the potential of deuterated water ( 2 H 2 O) as an affordable, substrate-neutral isotope tracer for studying central carbon metabolism. We apply 2 H 2 O labeling to investigate the reversibility of glycolytic reactions across three industrially relevant bacterial species -C. thermocellum, Z. mobilis, and E. coli-harboring distinct glycolytic pathways with unique thermodynamics. We demonstrate that 2 H 2 O labeling recapitulates previous reversibility and thermodynamic findings obtained with established 13 C and 2 H labeled nutrient substrates. Furthermore, we exemplify the utility of this 2 H 2 O labeling approach by applying it to high-substrate C. thermocellum fermentations -a setting in which the use of conventional tracers is impractical-thereby identifying the glycolytic enzyme phosphofructokinase as a major bottleneck during high-substrate fermentations and unveiling critical insights that will steer future engineering efforts to enhance ethanol production in this cellulolytic organism. This study demonstrates the utility of deuterated water as a substrate-agnostic isotope tracer for examining flux and reversibility of central carbon metabolic reactions, which yields biological insights comparable to those obtained using costly 2 H-labeled nutrient substrates.

09 BIOMASS FUELS↗
DOE OSTI2020

Operando S/TEM Reactions of Pt/TiO 2 Catalysts for Catalytic Fast Pyrolysis

Conversion of lignocellulosic biomass into the transportation fuel is an attractive concept. Using ex situ Catalytic Fast Pyrolysis (CFP) improves to upgrade bio-oils via catalytic deoxygenation of the biomass pyrolysis vapors. Zeolites are often used in this technique as the catalyst; however, in order to reduce minimum fuel selling price and improve carbon yields, ongoing research emphasizes catalyst optimization. By using bifunctional metal-acid catalysts and utilizing hydrogen, it is possible to improve carbon yields by minimizing the carbon-containing light gasses (since oxygen is removed aswater) and by reducing coke formation. Current research and development activities focuses on Pt/TiO 2 catalysts as the most promising catalyst candidates for the hydrodeoxygenation process. Here, our aim is to determine the structure-function relationships of the Pt/TiO 2 catalyst and the role of Pt dispersions within the catalyst on performance, using operando scanning transmission electron microscopy (S/TEM).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Insights into Mechanisms of Screw Feeder Plugging by Heated Pine Forestry Residues Using in-situ and Correlative Microscopy

Increasing concerns about global carbon emissions due to fossil fuel use has created interest in renewable fuel alternatives, such as lignocellulosic biomass. With an estimated global biomass production probability ten-fold higher than projected need, functionalizing and scaling biomass conversion processes, like pyrolysis, is a promising component of a diverse sustainable energy program (Kan, Strezov, & Evans, 2016). Pyrolysis reactors employed in biomass conversion often encounter the known problem of screw feeder plugging, halting work and reducing efficiency of biorefineries. Although the screw feeder is not heated directly, conductive heat transfer from the fluidized bed pyrolysis reactor creates a temperature gradient, where particles experience temperatures between 22°C and 500°C from the time they enter the feeder to being emptied into the reactor (Digman, Joo, & Kim, 2009; Nieminen & Folke, 1982). The impact of unintentional heating on this highly variable feedstock may result in particle morphology modification, surface texture transformation, and the evolution of viscous compounds and may contribute to screw feeder plugging (Haas, Nimlos, & Donohoe, 2009; Ingram et al., 2008). We hypothesized that particles of various anatomical fractions (including needles, branches, bark, cambium, and whitewood) will experience dramatic changes during this heating regime, which will be characterized by decreased particle size, increased surface roughness, degradation of key structural macromolecules, and generation of viscous compounds that would result in increased particle friction and cohesion, contributing to screw feeder plugging.

biofuels↗
DOE OSTI2024

Ectopic Production of 3,4-Dihydroxybenzoate in Planta Affects Cellulose Structure and Organization

Lignocellulosic biomass is a highly sustainable and largely carbon dioxide neutral feedstock for the production of biofuels and advanced biomaterials. Although thermochemical pretreatment is typically used to increase the efficiency of cell wall deconstruction, genetic engineering of the major plant cell wall polymers, especially lignin, has shown promise as an alternative approach to reduce biomass recalcitrance. Poplar trees with reduced lignin content and altered composition were previously developed by overexpressing bacterial 3-dehydroshikimate dehydratase (QsuB) enzyme to divert carbon flux from the shikimate pathway. In this work, three transgenic poplar lines with increasing QsuB expression levels and different lignin contents were studied using small-angle neutron scattering (SANS) and wide-angle X-ray scattering (WAXS). SANS showed that although the cellulose microfibril cross-sectional dimension remained unchanged, the ordered organization of the microfibrils progressively decreased with increased QsuB expression. This was correlated with decreasing total lignin content in the QsuB lines. WAXS showed that the crystallite dimensions of cellulose microfibrils transverse to the growth direction were not affected by the QsuB expression, but the crystallite dimensions parallel to the growth direction were decreased by ~20%. Cellulose crystallinity was also decreased with increased QsuB expression, which could be related to high levels of 3,4-dihydroxybenzoate, the product of QsuB expression, disrupting microfibril crystallization. In addition, the cellulose microfibril orientation angle showed a bimodal distribution at higher QsuB expression levels. Altogether, this study provides new structural insights into the impact of ectopic synthesis of small-molecule metabolites on cellulose organization and structure that can be used for future efforts aimed at reducing biomass recalcitrance.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Role of Silica Support in Phosphoric Acid Catalyzed Production of p -Xylene from 2,5-Dimethylfuran and Ethylene

p-Xylene is a commodity chemical of industrial importance for terephthalic acid production, for which renewable sourcing from naturally abundant lignocellulosic biomass is highly desired. Previous work demonstrated that phosphoric acid stabilized on siliceous zeolite supports (e.g., P-BEA, P-SPP) exhibits high selectivity toward p-xylene (>97%) from 2,5-dimethylfuran (DMF) and ethylene. However, the effect of the support and the contribution of heterogeneous versus homogeneous phosphoric acid on the observed catalytic behavior in the solvated reaction system have not been addressed. Here, we determine the phosphoric acid catalytic activity for DMF conversion and its selectivity to p-xylene when it is supported on a silica support as well as in the absence of a support. Specifically, phosphoric acid catalysis was studied in three different scenarios: (1) phosphoric acid was added in the liquid reaction mixture in the absence of any solid support, (2) phosphoric acid was added in the liquid reaction mixture along with inert silica support including siliceous zeolite (i.e., allowing for phosphoric acid–support assembly to proceed in the reaction mixture), and (3) phosphoric acid was first impregnated on the siliceous zeolite support and then the preassembled supported phosphoric acid catalyst was added in the liquid reaction mixture. We found that the reaction rate and selectivity to p-xylene are different in the above scenarios reflecting the effect of the solid support on the catalytic performance of phosphoric acid. In scenario 1, a low concentration of phosphoric acid (1.7 mM) in the absence of any solid support exhibited high selectivity to p-xylene (80% selectivity to p-xylene at 60% conversion of DMF), which decreased with increasing acid concentration. The selectivity to p-xylene and activity of phosphoric acid significantly increased by adding a silica support into the reaction system (scenario 2). Furthermore, this improvement was attributed to phosphoric acid partial association with the surface of the silica support under the reaction conditions (in situ catalyst assembly). Phosphoric acid predeposited on siliceous zeolite supports (e.g., P-BEA, P-SPP) synthesized via impregnation prior to the reaction (scenario 3) catalyzed the reaction heterogeneously without noticeable leaching and exhibited the highest activity and selectivity to p-xylene, suggesting an important role of the silica support and the need to ensure that phosphoric acid acts as a heterogeneous catalyst in order to accomplish selective conversion of DMF to p-xylene.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Effect of Solvent on the Interaction of Lignin with a Zeolite Nanosheet in the Condensed Phase

Lignin is the essential building block of lignocellulosic biomass, an excellent renewable source of different aromatic monomers for the polymer and biofuel industry. The depolymerization of lignin into value-added chemicals and fuels through the catalytic process poses a significant challenge due to the complex structure of lignin. Understanding lignin’s conformational diversity and dynamics in the liquid phase is crucial to designing an effective depolymerization process. Here, we conducted all-atom molecular dynamics simulations to understand the conformation and dynamics of softwood lignin on the all-silica zeolite nanosheet based on the MFI topology in a binary mixture of water–methanol at three different molar compositions (0%, 50%, and 100% methanol). We observed that the methanol–surface interaction is stronger than the water–surface interaction, and methanol readily diffused into the MFI core. Lignin surface contacts decrease with increasing methanol composition due to higher solubility and dynamics. Lignin dynamics on the surface in neat water is an order of magnitude smaller than methanol. Here, we also found that lignin adopts a slightly extended conformation when it stays on the surface than in the bulk solution phase for the pure water case, whereas for pure methanol and the binary solution structures are statistically similar.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Effect of Solvents on Lignin–Surface Interactions via Molecular Dynamics Simulations

Lignin, an essential building block of lignocellulosic biomass, is a potential abundant source of aromatic monomers for the polymer and chemical industry. Reductive catalytic fractionation (RCF) is one promising process that can produce high yields of phenolic monomers and oligomers from lignin under different catalytic conditions. An important choice in optimizing RCF is the selection of solvent; however, detailed insights into solvent effects on lignin behaviors and interactions remain limited. Here, in this work, we perform all-atom molecular dynamics simulations to study the solvation of lignin, solvent-mediated conformational changes, and the interaction of solvated lignin oligomers with model surfaces. We focus on the behavior of an oligomeric lignin model compound in methanol, ethanol, a binary mixture of ethanol and water, and water at both the RCF reaction temperature (473 K) and room temperature. Analysis of structural features of lignin suggests that these three organic solvent systems favorably solvate lignin, resulting in a more extended conformation suitable for catalytic conversion to valuable chemicals. We further introduce model palladium (Pd) and carbon (C) surfaces to understand how solvent choice impacts adsorption onto a representative catalytic surface and support, and to quantify the competition among the reactant and solvent molecules for the surface. Unbiased simulations suggest strong adsorption of lignin on both Pd and C surfaces at 473 K, with notable solvent-mediated differences in adsorption energies. Additionally, our findings indicate that lignin adsorption is promoted by the entropy change resulting from the displacement of solvent molecules from the surface. This study provides a molecular perspective of adsorption of lignin onto varying surfaces, which is a step towards understanding and optimizing the catalytic conversion of lignin into valuable chemicals.

adsorption↗
DOE OSTI2021

Structural Reorganization of Noncellulosic Polymers Observed In Situ during Dilute Acid Pretreatment by Small-Angle Neutron Scattering

Production of second-generation bioethanol from lignocellulosic biomass requires pretreatment to open the plant cell wall structure and improve enzyme access. Many different thermochemical pretreatments have been extensively developed and employed, but the exact nature of plant cell wall recalcitrance and the most efficient and economical approach to alter plant cell wall structure via pretreatment still remain elusive. In order to understand the role of noncellulosic switchgrass polymers on the overall efficiency of pretreatment, the structural evolution of the noncellulosic polymers of the plant cell wall were investigated during dilute acid pretreatment (DAP) by employing in-situ small-angle neutron scattering (in-situ SANS). In this study, we observed real-time structural changes not possible to observe by any other technique. To deconvolute the structural evolution of lignin and hemicellulose polymers during DAP, native switchgrass (NATV), and isolated holocellulose (HOLO) and cellulose (CELL) fractions from NATV were studied. Our results show that aggregate particles first appear around 80 °C for NATV and HOLO samples. Further, due to the low temperature and pretreatment severity condition, these particles are likely derived from hemicellulose. The formations of much larger aggregate particles, only observed in the NATV sample, were attributed to lignin. For the HOLO sample, as the temperature and pretreatment severity condition increased, hemicellulose-derived aggregate particle sizes increased, suggesting this process was the nucleation and early stage formation of pseudolignin particles. Consistent with our interpretation of structural evolutions in NATV and HOLO samples, no formation of aggregate particles was observed in CELL samples for the entire duration of the pretreatment. These results suggest that not only lignin but also hemicellulose can form aggregate particles within plant cell walls during pretreatment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

An Explainable Classification Framework for Determining and Understanding the Suitability of Solvent Extraction for Bioproduct Recovery

Lignocellulosic biomass is an abundant feedstock for producing sustainable fuels and chemicals. However, a key challenge in most biomass utilization strategies is the recovery of products from a dilute, typically aqueous, phase. In this respect, liquid–liquid extraction, which relies on a solvent to transfer a product of interest from one liquid phase to another (solvent-rich) phase, is a technology that can reduce the energy requirements for product recovery. To reduce solvent consumption, liquid–liquid extraction needs to be combined with another separation method (e.g., distillation) to recycle the solvent. Despite the research on solvent extraction, there are limited system-wide methods that allow us to determine when extraction is well suited to carry out a specific separation. Accordingly, we present a classification framework to predict whether extraction, coupled with distillation, is feasible and more economical than distillation. Our framework is based on features such as feed composition, liquid–liquid equilibrium constants, relative volatilities, and solvent price, and leads to trained classifiers that show good prediction accuracy. We further study how specific features influence the suitability of extraction. Furthermore, to showcase the applicability of the framework, we use it to analyze the separation of acetic acid from water.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

High-Throughput Screening and Accurate Prediction of Ionic Liquid Viscosities Using Interpretable Machine Learning

Ionic liquids (ILs) are a novel group of green solvents with great promise for various industrial applications, including carbon capture and lignocellulosic biomass deconstruction. However, the use of ILs at the industrial scale remains challenging due to their high viscosities at ambient temperatures. To develop ILs with lower viscosities, a systematic study of their quantitative structure–property relationship (QSPR) is desirable. Here, we developed four machine learning (ML) models to predict viscosity at various temperature and pressure ranges, trained over a wide range of ILs consisting of various cationic and anionic families. ML methods including two-factor polynomial regression (two-factor PR), support vector regression (SVR), feed-forward neural networks (FFNN), and categorical boosting (CATBoost) were developed based on features that have proven useful in previous ML studies: COSMO-RS (conductor-like screening model for real solvents)-derived surface screening charge densities (sigma profiles). FFNN and CATBoost were the most accurate in predicting IL viscosities with lower average absolute relative deviation and higher R2 values on the test set. Tanimoto similarity scores were calculated to characterize the chemical space and structural similarity of the investigated ions. Furthermore, SHapley Additive exPlanation (SHAP) analysis was employed to interpret the ML results. Temperature, the polar area of ILs, and the nonpolar regions of ions are key features that influence the viscosity predictions. Importantly, the IL viscosity prediction here is the most accurate reported to date.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Black Liquor Valorization by Using Marine Protist Thraustochytrium striatum and the Preliminary Metabolic Mechanism Study

Black liquor that contains various phenolic compounds from lignin solubilization has been the main byproduct of alkaline pretreatment of lignocellulosic biomass in the biorefinery. In this study, black liquor from alkaline pretreatment of corn stover was used as a sole carbon source for the cultivation of a marine protist, Thraustochytrium striatum. It was found that this strain can grow on black liquor and accumulate valuable products (e.g., fatty acids and carotenoids) simultaneously. Under optimal conditions (pH = 7 and NH 4 Cl = 2 g/L), the cell mass concentration reached 5.2 g/L with total aromatics decreased from 8.18 to 3.09 g/L within 7 day incubation. Fed-batch cultivation was adopted to increase the contents of total fatty acids and carotenoids to 13% and 0.24 mg/g dry cell mass, respectively. Although various compounds such as sugars and organic acids were detected in black liquor and consumed during microbial fermentation as carbon sources, lignin-derived compounds were identified as the major substrates for T. striatum fermentation. Of total aromatics consumed, monomers including p-coumaric acid, ferulic acid, vanillin, and syringaldehyde were observed to be consumed and converted while polymeric fragments were also depolymerized and degraded. Under optimal conditions, around 50% of the total aromatics was consumed. The dynamic changes of compounds in black liquor indicated that diverse metabolic processes were involved in black liquor degradation and utilization by T. striatum. A strong adaptation of T. striatum to a wide range of pH (3–9) was also observed during black liquor fermentation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Understanding the Competition between Alcohol Formation and Dimerization during Electrochemical Reduction of Aromatic Carbonyl Compounds

The electrochemical reductive dimerization of small aromatic carbonyl compounds derived from lignocellulosic biomass is a crucial C−C coupling reaction for upgrading small molecules to longchain hydrocarbons, particularly in the synthesis of drop-in sustainable aviation fuels. Although other electrochemical reduction reactions of these reactants (i.e., hydrogenation and hydrogenolysis) have undergone extensive mechanistic investigation, the understanding of dimerization remains relatively underdeveloped. Most importantly, there is a lack of understanding of the selectivity-determining step between dimerization and monomer reduction and critical factors that can affect this step. In this study, we provide a comprehensive mechanistic model to explain the competition between dimerization and monomer reduction of benzaldehyde under various conditions. Our model proposes that the selectivity between dimerization and monomer reduction depends on the competition between desorption of a ketyl radical from the electrode, necessary for dimerization, and further reduction of the ketyl radical to an alcohol on the electrode by proton-coupled electron transfer (PCET). Computationally comparing the adsorption/desorption energy and PCET activation barrier energy is challenging because conventional DFT calculations substantially underestimate the PCET kinetic barriers. In this study, we employed constrained DFTbased configuration interaction (CDFT-CI) to obtain a reliable comparison of these energies. Our mechanistic model was tested and supported by experimental results obtained with four electrodes (Cu, Pb, Bi, graphite), three pH conditions (acidic, neutral, basic), and three potentials. Our study offers a coherent mechanistic foundation that can explain how each of these conditions impacts the desorption and PCET processes and the selectivities for dimerization and alcohol production.

09 BIOMASS FUELS↗
DOE OSTI2020

Tailoring poplar lignin without yield penalty by combining a null and haploinsufficient CINNAMOYL-CoA REDUCTASE2 allele

Lignin causes lignocellulosic biomass recalcitrance to enzymatic hydrolysis. Engineered low-lignin plants have reduced recalcitrance but often exhibit yield penalties, offsetting their gains in fermentable sugar yield. Here, CRISPR/Cas9-generated CCR2(–/*) line 12 poplars have one knockout CCR2 allele while the other contains a 3-bp deletion, resulting in a 114I115A-to-114T conversion in the corresponding protein. Despite having 10% less lignin, CCR2(–/*) line 12 grows normally. On a plant basis, the saccharification efficiency of CCR2(–/*) line 12 is increased by 25–41%, depending on the pretreatment. Analysis of monoallelic CCR2 knockout lines shows that the reduced lignin amount in CCR2(–/*) line 12 is due to the combination of a null and the specific haploinsufficient CCR2 allele. Analysis of another CCR2(–/*) line shows that depending on the specific CCR2 amino-acid change, lignin amount and growth can be affected to different extents. Furthermore, our findings open up new possibilities for stably fine-tuning residual gene function in planta.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

A grass-specific cellulose–xylan interaction dominates in sorghum secondary cell walls

Abstract Sorghum ( Sorghum bicolor L. Moench) is a promising source of lignocellulosic biomass for the production of renewable fuels and chemicals, as well as for forage. Understanding secondary cell wall architecture is key to understanding recalcitrance i.e. identifying features which prevent the efficient conversion of complex biomass to simple carbon units. Here, we use multi-dimensional magic angle spinning solid-state NMR to characterize the sorghum secondary cell wall. We show that xylan is mainly in a three-fold screw conformation due to dense arabinosyl substitutions, with close proximity to cellulose. We also show that sorghum secondary cell walls present a high ratio of amorphous to crystalline cellulose as compared to dicots. We propose a model of sorghum cell wall architecture which is dominated by interactions between three-fold screw xylan and amorphous cellulose. This work will aid the design of low-recalcitrance biomass crops, a requirement for a sustainable bioeconomy.

59 BASIC BIOLOGICAL SCIENCES↗