Lignin Network Research Articles

Efficient synthesis of highly hydrophobic lignin nanoparticles and their application as nano fillers for multifunctional composite membranes

Controlling the hydrophobic behaviors of lignin nanoparticles (LNPs) is crucial and advantageous for their application as film Nano Fillers, yet it poses a significant challenge. Herein, we successfully developed a novel method for the preparation of LNPs with highly hydrophobic behaviors using ternary deep eutectic solution (DES)-H2O systems. The resulting LNPs exhibit a significantly reduced content of hydrophilic groups on their outer surface, leading to a zeta potential value of only −4.9 mV, and up to 140.0° of water contact angle (WCA). Afterwards, a “Dissolution-Restructuration” mechanism was proposed to explain the formation of the prepared LNPs. Firstly, DES demonstrates superior H-bonding capabilities, facilitating the complete disruption of inter- and intramolecular H-bonding in lignin, and resulting in the formation of a highly homogenized lignin network. Subsequently, the DES system undergoes compromise after adding water, triggering the reformation of both inter- and intramolecular H-bonding and π-π interactions. Consequently, lignin orderly self-assembles into LNPs with highly hydrophobic characteristics. Especially, using the as-prepared LNPs as Nano fillers, a series of LNPs-containing polyvinyl alcohol (PVA) films were successfully fabricated, exhibiting exceptional hydrophobic behaviors (with contact angles reaching up to 124.0°). Furthermore, the mechanical strength, UV-shielding capabilities, and biodegradability of the PVA films are significantly enhanced. This study introduces a sustainable and efficient approach for the synthesis of hydrophobic LNPs, thereby facilitating the broadening of applications for lignin-based functional composite film materials.

Construction of thermally-modified wood surface with superstrong UV-resistance by in-situ modification of lignin

Ultraviolet (UV)-induced discoloration and cracking pose formidable challenges for thermally modified wood (TMW) when used in outdoor applications. Herein, we propose a novel pretreatment strategy using deep eutectic solvent (DES) to enhance the weathering resistance of TMW. DES-assisted TMW (DES-TMW) was prepared by coating wood with choline chloride/citric acid (CA) DES, followed by thermal modification. During the DES-assisted thermal modification process, the cross-linking of the lignin network in DES-TMW was increased as a result of lignin self-polymerization, cross-linking with autologous molecules and furfural, as well as esterified connections caused by CA. This in-situ modification reduces the quantity of photosensitive phenolic hydroxyl groups within lignin by forming cross-linked structures, reducing phenoxy free radical generation during the weathering and obstructing chromophores production pathways, thus enhancing the photostability of lignin. Consequently, the DES-TMW exhibited remarkable resistance to discoloration and cracking compared to TMW. These findings provide evidence that our strategy can effectively enhance the photostability of wood, thereby contributing to the development and production of sustainable outdoor wood products capable of withstanding changing weather conditions.

N-doped carbon nanoflakes coordinate with amorphous Fe to activate ozone for degradation of p-nitrophenol

Due to their high catalytic performance, metal nitrogen-doped carbon materials are widely used in the field of environmental restoration of polluted water but there is limited research on metal nitrogen doped carbon composite materials as ozone catalysts. Herein, we report the preparation of amorphous iron-coordinated nitrogen-doped carbon nanosheets as a catalyst for ozone by the coordination of Fe-metal ions at the end of phenol chain in the lignin network. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), powder X-ray diffraction (XRD) and element mapping were used to characterize the Fe/D-NC composite material and investigate its morphology and composition. Highly uniform distribution of iron species was found through characterization. By exploring the degradation performance of composite materials of Fe/D-NC-T (700，800，900 ℃) prepared at different temperatures, it was found that the optimal Fe/D-NC-800 could effectively degrade p-nitrophenol (PNP) within 30 min. Quenching experiments and ESR analysis showed that both free and non-free radicals (•OH, O2•− and 1O2) and intrinsic Lewis acid sites (LAS) of the composite material Fe/D-NC-800 were involved and responsible for the degradation of PNP. This work not only offers new platforms for catalytic ozonation and may drive the development of metal-lignin-based catalytic ozonation for effective water treatment but also opens new avenues toward lignin valorization and biomass economy.

Automated quantification of fluorescence and morphological changes in pretreated wood cells by fluorescence macroscopy

BackgroundLignocellulosic biomass is a complex network of polysaccharides and lignin that requires a pretreatment step to overcome recalcitrance and optimize valorisation into biobased products. Pretreatment of biomass induces chemical and morphological changes. Quantification of these changes is critical to understand biomass recalcitrance and to predict lignocellulose reactivity. In this study, we propose an automated method for the quantification of chemical and morphological parameters through fluorescence macroscopy, which was applied on wood samples (spruce, beechwood) pretreated with steam explosion.ResultsResults in fluorescence macroscopy highlighted the impact of steam explosion on spruce and beechwood: fluorescence intensity of samples was highly altered, especially for the most severe conditions. Morphological changes were also revealed: shrinkage of cells and deformation of cell walls manifested as the loss of rectangularity or circular shape, for tracheids in spruce and vessels in beechwood respectively. Quantification of fluorescence intensity of cell walls and quantification of morphological parameters related to cell lumens were carried out accurately by applying the automated method onto the macroscopic images. The results showed that lumens area and circularity could be considered as complementary markers of cell deformation, and that fluorescence intensity of the cell walls could be related to morphological changes and to the conditions of pretreatment.ConclusionsThe developed procedure allows simultaneous and effective quantification of morphological parameters and fluorescence intensity of the cell walls. This approach can be applied to fluorescence macroscopy as well as other imaging techniques and provides encouraging results towards the understanding of biomass architecture.

Electrochemically Enhanced Delivery of Pemetrexed from Electroactive Hydrogels.

Electroactive hydrogels based on derivatives of polyethyleneglycol (PEG), chitosan and polypyrrole were prepared via a combination of photopolymerization and oxidative chemical polymerization, and optionally doped with anions (e.g., lignin, drugs, etc.). The products were analyzed with a variety of techniques, including: FT-IR, UV-Vis, 1H NMR (solution state), 13C NMR (solid state), XRD, TGA, SEM, swelling ratios and rheology. The conductive gels swell ca. 8 times less than the non-conductive gels due to the presence of the interpenetrating network (IPN) of polypyrrole and lignin. A rheological study showed that the non-conductive gels are soft (G' 0.35 kPa, G″ 0.02 kPa) with properties analogous to brain tissue, whereas the conductive gels are significantly stronger (G' 30 kPa, G″ 19 kPa) analogous to breast tissue due to the presence of the IPN of polypyrrole and lignin. The potential of these biomaterials to be used for biomedical applications was validated in vitro by cell culture studies (assessing adhesion and proliferation of fibroblasts) and drug delivery studies (electrochemically loading the FDA-approved chemotherapeutic pemetrexed and measuring passive and stimulated release); indeed, the application of electrical stimulus enhanced the release of PEM from gels by ca. 10-15% relative to the passive release control experiment for each application of electrical stimulation over a short period analogous to the duration of stimulation applied for electrochemotherapy. It is foreseeable that such materials could be integrated in electrochemotherapeutic medical devices, e.g., electrode arrays or plates currently used in the clinic.

Crop Lodging and The Roles of Lignin, Cellulose, and Hemicellulose in Lodging Resistance

With increasingly frequent extreme weather events, lodging has become an important limiting factor for crop yield and quality and for mechanical harvesting. Lodging resistance is a precondition for “super high yield” crops, and the question of how to achieve lodging resistance to guarantee high yield is an urgent scientific problem. Here, we summarize the anatomical results of lodging resistance stems and find that the lodging resistance of stems is closely related to stem components. Therefore, we focus on the roles of lignin, cellulose and hemicellulose, which provide stem rigidity and strength, in crop lodging resistance. By combing the synthetic regulatory molecular network of lignin, cellulose and hemicellulose, we find that only some of the genes involved in the biosynthesis and regulation of lignin, cellulose, and hemicellulose have been shown to significantly affect lodging resistance. However, many relevant genes remain to be studied in sufficient detail to determine whether they can be applied in breeding for lodging resistance. This work provides valuable information for future studies of lodging resistance.

Solvent Effect in Catalytic Lignin Hydrogenolysis

The solvent effect in the catalytic depolymerization of the three-dimensional network of lignin is discussed based on recent reports in this field. Also, the results of an experimental study on the depolymerization of kraft lignin are presented. The cleavage of ether bonds within the lignin network was promoted using ruthenium and platinum on activated carbon (Ru/C and Pt/C), two common hydrogenolysis catalysts. Methanol was identified as a suitable solvent. Noteworthy, under the chosen reaction conditions, the catalysts showed significant resilience to the sulfur present in kraft lignin. The conversion of kraft lignin to lignin oil was strongly affected by the reaction conditions. Although the Ru/C catalyst provided the highest yield at supercritical conditions, a maximum yield was obtained for the Pt/C catalyst at near-critical conditions. The formation of guaiacol, 4-alkylguaiacols, isoeugenol, and 4-ethyl-2,6-dimethoxyphenol is attributed to the solubility of oligomeric lignin fragments in the solvent and the relative propensity of specific groups to adsorb on the catalyst surface.

A Critical Review of the Physicochemical Properties of Lignosulfonates: Chemical Structure and Behavior in Aqueous Solution, at Surfaces and Interfaces

Lignosulfonates are bio-based surfactants and specialty chemicals, which are generated by breaking the near-infinite lignin network during sulfite pulping of wood. Due to their amphiphilic nature, lignosulfonates are used in manifold applications such as plasticizer, dispersant, and stabilizer formulations. Function and performance are determined by their behavior in aqueous solution and at surfaces and interfaces, which is in turn imposed by the chemical make-up. This review hence summarizes the efforts made into delineating the physicochemical properties of lignosulfonates, while also relating to their composition and structure. Lignosulfonates are randomly branched polyelectrolytes with abundant sulfonate and carboxylic acid groups to ensure water-solubility. In aqueous solution, their conformation, colloidal state, and adsorption at surfaces or interfaces can be affected by a range of parameters, such as pH, concentration of other electrolytes, temperature, and the presence of organic solvents. These parameters may also affect the adsorption behavior, which reportedly follows Langmuir isotherm and pseudo second-order kinetics. The relative hydrophobicity, as determined by hydrophobic interaction chromatography, is an indicator that can help to relate composition and behavior of lignosulfonates. More hydrophobic materials have been found to exhibit a lower charge density. This may improve dispersion stabilization, but it can also be disadvantageous if an electrokinetic charge needs to be introduced at solid surfaces or if precipitation due to salting out is an issue. In addition, the monolignol composition, molecular weight distribution, and chemical modification may affect the physicochemical behavior of lignosulfonates. In conclusion, the properties of lignosulfonates can be tailored by controlling aspects such as the production parameters, fractionation, and by subsequent modification. Recent developments have spawned a magnitude of products and technologies, which is also reflected in the wide variety of possible application areas.

Quantitative fermentation of unpretreated transgenic poplar by Caldicellulosiruptor bescii

Microbial fermentation of lignocellulosic biomass to produce industrial chemicals is exacerbated by the recalcitrant network of lignin, cellulose and hemicelluloses comprising the plant secondary cell wall. In this study, we show that transgenic poplar (Populus trichocarpa) lines can be solubilized without any pretreatment by the extreme thermophile Caldicellulosiruptor bescii that has been metabolically engineered to shift its fermentation products away from inhibitory organic acids to ethanol. Carbohydrate solubilization and conversion of unpretreated milled biomass is nearly 90% for two transgenic lines, compared to only 25% for wild-type poplar. Unexpectedly, unpretreated intact poplar stems achieved nearly 70% of the fermentation production observed with milled poplar as the substrate. The nearly quantitative microbial conversion of the carbohydrate content of unpretreated transgenic lignocellulosic biomass bodes well for full utilization of renewable biomass feedstocks.

Fabrication of Pd NPs-supported porous carbon by integrating the reducing reactivity and carbon-rich network of lignin

The renewable resource as a major feedstock to prepare porous carbon has showed many advantages compared to fossil-based materials. This study proposes a new strategy to synthesize palladium nanoparticles (Pd NPs)-supported porous carbon, utilizing both the chemical reactivity and the carbon-rich 3D network of lignin. The Pd NPs-supported porous carbons were prepared in one-pot synthesis, with Pd(NH3)2Cl2 as precursor, lignin as reducing and stabilizing agents of Pd NPs, nano SiO2 as hard-template, followed by carbonization and removal of the template. The results reveal a positive effect of Pd precursor dosage on the development and excellent texture of the Pd NPs-supported porous carbon. Accordingly, the synthesized porous carbon was proved to have large micropore volume and good micro-mesopore porous structure, revealing it a promising hydrogen adsorbent.

Preparation of graphene oxide and alkali lignin nanohybrids and its application to reinforcing polymer

Lignin has been widely used as an eco-friendly and sustainable filler in polymer composites, which is a promising reuse of lignin waste. However, it suffers from a dissatisfactory reinforcing effect for polymers due to the many surface functional groups of lignin. In this work, a small quantity of graphene oxide (GO) nanosheets was employed to help form a network of alkali lignin (AL) nanoparticles to improve their hardness. The morphologies and structures of GO–AL hybrids were characterized by transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis (TGA) and Raman spectra. Taking poly(vinyl alcohol) (PVA) as a model polymer, the reinforcing effect of GO–AL hybrids was examined. Dynamic mechanical analysis results showed that the storage modulus of PVA was improved more by GO–AL hybrids than AL, especially in the high-temperature region (50–120 °C). By contrast, the tensile strength and the Young’s modulus of PVA containing 4 wt% GO–AL (1:4) were increased by 84.4% and 335.3%, respectively. TGA analysis indicated that the thermal stability of the PVA nanocomposites was improved after incorporation of nanofillers. The main observation presented here could serve as the basis for the design and preparation of lignin and other biomass-based polymer nanocomposites.

Green mussel-inspired lignin magnetic nanoparticles with high adsorptive capacity and environmental friendliness for chromium(III) removal.

We report an ingenious technique to prepare magnetic alkaline lignin-dopamine nanoparticles (AL-DA/Fe3O4 NPs). Alkaline lignin, a kind of abundant waste from agriculture, pulping and bio-energy industry, was functionalized by the conjugation with DA molecules and nano-precipitation method. Benefiting from the three-dimensional network of lignin and mussel-inspired DA molecules, chromium(III) can be effectively removed by physisorption and chemisorption. The maximum Cr(III) adsorption capacity of AL-DA/Fe3O4 NPs was found to be 44.56 mg/g, which was among the highest of previously reported biomass-based Cr(III) adsorbents. Moreover, sensitive magnetic responsiveness (24.6 emu/g) of AL-DA/Fe3O4 NPs can be more helpful in recycling (over 90% recycled within 2 min) and multiple reusing. The preparation of this low-cost, high adsorptive capacity and good ecofriendly lignin-based nano-adsorbent is expected to become a sustainable technology to simultaneously achieve the wastewater reutilization from pulping and bio-energy industry and purification of other modern industries.

Comprehensive Model to Predict the Yield of the Pyrolysis Products of Kraft Lignin Based on Lumped Approach

This work presents a comprehensive model based on the lumping approach to quantit ively predict the products of the pyrolysis of kraft lignin. The yield of the primary pyrolysis products - biochar, bio - oil, and biogas - that are produced from the thermal decomposition of the lignin network are estimated. Different pyrolysis conditions and r aw material characteristics are considered . The impacts of the particle size of the raw material, pyrolysis heating rate, and reaction residence time are taken into the investigation. The comparison of the predicted results using the developed model agains t the experimental data showed the high capability of the presented models to predict the biochar, bio - oil, and biogas yield under the examined conditions.

Spectral characterization and surface morphology of delignification of Kraft pulp with carbamide peroxide

The study focuses on delignification of Kraft pulp using carbamide peroxide as bleaching agent. The Kappa number reduction of bleached pulp is favored at low consistency of pulp and higher reaction temperature. The optimal Kappa reduction was achieved at temperature of 68 °C, 0.8 g of carbamide peroxide per 100 ml of solution and 2% consistency in the range of variables studied. Fourier transform infrared spectral analysis done on bleached pulp to determine bond stretches and bending vibrations. X ray diffraction spectral data observation provided that the crystallinity index increased from 81.7% before bleaching to 85% after bleaching which indicates the removal of amorphous species in sample. FT-RAMAN spectral analysis concludes the possible conformational changes pre and post bleaching. The absence of some native lignin bands post bleaching indicates lignin removal. Scanning electron microscope images of bleached pulp samples were observed with less amounts of fibrillar type lignin network on surface of pulp fibers when compared to unbleached samples. The activation energy and rate constants were determined for delignification of pulp using carbamide peroxide process. Sequential treatment of Kraft pulp with carbamide peroxide and sodium percarbonate were also evaluated.

Inhibiting Polysulfide Shuttling with a Graphene Composite Separator for Highly Robust Lithium-Sulfur Batteries

Summary Lithium-sulfur (Li-S) batteries are of considerable interest for high-density energy storage. However, the adoption of Li-S batteries to date has been severely plagued by the polysulfide shuttling effect, whereby polysulfide molecules dissolve into the electrolyte and shuttle across the separator to react with the anode materials, leading to a rapidly fading capacity. Herein, by directly coating a thin layer of reduced graphene oxide (rGO)/sodium lignosulfonate (SL) composite on the standard polypropylene (PP) separator, we produce a rGO@SL/PP separator with abundant negatively charged sulfonic groups in the porous lignin network, which effectively suppress the translocation of the negatively charged polysulfide (PS) ions without compromising the transport of positively charged Li+ ions. Using the rGO@SL/PP separator, we demonstrate a highly robust Li-S battery with a capacity retention of 74% over 1,000 cycles. This study defines an effective strategy to inhibit the PS shuttling effect for highly robust Li-S batteries.

Facilitated delignification in CAD deficient transgenic poplar studied by confocal Raman spectroscopy imaging

Lignocellulosic biomass represents the only renewable carbon resource which is available in sufficient amounts to be considered as an alternative for our fossil-based carbon economy. However, an efficient biochemical conversion of lignocellulosic feedstocks is hindered by the natural recalcitrance of the biomass as a result of a dense network of cellulose, hemicelluloses, and lignin. These polymeric interconnections make a pretreatment of the biomass necessary in order to enhance the susceptibility of the polysaccharides. Here, we report on a detailed analysis of the favourable influence of genetic engineering for two common delignification protocols for lignocellulosic biomass, namely acidic bleaching and soda pulping, on the example of CAD deficient poplar. The altered lignin structure of the transgenic poplar results in a significantly accelerated and more complete lignin removal at lower temperatures and shorter reaction times compared to wildtype poplar. To monitor the induced chemical and structural alterations at the tissue level, confocal Raman spectroscopy imaging, FT-IR spectroscopy, and X-ray diffraction were used.

Screening of fungi for decomposition of lignin-derived products from Japanese cedar

Lignin is an aromatic polymer that makes a network by intertwining between cellulose fibers in plant. As the lignin network retards access to carbohydrates, it is regarded as a nuisance during biomass processing. When wood is processed into paper pulp or bioethanol, lignin is produced as a by-product and utilized as fuel or a soil amendment. Recently, there has been much interest in the aromatic structure of lignin in relation to the utilization of lignocellulose and the search for petroleum substitutes. Sulfur-free pulping methods, such as soda-anthraquinone cooking, provide more opportunity for using lignin than the alternative kraft process. Our aim was to expand the availability of soda lignin from Japanese cedar, the most planted tree in Japan, by fungal degradation. We performed degradation assays to identify suitable fungi for the efficient breakdown of soda lignin from cedar. Fourteen fungi from both white-rot and leaf-litter fungi were identified using the RBBR and Sundman and Näse assays. By nuclear magnetic resonance analysis we obtained water- and/or methanol-soluble degradation products from four fungi, and the patterns indicate specific degradation mechanisms for each fungi. These results suggest that the screened fungi have more than one mechanism for degrading soda lignin from Japanese cedar.

Highly Promiscuous Oxidases Discovered in the Bovine Rumen Microbiome.

The bovine rumen hosts a diverse microbiota, which is highly specialized in the degradation of lignocellulose. Ruminal bacteria, in particular, are well equipped to deconstruct plant cell wall polysaccharides. Nevertheless, their potential role in the breakdown of the lignin network has never been investigated. In this study, we used functional metagenomics to identify bacterial redox enzymes acting on polyaromatic compounds. A new methodology was developed to explore the potential of uncultured microbes to degrade lignin derivatives, namely kraft lignin and lignosulfonate. From a fosmid library covering 0.7 Gb of metagenomic DNA, three hit clones were identified, producing enzymes able to oxidize a wide variety of polyaromatic compounds without the need for the addition of copper, manganese, or mediators. These promiscuous redox enzymes could thus be of potential interest both in plant biomass refining and dye remediation. The enzymes were derived from uncultured Clostridia, and belong to complex gene clusters involving proteins of different functional types, including hemicellulases, which likely work in synergy to produce substrate degradation.

Molecular Level-based Analysis of Organosolv Wastewater

Background: Identification of monomeric and oligomeric organic compounds in Organosolv process wastewater is of growing importance in the context of isolating high value chemicals and producing biofuels. There were many studies devoted to identification of such compounds in precipitated Organosolv lignin, all of them using demanding, mostly hyphenated techniques such as HPLC-MS/MS and two dimensional NMR spectroscopy. However, the resulting Organosolv wastewater has not been studied as intensively in this respect, even though the application of these techniques to identify the components of dried/lyophilized Organosolv wastewater would be straightforward. Objective: The objective was to identify lignin-based breakdown products in Organosolv wastewater resulting from pulping of beech with aqueous ethanol solutions. Method: Low resolution GC/MS analysis in combination with derivatization reactions using nonlabeled and isotopically labeled derivatization agents and retention index information (where available) were used. Results: The application of isotopically labeled derivatization agents such as BSTFA-d9 (N,Obis( trimethylsilyl)trifluoracetamide-d9) turned out especially useful in structural identification work. In addition to monomers such as abundant syringaldehyde and vanillin, a multitude of dimeric products of the guaiacyl(syringyl) glycerol-β-guaiacyl(syringyl) ether-type, phenylcoumaran type and lignan-type could be detected, the most abundant surrogate being syringaresinol. Syringyl-type surrogates were more abundant compared to guaiacyl-type surrogates. Formation pathways of the monomeric breakdown products such as syringaldehyde and vanillin were proposed on the basis of the solvolytic cleavage of β-O-4 aryl ether linkages. Conclusion: Solvolytic cleavage of β(α)-O-4, β-5 and β-β linkages within the macromolecular lignin network under Organosolv process conditions results in dimeric products. Further activities should be focused on the use of high resolution MS and the synthesis of authentic standards. Keywords: Aryl ether bonds, derivatization, GC/MS analysis, lignin, NMR spectroscopy, organosolv wastewater.

Bioavailability of Carbohydrate Content in Natural and Transgenic Switchgrasses for the Extreme Thermophile Caldicellulosiruptor bescii.

Improving access to the carbohydrate content of lignocellulose is key to reducing recalcitrance for microbial deconstruction and conversion to fuels and chemicals. Caldicellulosiruptor bescii completely solubilizes naked microcrystalline cellulose, yet this transformation is impeded within the context of the plant cell wall by a network of lignin and hemicellulose. Here, the bioavailability of carbohydrates to C. bescii at 70°C was examined for reduced lignin transgenic switchgrass lines COMT3(+) and MYB Trans, their corresponding parental lines (cultivar Alamo) COMT3(-) and MYB wild type (WT), and the natural variant cultivar Cave-in-Rock (CR). Transgenic modification improved carbohydrate solubilization by C. bescii to 15% (2.3-fold) for MYB and to 36% (1.5-fold) for COMT, comparable to the levels achieved for the natural variant, CR (36%). Carbohydrate solubilization was nearly doubled after two consecutive microbial fermentations compared to one microbial step, but it never exceeded 50% overall. Hydrothermal treatment (180°C) prior to microbial steps improved solubilization 3.7-fold for the most recalcitrant line (MYB WT) and increased carbohydrate recovery to nearly 50% for the least recalcitrant lines [COMT3(+) and CR]. Alternating microbial and hydrothermal steps (T→M→T→M) further increased bioavailability, achieving carbohydrate solubilization ranging from 50% for MYB WT to above 70% for COMT3(+) and CR. Incomplete carbohydrate solubilization suggests that cellulose in the highly lignified residue was inaccessible; indeed, residue from the T→M→T→M treatment was primarily glucan and inert materials (lignin and ash). While C. bescii could significantly solubilize the transgenic switchgrass lines and natural variant tested here, additional or alternative strategies (physical, chemical, enzymatic, and/or genetic) are needed to eliminate recalcitrance.IMPORTANCE Key to a microbial process for solubilization of plant biomass is the organism's access to the carbohydrate content of lignocellulose. Economically viable routes will characteristically minimize physical, chemical, and biological pretreatment such that microbial steps contribute to the greatest extent possible. Recently, transgenic versions of plants and trees have been developed with the intention of lowering the barrier to lignocellulose conversion, with particular focus on lignin content and composition. Here, the extremely thermophilic bacterium Caldicellulosiruptor bescii was used to solubilize natural and genetically modified switchgrass lines, with and without the aid of hydrothermal treatment. For lignocellulose conversion, it is clear that the microorganism, plant biomass substrate, and processing steps must all be considered simultaneously to achieve optimal results. Whether switchgrass lines engineered for low lignin or natural variants with desirable properties are used, conversion will depend on microbial access to crystalline cellulose in the plant cell wall.