Erica Gjersing

Real-time monitoring of the deactivation of HZSM-5 during upgrading of pine pyrolysis vapors.

The conversion of pine pyrolysis vapors over fixed beds of HZSM-5 catalyst was studied as a function of deactivation of the catalyst, presumably by coking. Small laboratory reactors were used in this study in which the products were identified using a molecular beam mass spectrometer (MBMS) and gas chromatography mass spectrometry (GCMS). In all of these experiments, real-time measurements of the products formed were conducted as the catalyst aged and deactivated during upgrading. The results from these experiments showed the following: (1) Fresh catalyst produces primarily aromatic hydrocarbons and olefins with no detectable oxygen-containing species. (2) After pyrolysis of roughly the same weight of biomass as weight of catalyst, oxygenated products begin to appear in the product stream. This suite of oxygen containing products appears different from the products formed when the catalyst is fresh and when the catalyst is completely deactivated. In particular, phenol and cresols are measured while upgrading pine, cellulose and lignin pyrolysis vapors, suggesting that these products are intermediates or side products formed during upgrading. (3) After the addition of more pyrolysis vapors, the product stream consists of primary vapors from pine pyrolysis. Catalyst samples collected at various points during deactivation were analyzed using a variety of tools. The results show that carbon build-up is correlated with catalyst deactivation, suggesting that deactivation is due to coking. Further, studies of nitrogen adsorption on the used catalyst suggest that coking initially occurs on the outside of the catalyst, leaving the micropores largely intact. From a practical point of view, it appears that based upon this study and others in the literature, the amount of oxygen in the upgraded products can be related to the level of deactivation of the HZSM-5 catalyst, which can be determined by how much pyrolysis vapor is run over the catalyst.

Solid-State Selective 13C Excitation and Spin Diffusion NMR to Resolve Spatial Dimensions in Plant Cell Walls

The average spatial dimensions between major biopolymers within the plant cell wall can be resolved using a solid-state NMR technique referred to as a (13)C cross-polarization (CP) SELDOM (selectively by destruction of magnetization) with a mixing time delay for spin diffusion. Selective excitation of specific aromatic lignin carbons indicates that lignin is in close proximity to hemicellulose followed by amorphous and finally crystalline cellulose. (13)C spin diffusion time constants (T(SD)) were extracted using a two-site spin diffusion theory developed for (13)C nuclei under magic angle spinning (MAS) conditions. These time constants were then used to calculate an average lower-limit spin diffusion length between chemical groups within the plant cell wall. The results on untreated (13)C enriched corn stover stem reveal that the lignin carbons are, on average, located at distances ∼0.7-2.0 nm from the carbons in hemicellulose and cellulose, whereas the pretreated material had larger separations.

Knockdown of a laccase in Populus deltoides confers altered cell wall chemistry and increased sugar release.

Summary Plant laccases are thought to function in the oxidation of monolignols which leads to higher order lignin formation. Only a hand‐full of laccases in plants have been functionally evaluated, and as such little is known about the breadth of their impact on cell wall chemistry or structure. Here, we describe a previously uncharacterized laccase from Populus, encoded by locus Potri.008G064000, whose reduced expression resulted in transgenic Populus trees with changes in syringyl/guaiacyl ratios as well as altered sugar release phenotypes. These phenotypes are consistent with plant biomass exhibiting reduced recalcitrance. Interestingly, the transgene effect on recalcitrance is dependent on a mild pretreatment prior to chemical extraction of sugars. Metabolite profiling suggests the transgene modulates phenolics that are associated with the cell wall structure. We propose that this particular laccase has a range of functions related to oxidation of phenolics and conjugation of flavonoids that interact with lignin in the cell wall.

Rapid determination of sugar content in biomass hydrolysates using nuclear magnetic resonance spectroscopy

Large populations of potential cellulosic biomass feedstocks are currently being screened for fuel and chemical applications. The monomeric sugar content, released through hydrolysis, is of particular importance and is currently measured with time‐consuming HPLC methods. A method for sugar detection is presented here that employs 1H NMR spectra regressed against primary HPLC sugar concentration data to build partial least squares (PLS) models. The PLS2 model is able to predict concentrations of both major sugar components, like glucose and xylose, and minor sugars, such as arabinose and mannose, in biomass hydrolysates. The model was built with 65 samples from a variety of different biomass species and covers a wide range of sugar concentrations. Model predictions were validated with a set of 15 samples which were all within error of both HPLC and NMR integration measurements. The data collection time for these NMR measurements is less than 20 min, offering a significant improvement to the 1 h acquisition time that is required for HPLC. Biotechnol. Bioeng. 2013; 110: 721–728.

Biomass-derived monomers for performance-differentiated fiber reinforced polymer composites

Nearly all polymer resins used to manufacture critically important fiber reinforced polymer (FRP) composites are petroleum sourced. In particular, unsaturated polyesters (UPEs) are widely used as matrix materials and are often based on maleic anhydride, a four-carbon, unsaturated diacid. Typically, maleic anhydride is added as a reactant in a conventional step-growth polymerization to incorporate unsaturation throughout the backbone of the UPE, which is then dissolved in a reactive diluent (styrene is widely used) infused into a fiber mat and cross-linked. Despite widespread historical use, styrene has come under scrutiny due to environmental and health concerns; in addition, many conceivable UPEs are not soluble in styrene. In this study, we demonstrate that renewably-sourced monomers offer the ability to overcome these issues and improve overall composite performance. The properties of poly(butylene succinate)-based UPEs incorporating maleic anhydride are used as a baseline for comparison against UPEs derived from fumaric acid, cis,cis-muconate, and trans,trans-muconate, all of which can be obtained biologically. The resulting biobased UPEs are combined with styrene, methacrylic acid, or a mixture of methacrylic acid and cinnaminic acid, infused into woven fiberglass and cross-linked with the addition of a free-radical initiator and heat. This process produces a series of partially or fully bio-derived composites. Overall, the muconate-containing UPE systems exhibit a more favorable property suite than the maleic anhydride and fumaric acid counterparts. In all cases at the same olefinic monomer loading, the trans,trans-muconate polymers exhibit the highest shear modulus, storage modulus, and glass transition temperature indicating stronger and more thermally resistant materials. They also exhibit the lowest loss modulus indicating a greater adhesion to the glass fibers. The use of a mixture of methacrylic and cinnaminic acid as the reactive diluent results in a FRP composite with properties that can be matched to reinforced composites prepared with styrene. Significantly, at one-third the monomer loading (corresponding to two-thirds the number of double bonds), trans,trans-muconate produces approximately the same storage modulus and glass transition temperature as maleic anhydride, while exhibiting a superior loss modulus. Overall, this work demonstrates the novel synthesis of performance-differentiated FRP composites using renewably-sourced monomers.

Network-based integration of systems genetics data reveals pathways associated with lignocellulosic biomass accumulation and processing

Significance Carbon fixation and accumulation as lignocellulosic biomass is of global ecological and industrial importance and most significantly occurs in the form of wood development in trees. Traits of importance in biomass accumulation are highly complex and, aside from environmental factors, are affected by many pathways and thousands of genes. We have applied a network-based data integration method for a systems genetics analysis of genes, processes, and pathways underlying biomass and bioenergy-related traits using segregating Eucalyptus hybrid tree populations. We could link biologically meaningful sets of genes to complex traits and at the same time reveal the molecular basis of trait variation. Such a holistic view of the biology of wood formation will contribute to genetic improvement and engineering of plant biomass. As a consequence of their remarkable adaptability, fast growth, and superior wood properties, eucalypt tree plantations have emerged as key renewable feedstocks (over 20 million ha globally) for the production of pulp, paper, bioenergy, and other lignocellulosic products. However, most biomass properties such as growth, wood density, and wood chemistry are complex traits that are hard to improve in long-lived perennials. Systems genetics, a process of harnessing multiple levels of component trait information (e.g., transcript, protein, and metabolite variation) in populations that vary in complex traits, has proven effective for dissecting the genetics and biology of such traits. We have applied a network-based data integration (NBDI) method for a systems-level analysis of genes, processes and pathways underlying biomass and bioenergy-related traits using a segregating Eucalyptus hybrid population. We show that the integrative approach can link biologically meaningful sets of genes to complex traits and at the same time reveal the molecular basis of trait variation. Gene sets identified for related woody biomass traits were found to share regulatory loci, cluster in network neighborhoods, and exhibit enrichment for molecular functions such as xylan metabolism and cell wall development. These findings offer a framework for identifying the molecular underpinnings of complex biomass and bioprocessing-related traits. A more thorough understanding of the molecular basis of plant biomass traits should provide additional opportunities for the establishment of a sustainable bio-based economy.

Study of traits and recalcitrance reduction of field-grown COMT down-regulated switchgrass

BackgroundThe native recalcitrance of plants hinders the biomass conversion process using current biorefinery techniques. Down-regulation of the caffeic acid O-methyltransferase (COMT) gene in the lignin biosynthesis pathway of switchgrass reduced the thermochemical and biochemical conversion recalcitrance of biomass. Due to potential environmental influences on lignin biosynthesis and deposition, studying the consequences of physicochemical changes in field-grown plants without pretreatment is essential to evaluate the performance of lignin-altered plants. We determined the chemical composition, cellulose crystallinity and the degree of its polymerization, molecular weight of hemicellulose, and cellulose accessibility of cell walls in order to better understand the fundamental features of why biomass is recalcitrant to conversion without pretreatment. The most important is to investigate whether traits and features are stable in the dynamics of field environmental effects over multiple years.ResultsField-grown COMT down-regulated plants maintained both reduced cell wall recalcitrance and lignin content compared with the non-transgenic controls for at least 3 seasons. The transgenic switchgrass yielded 35–84% higher total sugar release (enzymatic digestibility or saccharification) from a 72-h enzymatic hydrolysis without pretreatment and also had a 25–32% increase in enzymatic sugar release after hydrothermal pretreatment. The COMT-silenced switchgrass lines had consistently lower lignin content, e.g., 12 and 14% reduction for year 2 and year 3 growing season, respectively, than the control plants. By contrast, the transgenic lines had 7–8% more xylan and galactan contents than the wild-type controls. Gel permeation chromatographic results revealed that the weight-average molecular weights of hemicellulose were 7–11% lower in the transgenic than in the control lines. In addition, we found that silencing of COMT in switchgrass led to 20–22% increased cellulose accessibility as measured by the Simons’ stain protocol. No significant changes were observed on the arabinan and glucan contents, cellulose crystallinity, and cellulose degree of polymerization between the transgenic and control plants. With the 2-year comparative analysis, both the control and transgenic lines had significant increases in lignin and glucan contents and hemicellulose molecular weight across the growing seasons.ConclusionsThe down-regulation of COMT in switchgrass resulting in a reduced lignin content and biomass recalcitrance is stable in a field-grown trial for at least three seasons. Among the determined affecting factors, the reduced biomass recalcitrance of the COMT-silenced switchgrass, grown in the field conditions for two and three seasons, was likely related to the decreased lignin content and increased biomass accessibility, whereas the cellulose crystallinity and degree of its polymerization and hemicellulose molecular weights did not contribute to the reduction of recalcitrance significantly. This finding suggests that lignin down-regulation in lignocellulosic feedstock confers improved saccharification that translates from greenhouse to field trial and that lignin content and biomass accessibility are two significant factors for developing a reduced recalcitrance feedstock by genetic modification.

The effects of high concentrations of ionic liquid on GB1 protein structure and dynamics probed by high-resolution magic-angle-spinning NMR spectroscopy

Ionic liquids have great potential in biological applications and biocatalysis, as some ionic liquids can stabilize proteins and enhance enzyme activity, while others have the opposite effect. However, on the molecular level, probing ionic liquid interactions with proteins, especially in solutions containing high concentrations of ionic liquids, has been challenging. In the present work the 13C, 15N-enriched GB1 model protein was used to demonstrate applicability of high-resolution magic-angle-spinning (HR-MAS) NMR spectroscopy to investigate ionic liquid–protein interactions. Effect of an ionic liquid (1-butyl-3-methylimidazolium bromide, [C4-mim]Br) on GB1was studied over a wide range of the ionic liquid concentrations (0.6–3.5 M, which corresponds to 10–60% v/v). Interactions between GB1 and [C4-mim]Br were observed from changes in the chemical shifts of the protein backbone as well as the changes in 15N ps-ns dynamics and rotational correlation times. Site-specific interactions between the protein and [C4-mim]Br were assigned using 3D methods under HR-MAS conditions. Thus, HR-MAS NMR is a viable tool that could aid in elucidation of molecular mechanisms of ionic liquid–protein interactions.

Downregulation of p-Coumaroyl Quinate/Shikimate 3'-Hydroxylase (C3'H) or Cinnamate-4-hydrolylase (C4H) in Eucalyptus urophylla×Eucalyptus grandis Leads to Increased Extractability

Lignin reduction through breeding and genetic modification has the potential to reduce costs in biomass processing in pulp and paper, forage, and lignocellulosic ethanol industries. Here, we present detailed characterization of the extractability and lignin structure of Eucalyptus urophylla × Eucalyptus grandis RNAi downregulated in p-coumaroyl quinate/shikimate 3′-hydroxylase (C3′H) or cinnamate-4-hydroxylase (C4H). Both the C3′H and C4H downregulated lines were found to have significantly higher extractability when exposed to NaOH base extraction, indicating altered cell wall construction. The molecular weight of isolated lignin was measured and lignin structure was determined by HSQC NMR-based lignin subunit analysis for control and the C3′H and C4H downregulated lines. The slight reductions in average molecular weights of the lignin isolated from the transgenic lines (C3′H = 7000, C4H = 6500, control = 7300) does not appear to explain the difference in extractability. The HSQC NMR-based lignin subunit analysis showed increases in H lignin content for the C3′H but only slight differences in the lignin subunit structure of the C3′H and C4H downregulated lines when compared to the control. The greatest difference between the C3′H and C4H downregulated lines is the total lignin content; therefore, it appears that overall lowered lignin content contributes greatly to reduced recalcitrance and increased extractability of cell wall biopolymers. Further studies will be conducted to determine how the reduction in lignin content creates a less rigid cell wall that is more prone to extraction and sugar release.

Improving wood properties for wood utilization through multi-omics integration in lignin biosynthesis

A multi-omics quantitative integrative analysis of lignin biosynthesis can advance the strategic engineering of wood for timber, pulp, and biofuels. Lignin is polymerized from three monomers (monolignols) produced by a grid-like pathway. The pathway in wood formation of Populus trichocarpa has at least 21 genes, encoding enzymes that mediate 37 reactions on 24 metabolites, leading to lignin and affecting wood properties. We perturb these 21 pathway genes and integrate transcriptomic, proteomic, fluxomic and phenomic data from 221 lines selected from ~2000 transgenics (6-month-old). The integrative analysis estimates how changing expression of pathway gene or gene combination affects protein abundance, metabolic-flux, metabolite concentrations, and 25 wood traits, including lignin, tree-growth, density, strength, and saccharification. The analysis then predicts improvements in any of these 25 traits individually or in combinations, through engineering expression of specific monolignol genes. The analysis may lead to greater understanding of other pathways for improved growth and adaptation.A systematic analysis of lignin biosynthetic genes to quantitatively understand their effect on wood properties is still lacking. Here, the authors integrate transcriptomic, proteomic, fluxomic and phenomic data to quantify the impact of perturbations of transcript abundance on lignin biosynthesis and wood properties.