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The structure of softwoods, which confers resistance to degradation through hydrolysis and decay, currently limits their use for the production of biofuels. However, since wood is very heterogeneous, it is possible that differences in wood properties within and between trees could differentially affect its process ability. In this research, heartwood (inner) and sapwood (outer) from Norway spruce (Picea abies (L.) Karst.) clones were enzymatically hydrolyzed by Trichoderma viride cellulases after concentrated acid pretreatment. Wood sections with two particle sizes were compared based on their susceptibility to enzymatic hydrolysis, evaluated by assaying the formation of hydrolysis products and measured as reducing sugar yield (RSY). We also studied the relationship between RSY and the susceptibility to Heterobasidion parviporum wood decay and whether these traits are reflected in wood density and yield. Wood from the outer section produced more RSY with higher glucan but lower lignin content than wood from the inner section. Furthermore, susceptibility to enzymatic hydrolysis was positively correlated with H. parviporum wood decay, while both processes were negatively correlated with wood density. Our results revealed the importance of clonal trials for identifying suitable lignocellulosic biomass when considering wood properties and indicate that potential genotypes for the production of biofuels are not necessarily the most productive. Resume: La structure du bois des resineux qui leur confere une resistance a la degradation par hydrolyse et par la carie limite presentement leur utilisation pour la production de biocarburants. Cependant, etant donne que le bois est tres heterogne, il est possible que les differences de proprietes du bois a l'interieur du meme arbre ou entre differents arbres puissent avoir des effets differents sur sa transformabilite. Dans cette recherche, du bois de coeur (interne) et du bois d'aubier (externe) de clones d'epicea commun (Picea abies (L.) Karst.) ont ete hydrolyses enzymatiquement a l'aide de cellulases de Trichoderma viride apres un pretraitement avec un acide concentre. Les sections de bois avec deux dimensions de particules ont ete comparees sur la base de leur susceptibilite a l'hydrolyse enzymatique qui a ete evaluee en dosant la formation des produits de l'hydrolyse et mesuree sous forme de rendement en sucres reducteurs (RSR). Nous avons egalement etudie la relation entre le RSR et la susceptibilite a la carie du bois causee par Heterobasidion parviporum et verifie si ces caracteristiques sont refletees dans le rendement et la densite du bois. Le bois d'aubier a eu un meilleur RSR, avec une teneur en glucane plus elevee mais une teneur en lignine plus faible que le bois de coeur. De plus, la susceptibilite a l'hydrolyse enzymatique etait positivement correlee avec la carie du bois causee par H. parviporum tandis que les deux processus etaient negativement correles avec la densite du bois. Nos resultats ont fait ressortir l'importance des tests clonaux pour identifier la biomasse lignocellulosique convenable lorsqu'on considere les proprietes du bois et montrent que les genotypes potentiels pour la production de biocarburants ne sont pas necessairement les plus productifs. [Traduit par la Redaction], Introduction Combating climate change through renewable energy and ensuring energy security are major drivers of the increasing utilization of lignocellulosic biomass for the production of second-generation transport fuels. In general, [...]

Previous studies on Melanocarpus albomyces laccase have shown that this enzyme is very interesting for both basic research purposes and industrial applications. In order to obtain a reliable and efficient source for this laccase, it was produced in the filamentous fungus Trichoderma reesei. Two approaches were used: production of a non-fused laccase and a hydrophobin-laccase fusion protein. Both proteins were expressed in T. reesei under the cbh1 promoter, and significantly higher activities were obtained with the non-fused laccase in shake-flask cultures (corresponding to about 230 mg [l.sup.-1]). Northern blot analyses showed rather similar mRNA levels from both expression constructs. Western analysis indicated intracellular accumulation and degradation of the hydrophobin-laccase fusion protein, showing that production of the fusion was limited at the post-transcriptional level. No induction of the unfolded protein response pathway by laccase production was detected in the transformants by Northern hybridization. The most promising transformant was grown in a fermenter in batch and fed-batch modes. The highest production level obtained in the fed-batch culture was 920 mg [l.sup.-1]. The recombinant laccase was purified from the culture supernatant after cleaving the major contaminating protein, cellobiohydrolase I, by papain. The recombinant and wild-type laccases were compared with regard to substrate kinetics, molecular mass, pH optimum, thermostability, and processing of the N-and C-termini, and they showed very similar properties.

Enzymatic hydrolysis studies on degradation of cotton cellulose by Trichoderma reesei endoglucanase I (EGI) and cellobiohydrolase II (CBHII) demonstrate synergy between EGI and CBHII in inhibiting sugar production, with EGI serving as a prominent degrading factor. Size exclusion chromatography of the tricarbanilate derivatives reveals no change in the molecular-size distribution of cellulose in the post-degradation phase. EGI selectively cleaves through the microfibrils, whereas CBHII releases soluble sugars from the degraded portions.

Abstract Background Due to the complexity of lignocellulosic materials, a complete enzymatic hydrolysis into fermentable sugars requires a variety of cellulolytic and xylanolytic enzymes. Addition of xylanases has been shown to significantly improve the performance of cellulases and to increase cellulose hydrolysis by solubilizing xylans in lignocellulosic materials. The goal of this work was to investigate the effect of acetyl xylan esterase (AXE) originating from Trichoderma reesei on xylan solubilization and enzymatic hydrolysis of cellulose. Results The solubilization of xylan in pretreated wheat straw and giant reed (Arundo donax) by xylanolytic enzymes and the impact of the sequential or simultaneous solubilization of xylan on the hydrolysis of cellulose by purified enzymes were investigated. The results showed that the removal of acetyl groups in xylan by AXE increased the accessibility of xylan to xylanase and improved the hydrolysis of xylan in pretreated wheat straw and giant reed. Solubilization of xylan led to an increased accessibility of cellulose to cellulases and thereby increased the hydrolysis extent of cellulose. A clear synergistic effect between cellulases and xylanolytic enzymes was observed. The highest hydrolysis yield of cellulose was obtained with a simultaneous use of cellulases, xylanase and AXE, indicating the presence of acetylated xylan within the cellulose matrix. Acetylated xylobiose and acetylated xylotriose were produced from xylan without AXE, as confirmed by atmospheric pressure matrix-assisted laser desorption/ionization ion trap mass spectrometry. Conclusions The results in this paper demonstrate that supplementation of xylanase with AXE enhances the solubilization of xylan to some extent and, consequently, increases the subsequent hydrolysis of cellulose. The highest hydrolysis yield was, however, obtained by simultaneous hydrolysis of xylan and cellulose, indicating a layered structure of cellulose and xylan chains in the cell wall substrate. AXE has an important role in the hydrolysis of lignocellulosic materials containing acetylated xylan.

Abstract Background The main technological impediment to widespread utilization of lignocellulose for the production of fuels and chemicals is the lack of low-cost technologies to overcome its recalcitrance. Organisms that hydrolyze lignocellulose and produce a valuable product such as ethanol at a high rate and titer could significantly reduce the costs of biomass conversion technologies, and will allow separate conversion steps to be combined in a consolidated bioprocess (CBP). Development of Saccharomyces cerevisiae for CBP requires the high level secretion of cellulases, particularly cellobiohydrolases. Results We expressed various cellobiohydrolases to identify enzymes that were efficiently secreted by S. cerevisiae. For enhanced cellulose hydrolysis, we engineered bimodular derivatives of a well secreted enzyme that naturally lacks the carbohydrate-binding module, and constructed strains expressing combinations of cbh1 and cbh2 genes. Though there was significant variability in the enzyme levels produced, up to approximately 0.3 g/L CBH1 and approximately 1 g/L CBH2 could be produced in high cell density fermentations. Furthermore, we could show activation of the unfolded protein response as a result of cellobiohydrolase production. Finally, we report fermentation of microcrystalline cellulose (Avicel™) to ethanol by CBH-producing S. cerevisiae strains with the addition of beta-glucosidase. Conclusions Gene or protein specific features and compatibility with the host are important for efficient cellobiohydrolase secretion in yeast. The present work demonstrated that production of both CBH1 and CBH2 could be improved to levels where the barrier to CBH sufficiency in the hydrolysis of cellulose was overcome.

Abstract Background In the hydrolysis of lignocellulosic materials, thermostable enzymes decrease the amount of enzyme needed due to higher specific activity and elongate the hydrolysis time due to improved stability. For cost-efficient use of enzymes in large-scale industrial applications, high-level expression of enzymes in recombinant hosts is usually a prerequisite. The main aim of the present study was to compare the biochemical and hydrolytic properties of two thermostable recombinant glycosyl hydrolase families 10 and 11 (GH10 and GH11, respectively) xylanases with respect to their potential application in the hydrolysis of lignocellulosic substrates. Results The xylanases from Nonomuraea flexuosa (Nf Xyn11A) and from Thermoascus aurantiacus (Ta Xyn10A) were purified by heat treatment and gel permeation chromatography. Ta Xyn10A exhibited higher hydrolytic efficiency than Nf Xyn11A toward birchwood glucuronoxylan, insoluble oat spelt arabinoxylan and hydrothermally pretreated wheat straw, and it produced more reducing sugars. Oligosaccharides from xylobiose to xylopentaose as well as higher degree of polymerization (DP) xylooligosaccharides (XOSs), but not xylose, were released during the initial hydrolysis of xylans by Nf Xyn11A, indicating its potential for the production of XOS. The mode of action of Nf Xyn11A and Ta Xyn10A on glucuronoxylan and arabinoxylan showed typical production patterns of endoxylanases belonging to GH11 and GH10, respectively. Conclusions Because of its high catalytic activity and good thermostability, T. aurantiacus xylanase shows great potential for applications aimed at total hydrolysis of lignocellulosic materials for platform sugars, whereas N. flexuosa xylanase shows more significant potential for the production of XOSs.

Abstract Background Thermostable enzymes have several benefits in lignocellulose processing. In particular, they potentially allow the use of increased substrate concentrations (because the substrate viscosity decreases as the temperature increases), resulting in improved product yields and reduced capital and processing costs. A short pre-hydrolysis step at an elevated temperature using thermostable enzymes aimed at rapid liquefaction of the feedstock is seen as an attractive way to overcome the technical problems (such as poor mixing and mass transfer properties) connected with high initial solid loadings in the lignocellulose to ethanol process. Results The capability of novel thermostable enzymes to reduce the viscosity of high-solid biomass suspensions using a real-time viscometric measurement method was investigated. Heterologously expressed enzymes from various thermophilic organisms were compared for their ability to liquefy the lignocellulosic substrate, hydrothermally pretreated wheat straw. Once the best enzymes were identified, the optimal temperatures for these enzymes to decrease substrate viscosity were compared. The combined hydrolytic properties of the thermostable preparations were tested in hydrolysis experiments. The studied mixtures were primarily designed to have good liquefaction potential, and therefore contained an enhanced proportion of the key liquefying enzyme, EGII/Cel5A. Conclusions Endoglucanases were shown to have a superior ability to rapidly reduce the viscosity of the 15% (w/w; dry matter) hydrothermally pretreated wheat straw. Based on temperature profiling studies, Thermoascus aurantiacus EGII/Cel5A was the most promising enzyme for biomass liquefaction. Even though they were not optimized for saccharification, many of the thermostable enzyme mixtures had superior hydrolytic properties compared with the commercial reference enzymes at 55°C.