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Xylanase

About: Xylanase is a research topic. Over the lifetime, 7099 publications have been published within this topic receiving 163793 citations.


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Journal ArticleDOI
TL;DR: The engineered strains express cellulase, xylanase, beta-glucosidase, and xylobiosidase enzymes under control of native E. coli promoters selected to optimize growth on model cellulosic and hemicellulosic substrates and provide an economical route to production of advanced biofuels.
Abstract: One approach to reducing the costs of advanced biofuel production from cellulosic biomass is to engineer a single microorganism to both digest plant biomass and produce hydrocarbons that have the properties of petrochemical fuels. Such an organism would require pathways for hydrocarbon production and the capacity to secrete sufficient enzymes to efficiently hydrolyze cellulose and hemicellulose. To demonstrate how one might engineer and coordinate all of the necessary components for a biomass-degrading, hydrocarbon-producing microorganism, we engineered a microorganism naive to both processes, Escherichia coli, to grow using both the cellulose and hemicellulose fractions of several types of plant biomass pretreated with ionic liquids. Our engineered strains express cellulase, xylanase, beta-glucosidase, and xylobiosidase enzymes under control of native E. coli promoters selected to optimize growth on model cellulosic and hemicellulosic substrates. Furthermore, our strains grow using either the cellulose or hemicellulose components of ionic liquid-pretreated biomass or on both components when combined as a coculture. Both cellulolytic and hemicellulolytic strains were further engineered with three biofuel synthesis pathways to demonstrate the production of fuel substitutes or precursors suitable for gasoline, diesel, and jet engines directly from ionic liquid-treated switchgrass without externally supplied hydrolase enzymes. This demonstration represents a major advance toward realizing a consolidated bioprocess. With improvements in both biofuel synthesis pathways and biomass digestion capabilities, our approach could provide an economical route to production of advanced biofuels.

357 citations

Journal ArticleDOI
TL;DR: Examination of the growth behavior of the different mutant strains of the H. jecorina genome pointed to the strongly reduced ability of the xyr1 deletion strain to utilize d-xylose and xylan, and transcriptional regulation of the major hydrolytic enzyme-encoding genes xyn1 and xyn2, cbh1 and cbh2, and egl1 (endoglucanase 1 and 2) is strictly dependent on Xyr1.
Abstract: Hypocrea jecorina (anamorph Trichoderma reesei) is a fungus of noteworthy industrial importance, mainly because of its employment in both fermentative production of native extracellular enzymes and heterologous protein production. Hydrolases secreted by this fungus have achieved broad areas of applications, e.g., in pulp and paper (4, 35, 50), food and feed (9, 27, 49), and textile (23, 26, 36) industries. The set of hydrolytic enzymes produced by H. jecorina comprises two main cellobiohydrolases, CBHI and CBHII (EC 3.2.1.91) (43); endo-β-1,4-glucanases EGI to EGV (EC 3.2.1.4) (37); 1,4-β-glucosidases BGLI and BGLII (EC 3.2.1.21) (8, 40); two major specific endo-β-1,4-xylanases, XYNI and XYNII (EC 3.2.1.8) (45); and one β-xylosidase, BXLI (EC 3.2.1.37) (17), to mention only the best characterized. This set of hydrolases is synergistically working together to attain a complete degradation of biopolymeric substrates, of which cellulose and xylan are predominant. In this particular breakdown process, these enzymes cause hydrolysis to smaller, soluble oligo- and monosaccharides which finally either act directly as low-molecular-weight inducer substances (e.g., xylobiose and xylose) (29, 53) or are converted to their respective inducers (e.g., sophorose) via the transglycosylation activity of some of these enzymes (46). Whereas in Aspergillus spp. the xylanolytic and cellulolytic systems are strictly coregulated via the inducer xylose (10, 15), enzymes participating in the respective T. reesei hydrolytic systems are not. Their differential expression levels have been reported in several studies. Briefly summarizing these findings, all discussed hydrolytic genes are inducible by their respective degradation and/or transglycosylation products of xylan and/or cellulose, e.g., the xyn1 (xylanase 1-encoding) gene is inducible by xylose (30), the xyn2 (xylanase 2-encoding) gene by xylobiose and sophorose (53), and the bxl1 (β-xylosidase 1-encoding) gene by xylobiose (33); cellulases such as the cbh1 (cellobiohydrolase 1-encoding) gene, the cbh2 (cellobiohydrolase 2-encoding) gene, and the egl1 (endoglucanase 1-encoding) gene (20); and the bgl1 (β-glucosidase 1-encoding) gene (8) and the bgl2 (β-glucosidase 2-encoding) gene (40) by soph-orose. We recently reported that during xylose-mediated induction of xyn1, Xyr1 (xylanase regulator 1) plays a main role in H. jecorina (38). Xyr1 is a zinc binuclear cluster protein binding to a GGCTAA motif arranged as an inverted repeat in the xyn1 promoter (38), closely resembling the consensus sequence for binding of the Aspergillus niger XlnR transactivator (48). XlnR is not only a central regulator protein responsible for activation of more than 10 genes involved in degradation of xylan and cellulose, it also contributes to the regulation of d-xylose metabolism (10, 15, 47). Ancillary to Xyr1/XlnR-mediated induction, the carbon catabolite repressor Cre1/A has for both organisms been described as a wide domain repressor of particular hydrolase-encoding genes (6, 7, 21, 30). In T. reesei, only some of the major hydrolases, namely cbh1 and xyn1, are under direct Cre1 control (21, 30), whereas other hydrolytic genes such as cbh2, xyn2, and bgl1 are not Cre1 regulation dependent (31, 33). In addition, the isolation of the two transcription factors Ace1 and Ace2, potentially involved in the regulation of hydrolase formation in H. jecorina, has been reported (2, 39). While the previously described repressor Ace1 (1) was proven to directly antagonize Xyr1 function by competing for one of its binding sites in the xyn1 promoter (38), deletion of ace2 was demonstrated to clearly reduce expression levels of the main cellulase genes and of the xyn2 gene cultivated on cellulose but did not affect induction on sophorose (2). A more detailed study revealed that Ace2 contacts the xylanase-activating element XAE (essential for xyn2 expression) in the xyn2 promoter (52) but is not involved in xyn1 transcription (2, 38). Up until now, no mechanisms involving respective orthologous regulators have been identified in the expression of Aspergillus hydrolases. In this study, we report the deletion of xyr1 from the H. jecorina genome. Strikingly reduced growth on d-xylose and restricted utilization of xylan by the xyr1 deletion strain could be observed compared to that of the wild type. Consequently, we identified Xyr1 as a general and essential transcriptional activator of not only xyn1 but also xyn2, cbh1, cbh2, and egl1 gene transcription. Furthermore, Xyr1 was demonstrated to strictly control xylanolytic as well as cellulolytic enzyme formation under inducing and noninducing conditions in H. jecorina. Moreover, Xyr1 could be shown to regulate the gene expression of at least some inducer-providing enzymes, e.g., BGLI and BXLI. Finally, we have proven the involvement of Xyr1 in d-xylose metabolism, namely, its strong impact on the expression of d-xylose reductase activity. Summarizing, we revealed Xyr1 to govern the expression of the xylanolytic and cellulolytic enzyme system as well as d-xylose metabolism in H. jecorina.

350 citations

Journal ArticleDOI
TL;DR: A novel yeast-based method to isolate transcriptional activators was applied to clone regulators binding to the cellulase promoter cbh1 of the filamentous fungus Trichoderma reesei, leading to the isolation of the cellulases activator ace2 encoding for a protein belonging to the class of zinc binuclear cluster proteins found exclusively in fungi.

334 citations

Book ChapterDOI
TL;DR: When the SSCF process is used, the fact that the xylan fraction is retained during pretreatment is a desirable feature since the overall bioconversion can be carried out in a single step without separate recovery of xylose from the pretreatment liquid.
Abstract: Soaking in aqueous ammonia (SAA) was investigated as a pretreatment method for corn stover. In this method, the feedstock was soaked in aqueous ammonia over an extended period (10–60 d) at room temperature. It was done without agitation at atmospheric pressure. SAA treatment removed 55–74% of the lignin, but retained nearly 100% of the glucan and 85% of the xylan. The xylan remaining in the corn stover after SAA treatment was hydrolyzed along with the glucan by xylanase present in the Spezyme CP enzyme. In the simultaneous saccharification and fermentation (SSF) test of SAA-treated corn stover, using S. cerevisiae (D5A), an ethanol yield of 73% of theoretical maximum was obtained on the basis of the glucan content in the treated corn stover. The accumulation of xylose in the SSF appears to inhibit the cellulase activity on glucan hydrolysis, which limits the yield of ethanol. In the simultaneous saccharification and co-fermentation (SSCF) test, using recombinant E. coli (KO11), both the glucan and xylose were effectively utilized, resulting in on overall ethanol yield of 77% based on the glucan and xylan content of the substrate. When the SSCF process is used, the fact that the xylan fraction is retained during pretreatment is a desirable feature since the overall bioconversion can be carried out in a single step without separate recovery of xylose from the pretreatment liquid.

314 citations

Journal ArticleDOI
TL;DR: All pretreated poplar solids required high protein loadings to realize good sugar yields via enzymatic hydrolysis, and performance tended to be better for low pH pretreatments by dilute sulfuric acid and sulfur dioxide, possibly due to higher xylose removal.
Abstract: Comparative data is presented on glucose and xylose release for enzymatic hydrolysis of solids produced by pretreatment of poplar wood by ammonia fiber expansion (AFEX), ammonia recycled percolation (ARP), controlled pH, dilute acid, flowthrough (FT), lime, and sulfur dioxide (SO(2)) technologies. Sugar solubilization was measured for times of up to 72 h using cellulase supplemented with beta-glucosidase at an activity ratio of 1:2, respectively, at combined protein mass loadings of 5.8-116 mg/g of glucan in poplar wood prior to pretreatment. In addition, the enzyme cocktail was augmented with up to 11.0 g of xylanase protein per gram of cellulase protein at combined cellulase and beta-glucosidase mass loadings of 14.5 and 29.0 mg protein (about 7.5 and 15 FPU, respectively)/g of original potential glucose to evaluate cellulase-xylanase interactions. All pretreated poplar solids required high protein loadings to realize good sugar yields via enzymatic hydrolysis, and performance tended to be better for low pH pretreatments by dilute sulfuric acid and sulfur dioxide, possibly due to higher xylose removal. Glucose release increased nearly linearly with residual xylose removal by enzymes for all pretreatments, xylanase leverage on glucan removal decreased at high cellulase loadings. Washing the solids improved digestion for all pretreatments and was particularly beneficial for controlled pH pretreatment. Furthermore, incubation of pretreated solids with BSA, Tween 20, or PEG6000 prior to adding enzymes enhanced yields, but the effectiveness of these additives varied with the type of pretreatment.

305 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023199
2022463
2021254
2020289
2019278
2018303