Showing papers on "Xylanase published in 2000"
TL;DR: A thermostable and cellulase-free xylanase has been produced from Streptomyces sp.
208 citations
TL;DR: The synergistic effect between ruminal and exogenous enzymes increases the hydrolytic potential within the rumen environment and is likely a significant mechanism by which enzyme additives improve feed digestion in ruminants.
180 citations
TL;DR: Four purified xylanase enzymes have been studied for the hydrolysis of the xylans and different xylanases have different activities against various xylan structures.
179 citations
TL;DR: Several xylanase-producing cultures are isolated and characterised, one of which (an alkalophilic Bacillus SSP-34) produced more than 100 IU ml(-1) of xylan enzyme activity, which makes them less suitable for pulp and paper industries.
Abstract: Xylanases are used mainly in the pulp and paper industries for the pretreatment of Kraft pulp prior to bleaching to minimize use of chlorine, the conventional bleaching agent. This application has great potential as an environmentally safe method. Hydrolysis by xylanases of relocated and reprecipitated xylan on the surface of cellulose fibres formed during Kraft cooking facilitates the removal of lignin by increasing permeability to oxidising agents. Most of the xylanases reported in the literature contained significant cellulolytic activity, which make them less suitable for pulp and paper industries. The need for large quantities of xylanases which would be stable at higher temperatures and pH values and free of cellulase activity has necessitated a search for novel enzymes. We have isolated and characterised several xylanase-producing cultures, one of which (an alkalophilic Bacillus SSP-34) produced more than 100 IU ml−1 of xylanase activity. The SSP-34 xylanases have optimum activity at 50°C in a pH range 6–8, with only small amounts of cellulolytic activity (CMCase (0.4 IU ml−1, pH 7), FPase (0.2 IU ml−1, pH 7) and no activity at pH 9).
176 citations
TL;DR: Xylanase and pectinase were stable over a broad pH range between 5.4 and 9.0, respectively, retaining more than 85% of their activity, and were optimally active at 60°C.
Abstract: Streptomyces sp. QG-11-3, which produces a cellulase-free thermostable xylanase (96 IU ml−1) and a pectinase (46 IU ml−1), was isolated on Horikoshi medium supplemented with 1% w/v wheat bran. Carbon sources that favored xylanase production were rice bran (82 IU ml−1) and birch-wood xylan (81 IU ml−1); pectinase production was also stimulated by pectin and cotton seed cake (34 IU ml−1 each). The partially purified xylanase and pectinase were optimally active at 60°C. Both enzymes were 100% stable at 50°C for more than 24 h. The half-lives of xylanase and pectinase at 70, 75 and 80°C were 90, 75 and 9 min, and 90, 53 and 7 min, respectively. The optimum pH values for xylanase and pectinase were 8.6 and 3.0, respectively, at 60°C. Xylanase and pectinase were stable over a broad pH range between 5.4 and 9.4 and 2.0 to 9.0, respectively, retaining more than 85% of their activity. Ca2+ stimulated the activity of both enzymes up to 7%, whereas Cd2+, Co2+, Cr3+, iodoacetic acid and iodoacetamide inhibited xylanase up to 35% and pectinase up to 63%; at 1 mM, Hg2+ inhibited both enzymes completely. Journal of Industrial Microbiology & Biotechnology (2000) 24, 396–402.
171 citations
TL;DR: A haloalkalophilic Staphylococcus sp.
Abstract: A haloalkalophilic Staphylococcus sp. SG-13 produced an alkalistable xylanase in wheat bran medium. A 12-fold purification was achieved by using standard purification techniques. The purified xylanase exhibited a dual pH optima of 7.5 and 9.2. The optimum temperature for enzyme activity was 50 degrees C. The enzyme was stable at 50 degrees C for more than 4 h. The xylanase exhibited Km and Vmax values of 4 mg ml-1, 90 micromol min-1 per mg for birchwood xylan and 7 mg ml-1, 55 micromol min-1 per mg for oatspelt xylan, respectively. The substrate binding affinity of xylanase was more for oatspelt xylan but birchwood xylan was hydrolysed more rapidly. The xylanase activity was stimulated by Fe2+, Ni2+, Cu2+ and dithiothreitol up to 60% and was strongly inhibited in the presence of Co2+, Hg2+, Pb2+, phenyl methane sulphonyl fluoride, ethylenediaminetetraacetic acid, and acetic anhydride up to 100%. The xylanase dose of 1.8 U g-1 moisture free pulp, exhibited bleach boosting of kraft pulps optimally at pH 9.5-10.0 and 50 degrees C after 4 h of reaction time. Pretreatment of pulp with xylanase and its subsequent treatment with 8% hypochlorite, reduced the kappa number by 30%, enhanced the brightness and viscosity by 11% and 1.8%, respectively, and improved the paper properties such as tensile strength and burst factor up to 10% and 17%, respectively.
170 citations
TL;DR: Although the drainage properties of the pulps could be improved by selected enzymes, the water retention capacity of the dried hornified fibers could not be recovered by any of the enzymes tested.
155 citations
TL;DR: Transposon mutagenesis and marker exchange studies revealed genes on the cloned DNA that were required for xylanase production and virulence and sequence analysis with transposon-specific primers revealed these genes were homologues of xps F and xps D, which encode components of a protein secretion system in Xanthomonas campestris pv.campestris.
Abstract: Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial leaf blight, a serious disease of rice. A virulence- and xylanase-deficient mutant of Xoo was isolated following ethyl methane sulfonate (EMS) mutagenesis. A cosmid clone that restored virulence and xylanase secretion was obtained from a genomic library by functional complementation. Transposon mutagenesis and marker exchange studies revealed genes on the cloned DNA that were required for xylanase production and virulence. Sequence analysis with transposon-specific primers revealed that these genes were homologues of xps F and xps D, which encode components of a protein secretion system in Xanthomonas campestris pv. campestris. Enzyme assays showed xylanase accumulation in the periplasmic space and cytoplasm of the xps F mutant and the complementing clone restored transport to the extracellular space.
155 citations
TL;DR: Results indicated that mixtures of hemicellulase activities can be chosen to enhance pulp bleachability by giving the most effective κ number reduction using a single incubation.
Abstract: Enzymatic pretreatment of softwood kraft pulp was investigated using xylanase A (XylA) from Neocallimastix patriciarum in combination with mannanase and α-galactosidase. Mannanase A (ManA) from Pseudomonas fluorescens subsp. cellulosa and ManA from Clostridium thermocellum, both family 26 glycosyl hydrolases, are structurally diverse and exhibit different pH and temperature optima. Although neither mannanase was effective in pretreating softwood pulp alone, both enzymes were able to enhance the production of reducing sugar and the reduction of single-stage bleached κ number when used with the xylanase. Sequential incubations with XylA and P. fluorescens ManA produced the largest final κ number reduction in comparison to control pretreated pulp. The release of galactose from softwood pulp by α-galactosidase A (AgaA) from P. fluorescens was enhanced by the presence of ManA from the same microorganism, and a single pretreatment with these enzymes, in combination with XylA, gave the most effective κ number reduction using a single incubation. Results indicated that mixtures of hemicellulase activities can be chosen to enhance pulp bleachability.
154 citations
TL;DR: Xylanase was produced by Aspergillus terreus cultivated on finely ground wheat straw in solid-state fermentation and showed high specificity towards oat spelt xylan and minute activities were observed with carboxymethyl cellulose and cellobiose.
151 citations
TL;DR: The presence of feruloyl esterase in the C. thermocellum cellulosome together with its other hydrolytic activities demonstrates a powerful enzymatic potential of this organelle in plant cell wall decomposition.
Abstract: The cellulosome of Clostridium thermocellum is a multiprotein complex with endo- and exocellulase, xylanase, beta-glucanase, and acetyl xylan esterase activities. XynY and XynZ, components of the cellulosome, are composed of several domains including xylanase domains and domains of unknown function (UDs). Database searches revealed that the C- and N-terminal UDs of XynY and XynZ, respectively, have sequence homology with the sequence of a feruloyl esterase of strain PC-2 of the anaerobic fungus Orpinomyces. Purified cellulosomes from C. thermocellum were found to hydrolyze FAXX (O-(5-O-[(E)-feruloyl]-alpha-L-arabinofuranosyl)-(1-->3)-O-beta-D- xyl opyranosyl-(1-->4)-D-xylopyranose) and FAX(3) (5-O-[(E)-feruloyl]-[O-beta-D-xylopyranosyl-(1-->2)]-O-alpha-L- arabinofuranosyl-[1-->3])-O-beta-D-xylopyranosyl-(1-->4)-D-xylopyranose) , yielding ferulic acid as a product, indicating that they have feruloyl esterase activity. Nucleotide sequences corresponding to the UDs of XynY and XynZ were cloned into Escherichia coli, and the expressed proteins hydrolyzed FAXX and FAX(3). The recombinant feruloyl esterase domain of XynZ alone (FAE(XynZ)) and with the adjacent cellulose binding domain (FAE-CBD(XynZ)) were characterized. FAE-CBD(XynZ) had a molecular mass of 45 kDa that corresponded to the expected product of the 1,203-bp gene. K(m) and V(max) values for FAX(3) were 5 mM and 12.5 U/mg, respectively, at pH 6.0 and 60 degrees C. PAX(3), a substrate similar to FAX(3) but with a p-coumaroyl group instead of a feruloyl moiety was hydrolyzed at a rate 10 times slower. The recombinant enzyme was active between pH 3 to 10 with an optimum between pH 4 to 7 and at temperatures up to 70 degrees C. Treatment of Coastal Bermuda grass with the enzyme released mainly ferulic acid and a lower amount of p-coumaric acid. FAE(XynZ) had similar properties. Removal of the 40 C-terminal amino acids, residues 247 to 286, of FAE(XynZ) resulted in protein without activity. Feruloyl esterases are believed to aid in a release of lignin from hemicellulose and may be involved in lignin solubilization. The presence of feruloyl esterase in the C. thermocellum cellulosome together with its other hydrolytic activities demonstrates a powerful enzymatic potential of this organelle in plant cell wall decomposition.
TL;DR: The results indicate that the cereal grain expression system may provide an economic means for large scale production of feed enzymes in the future.
Abstract: The feasibility of producing plant cell wall polysaccharide-hydrolysing feed enzymes in the endosperm of barley grain was investigated. The coding region of a modified xylanase gene (xynA) from the rumen fungus, Neocallimastix patriciarum, linked with an endosperm-specific promoter from cereal storage protein genes was introduced into barley by Agrobacterium-mediated transformation. Twenty-four independently transformed barley lines with the xylanase gene were produced and analysed. The fungal xylanase was produced in the developing endosperm under the control of either the rice glutelin B-1 (GluB-1) or barley B1 hordein (Hor2-4) promoter. The rice GluB-1 promoter provided an apparently higher expression level of recombinant proteins in barley grain than the barley Hor2-4 promoter in both transient and stable expression experiments. In particular, the mean value for the fungal xylanase activity driven by the GluB-1 promoter in the mature grains of transgenic barley was more than twice that with the Hor2-4 promoter. Expression of the xylanase transgene under these endosperm-specific promoters was not observed in the leaf, stem and root tissues. Accumulation of the fungal xylanase in the developing grains of transgenic barley followed the pattern of storage protein deposition. The xylanase was stably maintained in the grain during grain maturation and desiccation and post-harvest storage. These results indicate that the cereal grain expression system may provide an economic means for large scale production of feed enzymes in the future.
TL;DR: The non-covalent immobilization of a commercial preparation of xylanase from A. niger was carried out on a reversibly soluble-insoluble enteric polymer Eudragit(TM) L-100, finding that the soluble enzyme derivative may be useful for treatment of paper pulp bleaching in paper industry.
TL;DR: Analysis of computerized molecular models built up for both psychrophilic and mesophilic xylanases indicates that the adaptation to cold consists of discrete changes in the tridimensional structure, which lead mainly to a less compact hydrophobic packing and to a destabilization of the macrodipoles of the helices.
Abstract: A xylanase belonging to family 10 is produced by Cryptococcus adeliae, an Antarctic yeast that exhibits optimal growth at low temperature. The mature glycosylated xylanase secreted by C. adeliae is composed of 338 amino acid residues and 26 ± 3 osidic residues, and shares 84% identity with its mesophilic counterpart from C. albidus. The xylanase from C. adeliae is less thermostable than its mesophilic homologue when the residual activities are compared, and this difference was confirmed by differential scanning calorimetry experiments. In the range 0°–20°C, the cold-adapted xylanase displays a lower activation energy and a higher catalytic efficiency. All these observations suggest a less compact, more flexible molecular structure. Analysis of computerized molecular models built up for both psychrophilic and mesophilic xylanases indicates that the adaptation to cold consists of discrete changes in the tridimensional structure: of 53 substitutions, 22 are presumably involved in the adaptation process. These changes lead mainly to a less compact hydrophobic packing, to the loss of one salt bridge, and to a destabilization of the macrodipoles of the helices.
TL;DR: Enzymic formulations with suitable polygalacturonase and FPCAse activities were favourable to extract oil from the pulp of tropical fruits and oleaginous seeds.
TL;DR: A Bacillus spp.
TL;DR: B. circulans AB 16 isolated from a garbage dump produced appreciable quantities (19.28 IU/ml) of extracellular thermophilic xylanase, but negligible quantities of cellulase, when grown on 0.3% xylan.
TL;DR: The aim of this work was to extract and to purify xylanase, produced by Bacillus pumilus from the crude fermentation broth, using aqueous two-phase systems (ATPS).
TL;DR: Characteristics of the polysaccharide-degrading activities showed diversity of ruminal Prevotella species and suggested that the regulation of the xylanases was highly specific to xylan.
Abstract: Four ruminal Prevotella type strains, P. ruminicola JCM8958T, P. bryantii B14T, P. albensis M384T, and P. brevis ATCC19188T, were characterized for polysaccharide-degrading activities with the reducing sugar release assay and zymogram analyses. Carboxymethylcellulase, xylanase, and polygalacturonate (PG)-degrading enzyme activities were determined in cultures grown on oat spelt xylan, xylose, arabinose, cellobiose, and glucose as sole growth substrates. P. ruminicola and P. albensis showed carboxymethylcellulase induction patterns. When xylan was supplied as a sole growth substrate, xylanase activities produced by P. bryantii and P. albensis were at least 18- and 11-fold higher, respectively, than during growth on other carbohydrates, suggesting that the regulation of the xylanases was highly specific to xylan. All strains constitutively produced PG-degrading enzymes. The corresponding activity of P. bryantii was more than 40-fold higher than in other strains. Zymogram analyses routinely detected the presence of high-molecular-weight (100–170 kDa) polysaccharide-degrading enzymes in ruminal Prevotella. Characteristics of the polysaccharide-degrading activities showed diversity of ruminal Prevotella species.
TL;DR: Aspergillus niger xylanase is the first microbial xylan enzyme efficiently secreted and correctly processed by P. pastoris, and follows normal Michaelis–Menten kinetics with K m and V max values similar for both enzymes.
TL;DR: In this paper, a mesophilic Streptomyces isolate was investigated which grew optimally on 1% xylan and 10% wheat bran at pH 7 and 37 °C.
Abstract: Enzyme production by a new mesophilic Streptomyces isolate was investigated which grew optimally on 1% (w/v) xylan and 10% (w/v) wheat bran at pH 7 and 37 °C. Xylan induced only CMCase (0.29 U/ml) besides xylanase (22–35 U/ml, 40–49 U/mg protein). Wheat bran induced xylanase (105 U/ml, 17.5 U/mg protein), CMCase (0.74 U/ml), β-xylosidase (0.009 U/ml), β-glucosidase (0.026 U/ml), α-L-arabinofuranosidase (0.049 U/ml), amylase (1.6 U/ml) and phytase (0.432 U/ml). The isolate was amenable to solid state cultivation and produced increased levels of xylanase (146 U/ml, 28 U/mg protein). The pH and temperature optima of the crude xylanase activity were 5.5 and 65 °C respectively. The pI was 6.0 as determined by PEG precipitation. The crude enzyme was applied in treatment of paper pulp and predigestion of poultry feed and was found to be effective in releasing sugars from both and soluble phosphorus from the latter.
TL;DR: Corn cob could be utilised as a carbon source for economical production of xylanase by C. absonum CFR-702 and glucose and β-methyl xyloside reduced the activity.
TL;DR: The thermostability of beta-xylanases produced by nine thermophilic Thermomyces lanuginosus strains in a coarse corn cob medium was assessed and the xylanase produced on corn cobs was the most thermostable and showed an increase of approximately 6% from 70 degrees C to 80 degrees C.
TL;DR: The gene encoding XynA (xynA) was isolated from the genomic library of Penicillium sp.
Abstract: Penicillum sp. 40, which can grow in an extremely acidic medium at pH 2.0 was screened from an acidic soil. This fungus produces xylanases when grown in a medium containing xylan as a sole carbon source. A major xylanase was purified from the culture supernatant of Penicillium sp. 40 and designated XynA. The molecular mass of XynA was estimated to be 25,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. XynA has an optimum pH at 2.0 and is stable in pH 2.0-5.0. Western blot analysis using anit-XynA antibody showed that XynA was induced by xylan and repressed by glucose. Also, its production was increased by an acidic medium. The gene encoding XynA (xynA) was isolated from the genomic library of Penicillium sp. 40. The structural part of xynA was found to be 721 bp. The nucleotide sequence of cDNA amplified by RT-PCR showed that the open reading frame of xynA was interrupted by a single intron which was 58 bp in size and encoded 221 amino acids. Direct N-terminal amino acid sequencing showed that the precursor of XynA had a signal peptide composed of 31 amino acids. The molecular mass caliculated from the deduced amino acid sequence of XynA is 20,713. This is lower than that estimated by gel electrophoresis, suggesting that XynA is a glycoprotein. The predicted amino acid sequence of XynA has strong similarity to other family xylanases from fungi.
TL;DR: The results suggest that the most suitable conditions for hydrolysis of hemicellulose by these enzymes would be at 50 °C and pH’6·0.
Abstract: Thermophilic fungi producing extremely high beta-xylanase and their associated hemicellulases have attracted considerable attention because of potential industrial applications. Thermomyces lanuginosus strain SSBP isolated from soil, produced beta-xylanase activity of 59 600 nkat ml-1 when cultivated on a medium containing corn cobs as substrate and yeast extract as nitrogen source. Lower beta-xylanase activities were produced after growth on other xylan substrates, sugars and soluble starch. Other hemicellulases were produced extracellularly at significantly lower levels than the beta-xylanase activity produced on corn cobs. No cellulase activity was observed. The optimal conditions for beta-xylanase production were 50 degrees C and pH 6.5, whereas 70 degrees C and between pH 5. 5 and 9.5 were optimal for beta-xylanase activity. The temperature optima for other hemicellulases were less than the xylanase with the exception of beta-mannosidase. The pH optima of the other hemicellulases were between 5.0 and 6.5. Xylanase was stable up to 70 degrees C and between pH 5.5 and 9.0 for 30 min whereas the other hemicellulase were less stable. These results suggest that the most suitable conditions for hydrolysis of hemicellulose by these enzymes would be at 50 degrees C and pH 6.0.
TL;DR: Cryptococcus adeliensis sp.
Abstract: Cryptococcus adeliensis sp. nov. (CBS 8351) is described based on phenotypic characteristics and molecular sequence analysis of the D1/D2 large subunit and internal transcribed spacer regions of the ribosomal DNA. Molecular comparisons include species closely related to Cryptococcus albidus and several species isolated from the Antarctic. C. adeliensis, which has a cold-adapted xylanase, was isolated from Terre Adelie, Antarctica. ATCC 34633, which has a mesophilic xylanase, was identified as Cryptococcus albidosimilis.
TL;DR: The results suggest that these chimaeric enzymes inherit both their thermostability from TfxA-cat and their increased reactivity from SlxB-cat, and demonstrates that random shuffling between a mesophilic enzyme and its thermophilic counterpart represents a facile approach for the improvement of the thermostable of a mesophile enzyme.
Abstract: The thermostability of Streptomyces lividans xylanase B (SlxB-cat) was significantly increased by the replacement of its N-terminal region with the corresponding region from Thermomonospora fusca xylanase A (TfxA-cat) without observing a decrease in enzyme activity. In spite of the significant similarity between the amino acid sequences of the two xylanases, their thermostabilities are quite different. To facilitate an understanding of the contribution of structure to the thermostability observed, chimaeric enzymes were constructed by random gene shuffling and the thermostable chimaeric enzymes were selected for further study. A comparative study of the chimaeric and parental enzymes indicated that the N-terminus of TfxA-cat contributed to the observed thermostability. However, too many substitutions decreased both the thermostability and the activity of the enzyme. The mutants with the most desirable characteristics, Stx15 and Stx18, exhibited significant thermostabilities at 70 degrees C with optimum temperatures which were 20 degrees C higher than that of SlxB-cat and equal to that of TfxA-cat. The ability of these two chimaeric enzymes to produce reducing sugar from xylan was enhanced in comparison with the parental enzymes. These results suggest that these chimaeric enzymes inherit both their thermostability from TfxA-cat and their increased reactivity from SlxB-cat. Our study also demonstrates that random shuffling between a mesophilic enzyme and its thermophilic counterpart represents a facile approach for the improvement of the thermostability of a mesophilic enzyme.
TL;DR: A quantitative comparison of the structure and sequence of the present thermophilic xylanase (PVX) with other available native structures of mesophiles and thermophiles is carried out, the first such detailed analysis to be carried out on family-11 xylanases.
TL;DR: A thermophilic Bacillus circulans AB 16, isolated from a garbage dump produced novel extracellular cellulase-poor, thermostable xylanase in basal medium containing rice straw, which would be more useful for pulp bleaching than purified xylanases.
TL;DR: It was concluded that the stability of most fibrolytic enzymes in rumen fluid is not likely to be a limiting factor in the use of enzymes as feed additives for ruminants; but if the enzymes are not stable, means can be found for their stabilization.