The performance of fungal xylan-degrading enzyme preparations in elemental chlorine-free bleaching for Eucalyptus pulp

Cellulase-free xylan-degrading enzyme preparations from Acrophialophora nainiana, Humicola grisea var. thermoidea and two Trichoderma harzianum strains were used as bleaching agents for Eucalyptus kraft pulp, prior to a chlorine dioxide and alkaline bleaching sequence. In comparison to the control sequence (performed without xylanase pretreatment), the sequence incorporating enzyme treatment was more effective. Removal of residual lignin was indicated by a reduction in kappa number. Overall, enzyme preparations from T. harzianum were marginally more effective in reducing pulp viscosity and chlorine chemical consumption and improving the brightness of the kraft pulp. However, the highest reduction in pulp viscosity was mediated by the xylanase preparation from A. nainiana. Xylanase pretreatment compares very favorably with that of chemical pulping.

Molecular cloning, characterization, and expression analysis of the xynF3 gene from Aspergillus oryzae

The gene encoding xylanase F3 (xynF3) was isolated from a genomic library of Aspergillus oryzae KBN616, used for making shoyu koji. The structural part of xynF3 was found to be 1468 bp. The nucleotide sequence of cDNA amplified by RT-PCR showed that the open reading frame of xynF3 was interrupted by ten short introns and encoded 323 amino acids. Direct N-terminal amino acid sequencing showed that the precursor of XynF3 had a signal peptide of 22 amino acids. The predicted amino acid sequence of XynF3 has strong similarity to other family 10 xylanases from fungi. The xynF3 gene was successfully overexpressed in A. oryzae and the XynF3 was purified. The molecular mass of XynF3 estimated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was 32,000. This was almost the same as the molecular mass of 32,437 calculated from the deduced amino acid sequence. The purified XynF3 showed an optimum activity at pH 5.0 and 58 degrees C. It had a Km of 6.5 mg/ml and a Vmax of 435 micromol x min(-1) x mg(-1) when birch wood xylan was used as a substrate. Expression of the xynF3 gene was analyzed using an Escherichia coli beta-glucuronidase gene as a reporter. The result indicated that xynF3 is expressed in the medium containing wheat bran as a carbon source.

Preparative chromatography of xylanase using expanded bed adsorption

Expanded bed adsorption was used to purify a marketable xylanase often used in the kraft pulp bleaching process. Experiments in packed and expanded beds were carried out mainly to study the adsorption of xylanase on to a cationic adsorbent (Streamline SP) in the presence of cells. In order to study the presence of cells, a Bacillus pumilus mass (5% wet mass) was mixed with the enzyme extract and submitted to an expanded bed adsorption system. One xylanase was purified to homogeneity in the packed bed. However, the 5% cell content hampered purification.

Multiple endoxylanases of Butyrivibrio sp

Butyrivibrio sp. Mz 5 with a high xylanolytic activity was isolated. Four major xylanases were detected in the cell-associated fraction using the zymogram technique. The xylanolytic activity was inducible with the oat spelts xylan; two endoxylanases (51 and 145 kDa) were formed constitutively. The bulk of the xylanolytic activity was cell-bound and growth-phase dependent; the maximum activity in the cell-associated fraction was achieved after 16 h of incubation. The highest xylanolytic activity was determined in a medium with 0.5% oat spelts xylan. Under optimum conditions (the highest xylanolytic activity produced), the two cell-bound xylanases (51 and 58 kDa) were isolated by anion exchange chromatography on CIM DEAE 8 tubes attached to a MPLC system, and gel filtration.

Technical note: methods for detecting liquid enzyme additives added to animal feeds

Methods for detecting and measuring the quantity of fibrolytic enzyme preparations added to feeds were investigated by enzymatic and tracer methods. Enzyme preparations added to corn silage, ryegrass silage, and a total mixed ration containing both silages and a concentrate could not be detected using their enzymatic activities. Glycosidase activities of solubles washed from the feed were more than an order of magnitude greater than glycosidases in the added enzymes. Carboxymethylcellulase and xylanase activity determinations, using reducing sugar release as the measurement, were subject to interference from reducing sugars present in the feed. A fluorescent tracer method, using fluorescein added at a rate of 1 g/L of feed enzymes, or 2 g/t of feed, was developed that enabled sensitive detection of liquid enzyme additions to feeds.

Purification and characterization of an extracellular beta-xylosidase from a newly isolated Fusarium verticillioides

An extracellular beta-xylosidase from a newly isolated Fusarium verticillioides (NRRL 26518) was purified to homogeneity from the culture supernatant by concentration by ultrafiltration using a 10,000 cut-off membrane, ammonium sulfate precipitation, DEAE Bio-Gel A agarose column chromatography and SP-Sephadex C-50 column chromatography. The purified beta-xylosidase (specific activity, 57 U/mg protein) had a molecular weight (mol. wt.) of 94,500 and an isoelectric point at pH 7.8. The optimum temperature and pH for action of the enzyme were 65 degrees C and 4.5, respectively. It hydrolyzes xylobiose and higher xylooligosaccharides but is inactive against xylan. The purified beta-xylosidase had a K(m) value of 0.85 mM (p-nitrophenol-beta-D-xyloside, pH 4.5, 50 degrees C) and was competitively inhibited by xylose with a K(i) value of 6 mM. It did not require any metal ion for activity and stability.

Chemical mechanism of beta-xylosidase from Trichoderma reesei QM 9414: pH-dependence of kinetic parameters

The variation of kinetic parameters of beta-xylosidase from Trichoderma reesei QM 9414 with pH was used to elucidate the chemical mechanism of the p-nitrophenyl beta-D-xylopyranoside hydrolysis. The pH-dependence of V and V/K(m) showed that a group on the enzyme with a pK value of 3.20 must be unprotonated and a group with a pK value of 5.20 must be protonated for activity and both are involved in catalysis. Solvent-perturbation studies indicated that these groups are neutral acid type. Temperature dependence of kinetic parameters suggested the stickiness of the substrate at lower temperatures than the optimum and the calculated ionization enthalpies pointed to carboxyl groups as responsible for both pKs. Chemical modification with triethyloxonium tetrafluoroborate and protection with the substrate studies demonstrated essential carboxyl groups on the enzyme. Profiles of pK(i) for D-gluconic acid lactone indicated that a group with a pK value of 3.45 must be protonated for binding and it has been assigned to the carboxyl group of D-gluconic acid formed by lactone ring breakdown in solution.

Identification of a broad-specificity xylosidase/arabinosidase important for xylooligosaccharide fermentation by the ruminal anaerobe Selenomonas ruminantium GA192

Strains of Selenomonas ruminantium vary considerably in their capacity to ferment xylooligosaccharides. This ability ranges from strain GA192, which completely utilized xylose through xylotetraose and was able to ferment considerable quantities of larger oligosaccharides, to strain HD4, which used only the simple sugars present in the hydrolysate. The ability of S. ruminantium GA192 to utilize xylooligosaccharides was correlated with the presence of xylosidase and arabinosidase activities. The production of these activities appears to be regulated in response to carbon source used for growth. Both arabinosidase and xylosidase were induced by growth on xylose or xylooligosaccharides, but no activity was detected in glucose-or arabinose-grown cultures. A genetic locus from S. ruminantium GA192 was cloned into Escherichia coli JM83 that produced both xylosidase and arabinosidase activities. Analyses of crude extracts from the E. coli clone and S. ruminantium GA192 by using native polyacrylamide gel electrophoresis and methylumbelliferyl substrates indicated that a single protein was responsible for both activities. The enzyme expressed in E. coli was capable of degrading xylooligosaccharides derived from xylan. DNA sequencing of the locus demonstrated the presence of an open reading frame that encodes for a protein of 61,174 molecular weight.

Xylanase from a newly isolated Fusarium verticillioides capable of utilizing corn fiber xylan

A fungus, Fusarium verticillioides (NRRL 26518), was isolated by screening soil samples using corn fiber xylan as carbon source. The extracellular xylanase from this fungal strain was purified to apparent homogeneity from the culture supernatant by ultrafiltration using a 30,000 cut-off membrane, octyl-Sepharose chromatography and Bio gel A-0.5 m gel filtration. The purified xylanase (specific activity 492 U/mg protein; MW 24,000; pI 8.6) displayed an optimum temperature at 50 degrees C and optimum pH at 5.5, a pH stability range from 4.0 to 9.5 and thermal stability up to 50 degrees C. It hydrolyzed a variety of xylan substrates mainly to xylobiose and higher short-chain xylooligosaccharides. No xylose was formed. The enzyme did not require metal ions for activity and stability.

Free polymeric bioligands in aqueous two-phase affinity extractions of microbial xylanases and pullulanase

Two reversibly soluble-insoluble polymers (viz. Eudragit S-100 and alginate) were used as free macroaffinity bioligands in polyethylene glycol (PEG)/salt two-phase systems for separation of enzymes. Incorporation of Eudragit S-100 and alginate in the PEG phase led to considerable selectivity in separation of microbial xylanases and pullulanase, respectively. Xylanase from Aspergillus niger was recovered 93% with 56-fold purification, whereas the enzyme from Trichoderma reesei and Bacillus amyloliquefaciens was obtained with 93% activity recovery (31-fold purification) and 90% activity recovery (32-fold purification), respectively. From Bacillus acidopullulyticus pullulanase, 85% enzyme activity recovery with 44-fold purification was obtained. The approach described here shows the potential of developing into a general approach for use of reversibly soluble-insoluble macroaffinity ligand in two-phase affinity extraction.

Enzymatic synthesis and hydrolysis of xylogluco-oligosaccharides using the first archaeal alpha-xylosidase from Sulfolobus solfataricus

The first, recently identified, archaeal alpha-xylosidase from Sulfolobus solfataricus (XylS) shows high specificity for hydrolysis of isoprimeverose [alpha-D-xylopyranosyl-(1,6)-D-glucopyranose, (X)], the p-nitrophenyl-beta derivative of isoprimeverose, and xyloglucan oligosaccharides and has transxylosidic activity, forming, in a retaining mode, interesting alpha-xylosides. This article describes the synthesis of isoprimeverose, the disaccharidic repeating unit of xyloglucan, of the p-nitrophenyl-beta derivative of isoprimeverose, and of a trisaccharide based on isoprimeverose that is one of the trisaccharidic building blocks of xyloglucan. A substrate structure-activity relationship is recognized for both the hydrolysis and the synthesis reactions of XylS, it being a biocatalyst (i) active hydrolytically only on X-ending substrates liberating a xylose molecule and (ii) capable of transferring xylose only on the nonreducing end glucose of p-nitrophenyl-(PNP)-beta-D-cellobioside. The compounds synthesized by this enzyme are a starting point for enzymological studies of other new enzymes (i.e., xyloglucanases) for which suitable substrates are difficult to synthesize. This study also allows us to define the chemical characteristics of the xylose-transferring activity of this new archaeal enzyme, contributing to building up a library of different glycosidases with high specific selectivity for oligosaccharide synthesis.

Characterisation and effects of a xylanase enzyme preparation extracted from Thermomyces lanuginosus cultures

This paper describes the production of an enzyme preparation from the fungus Thermomyces lanuginosus. Thermal resistance, pH stability and lignocellulolytic activity of the enzyme preparation high in xylanase were studied on a variety of grains and forages. The enzyme preparation preserved more than 70% of its original xylanase activity for 4 and 1 h at 60 and 70 degrees C, respectively. The xylanase activity remained over 80% when the preparation was incubated for 30 min at pH 4.5. In vitro digestibility studies indicated that the enzyme digested 7.5, 8.5 and 8.0% of the dry matter (DM) of barley meal, wheat bran and oat meal samples, respectively. When applying 60-min incubation, 7.5, 7.3 and 8.4% of DM of the oat straw, alfalfa hay and triticale straw was digested, respectively. When the time of digestion was increased to 360 min, the sunflower hull showed 15.8% DM digestibility.

Xylanolytic activities of Streptomyces sp. 1--taxonomy, production, partial purification and utilization of agricultural wastes

Twenty-four different strains of Streptomyces spp. isolated from Egyptian soil were tested for their ability to produce extracellular xylanases. Of all these isolates a Streptomyces sp. that had the highest potential for xylanolytic activity was chosen. From various morphological, physiological and antagonistic properties, this isolate was found to belong to Streptomyces lividans. Factors affecting xylanase production by this organism in a basal salt medium containing purified sugar-cane bagasse xylan as a sole carbon source were examined. A noticeable increase in enzyme activity was observed in the presence of peptone or soyabean meal. However, a slight increase was noticed with ammonium sulphate. Optimum production for xylanase was achieved after five days incubation on a rotary shaker (180 rpm) at 30 degrees C. The initial pH values were around neutrality. In addition, this organism has high potential for xylanolytic activity when grown on lignocellulosic wastes including corn cobs, wheat bran, peanut shells, sawdust, wheat straw and sugar-cane-bagasse. Partial purification of the enzyme in the culture supernatant was achieved by salting out at 50-80% ammonium sulphate saturation with a purification of 9.03-fold and 57.9% recovery.

Purification and properties of the cell-associated beta-xylosidase from Aureobasidium

beta-Xylosidase was extracted from Aureobasidium sp. ATCC 20524 and purified to homogeneity. The molecular mass was estimated at 411 kDa. The enzyme contained 15.3% (w/w) carbohydrate. The optimum pH and temperature were pH 3.5 and 80 degrees C, respectively. The enzyme was stable at pH 3.5-9 after 3 h and at 80 degrees C after 15 min. The Michaelis constant (K(m)) and maximum velocity (V(max)) toward p-nitrophenyl-beta-D-xyloside were 2.0 mmol l(-1) and 0.94 mmol min(-1) mg(-1) protein, respectively. The enzyme was inhibited strongly by mercury, lead, and copper ions.

Rapid process for purification of an extracellular beta-xylosidase by aqueous two-phase extraction

A rapid process for purification of an extracellular beta-xylosidase with high purity was developed. The manipulation involved the precipitation of protein from culture medium and the extraction of enzyme from the resuspended crude protein solution by an aqueous-two phase separation. A linear random copolymer, PE62, with 20% ethylene oxide and 80% propylene oxide was employed in both stages of the purification. The enzyme was precipitated effectively by using 10% (w/v) PE62 and 5% (w/v) Na2HPO4. The aqueous two-phase extraction was performed with PE62 (10%)-NaH2PO4 (15%) as phase-forming reagent. SDS-PAGE analysis revealed that the purified enzyme is near homogeneity. The yield is about 100% with a purification factor of 8.8-fold. The whole process can be completed within an hour without any column chromatography.

Synthesis, processing and export of cytoplasmic endo-beta-1,4-xylanase from barley aleurone during germination

We have identified the major endo-beta-1,4-xylanase (XYN-1) in the aleurone of germinating barley grain, and show that it is expressed as a precursor of Mr 61 500 with both N- and C-terminal propeptides. XYN-1 is synthesized as an inactive enzyme in the cytoplasm, and only becomes active at a late stage of germination when the aleurone ceases to secrete hydrolases. A series of processing steps, mediated in part by aleurone cysteine endoproteases, yields a mature active enzyme of Mr 34 000. Processing and extracellular release of the mature enzyme coincide with the programmed cell death (PCD)-regulated disintegration of aleurone cells. We discuss the significance of delayed aleurone cell-wall degradation by endoxylanases in relation to the secretory capacity of the aleurone, and propose a novel role for aleurone PCD in facilitating the export of hydrolases.

Involvement of a lysine residue in the active site of a thermostable xylanase from Thermomonospora sp

A highly thermostable xylanase (Xyl I) produced by Thermomonospora sp. was purified to homogeneity and was classified as a family 10 xylanase based on its molecular weight (38,000 Da) and isoelectric point (4.1). K2d analysis showed that the secondary structure of Xyl I was made up of 38% alpha-helix and 10% beta-sheet. The optimal temperature for the activity of Xyl I was 80 degrees C. Xyl I was highly thermostable with half-lives of 86, 30, and 15 min at 80, 90, and 100 degrees C respectively. Xyl I was stable in an expansive pH range of 5 to 10 with more than 75% residual activity. Our present investigation using o-phthalaldehyde (OPTA) as the chemical initiator for fluorescent chemoaffinity labeling and trinitrobenzenesulphonic acid (TNBS) as chemical modifier have revealed the presence of a single lysine residue in the active site of Xyl I. The high pK value for the basic limb of the pH profile reflects the ionization of a lysine residue. The higher K(m) values and similar k(cat) values of the TNBS modified enzyme in comparison to native enzyme and the substrate protection against OPTA and TNBS, suggested the presence of the lysine residue in the substrate-binding site.

Purification and properties of a thermostable extracellular beta-D-xylosidase produced by a thermotolerant Aspergillus phoenicis

A beta-D-xylosidase was purified from cultures of a thermotolerant strain of Aspergillus phoenicis grown on xylan at 45 degrees C. The enzyme was purified to homogeneity by chromatography on DEAE-cellulose and Sephadex G-100. The purified enzyme was a monomer of molecular mass 132 kDa by gel filtration and SDS-PAGE. Treatment with endoglycosidase H resulted in a protein with a molecular mass of 104 kDa. The enzyme was a glycoprotein with 43.5% carbohydrate content and exhibited a pl of 3.7. Optima of temperature and pH were 75 degrees C and 4.0-4.5, respectively. The activity was stable at 60 degrees C and had a Km of 2.36 mM for p-nitrophenyl-beta-D-xylopiranoside. The enzyme did not exhibit xylanase, cellulase, galactosidase or arabinosidase activities. The purified enzyme was active against natural substrates, such as xylobiose and xylotriose.

Purification and characterization of an beta-D-xylosidase from Candida utilis IFO 0639

An intracellular beta-D-xylosidase from Candida utilis IFO 0639 was purified to homogeneity through four chromatographic steps. The molecular mass of the enzyme was estimated to be 92 kDa by SDS-PAGE. The enzyme had an isoelectric point at 5.6, and was most active at pH 6.0 and at around 40 degrees C. Ethanol at an optimal concentration (10%, v/v) stimulated the initial enzyme activity by 57%. D-Xylose, the product of the beta-D-xylosidase, has no effect on the enzyme activity at 300 mM. The beta-D-xylosidase was highly specific to the beta-D-xylopyranoside configuration. The enzyme hydrolyzed beta-1,4-linked xylo-oligosaccharides with chain lengths from 2 to 5 by releasing xylose from the non-reducing end. It showed no activity against xylan. The enzyme efficiently released monoterpenols from an aroma precursor extracted from Muscat grape juice. The fermentation of Muscat juice coupled with the enzyme addition produced a small increase in the concentration of monoterpenols.

Cloning, expression, and characterization of a family 52 beta-xylosidase gene (xysB) of a multiple-xylanase-producing bacterium, Aeromonas caviae ME-1

A lambda phage genomic library of Aeromonas caviae ME-1, a multiple-xylanase-producing bacterium, was screened for xylan degradation activities. We isolated one clone, B65, which had weak xylanase activity, by the DNS method, but gave no visible bands on zymogram assay using SDS-xylan-PAGE. Based on TLC analyses of enzymatic products and some glycosidase assays using p-nitrophenyl substrates, we established that pB65 encodes a beta-xylosidase gene. In the nucleotide sequence analysis, we found a 2190-bp open reading frame (ORF) named xysB. XysB protein is similar to some beta-xylosidases, which are categorized in the glycosyl hydrolase family 52. Another ORF (xyg), that showed similarity to the family 67 alpha-glucuronidase, was also found downstream of the xysB gene. The xysB ORF and its promoter region were cloned into the pT7-Blue vector and the transformant cells had beta-xylosidase activity. The relative molecular mass were estimated to be 75 kDa by SDS-PAGE and 159 kDa by gel filtration. These data showed that XysB has a dimeric structure of 80,697 Da subunits. This enzyme showed optimal activity at 50 degrees C and pH 6.0. It was stable below 40 degrees C and pH 5-8. The Km and Vmax were calculated to be 0.34 mM and 33 nmol x min(-1) x microg(-1), respectively. This enzyme also showed transglycosylation activity against X3 and produced X4 and X5.

Functional characterization of a novel xylanase from a corn strain of Erwinia chrysanthemi

A beta-1,4-xylan hydrolase (xylanase A) produced by Erwinia chrysanthemi D1 isolated from corn was analyzed with respect to its secondary structure and enzymatic function. The pH and temperature optima for the enzyme were found to be pH 6.0 and 35 degrees C, with a secondary structure under those conditions that consists of approximately 10 to 15% alpha-helices. The enzyme was still active at temperatures higher than 40 degrees C and at pHs of up to 9.0. The loss of enzymatic activity at temperatures above 45 degrees C was accompanied by significant loss of secondary structure. The enzyme was most active on xylan substrates with low ratios of xylose to 4-O-methyl-D-glucuronic acid and appears to require two 4-O-methyl-D-glucuronic acid residues for substrate recognition and/or cleavage of a beta-1,4-xylosidic bond. The enzyme hydrolyzed sweetgum xylan, generating products with a 4-O-methyl-glucuronic acid-substituted xylose residue one position from the nonreducing terminus of the oligoxyloside product. No internal cleavages of the xylan backbone between substituted xylose residues were observed, giving the enzyme a unique mode of action in the hydrolysis compared to all other xylanases that have been described. Given the size of the oligoxyloside products generated by the enzyme during depolymerization of xylan substrates, the function of the enzyme may be to render substrate available for other depolymerizing enzymes instead of producing oligoxylosides for cellular metabolism and may serve to produce elicitors during the initiation of the infectious process.

Cloning and heterologous expression of xylanase from Pichia stipitis in Escherichia coli

AIMS

The main goal of this study was to characterize the xylanase (xynA) gene from Pichia stipitis NRRL Y-11543.

METHODS AND RESULTS

The xylanase gene was cloned into pUC19 in Escherichia coli DH5alphaF' and selected by growth on RBB-xylan. All functional clones contained a recombinant plasmid with an insert of 2.4 kbp, as determined by restriction mapping. The nucleotide sequence of the P. stipitis xylanase gene consisted of 1146 bp and encoded a protein of 381 amino acids with a molecular weight of 43 649 Da. The sequence contained a putative 20-amino acid N-terminal signal sequence and four N-linked glycosylation sites. The Km values for non-glycosylated and glycosylated xylanases were 1.4 mg ml-1 and 4.2 mg ml-1, respectively, and Vmax values were 0.8 and 0.082 micromol min-1 mg-1 protein, respectively.

CONCLUSION

Xylanase, a rarely found enzyme in yeast species, has been characterized in detail.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study can be used to develop better xylanase-utilizing yeast strains.

Molecular cloning, overexpression, and purification of a major xylanase from Aspergillus oryzae

The gene encoding xylanase G2 (xynG2) was isolated from a genomic library of Aspergillus oryzae KBN616, used for making shoyu koji. The structural part of xynG2 was found to be 767 bp. The nucleotide sequence of cDNA amplified by RT-PCR showed that the open reading frame of xynG2 was interrupted by a single intron which was 71 bp in size and encoded 232 amino acids. Direct N-terminal amino acid sequencing showed that the precursor of XynG2 had a signal peptide of 44 amino acids. The predicted amino acid sequence of XynG2 has strong similarity to other family 11 xylanases from fungi. The xynG2 gene was successfully overexpressed in A. oryzae and the overpexpressed XynG2 was purified. The molecular weight of XynG2 estimated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was 21,000. This was almost the same as the molecular weight of 20,047 calculated from the deduced amino acid sequence. The purified XynG2 showed an optimum activity at pH 6.0 and 58 degrees C. It had a Km of 5.1 mg/ml and a Vmax of 123 micromol/min/mg when birch wood xylan was used as a substrate.