Low-molecular-weight xylanase from Trichoderma viride

pCold-assisted expression of a thermostable xylanase from Bacillus amyloliquefaciens: cloning, expression and characterization

The biotechnological application of bacterial xylanases requires a high thermostability, a catalytically active state for a broad pH range. The Bacillus amyloliquefaciens (MTCC 1270) xynA gene was amplified and cloned into the pCold vector and was expressed in Escherichia coli to evaluate the expressed proteins' thermostability. The pCold, compared to other similar vectors, has unique properties-including pH and temperature tolerance due to the presence of the cspA promoter. The recombinant xynA-pCold (rxynApC) showed the expression of xynA gene with a molecular weight of ~ 27 kDa, confirmed on SDS-PAGE. The rxynApC exhibits optimal activity at 70 °C and pH 8.0. The residual activity of the recombinant enzyme was 90% at pH 8.0. The thermal decomposition temperature (T d) value for the rxynApC enzyme was 93.33 °C obtained from the thermogravimetric analysis, indicating the potent stability of the cloned enzyme. The specific activity of native xylanase and rxynApC under optimal conditions was 32.35 and 105.5 U/mg, respectively. The structural model of the xynA gene was predicted using the in silico tool along with the active site (containing four important Tyr-166, Gly-7, Try-69 and Arg-112 amino acids). The predicted biophysical parameters of the in silico model were similar to the experimental results. The unique feature of the cspA promoter is that it gave a high expression of rxynApC enzyme having alkali and thermostable properties with high yield in surrogate host E. coli. Thus, the recombinant xynA gene can potentially be applied to different industrial needs by looking at its thermostability and enhanced enzyme activity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03315-y.

Enhanced Production, Cloning, and Expression of a Xylanase Gene from Endophytic Fungal Strain Trichoderma harzianum kj831197.1: Unveiling the In Vitro Anti-Fungal Activity against Phytopathogenic Fungi

Trichoderma sp. is extensively applied as a beneficial fungus for the management of plant diseases, plant growth promotion, induced resistance, and plays an important role in global sustainable agriculture. This study aimed to enhance the production of microbial xylanase in high titer from the endophytic fungus Trichoderma harzianum kj831197.1, and the cloning of xylanase genes in E. coli DH5α using a pUC19 vector. A combination of glucose, 0.1 mM, Tween 80 with lactose, and 2 mM galactose combined with malt extract boostedthe enzyme production. Xylanase production was maximized at a pH of 5.0, temp. of 30 °C, and agitation of 150 rpm in the presence of malt extract and bagasse as the best nitrogen source and waste, respectively, using submerged fermentation. The molecular weight of highly purified xylanase was 32 KDa, identified using SDS-PAGE. The xylanase gene of T. harzianum kj831197.1 was screened in fungal DNA using definite primers specified in the gene bank database. The identified region was excised using restriction enzymes HindIII and EcoRI and cloned into a pUC19 plasmid vector. Optimization of fermentation conditions improved xylanase production about 23.9-fold.The antifungal efficacy of xylanase toward different phytopathogenic fungi was determined. The highest inhibition was against Corynespora cassiicola, Alternaria sp., Fusarium oxysporum, and Botrytis fabae. This study offered an economical, simple, and efficient method using Trichoderma harzianum kj831197.1 for the production of the xylanase enzyme via the submerged fermentation method.

The ACEII recombinant Trichoderma reesei QM9414 strains with enhanced xylanase production and its applications in production of xylitol from tree barks

Background

ACEII transcription factor plays a significant role in regulating the expression of cellulase and hemicellulase encoding genes. Apart from ACEII, transcription factors such as XYR1, CRE1, HAP2/3/5 complex and ACEI function in a coordinated pattern for regulating the gene expression of cellulases and hemicellulases. Studies have demonstrated that ACEII gene deletion results in decreased total cellulase and xylanase activities with reduced transcript levels of lignocellulolytic enzymes.

Results

In this study, we have successfully transformed the ACEII transcription factor encoding gene in Trichoderma reesei to significantly improve its degrading abilities. Transformation experiments on parental strain T. reesei QM9414 has resulted in five genetically engineered strains T/Ace2-2, T/Ace2-5, T/Ace2-8, T/Ace5-4 and T/Ace10-1. Among which, T/Ace2-2 has exhibited significant increase in enzyme activity by twofolds, when compared to parental strain. The T/Ace2-2 was cultured on growth substrates containing 2% bark supplemented with (a) sugar free + MA medium (b) glucose + MA medium and (c) xylose + MA medium. The bark degradation efficiency of genetically modified T/Ace2-2 strain was assessed by analyzing the xylitol production yield using HPAEC. By 6th day, about 10.52 g/l of xylitol was produced through enzymatic conversion of bark (2% bark + MA + xylose) by the T/Ace2-2 strain and by 7th day the conversion rate was found to be 0.21 g/g. Obtained results confirmed that bark growth medium supplemented with d-xylose has profoundly increased the conversion rate of bark by T/Ace2-2 strain when compared to sugar free and glucose supplemented growth media. Results obtained from scanning electron microscopy has endorsed our current results. Bark samples inoculated with T/Ace2-2 strain has showed large number of degraded cells with clearly visible cavities and fractures, by exposing the microfibrillar interwoven complex.

Conclusion

We propose a cost effective and ecofriendly method for the degradation of lignocellulosic biomass such as bark to produce xylitol by using genetically modified T. reesei. Efficient conversion rate and production yield obtained in our current study provides a great scope for the xylitol industries, as our method bypasses the pretreatment of bark achieving clean and low-cost xylitol production.

A new acidophilic endo-β-1,4-xylanase from Penicillium oxalicum: cloning, purification, and insights into the influence of metal ions on xylanase activity

A new acidophilic xylanase (XYN11A) from Penicillium oxalicum GZ-2 has been purified, identified and characterized. Synchronized fluorescence spectroscopy was used for the first time to evaluate the influence of metal ions on xylanase activity. The purified enzyme was identified by MALDI TOF/TOF mass spectrometry, and its gene (xyn11A) was identified as an open reading frame of 706 bp with a 68 bp intron. This gene encodes a mature protein of 196 residues with a predicted molecular weight of 21.3 kDa that has the 100 % identity with the putative xylanase from the P. oxalicum 114-2. The enzyme shows a structure comprising a catalytic module family 10 (GH10) and no carbohydrate-binding module family. The specific activities were 150.2, 60.2, and 72.6 U/mg for beechwood xylan, birchwood xylan, and oat spelt xylan, respectively. XYN11A exhibited optimal activity at pH 4.0 and remarkable pH stability under extremely acidic condition (pH 3). The specific activity, K  m and V  max values were 150.2 U/mg, 30.7 mg/mL, and 403.9 μmol/min/mg for beechwood xylan, respectively. XYN11A is a endo-β-1,4-xylanase since it release xylobiose and xylotriose as the main products by hydrolyzing xylans. The activity of XYN11A was enhanced 155 % by 1 mM Fe2+ ions, but was inhibited strongly by Fe3+. The reason of enhancing the xylanase activity of XYN11A with 1 mM Fe2+ treatment may be responsible for the change of microenvironment of tryptophan residues studied by synchronous fluorescence spectrophotometry. Inhibition of the xylanase activity by Fe3+ was first time demonstrated to associate tryptophan fluorescence quenching.

Production of cellulolytic and xylanolytic enzymes by an Arthrographis species

A fungal isolate, Arthrographis sp. strain F4, when grown in shake-flask culture, produced cellulolytic and xylanolytic enzymes optimally at 30°C with an initial pH of 5.0 to 6.0. Coarsely-ground filter paper was the most suitable carbon substrate for production of the enzymes. Inorganic nitrogen sources gave higher activities of the enzymes than organic nitrogen sources: NH4NO3 and yeast extract was the most effective combination. Significant stimulation (P<0.05) of enzyme production was achieved with 0.1% (v/v) Tween 80.

Properties and Application of a Partially Purified Thermoalkali Stable Xylanase from Cellulosimicrobium sp. MTCC 10645 in Kraft Pulp Bleaching

The most promising application of xylanases (E.C. 3.2.1.8) is in the prebleaching of kraft pulp. The present paper reports bleaching effects of a thermoalkali stable xylanase from Cellulosimicrobium sp. MTCC 10645. The bacterium produced thermo-alkali stable xylanase in a basal medium supplemented with wheat bran (1% w/v), which was optimally active at pH 7.0 and 50°C. The xylanase was stable at temperature 50°C for 1 h and retained up to 86% of the activity. The xylanase was stable in a broad pH range of 6.0–11.0 for 1 h at 50°C. Metal ions Ca⁺², Hg⁺², and Pb⁺² were inhibitory for xylanase retaining 72.3%, 35.07% and 36.7% relative activity at 10 mM concentration, whereas Fe⁺², Cu⁺², Mn⁺², Na⁺², Co⁺², and Zn⁺² were inducers at concentrations of 5 mM and 10 mM. The enzyme exhibited greater binding affinity exclusively for xylans but not for avicel, CMC, cellobiose, starch, or p-nitrophenyl xylopyranoside. Parachloromercuric benzoate and iodoacetamide were found stimulatory, while potassium permanganate, cysteine, and cystine markedly reduced the activity. The xylanase dose of 2.0 U/g dry weight pulp of 10% consistency gave optimum bleach boosting of kraft pulp at pH 8.0 and temperature 50°C for 5 h reaction time.

Isolation, purification, and characterization of xylanase produced by a new species of bacillus in solid state fermentation

A thermoalkalophilic new species of Bacillus, similar to Bacillus arseniciselenatis DSM 15340, produced extracellular xylanase under solid state fermentation when wheat bran is used as carbon source. The extracellular xylanase was isolated by ammonium sulfate (80%) precipitation and purified using ion exchange chromatography. The molecular weight of xylanase was ~29.8 kDa. The optimum temperature and pH for the enzyme activity were 50°C and pH 8.0. The enzyme was active on birchwood xylan and little active on p-nitrophenyl xylopyranoside but not on Avicel, CMC, cellobiose, and starch, showing its absolute substrate specificity. For birchwood xylan, the enzyme gave a Km 5.26 mg/mL and Vmax 277.7 μmol/min/mg, respectively. In addition, the xylanase was also capable of producing high-quality xylo-oligosaccharides, which indicated its application potential not only in pulp biobleaching processes but also in the nutraceutical industry.

GH11 xylanases: Structure/function/properties relationships and applications

For technical, environmental and economical reasons, industrial demands for process-fitted enzymes have evolved drastically in the last decade. Therefore, continuous efforts are made in order to get insights into enzyme structure/function relationships to create improved biocatalysts. Xylanases are hemicellulolytic enzymes, which are responsible for the degradation of the heteroxylans constituting the lignocellulosic plant cell wall. Due to their variety, xylanases have been classified in glycoside hydrolase families GH5, GH8, GH10, GH11, GH30 and GH43 in the CAZy database. In this review, we focus on GH11 family, which is one of the best characterized GH families with bacterial and fungal members considered as true xylanases compared to the other families because of their high substrate specificity. Based on an exhaustive analysis of the sequences and 3D structures available so far, in relation with biochemical properties, we assess biochemical aspects of GH11 xylanases: structure, catalytic machinery, focus on their "thumb" loop of major importance in catalytic efficiency and substrate selectivity, inhibition, stability to pH and temperature. GH11 xylanases have for a long time been used as biotechnological tools in various industrial applications and represent in addition promising candidates for future other uses.

Purification and properties of a psychrotrophic Trichoderma sp. xylanase and its gene sequence

A psychrotrophic fungus identified as Trichoderma sp. SC9 produced 36.7 U/ml of xylanase when grown on a medium containing corncob xylan at 20 °C for 6 days. The xylanase was purified 37-fold with a recovery yield of 8.2%. The purified xylanase appeared as a single protein band on SDS-PAGE with a molecular mass of approximately 20.5 kDa. The enzyme had an optimal pH of 6.0, and was stable over pH 3.5-9.0. The optimal temperature of the xylanase was 42.5 °C and it was stable up to 35 °C at pH 6.0 for 30 min. The xylanase was thermolabile with a half-life of 23.9 min at 45 °C. The apparent K(m) values of the xylanase for birchwood, beechwood, and oat-spelt xylans were found to be 3, 2.1, and 16 mg/ml respectively. The xylanase hydrolyzed beechwood xylan and birchwood xylan to yield mainly xylobiose as end products. The enzyme-hydrolysed xylotriose, xylotetraose, and xylopentose to produce xylobiose, but it hardly hydrolysed xylobiose. A xylanase gene (xynA) with an open reading frame of 669 nucleotide base pairs (bp), encoding 222 amino acids, from the strain was cloned and sequenced. The deduced amino acid sequence of XynA showed 85% homology with Xyn2 from a mesophilic strain of Trichoderma viride.

A role of xylanase, alpha-L-arabinofuranosidase, and xylosidase in xylan degradation

Renewable natural resources such as xylans are abundant in many agricultural wastes. Penicillium sp. AHT-1 is a strong producer of xylanolytic enzymes. The sequential activities of its xylanase, alpha-L-arabinofuranosidase, and beta-xylosidase on model hemicellulose oat-spelt xylan was investigated. Optimum production of the enzymes was found in culture containing oat-spelt xylan at 30 degrees C and initial pH 7.0 after 6 days. The enzymes were partially purified by ammonium sulphate fractionation and anion-exchange chromatography on DEAE-Toyopearl 650 S. The apparent molecular mass was 21 kDa, and the protein displayed an "endo" mode of action. The xylanase exhibited glycotansferase activity. It synthesized higher oligosaccharides from the initial substrates, and xylotriose was the shortest unit of substrate transglycosylated. Xylanolytic enzymes (enzyme mixture) produced by this Penicillium sp. interacted cooperatively and sequentially in the hydrolysis of oat-spelt xylan in the following order: alpha-L-arabinofuranosidase --> xylanase --> beta-xylosidase. All three enzymes exhibited optimal activity under the same conditions (temperature, pH, cultivation), indicating that they alone are sufficient to completely depolymerize the test xylan. Results indicate that the xylanolytic enzyme mixture of Penicillium sp. AHT-1 could be useful for bioconversion of xylan-rich plant wastes to value-added products.

Biotechnology of microbial xylanases: enzymology, molecular biology, and application

Xylanases are hydrolases depolymerizing the plant cell wall component xylan, the second most abundant polysaccharide. The molecular structure and hydrolytic pattern of xylanases have been reported extensively and the mechanism of hydrolysis has also been proposed. There are several models for the gene regulation of which this article could add to the wealth of knowledge. Future work on the application of these enzymes in the paper and pulp, food industry, in environmental science, that is, bio-fueling, effluent treatment, and agro-waste treatment, etc. require a complete understanding of the functional and genetic significance of the xylanases. However, the thrust area has been identified as the paper and pulp industry. The major problem in the field of paper bleaching is the removal of lignin and its derivatives, which are linked to cellulose and xylan. Xylanases are more suitable in the paper and pulp industry than lignin-degrading systems.

A transcriptional activator, AoXlnR, controls the expression of genes encoding xylanolytic enzymes in Aspergillus oryzae

By deletion across the promoter region of the xynF1 gene encoding the major Aspergillus oryzae xylanase, a 53-bp DNA fragment containing the XlnR binding sequence GGCTAAA as well as two similar sequences was shown to confer xylan inducibility on the gene. Complementary and genomic DNAs encoding the Aspergillus niger xlnR homologous gene, abbreviated AoxlnR, were cloned from A. oryzae and sequenced. AoXlnR comprised 971 amino acids with a zinc binuclear cluster domain at the N-terminal region and revealed 77.5% identity to the A. niger XlnR. Recombinant AoXlnR protein encompassing the zinc cluster region of the N-terminal part bound to both the consensus binding sequence and its cognate sequence, GGCTGA, with an approximately 10 times lower affinity. GGCTA/GA is more appropriate as the XlnR consensus binding sequence. Both sequences functioned independently in vivo in XlnR-mediating induction of the xynF1 gene. This was further confirmed by using an AoxlnR disruptant. Neither the xynF1 nor the xylA gene was expressed in the disruptant, suggesting that the xylan-inducible genes in A. oryzae may also be controlled in the same manner as described for A. niger.

Regulation of the amylolytic and (hemi-)cellulolytic genes in aspergilli

Filamentous fungi produce high levels of polysaccharide-degrading enzymes and are frequently used for the production of industrial enzymes. Because of the high secretory capacity for enzymes, filamentous fungi are effective hosts for the production of foreign proteins. Genetic studies with Aspergillus nidulans have shown pathway-specific regulatory systems that control a set of genes that must be expressed to catabolize particular substrates. Besides the pathway-specific regulation, wide domain regulatory systems exist that affect a great many individual genes in different pathways. A molecular analysis of various regulated systems has confirmed the formal models derived from purely genetic data. In general, many genes are subject to more than one regulatory system. In this article, we describe two transcriptional activators, AmyR and XlnR, and an enhancer, Hap complex, in view of their regulatory roles in the expression of the amylolytic and (hemi-)cellulolytic genes mainly in aspergilli. The amyR gene has been isolated as a transcriptional activator involved in the expression of amylolytic genes from A. oryzae, A. niger, and A. nidulans, and the xlnR gene, which has been isolated from A. niger and A. oryzae, activates the expression of xylanolytic genes as well as some cellulolytic genes in aspergilli. Both AmyR and XlnR have a typical zinc binuclear cluster DNA-binding domain at their N-terminal regions. Hap complex, a CCAAT-binding complex, enhances the overall promoter activity and increases the expression levels of many fungal genes, including the Taka-amylase A gene. Hap complex comprises three subunits, HapB, HapC, and HapE, in A. nidulans and A. oryzae as well as higher eukaryotes, whereas HAP complex in Saccharomyces cerevisiae and Kluyveromyces lactis has the additional subunit, Hap4p, which is responsible for the transcriptional activation. Hap complex is suggested to enhance transcription by remodeling the chromatin structure. The regulation of gene expression in filamentous fungi of industrial interest could follow basically the same general principles as those discovered in A. nidulans. The knowledge of regulation of gene expression in combination with traditional genetic techniques is expected to be increasingly utilized for strain breeding. Furthermore, this knowledge provides a basis for the rational application of transcriptional regulators for biotechnological processes in filamentous fungi.

Stability and stabilization of potential feed additive enzymes in rumen fluid*

Four commercial preparations of fibrolytic enzymes, from Irpex lacteus, Trichoderma viride, Aspergillus niger, and a mixture designed to be similar to the I. lacteus extract, were incubated in vitro with digesta taken from the rumen of sheep receiving a grass hay/concentrate diet, and the survival of major enzyme activities was measured. Some activities, including the beta-1,4-endoglucanase and xylanase from the extract derived from Aspergillus niger, were stable for at least 6 h in rumen fluid. The same activities in the other extracts also retained substantial activity for several hours. beta-Glucosidase and beta-xylosidase activities were much more labile, most being almost completely destroyed after 1 h, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that most proteins in the extracts were digested extensively after up to 7 h of incubation. Adding bovine serum albumin (0.5 g/l) to the incubation increased the half-life of Trichoderma viride beta-glucosidase activity from less than 0.5 h to 3 h. Proteins extracted from plant materials, particularly the soybean 7S globulin fraction, also conferred protection from proteolytic breakdown, but none was as effective as bovine serum albumin. 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.

A novel class of protein from wheat which inhibits xylanases

We have purified a novel class of protein that can inhibit the activity of endo-beta-1,4-xylanases. The inhibitor from wheat (Triticum aestivum, var. Soisson) is a glycosylated, monomeric, basic protein with a pI of 8.7-8.9, a molecular mass of 29 kDa and a unique N-terminal sequence of AGGKTGQVTVFWGRN. We have shown that the protein can inhibit the activity of two family-11 endo-beta-1, 4-xylanases, a recombinant enzyme from Aspergillus niger and an enzyme from Trichoderma viride. The inhibitory activity is heat and protease sensitive. The kinetics of the inhibition have been characterized with the A. niger enzyme using soluble wheat arabinoxylan as a substrate. The Km for soluble arabinoxylan in the absence of inhibitor is 20+/-2 mg/ml with a kcat of 103+/-6 s-1. The kinetics of the inhibition of this reaction are competitive, with a Ki value of 0.35 microM, showing that the inhibitor binds at or close to the active site of free xylanase. This report describes the first isolation of a xylanase inhibitor from any organism.

Depression of the xylanase-encoding cgxA gene of Chaetomium gracile in Aspergillus nidulans

Regulation of the Chaetomium gracile xylanase A gene (cgxA) was investigated using Aspergillus nidulans as an intermediate host. Deletion of a 185 bp DNA fragment from its promoter region led to higher levels of the cgxA gene expression, indicating that the 185 bp DNA fragment contains an element involved in repression of the gene. A nuclear extract was assayed for proteins which bind to the 185 bp DNA fragment. A protein designated AnRP bound sequence specifically to the DNA fragment. The minimum sequence required for AnRP binding, 5'TTGACAAAT-3', was determined by means of gel mobility shift assays with various double-stranded oligonucleotides. Furthermore, this sequence repressed the expression of the cgxA gene when inserted at the 5' end of the cgxA gene on pXAH, which was deleted for the repressive element from the promoter region.

Solid-State Production of Beneficial Fungi on Apple Processing Wastes Using Glucosamine as the Indicator of Growth

Three Trichoderma species, a Penicillium species, and a Rhizopus species were grown on apple pomace at 25 degrees C through solid-state fermentation. The effects of CaCO(3), water, and nitrogen sources on the growth of selected fungi on apple pomace were investigated. Soluble protein and glucosamine contents of fermented pomace were measured as the parameters of fungal growth. The maximum growth of all fungi was established on apple pomace supplemented with 0.05 g of CaCO(3), 2 mL of water, and 0.05 g of NH(4)NO(3) or 0.3 mL of fish protein hydrolysate per gram of pomace. The optimal water activity of the medium for fungal growth was 0.96 at 25 degrees C. This research has provided a clear indication for using glucosamine as a proper indicator of fungal growth in heterogeneous solid-state systems. It also shows potentials for bioconversion of apple processing wastes by beneficial fungi into valuable bioinoculants that are being targeted for agricultural and environmental applications.

The alkaline xylanase III from Fusarium oxysporum F3 belongs to family F/10

Xylanase III from Fusarium oxysporum F3 was purified to homogeneity by ion-exchange chromatography and gel filtration. The enzyme has a molecular mass of 38 kDa, an isoelectric point of 9.5, and is maximally active on oat spelt xylan at pH 7 and 45 degrees C with a Km of 0.8 mg/mL. The xylanase displays remarkable stability at pH 9.0. It is not active on xylotriose but hydrolyzes the 4-methylumbelliferyl glycosides of beta-xylobiose and beta-D-glucopyranosyl-(1-->4)-beta-D-xylopyranose, and to a lower extent 4-methylumbelliferyl beta-cellobioside. When acted on xylooligosaccharides and xylan, analysis of reaction mixtures by high-pressure liquid chromatography shows preferred internal glycoside cleavage. Thus the purified enzyme appears to be a true endo-beta-1,4-xylanase. Partial amino acid analysis of xylanase III shows high sequence homology with xylanases of family F/10.

Purification and Characterization of Two Xylanases from Alkalophilic Cephalosporium sp. Strain RYM-202

Two different xylanases, CX-I and CX-II, from an alkalophilic fungus, Cephalosporium sp. strain RYM-202, have been purified to homogeneity. The enzymes had similar pH (7.5 to 8.0) and temperature (50(deg)C) optima and were stable over a wide pH range of 5.5 to 12.0. Both enzymes were shown to be cellulase-free endoxylanases with transglycosidation activity.

Two family G xylanase genes from Chaetomium gracile and their expression in Aspergillus nidulans

With oligonucleotides based on the amino-terminal and internal amino-acid sequences of a xylanase, two xylanase genes, cgxA and cgxB, were isolated and sequenced from Chaetomium gracile wild and mutant strains. Each gene isolated from both strains was essentially the same as far as nucleotide sequences were compared. The mature CgXA and CgXB xylanases comprise 189 and 211 amino acids, respectively, and share 68.5% homology. The CgXA was found to be the major enzyme in the mutant strain. Comparison of these amino-acid sequences with xylanase sequences from other origins showed that they have a high degree of identity to the family G xylanases. The cgxA and cgxB genes were introduced into Aspergillus nidulans and found to be expressed with their own promoters.

Release of ferulic acid from wheat bran by a ferulic acid esterase (FAE-III) from Aspergillus niger

Ferulic acid was efficiently released from a wheat bran preparation by a ferulic acid esterase from Aspergillus niger (FAE-III) when incubated together with a Trichoderma viride xylanase (a maximum of 95% total ferulic acid released after 5 h incubation). FAE-III by itself could release ferulic acid but at a level almost 24-fold lower than that obtained in the presence of the xylanase (2 U). Release of ferulic acid was proportional to the FAE-III concentration between 0.1 U and 1.3 U, but the presence of low levels of xylanase (0.1 U) increased the amount of ferulic acid released 6-fold. Total sugar release was not influenced by the action of FAE-III on the wheat bran, but the rate of release of the apparent end-products of xylanase action (xylose and xylobiose) was elevated by the presence of the esterase. The results show that FAE-III and the xylanase act together to break down feruloylated plant cell-wall polysaccharides to give a high yield of ferulic acid.

Purification and characterization of an extracellular endo-1,4-beta-xylanase from Fusarium oxysporum f. sp. melonis

Fusarium oxysporum f. sp. melonis produces extracellular endo-1,4-beta-xylanase and beta-xylosidase when grown in shaken culture at 26 degrees C in a mineral salts medium containing oat spelt xylan and glucose as carbon sources. Endo-1,4-beta-xylanase was purified 251 times from 5-day-old culture filtrates, by Sephacryl S-200, ion exchange and gel filtration HPLC. The purified sample yielded a single band in SDS polyacrylamide gels with a molecular mass of 80 kDa on electrophoretic mobility and 83 kDa by gel filtration behavior. High activity of the endo-1,4-beta-xylanase against xylan was observed between 5 and 8 pH, and between 40 and 60 degrees C, the optimum pH and temperature being 5.0 and 50 degrees C, respectively. Kinetic properties of the enzyme are similar to those of other fungal xylanases, showing high affinity towards oat spelt xylan with a Km of 1 mM expressed as xylose equivalent.

Regulation of the xylanase-encoding xlnA gene of Aspergillus tubigensis

A gene encoding an endo-1,4-beta-xylanase from Aspergillus tubigensis was cloned by oligonucleotide screening using oligonucleotides derived from amino acid sequence data obtained from the purified protein. The isolated gene was functional as it could be expressed in the very closely related fungus Aspergillus niger. The xylanase encoded by this gene is synthesized as a protein of 211 amino acids. After cleavage of the presumed prepropeptide this results in a mature protein of 184 amino acids with a molecular weight of 19 kDa and an isoelectric point of 3.6. The regulatory region of the xlnA gene was studied with respect to the response to xylan induction and carbon catabolite repression. By deletion analysis of the 5' upstream region of the gene a 158 bp region involved in the xylan specific induction was identified. To study this regulatory element a reporter system for transcriptional activating sequences was developed that is based on the A. niger glucose oxidase-encoding gene. From the results with this reporter system it is concluded that this 158 bp fragment not only contains the information required for induction of transcription but that it also plays a role in carbon catabolite repression of the xlnA gene. The region directly upstream of this fragment contains four potential CREA target sites; deletion of this region leads to an increase in the level of transcription. These results suggest that carbon catabolite repression of the xlnA gene is controlled at two levels, directly by repression of xlnA gene transcription and indirectly by repression of the expression of a transcriptional activator. This type of mechanism would be similar to the double lock mechanism for the regulation of gene expression of alcA in Aspergillus nidulans. The reporter system was also used to study the regulation of expression via the functions located on this fragment in A. niger and in A. nidulans. Essentially the same pattern of regulation was found in both of these hosts. Therefore, regulation of xylanase gene expression is basically conserved in all three aspergilli.

Xylanase B from Neocallimastix patriciarum contains a non-catalytic 455-residue linker sequence comprised of 57 repeats of an octapeptide

A Neocallimastix patriciarum cDNA library was screened for xylanase-expressing clones, which were distinct from the previously characterized N. patriciarum xynA cDNA encoding xylanase A. A single cDNA, designated xynB, which did not exhibit homology with xynA, was isolated. Northern-blot analysis of mRNA from Avicel-grown N. patriciarum showed that xynB hybridized to a 3.4 kb mRNA species. The nucleotide sequence of xynB revealed a single open reading frame of 2580 bp coding for a protein designated xylanase B (XYLB), of M(r) 88,066. The primary structure of XYLB was comprised of a 21-residue N-terminal signal peptide, followed by a 304-amino acid sequence that exhibited substantial homology with the catalytic domains of family F xylanases. The N-terminal domain was linked to a C-terminal 70-residue sequence by a putative linker region, comprising 12 tandem repeats of a sequence containing TLPG as the core sequence, followed by an octapeptide XSKTLPGG where X can be S, K or N, which was repeated in tandem 45 times. Truncated derivatives of xynB encoding the N-terminal 338 residues directed the synthesis of a functional xylanase, confirming that the region of XYLB, which exhibited homology with family F xylanases, constitutes the catalytic domain. To investigate the catalytic properties of XYLB, the catalytic domain was fused to the Escherichia coli maltose-binding protein, and the fusion protein purified by amylose affinity chromatography. The purified enzyme hydrolysed oat, rye and wheat arabinoxylan releasing primarily xylobiose, xylotriose and some xylose. The XYLB fusion did not cleave any cellulosic substrates. The data presented in this report suggest that the multiple xylanases of N. patriciarum arose, not through the duplication of a single gene, but by the transfer of distinct xylanase-encoding DNA sequences into the anaerobic fungus. The possible origin of the xynB gene is discussed.

The Two Major Xylanases from Trichoderma Reesei: Characterization of Both Enzymes and Genes

As a first step to exploit the potential of Trichoderma reesei to produce hemicellulases, we have purified two endo-beta-1,4-xylanases (1,4-beta-D-xylan xylanohydrolase, EC 3.2.1.8) and cloned their genes. The enzymes were isolated from culture filtrates of T. reesei C30 grown on xylan as a carbon source, using two steps of cation exchange chromatography. They exhibited molecular weights of 19 (XYN I) and 21 (XYN II) kD, and isoelectric points of 5.2 and 9.0, respectively. These enzymes differed in their pH optimum for activity and affinity for xylan, and accounted for more than 90% of the total xylanolytic activity of the fungus. The purified enzymes were subjected to N-terminal sequence analysis, and after cleavage with trypsin and endoproteinase Glu-C the resulting peptides were sequenced. Oligonucleotides based on these sequences were used to clone gene fragments via PCR, and these were used as probes to isolate full-length copies of xyn1 and xyn2 from a lambda gene bank of T. reesei. The products of xyn1 and xyn2 share considerable homology, but the enzyme encoded by xyn2 appears to more closely resemble several other bacterial and fungal xylanases than does that of xyn1.

Xylanase Activity of Phanerochaete chrysosporium

Xylan-degrading enzymes were induced when Phanerochaete chrysosporium was grown at 30�C in shake flask media containing xylan, Avicel PH 102, or ground corn stalks. The highest xylanase activity was produced in the corn stalk medium, while the xylan-based fermentation resulted in the lowest induction. Analytical and preparative isoelectric focusing were used to characterize xylanase multienzyme components. Preparative focusing was performed only with the cultures grown on Avicel and corn stalk. Of over 30 protein bands separated by analytical focusing from the Avicel and corn stalk media, three main groups (I, II, and III) of about five isoenzymes each showed xylanase activity when a zymogram technique with a xylan overlay was used. Enzyme assays revealed the presence of 1,4-β-endoxylanase and arabinofuranosidase activities in all three isoenzyme groups separated by preparative isoelectric focusing. β-Xylosidase activity appeared in the first peak and also as an independent peak between peaks II and III. Denatured molecular masses for the three isoenzyme groups were found to be between 18 and 90 kDa, and pI values were in the range of 4.2 to 6.0. β-Xylosidase has an apparent molecular mass of 20, 30, and 90 kDa (peak I) and 18 and 45 kDa (independent peak), indicating a trimer and dimer structure, respectively, with pI values of 4.2 and 5.78, respectively. Three more minor xylanase groups were produced on corn stalk medium: a double peak in the acidic range (pI 6.25 to 6.65 and 6.65 to 7.12) and two minor peaks in the alkaline range (pI 8.09 to 8.29 and 9.28 to 9.48, respectively). The profile of xylanases separated by isoelectric focusing (zymogram) of culture filtrate from cells grown on corn stalk media was more complex than that of culture supernatants from cells grown on cellulose. The pH optima of the three major xylanase groups are in the range of pH 4 to 5.5.

Purification and characterization of a xylanase from the thermophilic ascomycete Thelavia terrestris 255B

Thielavia terrestris 255B, a thermophilic ascomycete, produced two major forms of xylanase with pIs of 4.6 (xylanase I) and 6.1 (xylanase II). The latter enzyme could be purified to greater than 99% homogeneity using anion-exchange chromatography and gel filtration. Xylanase II had a mol wt of 25.7 kDa (SDS-PAGE) and a pH and a temperature optimum of 3.6-4.0 and 60-65 degrees C, respectively. The ratio of the enzyme's activity against xylan and carboxymethylcellulose was 500-1000 to 1, indicating a possible application of this enzyme in biobleaching processes. The amino acid sequence of this protein is being determined, and initial data suggest that the enzyme belongs to a group of low-mol wt xylanases that have been isolated from both bacteria and fungi.