Cloning of a gene encoding an acidophilic endo-β-1,4-xylanase obtained from Aspergillus niger CGMCC1067 and constitutive expression in Pichia pastoris

Digestion and utilization of plant-based diets by transgenic pigs secreting β-glucanase, xylanase, and phytase in their salivary glands

Novel transgenic (TG) pigs co-expressing three microbial enzymes, β-glucanase, xylanase, and phytase, in their salivary glands were previously generated, which exhibited reduced phosphorus and nitrogen emissions and improved growth performances. In the present study, we attempted to explore the age-related change of the TG enzymic activity, the residual activity of the enzymes in the simulated gastrointestinal tract, and the effect of the transgenes on the digestion of nitrogen and phosphorus content in the fiber-rich, plant-based diets. Results showed that all the three enzymes were stably expressed over the growing and finishing periods in the F2 generation TG pigs. In simulated gastric juice, all the three enzymes exhibited excellent gastrointestinal environment adaptability. The apparent total tract digestibility of phosphorus was increased by 69.05% and 499.64%, while fecal phosphate outputs were decreased by 56.66% and 37.32%, in the TG pigs compared with the wild-type littermates fed with low non-starch polysaccharides diets and high fiber diets, respectively. Over half of available phosphorus and water-soluble phosphorus in fecal phosphorus were reduced. We also found the performance of phosphorus, calcium, and nitrogen retention rates were significantly improved, resulting in faster growth performance in TG pigs. The results indicate that TG pigs can effectively digest the high-fiber diets and exhibit good growth performance compared with wild type pigs.

Cloning, Expression, and Characterization of Xylanase G2 from Aspergillus oryzae VTCC-F187 in Aspergillus niger VTCC-F017

The study focuses on engineering of recombinant Aspergillus niger to produce highly active xylanase. The xylanase G2 encoding gene originating from Aspergillus oryzae VTCC-F187 was cloned, amplified, and inserted into the pAN7.1GluA vector with specific primers possessing BamHI. The recombinant plasmid was introduced into Aspergillus niger VTCC-F017 by chemical methods. The recombinant strain was checked by polymerase chain reaction method and Southern blot. Next, the recombinant protein was expressed and purified by His-tag column. The molecular mass of the purified xylanase G2, as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), was 21 kDa with a specific activity of 1025 IU/mg towards 0.5% (w/v) of birchwood xylan. The optimal temperature and pH were 55°C and pH 6.5, respectively. The enzyme was stable in a temperature ranges 25–40°C and a pH ranges 5–7. The presence of Tween 80 enhanced xylanase activity. Triton X-100, however, had no impact on the function of the enzyme. The xylanase activity was reduced by Tween 20, SDS, and organic solvents. The enzyme was completely inhibited by Hg2+ and partially by Zn2+, Fe2+, and Ag+, while it was slightly stimulated by K+ and EDTA.

Generation of Multi-Transgenic Pigs Using PiggyBac Transposons Co-expressing Pectinase, Xylanase, Cellulase, β-1.3-1.4-Glucanase and Phytase

The current challenges facing the pork industry are to maximize feed efficiency and minimize fecal emissions. Unlike ruminants, pigs lack several digestive enzymes such as pectinase, xylanase, cellulase, β-1.3-1.4-glucanase, and phytase which are essential to hydrolyze the cell walls of grains to release endocellular nutrients into their digestive tracts. Herein, we synthesized multiple cellulase and pectinase genes derived from lower organisms and then codon-optimized these genes to be expressed in pigs. These genes were then cloned into our previously optimized XynB (xylanase)- EsAPPA (phytase) bicistronic construct. We then successfully generated transgenic pigs that expressed the four enzymes [Pg7fn (pectinase), XynB (xylanase), EsAPPA (phytase), and TeEGI (cellulase and β-glucanase)] using somatic cell cloning. The expression of these genes was parotid gland specific. Enzymatic assays using the saliva of these founders demonstrated high levels of phytase (2.0∼3.4 U/mL) and xylanase (0.25∼0.42 U/mL) activities, but low levels of pectinase (0.06∼0.08 U/mL) activity. These multi-transgenic pigs are expected to contribute to enhance feed utilization and reduce environmental impact.

Novel transgenic pigs with enhanced growth and reduced environmental impact

In pig production, inefficient feed digestion causes excessive nutrients such as phosphorus and nitrogen to be released to the environment. To address the issue of environmental emissions, we established transgenic pigs harboring a single-copy quad-cistronic transgene and simultaneously expressing three microbial enzymes, β-glucanase, xylanase, and phytase in the salivary glands. All the transgenic enzymes were successfully expressed, and the digestion of non-starch polysaccharides (NSPs) and phytate in the feedstuff was enhanced. Fecal nitrogen and phosphorus outputs in the transgenic pigs were reduced by 23.2–45.8%, and growth rate improved by 23.0% (gilts) and 24.4% (boars) compared with that of age-matched wild-type littermates under the same dietary treatment. The transgenic pigs showed an 11.5–14.5% improvement in feed conversion rate compared with the wild-type pigs. These findings indicate that the transgenic pigs are promising resources for improving feed efficiency and reducing environmental impact.

The bodily waste that pigs produce contains high levels of chemicals that can damage the environment, such as nitrogen and phosphorus. For example, when excessive amounts of these two compounds make their way into the water, they can cause blue-green algae to grow too much, which asphyxiates other life in the water.

Pigs produce a lot of nitrogen and phosphorus because they cannot efficiently digest their food. In particular, the animals lack the enzymes required to break down two types of molecules present in their feedstuff: phytates and non-starch polysaccharides (NSPs).

Zhang, Li et al. take four microbial genes which code for the enzymes needed to digest NSPs and phytates, and they add these DNA sequences into the genomes of pigs. The animals then produce enzymes in their saliva that transform NSPs and phytates into molecules which can be used by their digestive system. The pigs thus get more energy from their food, and they grow faster and bigger. They also produce less nitrogen and phosphorus in their waste.

Over 1.2 billion pigs are farmed each year, and they are the most economically important meat source in the world. Raising animals that can digest their food better would reduce the need for pig feed, increase productivity and reduce environmental pollution. However, discussions with policy makers and with the public will be necessary before these results can be adopted by the farming industry.

Lignocellulose degrading extremozymes produced by Pichia pastoris: current status and future prospects

In this review article, extremophilic lignocellulosic enzymes with special interest on xylanases, β-mannanases, laccases and finally cellulases, namely, endoglucanases, exoglucanases and β-glucosidases produced by Pichia pastoris are reviewed for the first time. Recombinant lignocellulosic extremozymes are discussed from the perspectives of their potential application areas; characteristics of recombinant and native enzymes; the effects of P. pastoris expression system on recombinant extremozymes; and their expression levels and applied strategies to increase the enzyme expression yield. Further, effects of enzyme domains on activity and stability, protein engineering via molecular dynamics simulation and computational prediction, and site-directed mutagenesis and amino acid modifications done are also focused. Superior enzyme characteristics and improved stability due to the proper post-translational modifications and better protein folding performed by P. pastoris make this host favourable for extremozyme production. Especially, glycosylation contributes to the structure, function and stability of enzymes, as generally glycosylated enzymes produced by P. pastoris exhibit better thermostability than non-glycosylated enzymes. However, there has been limited study on enzyme engineering to improve catalytic efficiency and stability of lignocellulosic enzymes. Thus, in the future, studies should focus on protein engineering to improve stability and catalytic efficiency via computational modelling, mutations, domain replacements and fusion enzyme technology. Also metagenomic data need to be used more extensively to produce novel enzymes with extreme characteristics and stability.

Expression of Aspergillus niger IA-001 Endo-β-1,4-xylanase in Pichia pastoris and analysis of the enzymic characterization

The xylanaseB (XynB) (JX560731.1) gene of Aspergillus niger IA-001 was optimized according to the codon usage of Pichia pastoris and expressed in P. pastoris GS115. The optimized XynB expression level was increased 2.8 times relative to that of the wild-type XynB, and the dual-copy XynB (optimized) expression level was increased 1.9 times relative to that of the single-copy XynB (optimized). The activity of the dual-copy XynB ((XynB-opt)2) was maximized at 15,158.23 ± 45.11 U/mL after 120 h of shaking. The optimal temperature and pH of (XynB-opt)2 were 50 °C and 5.0, respectively. (XynB-opt)2 showed a high specific activity of 6,853.00 ± 20.08 U/mg. IC analysis of the standard xylooligosaccharides showed that (XynB-opt)2 was an endo-xylanase with X2 as the main degradation product. (XynB-opt)2 was highly specific towards different natural xylans. After 24 h of hydrolysis, more than 90 % of the total hydrolysis products of xylan were X2 and X1, almost no X4 ~ X6. In addition, the enzyme exhibited resistance to many metal ions and low pH values. The superior catalytic properties of (XynB-opt)2 suggested its great potential as an effective additive in animal feed industry.

Molecular characterization of a glycosyl hydrolase family 10 xylanase from Aspergillus niger

A gene coding for an endo-β-1,4-xylanase (XlnA) (glycosyl hydrolase family 10) from Aspergillus niger DSM 1957 was cloned and sequenced. The cDNA sequence (984 bp) and its putative endoxylanase (327 aa protein with a predicted molecular mass of 35.5 kDa and pI 6.23) showed 91.3-99.5% and 96.3-99.1% identities with cDNA sequences and their corresponding endoxylanases from A. niger strains from GenBank, respectively. The cDNA was expressed in Pichia pastoris GS115 under the control of AOX1 promoter at a level of 46.4 U/ml culture supernatant, after 144 h of growth at 30°C in YP medium induced with 0.5% (v/v) of methanol. The molecular mass of the purified XlnA determined by SDS-PAGE was 35.5k Da with a specific activity of 808.5 U/mg towards 1% (w/v) of birch wood xylan. Temperature and pH optimum were observed at 50°C and pH 7.0, respectively. The enzyme was stable over a temperature range of 25-40°C and at pH range of 4.5-8.5 and resistant to Tween 80 and acetone. The K(m) and V(max) value obtained for the purified xylanase were 25.5mg/ml and 5000 μmol/min/mg protein with birch wood xylan as substrate, respectively. The xylanase was free of cellulase and mannanase activity but highly active towards birch wood xylan. The major products of the birch wood xylan hydrolysis were predicted as xylotriose, xylotetraose, and xylopentose. The biochemical characteristics suggested that the recombinant xylanase has a potential application, including use as a feed enzyme.

Analysis of functional xylanases in xylan degradation by Aspergillus niger E-1 and characterization of the GH family 10 xylanase XynVII

Xylanases produced by Aspergillus niger are industrially important and many types of xylanases have been reported. Individual xylanases have been well studied for their enzymatic properties, gene cloning, and heterologous expression. However, less attention has been paid to the relationship between xylanase genes carried on the A. niger genome and xylanases produced by A. niger strains. Therefore, we examined xylanase genes encoded on the genome of A. niger E-1 and xylanases produced in culture. Seven putative xylanase genes, xynI–VII (named in ascending order of the molecular masses of the deduced amino acid sequences), were amplified from the strain E-1 genome using primers designed from the genome sequence of A. niger CBS 513.88 by PCR and phylogenetically classified into three clusters. Additionally, culture supernatant analysis by DE52 anion–exchange column chromatography revealed that this strain produced three xylanases, XynII, XynIII, and XynVII, which were identified by N-terminal amino acid sequencing and MALDI-TOF-MS analyses, in culture when gown in 0.5% xylan medium supplemented with 50 mM succinate. Furthermore, XynVII, the only GH family 10 xylanase in A. niger E-1, was purified and characterized. The purified enzyme showed a single band with a molecular mass of 35 kDa by SDS-PAGE. The highest activity of purified XynVII was observed at 55°C and pH 5.5. The enzyme was stable in the broad pH range of 3–10 and up to 60°C and was resistant to most metal ions and modifying regents. XynVII showed high specificity against beechwood xylan with K_m and V_max values of 2.8 mg mL^–1 and 127 μmol min^–1mg^–1, respectively. TLC and MALDI-TOF-MS analyses showed that the final hydrolyzed products of the enzyme from beechwood xylan were xylose, xylobiose, and xylotriose substituted with a 4-o-metylglucuronic acid residue.

Characterization, cloning and functional expression of novel xylanase from Thermomyces lanuginosus SS-8 isolated from self-heating plant wreckage material

Extracellular cellulase free xylanase from Thermomyces lanuginosus sp. SS-8, isolated from self heating plant wreckage material was identified as β-1,4-endo-xylanase precursor, a monomer of 21.3 kDa with no carbohydrate residue. This xylanase retained 80 % activity at 60 °C for 96 h, was active at a wide pH range of 3-11 and uniquely hydrolyzed xylan to xylose without production of xylo-oligosaccharides. Gene xynSS8 encoding xylanase from T. lanuginosus SS-8 was cloned and functionally expressed in Escherichia coli XL1 Blue using pTZ57R/T plasmid and xynSS8/pQE-9 expression vector construct respectively. Gene xynSS8 was of 777 bp and deduced amino acid sequence was a mature xylanase of 258 amino acids. XynSS8 has extra 33 amino acids compared to its nearest homolog and was thermo-alkali tolerant as that of native protein. The xylanase could degrade pulp and release substantial chromophoric materials and lignin derived compounds indicating its effective utility in pulp bleaching. Novel characteristics of the enzyme may contribute to its wide industrial usage. This is first report of cloning and functional expression of the novel xylanase from T. lanuginosus SS-8.

Cloning and expression of a xylanase xynB from Aspergillus niger IA-001 in Pichia pastoris

The high-level expression of the xylanase GH11 gene from Aspergillus niger IA-001 called xynB was successfully completed in Pichia pastoris. The xynB gene encoding a mature xylanase of 225 amino acid was subcloned into the pPICZαA vector and was transformed into P. pastoris X-33 under the control of the alcohol oxidase I (AOX1) promoter. The xynB gene was ligated with a sequence encoding modified α-factor signal peptide (pPICZαmA) and the recombinant xylanase activity, which was measured 1280 U ml(-1), was 1.5-fold higher than when it was inserted into pPICZαA and was 19.39-fold greater than the native xylanase in the original strain. In a 10 L fermenter, the recombinant xylanase activity measured 10,035 U ml(-1) after 114 h. The SDS-PAGE analysis revealed that the purified xynB protein migrated as a single band with an apparent molecular weight of 24 kDa. The specific activity, using beechwood xylan as a substrate, was 1916 U mg(-1). The xylanase activity was optimal at pH 5.0 and at 50 °C. In addition, the xynB was active over a pH range of 2.2 to 10.0. The apparent Km and Vmax values were 4.429 mg ml(-1) and 1429 U mg(-1), respectively.

Production and characterization of acidophilic xylanolytic enzymes from Penicillium oxalicum GZ-2

Multiple acidophilic xylanolytic enzymes were produced by Penicillium oxalicum GZ-2 during growth on wheat straw, rice straw, corn stover, and wheat bran. The expression of xylanase isoforms was dependent on substrate type and nitrogen source. The zymograms produced by the SDS-PAGE resolution of the crude enzymes indicated that wheat straw was the best inducer, resulting in the highest xylanase (115.2U/mL) and β-xylosidase (89mU/mL) activities during submerged fermentation. The optimum temperature and pH for xylanase activity were 50°C and 4.0, respectively; however, the crude xylanase enzymes exhibited remarkable stability over a broad pH range and showed more than 90% activity at 50°C for 30min at pH 4.0-8.0. The results revealed that P. oxalicum GZ-2 is a promising acidophilic xylanase-producing microorganism that has great potential to be used in biofuels, animal feed, and food industry applications.

Amino acids interference on the quantification of reducing sugars by the 3,5-dinitrosalicylic acid assay mislead carbohydrase activity measurements

This study evaluated the interference of the amino acids tryptophan, cysteine, histidine, tyrosine, hydroxyproline, leucine, proline, serine, glycine, valine, glutamic acid, phenylalanine, and methionine on the measurement of reducing sugars using a phenol-free 3,5-dinitrosalicylic acid (DNS) reagent. It was found that in reaction mixtures containing 20mM of either tryptophan, cysteine, histidine, tyrosine, or hydroxyproline the measurement of 3.7 mM glucose was overestimated by 76%, 50%, 35%, 18%, and 10%, respectively. The amino acids valine, glutamic acid, and phenylalanine did not affect the DNS reaction, while methionine decreased the color development by 5%. The measurement of glucose, xylose, arabinose, and cellobiose at the 3.7-12.4 mM range in the presence of 20 mM cysteine resulted in an overestimated concentration of 34.8-50%. Enzymatic assays for measuring xylanolytic and filter paper activity (FPAse) were conducted in the presence of 20-60 mM cysteine, and compared to cysteine-free assays. In the presence of cysteine, the measured xylanase activity increased threefold and the FPAse activity increased twofold due to the overestimation of the reducing sugar concentrations in the assays. The interference from cysteine was reduced to a maximum of 8.6% when a DNS reagent containing phenol was used.

Functional characterization and synergic action of fungal xylanase and arabinofuranosidase for production of xylooligosaccharides

Plant cell wall degrading enzymes are key technological components in biomass bioconversion platforms for lignocellulosic materials transformation. Cost effective production of enzymes and identification of efficient degradation routes are two economic bottlenecks that currently limit the use of renewable feedstocks through an environmental friendly pathway. The present study describes the hypersecretion of an endo-xylanase (GH11) and an arabinofuranosidase (GH54) by a fungal expression system with potential biotechnological application, along with comprehensive characterization of both enzymes, including spectrometric analysis of thermal denaturation, biochemical characterization and mode of action description. The synergistic effect of these enzymes on natural substrates such as sugarcane bagasse, demonstrated the biotechnological potential of using GH11 and GH54 for production of probiotic xylooligosaccharides from plant biomass. Our findings shed light on enzymatic mechanisms for xylooligosaccharide production, as well as provide basis for further studies for the development of novel enzymatic routes for use in biomass-to-bioethanol applications.

Enhancing catalytic activity of a hybrid xylanase through single substitution of Leu to Pro near the active site

A modified error-prone PCR and high-throughout screening system based on 96-well plate were employed to improve catalytic activity of a hybrid xylanase (ATx). The mutant (FSI-A124) with enhanced activity was further heterologously expressed in Pichia pastoris under the control of GAP promoter. The recombinant xylanase driven by the Saccharomyces cerevisiae α-mating factor was secreted into culture medium. After growth in YPD medium for 96 h, xylanase activity in the culture supernatant reached 66.1 U ml(-1), which was 2.92 times as that of its parent. 6 × His-tagged purification increased the specific activity to 1557.61 U mg(-1). The optimum temperature and pH of recombinant xylanase were 55°C and 6.0, respectively. A single amino acid substitution (L49P) was observed within sequence of the mutant. Insight of the three dimensional structure revealed that proline possibly produced weaker hydrogen bond, van der Waals force and hydrophobic interaction with other residues nearby than leucine, especially for V174, contributing to the flexibility of catalytic residue E177. In this study, FSI-A124 exhibited higher xylanase activity but poorer thermostability than its parent, indicating that activity and stability might be negatively correlated.

Cloning and optimized expression of a GH-11 xylanase from Fusarium oxysporum in Pichia pastoris

The endo-1,4-β-xylanase gene xyn11a from Fusarium oxysporum, member of the fungal glycosyl hydrolase (GH) family 11, was cloned and expressed in Pichia pastoris. The mature xylanase gene, which generates after the excision of one intron and the secreting signal peptide, was placed under the control of an alcohol oxidase promoter (AOX1) in the plasmid pPICZαC. The final construction was integrated into the genome of the methylotrophic yeast P. pastoris X33 and the ability to produce xylanase activity was evaluated in flask cultures. Recombinant P. pastoris efficiently secreted xylanase into the medium and produced high level of enzymatic activity (110 U/ml) after 216 hours of growth, under methanol induction. To achieve higher enzyme production, the influence of initial pH, methanol concentration, agitation and flask design was evaluated. Under optimum culture conditions, production of the recombinant xylanase increased by 50%, reaching a final yield of 170 U/ml, underpinning aeration as the most important factor in improving enzyme production.

Cloning and sequence analysis of a novel xylanase gene, Auxyn10A, from Aspergillus usamii

A full-length cDNA sequence, encoding a novel endo-1,4-β-D: -xylanase (AuXyn10A) of Aspergillus usamii, was obtained by using rapid amplification of cDNA ends (RACE) methods and cloned into the pUCm-T vector, followed by DNA sequencing. The cDNA gene, designated as Auxyn10A, is 1,235 bp in length harboring 5'- and 3'-non-encoding regions, as well as an ORF of 984 bp that encodes a 19-aa signal peptide, a 6-aa propeptide and a 302-aa mature peptide with a calculated MW of 32,756 Da. The AuXyn10A displays high similarity to the xylanases of Aspergillus niger, Aspergillus kawachii and Aspergillus niger, members of the glycoside hydrolase family 10. Its three-dimensional structure was predicted using http://swiss-model.expasy.org/on-line programs based on the crystal structure of Penicillium simplicissimum xylanase (1B30_A) from the family 10. The complete DNA gene was cloned from the genomic DNA of A. usamii using conventional PCR and hairpin structure-mediated PCR techniques. The DNA gene is 2,255 bp in length, containing a 510 bp of 5'-flanking promoter region and a 1,745 bp of downstream fragment that consists of ten exons and nine short introns ranging from 52 to 62 bp.

Molecular cloning of fungal xylanases: an overview

Xylanases have received great attention in the development of environment-friendly technologies in the paper and pulp industry. Their use could greatly improve the overall lignocellulosic materials for the generation of liquid fuels and chemicals. Fungi are widely used as xylanase producers and are generally considered as more potent producers of xylanases than bacteria and yeasts. Large-scale production of xylanases is facilitated with the advent of genetic engineering. Recent breakthroughs in genomics have helped to overcome the problems such as limited enzyme availability, substrate scope, and operational stability. Genes encoding xylanases have been cloned in homologous and heterologous hosts with the objectives of overproducing the enzyme and altering its properties to suit commercial applications. Owing to the industrial importance of xylanases, a significant number of studies are reported on cloning and expression of the enzymes during the last few years. We, therefore, have reviewed recent knowledge regarding cloning of fungal xylanase genes into various hosts for heterologous production. This will bring an insight into the current status of cloning and expression of the fungal xylanases for industrial applications.

Improvement of Aspergillus sulphureus endo-beta-1,4-xylanase expression in Pichia pastoris by codon optimization and analysis of the enzymic characterization

The gene xynB from Aspergillus sulphureus encoding the endo-beta-1,4-xylanase was de novo synthesized by splicing overlap extension polymerase chain reaction according to Pichia pastoris protein's codon bias. The synthetic DNA and wild-type DNA were placed under the control of a glyceraldehyde-3-phosphate dehydrogenase gene promoter (GAP) in the constitutive expression vector plasmid pGAPzalphaA and electrotransformed into the P. pastoris X-33 strain, respectively. The transformants screened by Zeocin were able to constitutively secrete the xylanase in YPD liquid medium. The maximum yield of the recombinant xylanase produced by the synthetic DNA was 105 U ml(-1), which was about 5-fold higher than that by wild-type DNA under the flask culture at 28 degrees Celsius for 3 days. The enzyme showed optimal activity at 50 degrees Celsius and pH 5.0. The residual activity remained above 90% after the recombinant xylanase was pretreated in Na(2)HPO(4)-citric acid buffer (pH 2.4) for 2 h. The xylanase activity was significantly improved by Zn(2+). These biochemical characteristics suggest that the recombinant xylanase has a prospective application in feed industry as an additive.

De novo synthesis, constitutive expression of Aspergillus sulphureus beta-xylanase gene in Pichia pastoris and partial enzymic characterization

The endo-beta-1, 4-xylanase gene xynA from Aspergillus sulphureus, encoded a lack-of-signal peptide protein of 184 amino acids, was de novo synthesized by splicing overlap extension polymerase chain reaction according to Pichia pastoris protein's codon bias. The synthetic DNA, composed of 572 nucleotides, was ligated into the downstream sequence of an alpha-mating factor in a constitutive expression vector pGAPzalphaA and electrotransformed into the P. pastoris X-33 strain. The transformed yeast screened by Zeocin was able to constitutively secrete the xylanase in yeast-peptone-dextrose liquid medium. The heterogenous DNA was stabilized in the strain by 20-times passage culture. The recombinant enzyme was expressed with a yield of 120 units/mL under the flask culture at 28 degrees C for 3 days. The enzyme showed optimal activity at 50 degrees C and pH 2.4-3.4. Residual activity of the raw recombinant xylanase was not less than 70% when fermentation broth was directly heated at 80 degrees C for 30 min. However, the dialyzed xylanase supernatant completely lost the catalytic activity after being heated at 60 degrees C for 30 min. The recombinant xylanase showed no obvious activity alteration by being pretreated with Na(2)HPO(4)-citric acid buffer of pH 2.4 for 2 h. The xylanase also showed resistance to certain metal ions (Na(+), Mg(2+), Ca(2+), K(+), Ba(2+), Zn(2+), Fe(2+), and Mn(2+)) and EDTA. These biochemical characteristics suggest that the recombinant xylanase has a prospective application in feed industry as an additive.