An extreme halophilic xylanase from camel rumen metagenome with elevated catalytic activity in high salt concentrations

Genomic analysis of a halophilic bacterium Nesterenkonia sp. CL21 with ability to produce a diverse group of lignocellulolytic enzymes

Halophilic bacteria are extremophiles that thrive in saline environment. Their ability to withstand such harsh conditions makes them an ideal choice for industrial applications such as lignocellulosic biomass degradation. In this study, a halophilic bacterium with the ability to produce extracellular cellulases and hemicellulases, designated as Nesterenkonia sp. CL21, was isolated from mangrove sediment in Tanjung Piai National Park, Malaysia. Thus far, studies on lignocellulolytic enzymes concerning bacterial species under this genus are limited. To gain a comprehensive understanding of its lignocellulose-degrading potential, the whole genome was sequenced using the Illumina NovaSeq 6000 platform. The genome of strain CL21 was assembled into 25 contigs with 3,744,449 bp and a 69.74% GC content and was predicted to contain 3,348 coding genes. Based on taxonomy analysis, strain CL21 shares 73.8 to 82.0% average nucleotide identity with its neighbouring species, below the 95% threshold, indicating its possible status as a distinct species in Nesterenkonia genus. Through in-depth genomic mining, a total of 81 carbohydrate-active enzymes were encoded. Among these, 24 encoded genes were identified to encompass diverse cellulases (GH3), xylanases (GH10, GH11, GH43, GH51, GH127 and CE4), mannanases (GH38 and GH106) and pectinases (PL1, PL9, and PL11). The production of lignocellulolytic enzymes was tested in the presence of several substrates. This study revealed that strain CL21 can produce a diverse array of enzymes which are active at different time points. By combining experimental data with genomic information, the ability of strain CL21 to produce lignocellulolytic enzymes has been elucidated, with potential applications in biorefinery industry.

Halophilic filamentous fungi and their enzymes: Potential biotechnological applications

Recently, interest in the study of microorganisms growing under extreme conditions, particularly halophiles, has increased due to their potential use in industrial processes. Halophiles are the class of microorganisms that grow optimally at high NaCl concentrations and are capable of producing halophilic enzymes capable of catalyzing reactions under harsh conditions. So far, fungi are the least studied halophilic microorganisms, even though they have been shown to counteract these extreme conditions by producing secondary metabolites with very interesting properties. This review highlights mechanisms that allow halophilic fungi to adapt high salinity and the specificity of their enzymes to a spectrum of action in industrial and environmental applications. The peculiarities of these enzymes justify the urgent need to apply green alternative compounds in industries.

Precision enzyme discovery through targeted mining of metagenomic data

Metagenomics has opened new avenues for exploring the genetic potential of uncultured microorganisms, which may serve as promising sources of enzymes and natural products for industrial applications. Identifying enzymes with improved catalytic properties from the vast amount of available metagenomic data poses a significant challenge that demands the development of novel computational and functional screening tools. The catalytic properties of all enzymes are primarily dictated by their structures, which are predominantly determined by their amino acid sequences. However, this aspect has not been fully considered in the enzyme bioprospecting processes. With the accumulating number of available enzyme sequences and the increasing demand for discovering novel biocatalysts, structural and functional modeling can be employed to identify potential enzymes with novel catalytic properties. Recent efforts to discover new polysaccharide-degrading enzymes from rumen metagenome data using homology-based searches and machine learning-based models have shown significant promise. Here, we will explore various computational approaches that can be employed to screen and shortlist metagenome-derived enzymes as potential biocatalyst candidates, in conjunction with the wet lab analytical methods traditionally used for enzyme characterization.

Characterization of a GH10 extremely thermophilic xylanase from the metagenome of hot spring for prebiotic production

A xylanase gene (named xyngmqa) was identified from the metagenomic data of the Gumingquan hot spring (92.5 °C, pH 9.2) in Tengchong City, Yunnan Province, southwest China. It showed the highest amino acid sequence identity (82.70%) to endo-1,4-beta-xylanase from Thermotoga caldifontis. A constitutive expression plasmid (denominated pSHY211) and double-layer plate (DLP) method were constructed for cloning, expression, and identification of the XynGMQA gene. The XynGMQA gene was synthesized and successfully expressed in Escherichia coli DH5α. XynGMQA exhibited optimal activity at 90 °C and pH 4.6, being thermostable by maintaining 100% of its activity after 2 h incubated at 80 °C. Interestingly, its enzyme activity was enhanced by high temperatures (70 and 80 °C) and low pH (3.0-6.0). About 150% enzyme activity was detected after incubation at 70 °C for 20 to 60 min or 80 °C for 10 to 40 min, and more than 140% enzyme activity after incubation at pH 3.0 to 6.0 for 12 h. Hydrolytic products of beechwood xylan with XynGMQA were xylooligosaccharides, including xylobiose (X2), xylotriose (X3), and xylotetraose (X4). These properties suggest that XynGMQA as an extremely thermophilic xylanase, may be exploited for biofuel and prebiotic production from lignocellulosic biomass.

Nanohaloarchaea as beneficiaries of xylan degradation by haloarchaea

Climate change, desertification, salinisation of soils and the changing hydrology of the Earth are creating or modifying microbial habitats at all scales including the oceans, saline groundwaters and brine lakes. In environments that are saline or hypersaline, the biodegradation of recalcitrant plant and animal polysaccharides can be inhibited by salt-induced microbial stress and/or by limitation of the metabolic capabilities of halophilic microbes. We recently demonstrated that the chitinolytic haloarchaeon Halomicrobium can serve as the host for an ectosymbiont, nanohaloarchaeon 'Candidatus Nanohalobium constans'. Here, we consider whether nanohaloarchaea can benefit from the haloarchaea-mediated degradation of xylan, a major hemicellulose component of wood. Using samples of natural evaporitic brines and anthropogenic solar salterns, we describe genome-inferred trophic relations in two extremely halophilic xylan-degrading three-member consortia. We succeeded in genome assembly and closure for all members of both xylan-degrading cultures and elucidated the respective food chains within these consortia. We provide evidence that ectosymbiontic nanohaloarchaea is an active ecophysiological component of extremely halophilic xylan-degrading communities (although by proxy) in hypersaline environments. In each consortium, nanohaloarchaea occur as ectosymbionts of Haloferax, which in turn act as scavenger of oligosaccharides produced by xylan-hydrolysing Halorhabdus. We further obtained and characterised the nanohaloarchaea-host associations using microscopy, multi-omics and cultivation approaches. The current study also doubled culturable nanohaloarchaeal symbionts and demonstrated that these enigmatic nano-sized archaea can be readily isolated in binary co-cultures using an appropriate enrichment strategy. We discuss the implications of xylan degradation by halophiles in biotechnology and for the United Nation's Sustainable Development Goals.

Lignocellulose degradation by rumen bacterial communities: New insights from metagenome analyses

Ruminant animals house a dense and diverse community of microorganisms in their rumen, an enlarged compartment in their stomach, which provides a supportive environment for the storage and microbial fermentation of ingested feeds dominated by plant materials. The rumen microbiota has acquired diverse and functionally overlapped enzymes for the degradation of plant cell wall polysaccharides. In rumen Bacteroidetes, enzymes involved in degradation are clustered into polysaccharide utilization loci to facilitate coordinated expression when target polysaccharides are available. Firmicutes use free enzymes and cellulosomes to degrade the polysaccharides. Fibrobacters either aggregate lignocellulose-degrading enzymes on their cell surface or release them into the extracellular medium in membrane vesicles, a mechanism that has proven extremely effective in the breakdown of recalcitrant cellulose. Based on current metagenomic analyses, rumen Bacteroidetes and Firmicutes are categorized as generalist microbes that can degrade a wide range of polysaccharides, while other members adapted toward specific polysaccharides. Particularly, there is ample evidence that Verrucomicrobia and Spirochaetes have evolved enzyme systems for the breakdown of complex polysaccharides such as xyloglucans, peptidoglycans, and pectin. It is concluded that diversity in degradation mechanisms is required to ensure that every component in feeds is efficiently degraded, which is key to harvesting maximum energy by host animals.

Production, purification, characterization and application of two novel endoglucanases from buffalo rumen metagenome

BACKGROUND

Lignocellulose biomass is the most abundant and renewable material in nature. The objectives of this study were to characterize two endoglucanases TrepCel3 and TrepCel4, and determine the effect of the combination of them (1.2 mg TrepCel3, 0.8 mg TrepCel4) on in vitro rumen fermentation characteristics. In this study, three nature lignocellulosic substrates (rice straw, RS; wheat straw, WS; leymus chinensis, LC) were evaluated for their in vitro digestibility, gas, NH3-N and volatile fatty acid (VFA) production, and microbial protein (MCP) synthesis by adding enzymatic combination.

METHODS

Two endoglucanases' genes were successfully expressed in Escherichia coli (E. coli) BL21 (DE3), and enzymatic characteristics were further characterized. The combination of TrepCel3 and TrepCel4 was incubated with lignocellulosic substrates to evaluate its hydrolysis ability.

RESULTS

The maximum enzymatic activity of TrepCel3 was determined at pH 5.0 and 40 °C, while TrepCel4 was at pH 6.0 and 50 °C. They were stable over the temperature range of 30 to 60 °C, and active within the pH range of 4.0 to 9.0. The TrepCel3 and TrepCel4 had the highest activity in lichenan 436.9 ± 8.30 and 377.6 ± 6.80 U/mg, respectively. The combination of TrepCel3 and TrepCel4 exhibited the highest efficiency at the ratio of 60:40. Compared to maximum hydrolysis of TrepCel3 or TrepCel4 separately, this combination was shown to have a superior ability to maximize the saccharification yield from lignocellulosic substrates up to 188.4% for RS, 236.7% for wheat straw WS, 222.4% for LC and 131.1% for sugar beet pulp (SBP). Supplemental this combination enhanced the dry matter digestion (DMD), gas, NH3-N and VFA production, and MCP synthesis during in vitro rumen fermentation.

CONCLUSIONS

The TrepCel3 and TrepCel4 exhibited the synergistic relationship (60:40) and significantly increased the saccharification yield of lignocellulosic substrates. The combination of them stimulated in vitro rumen fermentation of lignocellulosic substrates. This combination has the potential to be a feed additive to improve agricultural residues utilization in ruminants. If possible, in the future, experiments in vivo should be carried out to fully evaluate its effect.

Characterization of a novel bifunctional enzyme from buffalo rumen metagenome and its effect on in vitro ruminal fermentation and microbial community composition

To efficiently use lignocellulosic materials in ruminants, it is crucial to explore effective enzymes, especially bifunctional enzymes. In this study, a novel stable bifunctional cellulase-xylanase protein from buffalo rumen metagenome was expressed and characterized, CelXyn2. The enzyme displayed optimal activity at pH 6.0 and 45 °C. The residual endoglucanase and xylanase activities were 90.6% and 86.4% after a 60-min pre-incubation at 55 °C. Hydrolysis of rice straw, wheat straw, sheepgrass and sugar beet pulp by CelXyn2 showed its ability to degrade both cellulose and hemicellulose polymers. Treatment with CelXyn2 improved the hydrolysis of agricultural residues with an evident increase in production of total gas, lactate and volatile fatty acids. The results of 16S rRNA and real-time PCR showed that the effect on in vitro ruminal microbial community depended on fermentation substrates. This study demonstrated that CelXyn2 could strengthen lignocellulose hydrolysis and in vitro ruminal fermentation. These characteristics of CelXyn2 distinguish it as a promising candidate for agricultural application.

Characteristics of recombinant xylanase from camel rumen metagenome and its effects on wheat bran hydrolysis

In the present study, we explored the effects of a novel xylanase from camel rumen metagenome (CrXyn) on wheat bran hydrolysis. CrXyn was heterologously expressed in Escherichia coli and showed maximum activity at 40 °C and pH 7.0. Furthermore, CrXyn exhibited preferential hydrolysis of xylan, but no obvious activity toward other substrates, including carboxymethylcellulose and Avicel. Using wheat straw xylan as a substrate, the Km and Vmax values for CrXyn were 5.98 g/L and 179.9 μmol xylose/min/mg protein, respectively. Mn²⁺ was a strong accelerator and significantly enhanced CrXyn activity. However, CrXyn activity was inhibited (~50 %) by 1 mM and 5 mM ethylenediaminetetraacetic acid (EDTA) and completely inactivated by 5 mM Cu²⁺. CrXyn tolerated 5 mM sodium dodecyl sulphate (SDS) and 15 % methanol, ethanol, and dimethyl sulfoxide (DMSO), with >50 % residual activity. CrXyn effectively hydrolyzed wheat bran, with xylobiose and xylotetraose accounting for 79.1 % of total sugars produced. A remarkable synergistic effect was found between CrXyn and protease, leading to an obvious increase in amino acids released from wheat bran compared with the control. CrXyn also enhanced the in vitro hydrolysis of wheat bran. Thus, CrXyn exhibits great potential as a feed additive to improve the utilization of wheat bran in monogastric animal production.

Metagenomic psychrohalophilic xylanase from camel rumen investigated for bioethanol production from wheat bran using Bacillus subtilis AP

Bioethanol produced from lignocellulosic biomass is regarded as a clean and sustainable energy source. The recalcitrant structure of lignocellulose is a major drawback to affordable bioethanol production from plant biomass. In this study, a novel endo-1,4-xylanase, named Xyn-2, from the camel rumen metagenome, was characterized and evaluated for hydrolysis of agricultural wastes. The enzyme was identified as a psychrohalophilic xylanase with maximum activity at 20 °C, keeping 58% of the activity at 0 °C, and exhibiting twice as much activity in 0.5–4 M NaCl concentrations. Xyn-2 was able to hydrolyze wheat bran (100%), sunflower-seed shell (70%), wheat straw (56%), rice straw (56%), and rice bran (41%), in the relative order of efficiency. Besides, the ethanologenic B. subtilis AP was evaluated without and with Xyn-2 for bioethanol production from wheat bran. The strain was able to produce 5.5 g/L ethanol with a yield of 22.6% in consolidated bioprocessing (CBP). The contribution of Xyn-2 to ethanol production of B. subtilis AP was studied in an SSF system (simultaneous saccharification and fermentation) giving rise to a significant increase in ethanol production (p ≤ 0.001) to a final concentration of 7.3 g/L with a yield of 26.8%. The results revealed that the camel rumen metagenome might be an invaluable source of novel xylanolytic enzymes with potential application in lignocellulosic biomass valorization. At the same time, the results suggest that B. subtilis with a diverse carbon-source preference and sophisticated systems for production and secretion of enzymes might be a promising candidate for strain development for bioethanol production from plant biomass. It might be assumed that the fortification of B. subtilis enzymatic arsenal with select xylanolytic enzymes from camel rumen metagenome may have a great impact on bioethanol production.

Lowering energy consumption for fermentable sugar production from Ramulus mori: Engineered xylanase synergy and improved pretreatment strategy

Biorefinery of Ramulus mori with lower energy consumption through improved enzyme and pretreatment strategies was reported. Directed evolution and saturation mutagenesis were used for the modification of xylanase, the yield of fermentable sugars and the degree of synergy (DS) were determined for different pretreatment (seawater/non-seawater) and enzyme treatment groups (xylanase/cellulase/co-treatment). The dominant mutant I133A/Q143Y of Bispora sp. xylanase XYL10C_ΔN was obtained with improved specific activity (1860 U/mg), catalytic efficiency (1150 mL/s∙mg) at 40 °C, and thermostability (T₅₀ increased by 7 °C). With the pretreatment of seawater immersion, the highest yield of fermentable sugars for Ramulus mori at 40 °C reached 199 μmol/g when hydrolyzed with cellulase and I133A/Q143Y, with the highest DS of 2.6; this was 4.5-fold that of the group hydrolyzed by cellulase alone with non-seawater pretreatment. Thus, bioconversion of reducing sugar from Ramulus mori was improved significantly at lower temperatures, which provides an efficient and energy-saving wayfor biofuel production.

Understanding the Role of Prevotella Genus in the Digestion of Lignocellulose and Other Substrates in Vietnamese Native Goats' Rumen by Metagenomic Deep Sequencing

Simple Summary

Prevotella is an abundant genus which plays an important role for lignocellulose digestion in goat rumen and is significant to the yield and quality of milk and meat in cows. In a previous study, we sequenced bacterial metagenome from Vietnamese native goat rumen to get 8.4 GB clean data and found very diverse genes related to lignocellulose degradation. However, due to the limitation in the metagenomic size, low amount of complete lignocellulase genes, and high bacterial diversity, further analysis was restricted. In this study, metagenomic deep sequencing was used to obtain 48.66 GB of reliable data, thus some lignocellulolytic enzymes were first seen and a picture of bacterial enzymes involved in lignocellulose digestion in the goat rumen was drawn. The loci for galactan-, xylan-, and arabinan-processing in Prevotella were observed for the first time. We confirm that Prevotella plays pivotal role for hemicellulose digestion and significantly participates in starch, cellulose, hemicellulose, and pectin conversion in the goat rumen. A gene coding endoxylanase was expressed in E. coli. The recombinant enzyme was tolerant with some salts, detergents, and had high activity, thus is a good candidate for lignocellulose processing and as an animal feed food additive to effectively improve xylooligosaccharide production.

Abstract

Bacteria in rumen play pivotal roles in the digestion of nutrients to support energy for the host. In this study, metagenomic deep sequencing of bacterial metagenome extracted from the goats’ rumen generated 48.66 GB of data with 3,411,867 contigs and 5,367,270 genes. The genes were mainly functionally annotated by Kyoto Encyclopedia of Genes and Genomes (KEGG) Carbohydrate-Active enZYmes (CAZy), and HMMER database, and taxonomically classified by MEGAN. As a result, 65,554 genes encoding for 30 enzymes/proteins related to lignocellulose conversion were exploited, in which nine enzymes were seen for the first time in goat rumen. Prevotella was the most abundant genus, contributing 30% hemicellulases and 36% enzymes/proteins for lignocellulose pretreatment, and supporting 98.8% of feruloyl esterases and 71.7% acetylxylan esterases. In addition, 18 of the 22 most lignocellulose digesting- potential contigs belonged to Prevotella. Besides, Prevotella possessed many genes coding for amylolytic enzymes. One gene encoding for endoxylanase was successfully expressed in E. coli. The recombinant enzyme had high Vmax, was tolerant to some salts and detergents, worked better at pH 5.5–6.5, temperature 40–50 °C, and was capable to be used in practices. Based on these findings, we confirm that Prevotella plays a pivotal role for hemicellulose digestion and significantly participates in starch, cellulose, hemicellulose, and pectin digestion in the goat rumen.

Extremophilic Prokaryotic Endoxylanases: Diversity, Applicability, and Molecular Insights

Extremophilic endoxylanases grabbed attention in recent years due to their applicability under harsh conditions of several industrial processes. Thermophilic, alkaliphilic, and acidophilic endoxylanases found their employability in bio-bleaching of paper pulp, bioconversion of lignocellulosic biomass into xylooligosaccharides, bioethanol production, and improving the nutritious value of bread and other bakery products. Xylanases obtained from extremophilic bacteria and archaea are considered better than fungal sources for several reasons. For example, enzymatic activity under broad pH and temperature range, low molecular weight, cellulase-free activity, and longer stability under extreme conditions of prokaryotic derived xylanases make them a good choice. In addition, a short life span, easy cultivation/harvesting methods, higher yield, and rapid DNA manipulations of bacterial and archaeal cells further reduces the overall cost of the product. This review focuses on the diversity of prokaryotic endoxylanases, their characteristics, and their functional attributes. Besides, the molecular mechanisms of their extreme behavior have also been presented here.

Synthetic dyes degradation using lignolytic enzymes produced from Halopiger aswanensis strain ABC_IITR by Solid State Fermentation

The present work focuses on studying the degradation of industrial synthetic dyes, which poses serious health hazards and a drastic impact on the environment. Currently available enzymatic processes have higher production and operational costs. However, most enzymes are active at acidic pH, which limits its application in textile dye degradation. This problem can be overcome by lignolytic enzymes obtained from halo-alkaliphile through Solid State Fermentation (SSF) using wheat bran (agro-byproduct) as a substrate. The major lignolytic enzymes studied were Lignin Peroxidase (LiP), Manganese Peroxidase (MnP), and laccase. The results demonstrated the highest activity of 215.4 ± 1.57 of LiP, 36.8 ± 2.38 of MnP, and 8.34 ± 0.21 IU/gds of laccase. Crude enzymes were used to treat synthetic dyes (mainly azo dyes), and their potential for its degradation was confirmed by spectrophotometric, GC-MS, and HPLC analysis. The highest decolorization of 82-93% of Malachite Green (MG) was achieved in LiP and MnP mediated reaction system within 2 hours. The laccase reaction system showed degradation of 53.87% of methyl orange without adding any redox mediator. After obtaining these results, the crude LiP and MnP in the reaction system were further subjected to decolorization at a higher MG concentration of 100-600 mg/L without a redox mediator. As a result, both LiP and MnP decolorized MG by 72-89%. Further, GC-MS analysis of MG biodegradation products confirmed the formation of less toxic low molecular weight products such as benzaldehyde and methanone.

Characterization of a new bifunctional endo-1,4-β-xylanase/esterase found in the rumen metagenome

Metagenomic data mining of the Nellore cattle rumen microbiota identified a new bifunctional enzyme, endo-1,4-β-xylanase/esterase, which was subsequently overexpressed in E. coli BL21 (DE3). This enzyme was stable at pH intervals of 5 to 6.5 and temperatures between 30 and 45 °C, and under the test conditions, it had a V_max of 30.959 ± 2.334 µmol/min/mg, K_m of 3.6 ± 0.6 mM and k_cat of 2.323 ± 175 s^-1. Additionally, the results showed that the enzyme is tolerant to NaCl and organic solvents and therefore is suitable for industrial environments. Xylanases are widely applicable, and the synergistic activity of endo-1,4-β-xylanase/esterase in a single molecule will improve the degradation efficiency of heteroxylans via the creation of xylanase binding sites. Therefore, this new molecule has the potential for use in lignocellulosic biomass processing and as an animal feed food additive and could improve xylooligosaccharide production efficiency.

Characterization of efficient xylanases from industrial-scale pulp and paper wastewater treatment microbiota

Xylanases are widely used enzymes in the food, textile, and paper industries. Most efficient xylanases have been identified from lignocellulose-degrading microbiota, such as the microbiota of the cow rumen and the termite hindgut. Xylanase genes from efficient pulp and paper wastewater treatment (PPWT) microbiota have been previously recovered by metagenomics, assigning most of the xylanase genes to the GH10 family. In this study, a total of 40 GH10 family xylanase genes derived from a certain PPWT microbiota were cloned and expressed in Escherichia coli BL21 (DE3). Among these xylanase genes, 14 showed xylanase activity on beechwood substrate. Two of these, PW-xyl9 and PW-xyl37, showed high activities, and were purified to evaluate their xylanase properties. Values of optimal pH and temperature for PW-xyl9 were pH 7 and 60 ℃, respectively, while those for PW-xyl37 were pH 7 and 55 ℃, respectively; their specific xylanase activities under optimal conditions were 470.1 U/mg protein and 113.7 U/mg protein, respectively. Furthermore, the Km values of PW-xyl9 and PW-xyl37 were determined as 8.02 and 18.8 g/L, respectively. The characterization of these two xylanases paves the way for potential application in future pulp and paper production and other industries, indicating that PPWT microbiota has been an undiscovered reservoir of efficient lignocellulase genes. This study demonstrates that a metagenomic approach has the potential to screen efficient xylanases of uncultured microorganisms from lignocellulose-degrading microbiota. In a similar way, other efficient lignocellulase genes might be identified from PPWT treatment microbiota in the future.

Xylanolytic Extremozymes Retrieved From Environmental Metagenomes: Characteristics, Genetic Engineering, and Applications

Xylanolytic enzymes have extensive applications in paper, food, and feed, pharmaceutical, and biofuel industries. These industries demand xylanases that are functional under extreme conditions, such as high temperature, acidic/alkaline pH, and others, which are prevailing in bioprocessing industries. Despite the availability of several xylan-hydrolyzing enzymes from cultured microbes, there is a huge gap between what is available and what industries require. DNA manipulations as well as protein-engineering techniques are also not quite satisfactory in generating xylan-hydrolyzing extremozymes. With a compound annual growth rate of 6.6% of xylan-hydrolyzing enzymes in the global market, there is a need for xylanolytic extremozymes. Therefore, metagenomic approaches have been employed to uncover hidden xylanolytic genes that were earlier inaccessible in culture-dependent approaches. Appreciable success has been achieved in retrieving several unusual xylanolytic enzymes with novel and desirable characteristics from different extreme environments using functional and sequence-based metagenomic approaches. Moreover, the Carbohydrate Active Enzymes database includes approximately 400 GH-10 and GH-11 unclassified xylanases. This review discusses sources, characteristics, and applications of xylanolytic enzymes obtained through metagenomic approaches and their amelioration by genetic engineering techniques.