A novel halotolerant xylanase from marine isolate Bacillus subtilis cho40: gene cloning and sequencing

Marine enzymes: Classification and application in various industries

Oceans are regarded as a plentiful and sustainable source of biological compounds. Enzymes are a group of marine biomaterials that have recently drawn more attention because they are produced in harsh environmental conditions such as high salinity, extensive pH, a wide temperature range, and high pressure. Hence, marine-derived enzymes are capable of exhibiting remarkable properties due to their unique composition. In this review, we overviewed and discussed characteristics of marine enzymes as well as the sources of marine enzymes, ranging from primitive organisms to vertebrates, and presented the importance, advantages, and challenges of using marine enzymes with a summary of their applications in a variety of industries. Current biotechnological advancements need the study of novel marine enzymes that could be applied in a variety of ways. Resources of marine enzyme can benefit greatly for biotechnological applications duo to their biocompatible, ecofriendly and high effectiveness. It is beneficial to use the unique characteristics offered by marine enzymes to either develop new processes and products or improve existing ones. As a result, marine-derived enzymes have promising potential and are an excellent candidate for a variety of biotechnology applications and a future rise in the use of marine enzymes is to be anticipated.

Cloning, Expression, and Characterization of a GHF 11 Xylanase from Alteromonas macleodii HY35 in Escherichia coli

A xylanase gene xynZT-1 from Alteromonas macleodii HY35 was cloned and expressed in Escherichia coli (E. coli). The sequencing results showed that the ORF of xynZT-1 was 831 bp. The xylanase DNA sequence encoded a 29 amino acids (aa) signal peptide and a 247-aa mature peptide. The XynZT-1 has been a calculated molecular weight (MW) of 27.93 kDa, isoelectric point (pI) of 5.11 and the formula C₁₂₆₆H₁₈₂₉N₃₂₇O₃₈₄S₅. The amino acid sequence of the xynZT-1 had a high similarity with that of glycosyl hydrolase family 11 (GHF11) reported from other microorganisms. The DNA sequence encoding mature peptide was subcloned into pET-28a(+) expression vector. The resulted plasmid pET-28a-xynZT-1 was transformed into E. coli BL21(DE3), and the recombinant strain BL21(DE3)/xynZT-1 was obtained. The optimum temperature and pH of the recombinant XynZT-1 were 45 ℃ and 5.0, respectively.

Three-Step Purification and Characterization of Organic Solvent-Tolerant and Alkali-Thermo-Tolerant Xylanase from Bacillus paramycoides T4 [MN370035]

In the present study, an extracellular alkali-thermo-tolerant xylanase from Bacillus paramycoides was produced in the presence of an organic solvent. The enzyme was purified by ammonium sulphate precipitation, gel filtration, and ion exchange chromatography, with an overall recovery of 25.9%. The purified enzyme hada 70 kDa molecular weight (MW) confirmed by SDS-PAGE gel analysis. The maximum enzyme activity was reported at 55 °C and pH 7.0. Xylanase activity and stability were improved in the presence of 30% (v/v) n-dodecane, iso-octane, n-decane, and cyclohexane (7 days). The enzyme activity was improved by Co2+, EDTA, and Triton-X-100 while vigorously repressed by Hg2+ and Cu2+. The purified enzyme showed 1.473 mg/mL Km and 654.017 µg/mL/min Vmax values. The distinctive assets of the isolate verified the potential application in the field of biomass conversion into fuel and other industrial processes. Organic solvent-tolerant xylanases can be used for concurrent saccharification and bioethanol production, the amplification of intoxicating beverages, and the fermenting industry.

Shallow Hydrothermal Vent Bacteria and Their Secondary Metabolites with a Particular Focus on Bacillus

Extreme environments are hostile for most organisms, but such habitats represent suitable settings to be inhabited by specialized microorganisms. A marine shallow-water hydrothermal vent field is located offshore in northeast Taiwan, near the shallow shore of the southeast of Kueishantao Island (121°55' E, 24°50' N). Research on extremophilic microorganisms makes use of the biotechnological potential associated with such microorganisms and their cellular products. With the notion that extremophiles are capable of surviving in extreme environments, it is assumed that their metabolites are adapted to function optimally under such conditions. As extremophiles, they need specific culture conditions, and only a fraction of species from the original samples are recovered in culture. We used different non-selective and selective media to isolate bacterial species associated with the hydrothermal vent crab Xenograpsus testudinatus and the sediments of its habitat. The highest number of colonies was obtained from Zobell marine agar plates with an overall number of 29 genetically distinct isolates. 16sRNA gene sequencing using the Sanger sequencing method revealed that most of the bacterial species belonged to the phylum Firmicutes and the class Bacilli. The present study indicates that hydrothermal vent bacteria and their secondary metabolites may play an important role for the reconstruction of the evolutionary history of the phylum Procaryota.

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.

Biotechnological Aspects of Salt-Tolerant Xylanases: A Review

β-1,4-Xylan is the main component of hemicelluloses in land plant cell walls, whereas β-1,3-xylan is widely found in seaweed cell walls. Complete hydrolysis of xylan requires a series of synergistically acting xylanases. High-saline environments, such as saline-alkali lands and oceans, frequently occur in nature and are also involved in a broad range of various industrial processes. Thus, salt-tolerant xylanases may contribute to high-salt and marine food processing, aquatic feed production, industrial wastewater treatment, saline-alkali soil improvement, and global carbon cycle, with great commercial and environmental benefits. This review mainly introduces the definition, sources, classification, biochemical and molecular characteristics, adaptation mechanisms, and biotechnological applications of salt-tolerant xylanases. The scope of development for salt-tolerant xylanases is also discussed. It is anticipated that this review would serve as a reference for further development and utilization of salt-tolerant xylanases and other salt-tolerant enzymes.

Xylanase from Marine Filamentous Fungus Pestalotiopsis sp. AN-7 Was Activated with Diluted Salt Solution Like Brackish Water

The genus Pestalotiopsis are endophytic fungi that have recently been identified as cellulolytic system producers. We herein cloned a gene coding for a xylanase belonging to glycoside hydrolase (GH) family 10 (PesXyn10A) from Pestalotiopsis sp. AN-7, which was isolated from the soil of a mangrove forest. This protein was heterologously expressed by Pichia pastoris as a host, and its enzymatic properties were characterized. PesXyn10A was produced as a glycosylated protein and coincident to theoretical molecular weight (35.3 kDa) after deglycosylation by peptide-NfF-glycosidase F. Purified recombinant PesXyn10A exhibited maximal activity at pH 6.0 and 50 °C, and activity was maintained at 90 % at pH 5.0 and temperatures lower than 30 °C for 24 h. The substrate specificity of PesXyn10A was limited and it hydrolyzed glucuronoxylan and arabinoxylan, but not β-glucan. The final hydrolysis products from birchwood xylan were xylose, xylobiose, and 1,2³-α-D-(4-O-methyl-glucuronyl)-1,4-β-D-xylotriose. The addition of metallic salts (NaCl, KCl, MgCl₂, and CaCl₂) activated PesXyn10A for xylan degradation, and maximal activation by these divalent cations was approximately 160 % at a concentration of 5 mM. The thermostability of PesXyn10A significantly increased in the presence of 50 mM NaCl or 5 mM MgCl₂. The present results suggest that the presence of metallic salts at a low concentration, similar to brackish water, exerts positive effects on the enzyme activity and thermal stability of PesXyn10A.

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.

Biochemical characterization and molecular docking of cloned xylanase gene from Bacillus subtilis RTS expressed in E. coli

This study employed mesophilic Bacillus subtilis RTS strain isolated from soil with high xylanolytic activity. A 642 bp (xyn) xylanase gene (GenBank accession number MT677937) was extracted from Bacillus subtilis RTS and cloned in Escherichia coli BL21 cells using pET21c expression system. The cloned gene belongs to glycoside hydrolase family 11 with protein size of approximately 23 KDa. The recombinant xylanase showed optimal enzyme activity at 60 °C and at pH 6.5. Thermostability of recombinant xylanase was observed between the temperature range of 30-60 °C. Xylanase also remained stable in different concentration of various organic solvents (ethanol, butanol). This might be due to the formation of protein/organic solvent interface which prevents stripping of essential water molecules from enzyme, thus enzyme conformation and activity remained stable. Finally, the molecular docking analysis through AutoDock Vina showed the involvement of Tyr 108, Arg140 and Pro144 in protein-ligand interaction, which stabilizes this complex. The observed stability of recombinant xylanase at higher temperature and in the presence of organic solvent (ethanol, butanol) suggested possible application of this enzyme in biofuel and other industrial applications.

A thermophilic and thermostable xylanase from Caldicoprobacter algeriensis: Recombinant expression, characterization and application in paper biobleaching

A novel xylanase gene xynBCA, encoding a polypeptide of 439 residues (XynBCA), was cloned from Caldicoprobacter algeriensis genome and recombinantly expressed in Escherichia coli BL21(DE3). The amino acid sequence analysis showed that XynBCA belongs to the glycoside hydrolase family 10. The purified recombinant enzyme has a monomeric structure of 52 kDa. It is active and stable in a wide range of pH from 3 to 10 with a maximum activity at 6.5. Interestingly, XynBCA was highly thermoactive with an optimum temperature of 80 °C, thermostable with a half-life of 20 min at 80 °C. The specific activity was 117 U mg^-1, while the K_m and V_max were 1.247 mg ml^-1, and 114.7 μmol min^-1 mg^-1, respectively. The investigation of XynBCA in kraft pulp biobleaching experiments showed effectiveness in releasing reducing sugars and chromophores, with best achievements at 100 U g^-1 of pulp and 1 h of incubation. The comparative molecular modeling studies with the less thermostable Xylanase B from Clostridium stercorarium, revealed extra charged residues at the surface of XynBCA potentially participating in the formation of intermolecular hydrogen bonds with solvent molecules or generating salt bridges, therefore contributing to the higher thermal stability.

Biodiversity of Bacteria Associated with Eight Pleurotus ostreatus (Fr.) P. Kumm. Strains from Poland, Japan and the USA

Few publications report the occurrence of bacteria associated with fungal cells. The presence of bacteria associated with one strain of Pleurotus ostreatus (Fr.) P. Kumm. was described in the literature. We describe the biodiversity of bacteria associated with eight oyster mushroom strains from Japan, Poland, and the USA. The presence of microorganisms associated with all tested P. ostreatus strains was confirmed using fluorescent microscopy. Among 307 sequences, 233 of clones representing 34 genera and 74 sequences were identified as Bacteria. Most of the bacteria associated with the strain PUSAS were related to E. coli and two clones were related to Cupriavidus genus. The biodiversity of clones isolated from fungal strains originating from Japan and Poland ranged from 15 to 32 different bacterial clones. The most often the bacteria related to genus Curvibacter, Pseudomonas, Bacillus, Cupriavidus, Pelomonas, and Propionibacterium were associated with the strains of fungi mentioned above. Laccase-like (LMCO) genes were identified in whole bacterial DNA isolated from the associated bacteria but β-glucosidase and β-xylanase genes were not detected.

Few publications report the occurrence of bacteria associated with fungal cells. The presence of bacteria associated with one strain of Pleurotus ostreatus (Fr.) P. Kumm. was described in the literature. We describe the biodiversity of bacteria associated with eight oyster mushroom strains from Japan, Poland, and the USA. The presence of microorganisms associated with all tested P. ostreatus strains was confirmed using fluorescent microscopy. Among 307 sequences, 233 of clones representing 34 genera and 74 sequences were identified as Bacteria. Most of the bacteria associated with the strain PUSAS were related to E. coli and two clones were related to Cupriavidus genus. The biodiversity of clones isolated from fungal strains originating from Japan and Poland ranged from 15 to 32 different bacterial clones. The most often the bacteria related to genus Curvibacter, Pseudomonas, Bacillus, Cupriavidus, Pelomonas, and Propionibacterium were associated with the strains of fungi mentioned above. Laccase-like (LMCO) genes were identified in whole bacterial DNA isolated from the associated bacteria but β-glucosidase and β-xylanase genes were not detected.

A computational method for prediction of xylanase enzymes activity in strains of Bacillus subtilis based on pseudo amino acid composition features

Xylanases are hydrolytic enzymes which based on physicochemical properties, structure, mode of action and substrate specificities are classified into various glycoside hydrolase (GH) families. The purpose of this study is to show that the activity of the members of the xylanase family in the specified pH and temperature conditions can be computationally predicted. The proposed computational regression model was trained and tested with the Pseudo Amino Acid Composition (PseAAC) features extracted solely from the amino acid sequences of enzymes. The xylanases with experimentally determined activities were used as the training dataset to adjust the model parameters. To develop the model, 41 strains of Bacillus subtilis isolated from field soil were screened. From them, 28 strains with the highest halo diameter were selected for further studies. The performance of the model for prediction of xylanase activity was evaluated in three different temperature and pH conditions using stratified cross-validation and jackknife methods. The trained model can be used for determining the activity of newly found xylanases in the specified condition. Such computational models help to scale down the experimental costs and save time by identifying enzymes with appropriate activity for scientific and industrial usage. Our methodology for activity prediction of xylanase enzymes can be potentially applied to the members of the other enzyme families. The availability of sufficient experimental data in specified pH and temperature conditions is a prerequisite for training the learning model and to achieve high accuracy.

Novel Salt-Tolerant Xylanase from a Mangrove-Isolated Fungus Phoma sp. MF13 and Its Application in Chinese Steamed Bread

A novel glycosyl hydrolase family 11 xylanase gene, xynMF13A, was cloned from Phoma sp. MF13, a xylanase-producing fungus isolated from mangrove sediment. xynMF13A was heterologously expressed in Pichia pastoris, and the recombinant XynMF13A (rXynMF13A) was purified by Ni-affinity chromatography. The temperature and pH optima of purified rXynMF13A were 45 °C and pH 5.0, respectively. rXynMF13A showed a high level of salt tolerance, with maximal enzyme activity being seen at 0.5 M NaCl and as much as 53% of maximal activity at 4 M NaCl. The major rXynMF13A hydrolysis products from corncob xylan were xylobiose, xylotriose, xylotetraose, and xylopentaose, but no xylose was found. These hydrolysis products suggest an important potential for XynMF13A in the production of xylooligosaccharides (XOs). Furthermore, rXynMF13A had beneficial effects on Chinese steamed bread production, by increasing specific volume and elasticity while decreasing hardness and chewiness. These results demonstrate XynMF13A to be a novel xylanase with potentially significant applications in baking, XOs production, and seafood processing.

Gene Expression and Molecular Characterization of a Xylanase from Chicken Cecum Metagenome

A xylanase gene xynA_MG1 with a 1,116-bp open reading frame, encoding an endo-β-1,4-xylanase, was cloned from a chicken cecum metagenome. The translated XynA_MG1 protein consisted of 372 amino acids including a putative signal peptide of 23 amino acids. The calculated molecular mass of the mature XynA_MG1 was 40,013 Da, with a theoretical pI value of 5.76. The amino acid sequence of XynA_MG1 showed 59% identity to endo-β-1,4-xylanase from Prevotella bryantii and Prevotella ruminicola and 58% identity to that from Prevotella copri. XynA_MG1 has two conserved motifs, DVVNE and TEXD, containing two active site glutamates and an invariant asparagine, characteristic of GH10 family xylanase. The xynA_MG1 gene without signal peptide sequence was cloned and fused with thioredoxin protein (Trx.Tag) in pET-32a plasmid and overexpressed in Escherichia coli Tuner™(DE3)pLysS. The purified mature XynA_MG1 was highly salt-tolerant and stable and displayed higher than 96% of its catalytic activity in the reaction containing 1 to 4 M NaCl. It was only slightly affected by common organic solvents added in aqueous solution to up to 5 M. This chicken cecum metagenome-derived xylanase has potential applications in animal feed additives and industrial enzymatic processes requiring exposure to high concentrations of salt and organic solvents.

Building a bio-based industry in the Middle East through harnessing the potential of the Red Sea biodiversity

The incentive for developing microbial cell factories for production of fuels and chemicals comes from the ability of microbes to deliver these valuable compounds at a reduced cost and with a smaller environmental impact compared to the analogous chemical synthesis. Another crucial advantage of microbes is their great biological diversity, which offers a much larger "catalog" of molecules than the one obtainable by chemical synthesis. Adaptation to different environments is one of the important drives behind microbial diversity. We argue that the Red Sea, which is a rather unique marine niche, represents a remarkable source of biodiversity that can be geared towards economical and sustainable bioproduction processes in the local area and can be competitive in the international bio-based economy. Recent bioprospecting studies, conducted by the King Abdullah University of Science and Technology, have established important leads on the Red Sea biological potential, with newly isolated strains of Bacilli and Cyanobacteria. We argue that these two groups of local organisms are currently most promising in terms of developing cell factories, due to their ability to operate in saline conditions, thus reducing the cost of desalination and sterilization. The ability of Cyanobacteria to perform photosynthesis can be fully exploited in this particular environment with one of the highest levels of irradiation on the planet. We highlight the importance of new experimental and in silico methodologies needed to overcome the hurdles of developing efficient cell factories from the Red Sea isolates.

Recombinant Xylanase from Bacillus tequilensis BT21: Biochemical Characterisation and Its Application in the Production of Xylobiose from Agricultural Residues

Bacterial strain Bacillus tequilensis BT21 isolated from marine sediments was found to produce extracellular xylanase. The xynBT21 gene encoding xylanase enzyme was cloned and expressed in Escherichia coli. The gene encoded a protein consisting of 213 amino acid residues with calculated molecular mass of 23.3 kDa. Purified recombinant xylanase had optimum activity at 60 °C and pH=6. The enzyme was highly stable in alkaline pH, at pH=7 it remained 100% active for 24 h, while its activity increased at pH=8 and 9 during incubation. B. tequilensis BT21 xylanase had alkaline pI of 9.4 and belongs to glycosyl hydrolase family 11. The mode of action of XynBT21 on beechwood xylan and xylooligosaccharides was studied. It hydrolysed xylooligosaccharides and beechwood xylan yielding mainly xylobiose (X₂) with a small amount of xylose (X₁), indicating that XynBT21 was probably an endo-acting xylanase. Enzymatic hydrolysis using wheat bran as a substrate revealed that xylanase reported here has the potential to produce xylobiose from wheat bran. Xylooligosaccharides, especially xylobiose, have strong bifidogenic properties and are increasingly used as a prebiotic. This is the first report that describes this novel xylanase enzyme from marine B. tequilensis BT21 used for the release of xylobiose from wheat bran.

Extremozymes from Marine Actinobacteria

Marine microorganisms that have the possibility to survive in diverse conditions such as extreme temperature, pH, pressure, and salinity are known as extremophiles. They produce biocatalysts so named as extremozymes that are active and stable at extreme conditions. These enzymes have numerous industrial applications due to its distinct properties. Till now, only a fraction of microorganisms on Earth have been exploited for screening of extremozymes. Novel techniques used for the cultivation and production of extremophiles, as well as cloning and overexpression of their genes in various expression systems, will pave the way to use these enzymes for chemical, food, pharmaceutical, and other industrial applications.

Xylan degradation improved by a combination of monolithic columns bearing immobilized recombinant β-xylosidase from Aspergillus awamori X-100 and Grindamyl H121 β-xylanase

Synergistic action of exo- and endohydrolazes is preferred for effective destruction of biopolymers. The main purpose of the present work was to develop an efficient tool for degradation of xylan. Macroporous lab-made monolithic columns and commercial CIM-Epoxy disk were used to immobilize the recombinant β-xylosidase from Aspergillus awamori and Grindamyl β-xylanase. The efficiency of xylan degradation using the low-loaded β-xylosidase column appeared to be four times higher than for the in-solution process and about six times higher than for the high-loaded bioreactor. Disk bioreactor with the Grindamil β-xylanase operated in a recirculation mode has shown noticeable advantages over the column design. Additionally, a system comprised of two immobilized enzyme reactors (IMERs) was tested to accelerate the biopolymer hydrolysis, yielding total xylan conversion into xylose within 20 min. Fast online monitoring HPLC procedure was developed where an analytical DEAE CIM disk was added to the two-enzyme system in a conjoint mode. A loss of activity of immobilized enzymes did not exceed 7% after 5 months of the bioreactor usage. We can therefore conclude that the bioreactors developed exhibit high efficiency and remarkable long-term stability.

Secretory expression and characterization of two hemicellulases, xylanase, and β-xylosidase, isolated from Bacillus subtilis M015

Microbial hydrolysis of lignocellulosic biomass is becoming increasingly important for the production of renewable biofuels to address global energy concerns. Hemicellulose is the second most abundant lignocellulosic biopolymer consisting of mostly xylan and other polysaccharides. A variety of enzymes is involved in complete hydrolysis of xylan into its constituent sugars for subsequent biofuel fermentation. Two enzymes, endo-β-xylanase and β-xylosidase, are particularly important in hydrolyzing the xylan backbone into xylooligosaccharides and individual xylose units. In this study, we describe the cloning, expression, and characterization of xylanase and β-xylosidase isolated from Bacillus subtilis M015 in Escherichia coli. The genes were identified to encode a 213 amino acid protein for xylanase (glycoside hydrolase (GH) family 11) and a 533 amino acid protein for β-xylosidase (GH family 43). Recombinant enzymes were produced by periplasmic-leaky E. coli JE5505 and therefore secreted into the supernatant during growth. Temperature and pH optima were determined to be 50 °C and 5.5–6 for xylanase and 35 °C and 7.0–7.5 for β-xylosidase using beech wood xylan and p-nitrophenyl-β-D-xylopyranoside as the substrates, respectively. We have also investigated the synergy of two enzymes on xylan hydrolysis and observed 90 % increase in total sugar release (composed of xylose, xylobiose, xylotriose, and xylotetraose) for xylanase/β-xylosidase combination as opposed to xylanase alone.

Comparison of bacterial biodiversity and enzyme production in three hypersaline lakes; urmia, howz-soltan and aran-bidgol

This research is a comparative study on the diversity of halophilic bacteria with hydrolytic activities in three significant hypersaline lakes; Urmia in the northwest and Howz-Soltan and Aran-Bidgol in the central desert in Iran. Isolated strains from these saline lakes were found to be halotolerant, moderately and extremely halophilic bacteria. The bacteria in each saline lake were able to produce different hydrolytic enzymes including amylase, protease, lipase, DNase, inulinase, xylanase, carboxy methyl cellulase, pectinase and pullulanase. 188, 302, 91 halophilic strains were isolated from Urmia Lake, Howz-Soltan and Aran-Bidgol playa, respectively. The numbers of Gram-positive strains were more than Gram-negatives, and among Gram-positive bacteria; spore-forming bacilli were most abundant. Due to the unique physico-chemical conditions of the lake environments, the hydrolytic activities of isolated strains were significantly different. For instance, isolated strains from Howz-Soltan playa did not produce pectinase, DNase, amylase, lipase and inulinase, while the isolates from Aran-Bidgol playa had a great ability to produce pectinase and DNase. The strains from Urmia Lake were also good producers of DNase but failed to show any chitinase activity. The diversity of halophilic bacteria from the mentioned three saline lakes was also determined using PCR-amplified 16S rRNA followed by phylogenetic analysis of the partial 16S rRNA sequences.

Cloning, over-expression and characterization of a thermo-tolerant xylanase from Thermotoga thermarum

The xyn10B gene, encoding the endo-1,4-β-xylanase Xyn10B from Thermotoga thermarum, was cloned and expressed in Escherichia coli. The ORF of the xyn10B was 1,095 bp and encoded to mature peptide of 344 amino acids with a calculated MW of 40,531 Da. The recombinant xylanase was optimally active at 80 °C, pH 6.0 and retained approx. 60 % of its activity after 2 h at 75 °C. Apparent K m , k cat and k cat /K m values of the xylanase for beechwood xylan were 1.8 mg ml(-1), 520 s(-1) and 289 ml mg(-1) s(-1), respectively. The end products of the hydrolysis of beechwood xylan were mainly oligosaccharides but without xylose after 2 h hydrolysis.

A novel highly thermostable xylanase stimulated by Ca2+ from Thermotoga thermarum: cloning, expression and characterization

BACKGROUND

Xylanase is an important component of hemicellulase enzyme system. Since it plays an important role in the hydrolysis of hemicellulose into xylooligosaccharides (XOs), high thermostable xylanase has been the focus of much recent attention as powerful enzyme as well as in the field of biomass utilization.

RESULTS

A xylanase gene (xyn10A) with 3,474 bp was cloned from the extremely thermophilic bacterium Thermotoga thermarum that encodes a protein containing 1,158 amino acid residues. Based on amino acid sequence homology, hydrophobic cluster and three dimensional structure analyses, it was attested that the xylanase belongs to the glycoside hydrolase (GH) families 10 with five carbohydrate binding domains. When the xylanase gene was cloned and expressed in Escherichia coli BL21 (DE3), the specific enzyme activity of xylanase produced by the recombinant strain was up to 145.8 U mg-1. The xylanase was optimally active at 95°C, pH 7.0. In addition, it exhibited high thermostability over broad range of pH 4.0-8.5 and temperature 55-90°C upon the addition of 5 mM Ca2+. Confirmed by Ion Chromatography System (ICS) analysis, the end products of the hydrolysis of beechwood xylan were xylose, xylobiose, xylotriose, xylotetraose, xylopentaose and xylohexaose.

CONCLUSIONS

The xylanase from T. thermarum is one of the hyperthermophilic xylanases that exhibits high thermostability, and thus, is a suitable candidate for generating XOs from cellulosic materials such as agricultural and forestry residues for the uses as prebiotics and precursors for further preparation of furfural and other chemicals.