Characterization of a recombinant thermostable xylanase from deep-sea thermophilic Geobacillus sp. MT-1 in East Pacific

Gene cloning, expression, and characterization of a thermostable xylanase from Nesterenkonia xinjiangensis CCTCC AA001025

An endo-beta-1,4-xylanase-encoding gene, xyn11NX, was cloned from Nesterenkonia xinjiangensis CCTCC AA001025 and expressed in Escherichia coli. The gene encoded a 192-amino acid polypeptide and a putative 50-amino acid signal peptide. The deduced amino acid sequence exhibited a high degree of similarity with the xylanases from Streptomyces thermocyaneoviolaceus (68%) and Thermobifida fusca (66%) belonging to glycoside hydrolase family 11. After purification to homogeneity, the recombinant Xyn11NX exhibited optimal activity at pH 7.0 and 55 degrees C and remained stable at weakly acidic to alkaline pH (pH 5.0-11.0). The enzyme was thermostable, retaining more than 80% of the initial activity after incubation at 60 degrees C for 1 h and more than 40% of the activity at 90 degrees C for 15 min. The K (m) and V (max) values for oat spelt xylan and birchwood xylan were 16.08 mg ml(-1) and 45.66 micromol min(-1) mg(-1) and 9.22 mg ml(-1) and 16.05 micromol min(-1) mg(-1), respectively. The predominant hydrolysis products were xylobiose and xylotriose when using oat spelt xylan or birchwood xylan as substrate.

Gene cloning, expression and characterization of a new cold-active and salt-tolerant endo-beta-1,4-xylanase from marine Glaciecola mesophila KMM 241

Although a lot of xylanases are studied, only a few xylanases from marine microorganisms have been reported. A new xylanase gene, xynA, was cloned from marine bacterium Glaciecola mesophila KMM 241. Gene xynA contains 1,272 bp and encodes a 423-amino acid xylanase precursor. The recombinant xylanase, XynA, expressed in Escherichia coli BL21 is a monomer with a molecular mass of 43 kDa. Among the characterized xylanases, XynA shares the highest identity (46%) to the xylanase from Flavobacterium sp. strain MSY2. The optimum pH and temperature for XynA is 7.0 and 30 degrees C. XynA retains 23% activity and 27% catalytic efficiency at 4 degrees C. XynA has low thermostability, remaining 20% activity after 60-min incubation at 30 degrees C. Its apparent melting temperature (T (m)) is 44.5 degrees C. These results indicate that XynA is a cold-active xylanase. XynA shows a high level of salt-tolerance, with the highest activity at 0.5 M NaCl and retaining 90% activity in 2.5 M NaCl. It may be the first salt-tolerant xylanase reported. XynA is a strict endo-beta-1,4-xylanase with a demand of at least four sugar moieties for effective cleavage. It efficiently hydrolyzes xylo-oligosaccharides and xylan into xylobiose and xylotriose without producing xylose, suggesting its potential in xylo-oligosaccharides production.

Immobilization of Neocallimastix patriciarum xylanase on artificial oil bodies and statistical optimization of enzyme activity

A thermally stable and alkalophilic xylanase, XynCDBFV, from Neocallimastix patriciarum was overexpressed in Escherichia coli as a recombinant protein fused to the N-terminus of oleosin, a unique structural protein of seed oil bodies. As a result of the reconstitution of the artificial oil bodies (AOBs), the immobilization of active xylanase was accomplished. Response surface methodology (RSM) was employed for the optimization of the immobilized xylanase activity. The central composite design (CCD) and regression analysis methods were effective for determination of optimized temperature and pH conditions for the AOB-immobilized XynCDBFV. The optimal condition for the highest immobilized xylanase activity (3.93IU/mg of total protein) was observed at 59 degrees C and pH 6.0. Further, AOB-immobilized XynCDBFV retained 50% of its maximal activity after 120min at 60 degrees C, and it could be easily and simply recovered from the surface of the solution by brief centrifugation, and could be reused eight times while retaining more than 60% of its activity. These results proved it is a simple and effective method for direct immobilization of xylanases.

Cloning of a rumen fungal xylanase gene and purification of the recombinant enzyme via artificial oil bodies

A gene encoding a xylanase, named xynS20, was cloned from the ruminal fungus Neocallimastix patriciarum. The DNA sequence of xynS20 revealed that the gene was 1,008 bp in size and encoded amino acid sequences with a predicted molecular weight of 36 kDa. The amino acid sequence alignment showed that the highest sequence identity (28.4%) is with insect gut xylanase XYL6805. According to the sequence-based classification, a putative conserved domain of glycosyl hydrolase family 11 was detected at the N-terminus of XynS20 and a putative conserved domain of family 1 carbohydrate-binding module (CBM) was observed at the C-terminus of XynS20. An Asn-rich linker sequence was found between the N-terminal catalytic domain and the C-terminal CBM of XynS20. To examine the activity of the gene product, xynS20 gene was cloned as an oleosin-fused protein, expressed in Escherichia coli, affinity-purified by formation of artificial oil bodies, released from oleosin by intein-mediated peptide cleavage, and finally harvested by concentration of the supernatant. The specific activity of purified XynS20 toward oat spelt xylan was 1,982.8 U mg(-1). The recombinant XynS20 was stable in the mild acid pH range from 5.0 to 6.0, and the optimum pH was 6.0. The optimal reaction temperature of XynS20 was 45 degrees C; at temperatures below 30 and above 55 degrees C, enzyme activity was less than 50% of that at the optimal temperature.

Development of a versatile shuttle vector for gene expression in Geobacillus spp

An improved, versatile shuttle vector has been created for the metabolic engineering of Geobacillus spp. As kanamycin is the most thermo-tolerant of commonly used antibiotics, the gene encoding a thermostable kanamycin nucleotidyltransferase, together with the origin of replication from the G. stearothermophilus plasmid pBST1 were cloned into the Escherichia coli cloning vector pUC18. The resulting vector, named pUCG18, replicated in both organisms and could be transformed with an efficiency of 1 x 10(4) transformants per microg of DNA in G. thermoglucosidasius and was stable up to 68 degrees C with antibiotic selection. It was used to demonstrate expression of the pyruvate decarboxylase (pdc) gene from Zymomonas palmae in G. thermoglucosidasius at 45 degrees C. Sequence analysis of the pBST1 derived origin of replication revealed homology with a family of theta replicons that have previously only been found in strains of Bacillus megaterium.