Xylanase encoded by genetically engineered Clostridium thermocellum gene in Bacillus subtilis

Summary Xylanase was produced with Bacillus subtilis(pJX18), constructed previously, which contains Clostridium thermocellum xylanase gene expressing with a strong Bacillus promoter. The enzyme hydrolyzed oat spelt xylan to mostly xylobiose and xylotriose which are preferred for industrial applications. The optimal temperature and pH for the activity of this enzyme were 60°C and 5.4, respectively, with moderate stability under these conditions.     

Expression of a xylanase gene of Bacillus pumilus in Escherichia coli and Bacillus subtilis

Summary A hybrid plasmid, pOXN29 (10.4 Mdal), coding the xylanase (xynA) and -xylosidase (xynB) genes of Bacillus pumilus IPO was constructed by the ligation of pBR322 and a 7.7 Mdal PstI-fragment of chromosomal DNA as reported in our previous paper (Panbangred et al. 1983). A deletion plasmid of pOXN29, pOXN293 (9.2 Mdal), which contains xynA and xynB, was ligated with pUB110 at an EcoRI site, and used to transform B. subtilis MI111. Two selected clones of B. subtilis as xylanase hyper-producers contained plasmids pOXW11 (4.2 Mdal) and pOXW12 (4.0 Mdal), both consisting of only pUB110, xynA, and its flanking regions, as the result of spontaneous deletion. These B. subtilis clones produced 2.7–3.0 times as much xylanase as B. pumilus. Escherichia coli and B. subtilis clones harbouring the hybrid plasmids synthesized xylanase and -xylosidase constitutively, whereas both enzymes were induced by xylose in B. pumilus.Xylanase synthesized by B. subtilis harbouring pOXW11 or pOXW12 was excreted into the medium like that of B. pumilus IPO, but xylanase synthesized in E. coli harbouring pOXN29, 293 or pOXW1 coding xynA was intracellular. In a previous investigation (Panbangred et al. 1983), xylanase was found to be located in the cytoplasm, not the periplasm nor the membrane fraction in E. coli cells harbouring pOXN29 derivatives. In spite of the abnormal location of xylanase synthesized in E. coli, the signal peptide was processed in the same way as in B. pumilus, with the same molecular weight and the same amino terminal sequences of xylanase prepared from E. coli cells and B. pumilus culture fluid.     

Synthesis and secretion of a heat-stable carboxymethylcellulose from Clostridium thermocellum in Bacillus subtilis and Bacillus stearothermophilus

Summary The cellulase gene celA of Clostridium thermocellum coding for the thermostable endoglucanase A was transferred from Escherichia coli to Bacillus subtilis 168 and B. stearothermophilus CU21 using plasmids derived from the Bacillus vector pUB110. When the structural part of the gene was joined to a pUB110 promoter the recombinant plasmids (pSE102, pSE105) were stably maintained and expressed carboxymethylcellulase (CMCase) activity. In B. stearothermophilus CU21 (pSE105) the clostridial CMCase was produced over a wide temperature range up to the maximal growth temperature (68° C). In contrast to E. coli, all of the CMCase synthesized in bacilli was released into the culture medium. About 50% of the extracellular protein secreted by B. subtilis 168 (pSE102) carrying the celA gene consisted of endoglucanase A. These findings demonstrate the feasibility of producing cellulolytic enzymes from thermophilic anaerobes in bacilli.     

Molecular cloning of a Bacillus subtilis xylanase gene in Escherichia coli

A gene coding for xylanase synthesis in Bacillus subtilis was isolated by direct shotgun cloning using Escherichia coli as a host. Following partial digestion of B. subtilis chromosomal DNA with PstI or EcoRI restriction enzymes, fragments ranging from 3 to 7 kb were introduced into the PstI or EcoRI sites of pBR325. Transformed colonies having lost either the ampicillin or chloramphenicol resistance markers were screened directly on 1% xylan plates. Out of 8000 transformants, ten xylanase-positive clones were identified by the clearing zone around lysozyme-treated colonies. Further characterization of one of the clones showed that the xylanase gene was present in a 3.9-kb insert within the PstI site of the plasmid pBR325. Retransformation of E. coli strain with the xylanase-positive hybrid plasmid pRH271 showed 100% transformation to xylanase production. The intracellular xylanase produced by the transformed E. coli was purified by ion exchange and gel permeation chromatography. The electrophoretic mobility of the purified xylanase indicated an Mr of 22 000.     

Expression of a Clostridium thermocellum endoglucanase gene in Lactobacillus plantarum.

Recombinant plasmid pM25 containing the celE gene of Clostridium thermocellum, which codes for an enzymatically active endoglucanase, was transformed into Lactobacillus plantarum by electroporation. Strains harboring pM25 expressed thermostable endoglucanase, which was found predominantly in the culture medium. Two other plasmids, pGK12 and pSA3, were transformed into L. plantarum, and the stability of each plasmid was evaluated.     

Decoding Biomass-Sensing Regulons of Clostridium thermocellum Alternative Sigma-I Factors in a Heterologous Bacillus subtilis Host System

The Gram-positive, anaerobic, cellulolytic, thermophile Clostridium (Ruminiclostridium) thermocellum secretes a multi-enzyme system called the cellulosome to solubilize plant cell wall polysaccharides. During the saccharolytic process, the enzymatic composition of the cellulosome is modulated according to the type of polysaccharide(s) present in the environment. C. thermocellum has a set of eight alternative RNA polymerase sigma (σ) factors that are activated in response to extracellular polysaccharides and share sequence similarity to the Bacillus subtilis σ^I factor. The aim of the present work was to demonstrate whether individual C. thermocellum σ^I-like factors regulate specific cellulosomal genes, focusing on C. thermocellum σ^I6 and σ^I3 factors. To search for putative σ^I6- and σ^I3-dependent promoters, bioinformatic analysis of the upstream regions of the cellulosomal genes was performed. Because of the limited genetic tools available for C. thermocellum, the functionality of the predicted σ^I6- and σ^I3-dependent promoters was studied in B. subtilis as a heterologous host. This system enabled observation of the activation of 10 predicted σ^I6-dependent promoters associated with the C. thermocellum genes: sigI6 (itself, Clo1313_2778), xyn11B (Clo1313_0522), xyn10D (Clo1313_0177), xyn10Z (Clo1313_2635), xyn10Y (Clo1313_1305), cel9V (Clo1313_0349), cseP (Clo1313_2188), sigI1 (Clo1313_2174), cipA (Clo1313_0627), and rsgI5 (Clo1313_0985). Additionally, we observed the activation of 4 predicted σ^I3-dependent promoters associated with the C. thermocellum genes: sigI3 (itself, Clo1313_1911), pl11 (Clo1313_1983), ce12 (Clo1313_0693) and cipA. Our results suggest possible regulons of σ^I6 and σ^I3 in C. thermocellum, as well as the σ^I6 and σ^I3 promoter consensus sequences. The proposed -35 and -10 promoter consensus elements of σ^I6 are CNNAAA and CGAA, respectively. Additionally, a less conserved CGA sequence next to the C in the -35 element and a highly conserved AT sequence three bases downstream of the -10 element were also identified as important nucleotides for promoter recognition. Regarding σ^I3, the proposed -35 and -10 promoter consensus elements are CCCYYAAA and CGWA, respectively. The present study provides new clues for understanding these recently discovered alternative σ^I factors.     

Molecular characterization of xynX, a gene encoding a multidomain xylanase with a thermostabilizing domain from Clostridium thermocellum

A Clostridium thermocellum gene, xynX, coding for a xylanase was cloned and the complete nucleotide sequence was determined. The xylanase gene of Clostridium thermocellum consists of an ORF of 3261 nucleotide encoding a xylanase (XynX) of 1087 amino acid residues (116 kDa). Sequence analysis of XynX showed a multidomain structure that consisted of four different domains: an N-terminal thermostabilizing domain homologous to sequences found in several thermophilic enzymes, a catalytic domain homologous to family 10 glycosyl hydrolases, a duplicated cellulose-binding domain (CBD) homologous to family IX CBDs, and a triplicated S-layer homologous domain. A deletion mutant of xynX having only the catalytic region produced a mutant enzyme XynX-C which retained catalytic activity but lost thermostability. In terms of half-life at 70 °C, the thermostability of XynX-C was about six times lower than that of the other mutant enzyme, XynX-TC, produced by a mutant containing both the thermostabilizing domain and the catalytic domain. The optimum temperature of XynX-C was about 5–10 °C lower than that of XynX-TC. Received: 12 January 2000 / Received revision: 24 April 2000 / Accepted: 1 May 2000     

Nucleotide sequence and deletion analysis of the xylanase gene (xynZ) of Clostridium thermocellum.

The nucleotide sequence of the xynZ gene, encoding the extracellular xylanase Z of Clostridium thermocellum, was determined. The putative xynZ gene was 2,511 base pairs long and encoded a polypeptide of 837 amino acids. A region of 60 amino acids containing a duplicated segment of 24 amino acids was found between residues 429 and 488 of xylanase Z. This region was strongly similar to the conserved domain found at the carboxy-terminal ends of C. thermocellum endoglucanases A, B, and D. Deletions removing up to 508 codons from the 5' end of the gene did not affect the activity of the encoded polypeptide, showing that the active site was located in the C-terminal half of the protein and that the conserved region was not involved in catalysis. Expression of xylanase activity in Escherichia coli was increased up to 220-fold by fusing fragments containing the 3' end of the gene with the start of lacZ present in pUC19. An internal translational initiation site which was efficiently recognized in E. coli was tentatively identified 470 codons downstream from the actual start codon.     

Identification of three distinct Clostridium thermocellum xylanase genes by molecular cloning

Three genes coding for xylanase synthesis in Clostridium thermocellum were cloned and expressed in Escherichia coli. Genomic DNA from Clostridium thermocellum was digested to completion with HindIII, BamHI, and SalI. The fragments were ligated into the corresponding sites of pUC19 and transformed into Escherichia coli. Two of the genes encoded for xylanases which depolymerized xylans but were unable to extensively convert these substrates to reducing sugar. The third gene encoded for an enzyme that extensively hydrolyzed xylan. The insert containing the latter gene was subjected to extensive mapping and was found to encode for a xylanase with a molecular weight of approximately 25,000. The protein product of the cloned gene was obtained in a relatively pure form by heat treatment, ion exchange and gel permeation steps. The enzyme was quite stable to high temperatures with a half-life of 24 h at 70°C.Issued as National Research Council of Canada No. 30545     

Expression of a Bacillus megaterium sporulation-specific gene during sporulation of Bacillus subtilis

The gene for the Bacillus megaterium spore C protein, a sporulation-specific gene, has been transferred into Bacillus subtilis. The B. megaterium gene was expressed little, if at all, during log-phase and early-stationary-phase growth, but was expressed during sporulation with the same kinetics as and at a level similar to that of the analogous B. subtilis genes. This finding is most consistent with the regulation of this class of genes by a mechanism of positive control.     

Cloning and expression of Clostridium thermocellum F7 cellulase genes in Escherichia coli and Bacillus subtilis cells

The Clostridium thermocellum total DNA Sau 3A fragments' library was constructed on the basis of shuttle vector pMK4 for the Escherichia coli - Bacillus subtilis. 14 clones with endoglucanase activity and one with beta-glucosidase activity were selected in E. coli cells. Recombinant plasmids pCE were characterized by structural instability of various degree in B. subtilis cells. The results of the physical mapping, analysis of gene products in E. coli mini-cells as well as the DNA-DNA blot hybridization have led to conclusion on cloning of 7 individual genes for endoglucanases. Up to 3 polypeptides of various molecular weight corresponding to the products of cel gene were revealed in E. coli mini-cells containing the recombinant plasmids. The hybridization analysis demonstrated considerable homology of the majority of cel genes.     

Expression of a thermostable xylanase gene from Bacillus coagulans ST-6 in Lactococcus lactis

AIMS: The aim of the study is to evaluate whether xylanase can be used as a potential reporter gene for cloning and expression studies in Lactococcus. METHODS AND RESULTS: The 750 bp xylanase gene was amplified and subcloned into the unique NheI restriction enzyme site of pMG36e and subsequently transformed into competent Escherichia coli XLI-blue MRF cells and Lactococcus lactis cells. Bacterial culture containing pMG36e-Xy has an enzyme activity of 390 microg xylose ml(-1) culture 30 min(-1), respectively, when compared with 40 microg xylose ml(-1) culture 30 min(-1) for the negative control (plasmidless strain). CONCLUSIONS: The thermostable xylanase gene was successfully expressed in both E. coli and L. lactis. The activity of xylanase can be easily detected by the formation of visible clearing zones around the transformed colonies on Remazol Brilliant Blue-Xylan (RBB-Xylan) agar media. However, there were some significant differences in the optimum growth temperature and plasmid stability in the new clones. SIGNIFICANCE AND IMPACT OF THE STUDY: The constructed reporter vector has the potential to be used as a reporter system for Lactococcus as well as E. coli, and it is an addition to the pool of lactococcal vector systems.