Characteristics of thermostable endoxylanase and β-xylosidase of the extremely thermophilic bacterium Geobacillus thermodenitrificans TSAA1 and its applicability in generating xylooligosaccharides and xylose from agro-residues

An extremely thermophilic bacterial isolate that produces a high titer of thermostable endoxylanase and β-xylosidase extracellularly in an inducible manner was identified as Geobacillus thermodenitrificans TSAA1. The distinctive features of this strain are alkalitolerance and halotolerance. The endoxylanase is active over a broad range of pH (5.0–10.0) and temperatures (30–100 °C) with optima at pH 7.5 and 70 °C, while β-xylosidase is optimally active at pH 7.0 and 60 °C. The T _1/2 values of the endoxylanase and β-xylosidase are 30 min at 80 °C, and 180 min at 70 °C, respectively. The endoxylanase activity is stimulated by dithiothreitol, but inhibited strongly by EDAC and Woodward’s reagent K. N-BS and DEPC strongly inhibited β-xylosidase. MALDI-ToF (MS/MS) analysis of tryptic digest of β-xylosidase revealed similarity with that of G. thermodenitrificans NG 80-2, and suggested that this belongs to the GH 52 glycosyl hydrolase super family. The action of endoxylanase on birch wood xylan and agro-residues such as wheat bran and wheat straw liberated xylooligosaccharides similar to endoxylanases of the family 10 glycoside hydrolases, while the enzyme preparation having both endoxylanase and β-xylosidase liberated xylose as main hydrolysis product.     

Heterologous expression,purification and characterization of a highly thermolabile endoxylanase from the Antarctic fungus Cladosporium sp.

Numerous endoxylanases from mesophilic fungi have been purified and characterized. However, endoxylanases from cold-adapted fungi, especially those from Antarctica, have been less studied. In this work, a cDNA from the Antarctic fungus Cladosporium sp. with similarity to endoxylanases from glycosyl hydrolase family 10, was cloned and expressed in Pichia pastoris. The pure recombinant enzyme (named XynA) showed optimal activity on xylan at 50 °C and pH 6–7. The enzyme releases xylooligosaccharides but not xylose, indicating that XynA is a classical endoxylanase. The enzyme was most active on xylans with high content of arabinose (rye arabinoylan and wheat arabinoxylan) than on xylans with low content of arabinose (oat spelts xylan, birchwood xylan and beechwood xylan). Finally, XynA showed a very low thermostability. After 20–30 min of incubation at 40 °C, the enzyme was completely inactivated, suggesting that XynA would be the most thermolabile endoxylanase described so far in filamentous fungi. This is one of the few reports describing the heterologous expression and characterization of a xylanase from a fungus isolated from Antarctica.     

XIP-I, a xylanase inhibitor protein from wheat: a novel protein function

Endo-(1,4)-beta-xylanases of plant and fungal origin play an important role in the degradation of arabinoxylans. Two distinct classes of proteinaceous endoxylanase inhibitors, the Triticum aestivum xylanase inhibitor (TAXI) and the xylanase inhibitor protein (XIP), have been identified in cereals. Engineering of proteins in conjunction with enzyme kinetics, thermodynamic, real-time interaction, and X-ray crystallographic studies has provided knowledge on the mechanism of inhibition of XIP-I towards endoxylanases. XIP-I is a 30 kDa protein which belongs to glycoside hydrolase family 18, and folds as a typical (beta/alpha)8 barrel. Although the inhibitor shows highest homology with plant chitinases, XIP-I does not hydrolyse chitin; probably due to structural differences in the XIP-I binding cleft. The inhibitor is specific for fungal xylanases from glycoside hydrolases families 10 and 11, but does not inhibit bacterial enzymes. The inhibition is competitive and, depending on the xylanase, the Ki value can be as low as 3.4 nM. Site-directed mutagenesis of a xylanase from Aspergillus niger suggested that the XIP-I binding site was the conserved hairpin loop "thumb" region of family 11 xylanases. Furthermore, XIP-I shows the ability to inhibit barley alpha-amylases of glycoside hydrolase family 13, providing the first example of a protein able to inhibit members of different glycoside hydrolase families (10, 11, and 13), and additionally a novel function for a protein of glycoside hydrolase family 18.     

Cloning, expression, and characterization of a family 52 beta-xylosidase gene (xysB) of a multiple-xylanase-producing bacterium, Aeromonas caviae ME-1

A lambda phage genomic library of Aeromonas caviae ME-1, a multiple-xylanase-producing bacterium, was screened for xylan degradation activities. We isolated one clone, B65, which had weak xylanase activity, by the DNS method, but gave no visible bands on zymogram assay using SDS-xylan-PAGE. Based on TLC analyses of enzymatic products and some glycosidase assays using p-nitrophenyl substrates, we established that pB65 encodes a beta-xylosidase gene. In the nucleotide sequence analysis, we found a 2190-bp open reading frame (ORF) named xysB. XysB protein is similar to some beta-xylosidases, which are categorized in the glycosyl hydrolase family 52. Another ORF (xyg), that showed similarity to the family 67 alpha-glucuronidase, was also found downstream of the xysB gene. The xysB ORF and its promoter region were cloned into the pT7-Blue vector and the transformant cells had beta-xylosidase activity. The relative molecular mass were estimated to be 75 kDa by SDS-PAGE and 159 kDa by gel filtration. These data showed that XysB has a dimeric structure of 80,697 Da subunits. This enzyme showed optimal activity at 50 degrees C and pH 6.0. It was stable below 40 degrees C and pH 5-8. The Km and Vmax were calculated to be 0.34 mM and 33 nmol x min(-1) x microg(-1), respectively. This enzyme also showed transglycosylation activity against X3 and produced X4 and X5.     

The multidomain xylanase A of the hyperthermophilic bacterium Thermotoga neapolitana is extremely thermoresistant

 The nucleotide sequence of the xynA gene, encoding extracellular xylanase A of Thermotoga neapolitana, was determined. The xynA gene was 3264 base pairs (bp) long and encoded a putative polypeptide of 1055 amino acids. Three different domains were identified by sequence comparison and functional analysis of proteins with N- and/or C-terminal deletions. The core domain displayed significant homology to members of the glycosyl hydrolase family 10. N- and C-terminal domains were dispensable for enzymatic activity and seemed to be responsible for thermostability and cellulose binding, respectively. The intact gene and its truncated variants were expressed in Escherichia coli and purified for biochemical characterization. The enzyme was shown to act as an endo-1,4-β-xylanase, but minor activities against lichenan, barley glucan, methylumbelliferyl cellobioside and p-nitrophenyl xyloside were also detected. The specific activity and pH and temperature optima for hydrolysis of oat xylan were 111.3 U⋅mg^-1, 5.5 and 102^°C, respectively. The endoxylanase was stable at 90^°C and retained 50% activity when incubated for 2 h at 100^°C. Received: 19 May 1995/Received revision: 31 July 1995/Accepted: 7 September 1995     

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.     

A novel family 8 xylanase,functional and physicochemical characterization

Xylanases are generally classified into glycosyl hydrolase families 10 and 11 and are found to frequently have an inverse relationship between their pI and molecular mass values. However, we have isolated a psychrophilic xylanase that belongs to family 8 and which has both a high pI and high molecular mass. This novel xylanase, isolated from the Antarctic bacterium Pseudoalteromonas haloplanktis, is not homologous to family 10 or 11 enzymes but has 20-30% identity with family 8 members. NMR analysis shows that this enzyme hydrolyzes with inversion of anomeric configuration, in contrast to other known xylanases which are retaining. No cellulase, chitosanase or lichenase activity was detected. It appears to be functionally similar to family 11 xylanases. It hydrolyzes xylan to principally xylotriose and xylotetraose and is most active on long chain xylo-oligosaccharides. Kinetic studies indicate that it has a large substrate binding cleft, containing at least six xylose-binding subsites. Typical psychrophilic characteristics of a high catalytic activity at low temperatures and low thermal stability are observed. An evolutionary tree of family 8 enzymes revealed the presence of six distinct clusters. Indeed classification in family 8 would suggest an (alpha/alpha)(6) fold, distinct from that of other currently known xylanases.     

Comparison of chitinolytic enzymes from an alkaline, hypersaline lake and an estuary

We examined the genetic and physiological characteristics of chitin degrading enzymes expressed by fosmids cloned from two strains of chitinolytic gammaproteobacteria isolated from alkaline, hypersaline Mono Lake, California; and from a metagenomic library derived from an estuarine bacterial community (Dean Creek, Sapelo Island, GA, USA). The Mono Lake chitinolytic enzymes presented unique adaptations in terms of halo- and alkalitolerance. The sequence from one of the Mono Lake isolates (strain 12A) was a conventional family 18 glycosyl hydrolase; however, the expressed protein had a novel secondary activity peak at pH 10. We obtained a novel family 20 glycosyl hydrolase sequence from Mono Lake strain AI21. The activity of the expressed protein had a pH optimum of 10, several pH units higher than any other enzyme currently assigned to this family, and the enzyme retained 80% of its activity at pH 11. The enzyme was also halotolerant, retaining activity in salt solutions of up to 225 g l(-1). Sequence analysis indicated a molecular weight of approximately 90 kDa for the protein, and that it contained two active sites. Culture supernatant contained two chitinolytic proteins, 45 and 31 kDa, suggesting possible post-expression modification of the gene product. In contrast, the sequence found in the estuarine metagenomic library and the functional characteristics of the protein expressed from it were those of a conventional family 18 glycosyl hydrolase.     

Cloning, characterization and phylogenetic relationships of stxI, a endoxylanase-encoding gene from Streptomyces thermonitrificans NTU-88

A thermostable xylanase gene (stxI) obtained from Streptomyces thermonitrificans NTU-88 on domain analysis revealed an N-terminal catalytic domain featuring homology to a known xylanase within the glycoside hydrolase family 11. Recombinant STXI retained more than 60% of its activity following its incubation for at 60 degrees C for 24h. These characteristics were close to thermophile and mesophile Streptomyces strains. The main hydrolysis products of xylan degraded by STXI included large xylooligosaccharide fragments. These results indicated that STXI was a typical endoxylanase. As regards the phylogenetic relationships of GH11, STXI and the other xylanase deriving from Streptomyces were included in a subgroup of the aerobic bacterial group. This result implied that the evolutionary relationships between the various xylanases deriving from Streptomyces strains were convergent.     

Cloning, expression, and characterization of an alkaline thermostable GH11 xylanase from Thermobifida halotolerans YIM 90462T

A xylanase gene (thxyn11A) from the Thermobifida halotolerans strain YIM 90462(T) was cloned and expressed in Escherichia coli. The open reading frame (ORF) of thxyn11A has 1,008 bp encoding a mature xylanase with a high degree of similarity (80 %) to the xylanase from Nocardiopsis dassonvillei subsp. dassonvillei DSM 43111. This enzyme (Thxyn11A) also possesses a glycosyl hydrolases family 11 (GH11) domain and a high isoelectric point (pI = 9.1). However, Thxyn11A varies from most GH11 xylanases, due to its large molecular mass (34 kDa). Recombinant Thxyn11A demonstrated a strong pH and temperature tolerance with a maximum activity at pH 9.0 and 70 °C. Xylotriose, the end-product of xylan hydrolysis by Thxyn11A, serves as a catalyst for hemicellulose pretreatment in industrial applications and can also function as a food source or supplement for enterobacteria. Due to its attractive biochemical properties, Thxyn11A may have potential value in many commercial applications.     

Characterization of a Neocallimastix patriciarum xylanase gene and its product

A xylanase gene (xynC) isolated from the anaerobic ruminal fungus Neocallimastix patriciarum was characterized. The gene consists of an N-terminal catalytic domain that exhibited homology to family 11 of glycosyl hydrolases, a C-terminal cellulose binding domain (CBD) and a putative dockerin domain in between. Each domain was linked by a short linker domain rich in proline and alanine. Deletion analysis demonstrated that the CBD was essential for optimal xylanase activity of the enzyme, while the putative dockerin domain may not be required for enzyme function.     

Molecular cloning and characterization of a bifunctional xylanolytic enzyme from Neocallimastix patriciarum

A cDNA encoding a bifunctional acetylxylan esterase/xylanase, XynS20E, was cloned from the ruminal fungus Neocallimastix patriciarum. A putative conserved domain of carbohydrate esterase family 1 was observed at the N-terminus and a putative conserved domain of glycosyl hydrolase family 11 was detected at the C-terminus of XynS20E. To examine the enzyme activities, XynS20E was expressed in Escherichia coli as a recombinant His₆ fusion protein and purified by immobilized metal ion-affinity chromatography. Response surface modeling combined with central composite design and regression analysis was then applied to determine the optimal temperature and pH conditions of the recombinant XynS20E. The optimal conditions for the highest xylanase activity of the recombinant XynS20E were observed at a temperature of 49°C and a pH of 5.8, while those for the highest carbohydrate esterase activity were observed at a temperature of 58°C and a pH of 8.2. Under the optimal conditions for the enzyme activity, the xylanase and acetylxylan esterase specific activities of the recombinant XynS20E toward birchwood xylan were 128.7 and 873.1 U mg⁻¹, respectively. To our knowledge, this is the first report of a bifunctional xylanolytic enzyme with acetylxylan esterase and xylanase activities from rumen fungus.     

Changes in the activity of the multifunctional β-glycosyl hydrolase (Cel44C-Man26A) from Paenibacillus polymyxa by removal of the C-terminal region to minimum size

Paenibacillus polymyxa GS01 secretes Cel44C-Man26A as a multifunctional enzyme with cellulase, xylanase, lichenase, and mannanase activities. Cel44C-Man26A consists of 1,352 amino acids in which present a catalytic domain (CD) of the glycosyl hydrolase family 44 (GH44), fibronectin domain type 3 (Fn3), catalytic domain of glycosyl hydrolase family 26 (GH26), and a cellulose-binding module type 3 (CBM3). A truncated Cel44C-Man26A protein, consisting of 549 amino acid residues, reacted as a multifunctional mature enzyme despite the absence of the 10 amino acids containing GH44, Fn3, GH26, and CBM3. However, the multifunctional activity was not found in the mature Cel44C-Man26A protein truncated to less than 548 amino acids. The truncated Cel44C-Man26A proteins showed the optimum pH for the lichenase activity was pH 7.0, pH 6.0 for the xylanase and mannanase, and pH 5.0 for the cellulase. The truncated Cel44C-Man26A proteins exhibited enzymatic activity 40–120% higher than the full-length Cel44C.     

A cel44C-man26A gene of endophytic Paenibacillus polymyxa GS01 has multi-glycosyl hydrolases in two catalytic domains

A bacterial strain Paenibacillus polymyxa GS01 was isolated from the interior of the roots of Korean cultivars of ginseng (Panax ginseng C. A. Meyer). The cel44C-man26A gene was cloned from this endophytic strain. This 4,056-bp gene encodes for a 1,352-aa protein which, based on BLAST search homologies, contains a glycosyl hydrolase family 44 (GH44) catalytic domain, a fibronectin domain type 3, a glycosyl hydrolase family 26 (GH26) catalytic domain, and a cellulose-binding module type 3. The multifunctional enzyme domain GH44 possesses cellulase, xylanase, and lichenase activities, while the enzyme domain GH26 possesses mannanase activity. The Cel44C enzyme expressed in and purified from Escherichia coli has an optimum pH of 7.0 for cellulase and lichenase activities, but is at an optimum pH of 5.0 for xylanase and mannanase activities. The optimum temperature for enzymatic activity was 50°C for all substrates. No detectable enzymatic activity was detected for the Cel44C-Man26A mutants E91A and E222A. These results suggest that the amino acid residues Glu₉₁ and Glu₂₂₂ may play an important role in the glycosyl hydrolases activity of Cel44C-Man26A.     

Chemical modification of a xylanase from a thermotolerant Streptomyces. Evidence for essential tryptophan and cysteine residues at the active site.

Extracellular xylanase produced in submerged culture by a thermotolerant Streptomyces T7 growing at 37-50 degrees C was purified to homogeneity by chromatography on DEAE-cellulose and gel filtration on Sephadex G-50. The purified enzyme has an Mr of 20,463 and a pI of 7.8. The pH and temperature optima for the activity were 4.5-5.5 and 60 degrees C respectively. The enzyme retained 100% of its original activity on incubation at pH 5.0 for 6 days at 50 degrees C and for 11 days at 37 degrees C. The Km and Vmax. values, as determined with soluble larch-wood xylan, were 10 mg/ml and 7.6 x 10(3) mumol/min per mg of enzyme respectively. The xylanase was devoid of cellulase activity. It was completely inhibited by Hg2+ (2 x 10(-6) M). The enzyme degraded xylan, producing xylobiose, xylo-oligosaccharides and a small amount of xylose as end products, indicating that it is an endoxylanase. Chemical modification of xylanase with N-bromosuccinimide, 2-hydroxy-5-nitrobenzyl bromide and p-hydroxymercuribenzoate (PHMB) revealed that 1 mol each of tryptophan and cysteine per mol of enzyme were essential for the activity. Xylan completely protected the enzyme from inactivation by the above reagents, suggesting the presence of tryptophan and cysteine at the substrate-binding site. Inactivation of xylanase by PHMB could be restored by cysteine.     

X-ray diffraction structure of a plant glycosyl hydrolase family 32 protein: fructan 1-exohydrolase IIa of Cichorium intybus

Fructan 1-exohydrolase, an enzyme involved in fructan degradation, belongs to the glycosyl hydrolase family 32. The structure of isoenzyme 1-FEH IIa from Cichorium intybus is described at a resolution of 2.35 A. The structure consists of an N-terminal fivefold beta-propeller domain connected to two C-terminal beta-sheets. The putative active site is located entirely in the beta-propeller domain and is formed by amino acids which are highly conserved within glycosyl hydrolase family 32. The fructan-binding site is thought to be in the cleft formed between the two domains. The 1-FEH IIa structure is compared with the structures of two homologous but functionally different enzymes: a levansucrase from Bacillus subtilis (glycosyl hydrolase family 68) and an invertase from Thermotoga maritima (glycosyl hydrolase family 32).     

The C-terminal region of xylanase domain in Xyn11A from Paenibacillus curdlanolyticus B-6 plays an important role in structural stability

Paenibacillus curdlanolyticus B-6 produces an extracellular multienzyme complex containing a major xylanase subunit, designated Xyn11A, which includes two functional domains belonging to glycosyl hydrolase family-11 (GH11) and carbohydrate binding module family-36 (CBM36) and possesses a glycine and asparagine-rich linker (linker). To clarify the roles of each functional domain, recombinant proteins XynXL and XynX (CBM36 deleted and CBM36 and linker deleted, respectively) were constructed. Their xylanase activities were similar toward soluble xylan, whereas XynXL showed decreased hydrolysis activity toward insoluble xylan while XynX had no xylanase activity. To determine the significance of the linker and its neighbor region, XynX was subjected to secondary structural alignments using circular dichroism (CD) spectroscopy and three-dimensional (3D) structural analysis. A seven amino acid (NTITIGG) neighbor linker sequence was highly conserved among GH11 xylanases of Paenibacillus species. Although XynX exhibited a typical GH11 xylanase structure, conformational gaps were observed in the β6- and β12-sheets and in CD spectra. Flipping of the Arg163 side chains in the subsite was also observed upon analysis of superimposed models. Docking analysis using xylohexaose indicated that flipping of the Arg163 side chains markedly affected substrate binding in the subsite. To identify the amino acids related to stabilizing the substrate binding site, XynX with an extended C-terminal region was designed. At least seven amino acids were necessary to recover substrate binding and xylanase activity. These results indicated that the seven amino acid neighbor Xyn11A linker plays an important role in the activity and conformational stability of the xylanase domain.     

Characterization of a neutral recombinant xylanase from <Emphasis Type="Italic">Thermoactinospora rubra</Emphasis> YIM 77501<Superscript>T</Superscript>

A xylanase gene (TrXyn10) from Thermoactinospora rubra YIM 77501^T was cloned and expressed in Escherichia coli. The amino acid sequence displayed 78% homology with Microbispora mesophila xylanase (WP_062413927.1). The recombinant xylanase (TrXyn10), with MW 46.1 kDa, could hydrolyse beechwood, birchwood and oatspelt xylan. Based on the sequence, enzymatic properties and tertiary structure of the protein, TrXyn10 belongs to glycoside hydrolase family 10 (GH10). The optimal pH and temperature for the recombinant enzyme were determined to be 7.0 and 55 °C, respectively. TrXyn10 was stable over a wide pH range, and it retained more than 45% of the total activity at pH 6.0–12.0 for 12 h. In addition, the activity was greatly promoted, by approximately 200% of the initial activity, after incubation at pH 6.0 and 7.0 for 12 h. Based on enzymatic properties and product analysis, we showed that TrXyn10 is a neutral endoxylanase.     

Microbiome of fungus-growing termites: a new reservoir for lignocellulase genes

Fungus-growing termites play an important role in lignocellulose degradation and carbon mineralization in tropical and subtropical regions, but the degradation potentiality of their gut microbiota has long been neglected. The high quality and quantity of intestinal microbial DNA are indispensable for exploring new cellulose genes from termites by function-based screening. Here, using a refined intestinal microbial DNA extraction method followed by multiple-displacement amplification (MDA), a fosmid library was constructed from the total microbial DNA isolated from the gut of a termite growing in fungi. Functional screening for endoglucanase, cellobiohydrolase, β-glucosidase, and xylanase resulted in 12 β-glucosidase-positive clones and one xylanase-positive clone. The sequencing result of the xylanase-positive clone revealed an 1,818-bp open reading frame (ORF) encoding a 64.5-kDa multidomain endo-1,4-β-xylanase, designated Xyl6E7, which consisted of an N-terminal GH11 family catalytic domain, a CBM_4_9 domain, and a Listeria-Bacteroides repeat domain. Xyl6E7 was a highly active, substrate-specific, and endo-acting alkaline xylanase with considerably wide pH tolerance and stability but extremely low thermostability.     

Characterization of XynC from Bacillus subtilis subsp. subtilis strain 168 and analysis of its role in depolymerization of glucuronoxylan

Secretion of xylanase activities by Bacillus subtilis 168 supports the development of this well-defined genetic system for conversion of methylglucuronoxylan (MeGAXn [where n represents the number of xylose residues]) in the hemicellulose component of lignocellulosics to biobased products. In addition to the characterized glycosyl hydrolase family 11 (GH 11) endoxylanase designated XynA, B. subtilis 168 secretes a second endoxylanase as the translated product of the ynfF gene. This sequence shows remarkable homology to the GH 5 endoxylanase secreted by strains of Erwinia chrysanthemi. To determine its properties and potential role in the depolymerization of MeGAXn, the ynfF gene was cloned and overexpressed to provide an endoxylanase, designated XynC, which was characterized with respect to substrate preference, kinetic properties, and product formation. With different sources of MeGAXn as the substrate, the specific activity increased with increasing methylglucuronosyl substitutions on the beta-1,4-xylan chain. With MeGAXn from sweetgum as a preferred substrate, XynC exhibited a Vmax of 59.9 units/mg XynC, a Km of 1.63 mg MeGAXn/ml, and a k(cat) of 2,635/minute at pH 6.0 and 37 degrees C. Matrix-assisted laser desorption ionization-time of flight mass spectrometry and 1H nuclear magnetic resonance data revealed that each hydrolysis product has a single glucuronosyl substitution penultimate to the reducing terminal xylose. This detailed analysis of XynC from B. subtilis 168 defines the unique depolymerization process catalyzed by the GH 5 endoxylanases. Based upon product analysis, B. subtilis 168 secretes both XynA and XynC. Expression of xynA was subject to MeGAXn induction; xynC expression was constitutive with growth on different substrates. Translation and secretion of both GH 11 and GH 5 endoxylanases by the fully sequenced and genetically malleable B. subtilis 168 recommends this bacterium for the introduction of genes required for the complete utilization of products of the enzyme-catalyzed depolymerization of MeGAXn. B. subtilis may serve as a model platform for development of gram-positive biocatalysts for conversion of lignocellulosic materials to renewable fuels and chemicals.