A new GH43 α-arabinofuranosidase from Humicola insolens Y1: biochemical characterization and synergistic action with a xylanase on xylan degradation

A novel bifunctional type I α-l-arabinofuranosidase of family 43 glycoside hydrolase (BoGH43_35) from Bacteroides ovatus with endo-β-1,4-xylanase activity

The gut bacterium Bacteroides ovatus harbors a diverse arsenal of glycoside hydrolases (GHs), which play pivotal roles in degrading dietary polysaccharides. In this study, we characterized a novel glycoside hydrolase from family 43 and subfamily 35 (BoGH43_35), cloned from B. ovatus. The 1956 bp gene was expressed in Escherichia coli BL21 (DE3), yielding a homogeneous soluble recombinant enzyme (∼74 kDa) upon purification through immobilized metal-ion affinity chromatography (IMAC). BoGH43_35 exhibited a remarkable specificity for arabinoxylans, with maximum catalytic activity (4.9 U mg-1) against wheat arabinoxylan (low-viscosity), followed by 3.0 U mg-1 against rye arabinoxylan (high viscosity) and beechwood xylan (2.3 U mg-1). Optimal enzymatic performance was achieved at 37 °C and pH 7.0 having kinetic parameters of Vmax 5.7 U mg-1 and KM calculated to be 2.7 mg mL-1 for wheat arabinoxylan. Notably, BoGH43_35 retained stability within an acidic pH range (4-5) and displayed a half-life of 89 min at 30 °C. Protein thermal stability assays revealed a melting temperature (Tm) of 41.0 °C. Thin-layer chromatography (TLC) and 1H NMR analyses of hydrolysed products confirmed the enzyme's dual functionality: an initial α-l-arabinofuranosidase (EC 3.2.1.55) activity, followed by an endo-β-1,4-xylanase (EC 3.2.1.8) activity, as evidenced by the release of xylooligosaccharides, including xylobiose and xylotriose, from xylans. Further structural analysis demonstrated BoGH43_35's ability to hydrolyze monosubstituted arabinofuranosyl residues from α-1,2- or α-1,3-linked arabinoxylan, confirming its type I α-l-arabinofuranosidase activity. This multifunctional enzyme holds potential in the valorization of hemicellulosic biomass and the production of prebiotic oligosaccharides and other biotechnological applications.

A metagenomic survey of the fecal microbiome of the African savanna elephant (Loxodonta africana)

The African savanna elephant (Loxodonta africana) is the largest terrestrial animal on Earth and is found primarily in Southern and Eastern Africa. It is a hindgut, colonic fermenter and subsists on a diet of raw plant materials found in its grazing area. In this study the bacterial, archaeal and fungal populations of seven African savanna elephant fecal metagenomes were first characterized using amplicon sequencing. On the genus level it was observed that the p-1088-a5 gut group in the bacteriome, Methanocorpusulum and Methanobrevibacter in the archaeome and Alternaria, Aurobasidium, Didymella and Preussia in the mycome, predominated. Subsequently, metagenomic shotgun sequencing was employed to identify possible functional pathways and carbohydrate-active enzymes (CAZymes). Carbohydrate catabolic pathways represented the main degradation pathways, and the fecal metagenome was enriched in the glycohydroside (GH) class of CAZymes. Additionally, the top GH families identified - GH43, GH2, GH13 and GH3 - are known to be associated with cellulytic, hemicellulytic and pectolytic activities. Finally, the CAZymes families identified in the African savanna elephant were compared with those found in the Asian elephant and it was demonstrated that there is a unique repository of CAZymes that could be leveraged in the biotechnological context such as the degradation of lignocellulose for the production of second-generation biofuels and energy.

Characterization of a novel thermostable α-l-arabinofuranosidase for improved synergistic effect with xylanase on lignocellulosic biomass hydrolysis without prior pretreatment

Utilizing thermostable enzymes in biomass conversion processes presents a promising approach to bypass pretreatment, garnering significant attention from the biorefinery industry. A novel discovered α-l-arabinofuranosidase, Abf4980, exhibits exceptional thermostability by maintaining full activity after 24 h of incubation at 70 °C. It effectively acts on polyarabinosides, cleaving α-1,2- and α-1,3-linked arabinofuranose side chains from water-soluble wheat arabinoxylan while releasing xylose. When synergistically combined with the thermostable bifunctional xylanase/β-glucanase CbXyn10C from Caldicellulosiruptor bescii at an enzyme-activity ratio of 6:1, Abf4980 achieves the highest degradation efficiency for wheat arabinoxylan. Furthermore, Abf4980 and CbXyn10C demonstrated remarkable efficacy in hydrolyzing unmodified wheat bran and corn cob to generate arabinose and xylooligosaccharides. This discovery holds promising opportunities for improving the efficiency of lignocellulosic biomass conversion into fermentable sugars.

Enzyme synergy for plant cell wall polysaccharide degradation

Valorizing plant cell wall, marine and algal polysaccharides is of utmost importance for the development of the circular bioeconomy. This is because polysaccharides are by far the most abundant organic molecules found in nature with complex chemical structures that require a large set of enzymes for their degradation. Microorganisms produce polysaccharide-specific enzymes that act in synergy when performing hydrolysis. Although discovered since decades enzyme synergy is still poorly understood at the molecular level and thus it is difficult to harness and optimize. In the last few years, more attention has been given to improve and characterize enzyme synergy for polysaccharide valorization. In this review, we summarize literature to provide an overview of the different type of synergy involving carbohydrate modifying enzymes and the recent advances in the field exemplified by plant cell-wall degradation.

Two Subgroups within the GH43_36 α-l-Arabinofuranosidase Subfamily Hydrolyze Arabinosyl from Either Mono-or Disubstituted Xylosyl Units in Wheat Arabinoxylan

Fungal arabinofuranosidases (ABFs) catalyze the hydrolysis of arabinosyl substituents (Ara) and are key in the interplay with other glycosyl hydrolases to saccharify arabinoxylans (AXs). Most characterized ABFs belong to GH51 and GH62 and are known to hydrolyze the linkage of α-(1→2)-Ara and α-(1→3)-Ara in monosubstituted xylosyl residues (Xyl) (ABF-m2,3). Nevertheless, in AX a substantial number of Xyls have two Aras (i.e., disubstituted), which are unaffected by ABFs from GH51 and GH62. To date, only two fungal enzymes have been identified (in GH43_36) that specifically release the α-(1→3)-Ara from disubstituted Xyls (ABF-d3). In our research, phylogenetic analysis of available GH43_36 sequences revealed two major clades (GH43_36a and GH43_36b) with an expected substrate specificity difference. The characterized fungal ABF-d3 enzymes aligned with GH43_36a, including the GH43_36 from Humicola insolens (HiABF43_36a). Hereto, the first fungal GH43_36b (from Talaromyces pinophilus) was cloned, purified, and characterized (TpABF43_36b). Surprisingly, TpABF43_36b was found to be active as ABF-m2,3, albeit with a relatively low rate compared to other ABFs tested, and showed minor xylanase activity. Novel specificities were also discovered for the HiABF43_36a, as it also released α-(1→2)-Ara from a disubstitution on the non-reducing end of an arabinoxylooligosaccharide (AXOS), and it was active to a lesser extent as an ABF-m2,3 towards AXOS when the Ara was on the second xylosyl from the non-reducing end. In essence, this work adds new insights into the biorefinery of agricultural residues.

Co-production of Xylooligosaccharides and Xylose From Poplar Sawdust by Recombinant Endo-1,4-β-Xylanase and β-Xylosidase Mixture Hydrolysis

As is well-known, endo-1,4-β-xylanase and β-xylosidase are the rate-limiting enzymes in the degradation of xylan (the major hemicellulosic component), main functions of which are cleavaging xylan to release xylooligosaccharides (XOS) and xylose that these two compounds have important application value in fuel, food, and other industries. This study focuses on enzymatic hydrolysis of poplar sawdust xylan for production of XOS and xylose by a GH11 endo-1,4-β-xylanase MxynB-8 and a GH39 β-xylosidase Xln-DT. MxynB-8 showed excellent ability to hydrolyze hemicellulose of broadleaf plants, such as poplar. Under optimized conditions (50°C, pH 6.0, dosage of 500 U/g, substrate concentration of 2 mg/mL), the final XOS yield was 85.5%, and the content of XOS2-3 reached 93.9% after 18 h. The enzymatic efficiency by MxynB-8 based on the poplar sawdust xylan in the raw material was 30.5%. Xln-DT showed excellent xylose/glucose/arabinose tolerance, which is applied as a candidate to apply in degradation of hemicellulose. In addition, the process and enzymatic mode of poplar sawdust xylan with MxynB-8 and Xln-DT were investigated. The results showed that the enzymatic hydrolysis yield of poplar sawdust xylan was improved by adding Xln-DT, and a xylose-rich hydrolysate could be obtained at high purity, with the xylose yield of 89.9%. The enzymatic hydrolysis yield was higher (32.2%) by using MxynB-8 and Xln-DT together. This study provides a deep understanding of double-enzyme synergetic enzymolysis of wood polysaccharides to valuable products.

Development of a thermophilic coculture for corn fiber conversion to ethanol

The fiber in corn kernels, currently unutilized in the corn to ethanol process, represents an opportunity for introduction of cellulose conversion technology. We report here that Clostridium thermocellum can solubilize over 90% of the carbohydrate in autoclaved corn fiber, including its hemicellulose component glucuronoarabinoxylan (GAX). However, Thermoanaerobacterium thermosaccharolyticum or several other described hemicellulose-fermenting thermophilic bacteria can only partially utilize this GAX. We describe the isolation of a previously undescribed organism, Herbinix spp. strain LL1355, from a thermophilic microbiome that can consume 85% of the recalcitrant GAX. We sequence its genome, and based on structural analysis of the GAX, identify six enzymes that hydrolyze GAX linkages. Combinations of up to four enzymes are successfully expressed in T. thermosaccharolyticum. Supplementation with these enzymes allows T. thermosaccharolyticum to consume 78% of the GAX compared to 53% by the parent strain and increases ethanol yield from corn fiber by 24%.

Corn fiber is a difficult feedstock to utilize due to its recalcitrant hemicellulose. Here, the authors characterize the recalcitrant structures, isolate a new bacterium to consume the hemicellulose, identify its enzymes, and show the benefit with increased conversion of corn fiber to ethanol.

A mini review of xylanolytic enzymes with regards to their synergistic interactions during hetero-xylan degradation

This review examines the recent models describing the mode of action of various xylanolytic enzymes and how these enzymes can be applied (sequentially or simultaneously) with their distinctive roles in mind to achieve efficient xylan degradation. With respect to homeosynergy, synergism appears to be as a result of β-xylanase and/or oligosaccharide reducing-end β-xylanase liberating xylo-oligomers (XOS) that are preferred substrates of the processive β-xylosidase. With regards to hetero-synergism, two cross relationships appear to exist and seem to be the reason for synergism between the enzymes during xylan degradation. These cross relations are the debranching enzymes such as α-glucuronidase or side-chain cleaving enzymes such as carbohydrate esterases (CE) removing decorations that would have hindered back-bone-cleaving enzymes, while backbone-cleaving-enzymes liberate XOS that are preferred substrates of the debranching and side-chain-cleaving enzymes. This interaction is demonstrated by high yields in co-production of xylan substituents such as arabinose, glucuronic acid and ferulic acid, and XOS. Finally, lytic polysaccharide monooxygenases (LPMO) have also been implicated in boosting whole lignocellulosic biomass or insoluble xylan degradation by glycoside hydrolases (GH) by possibly disrupting entangled xylan residues. Since it has been observed that the same enzyme (same Enzyme Commission, EC, classification) from different GH or CE and/or AA families can display different synergistic interactions with other enzymes due to different substrate specificities and properties, in this review, we propose an approach of enzyme selection (and mode of application thereof) during xylan degradation, as this can improve the economic viability of the degradation of xylan for producing precursors of value added products.

A GH51 α-L-arabinofuranosidase from Talaromyces leycettanus strain JCM12802 that selectively drives synergistic lignocellulose hydrolysis

Background

The development of sustainable technologies for plant cell wall degradation greatly depends on enzymes with hydrolytic activities against carbohydrates. The waste by-products of agricultural cereals are important biomass sources because they contain large amounts of saccharides. Achieving efficient debranching and depolymerization are two important objectives for increasing the utilization of such renewable bioresources. GH51 α-l-arabinofuranosidases are important in biomass pretreatment because they act synergistically with other enzymes during hemicellulose hydrolysis.

Results

A GH51 α-l-arabinofuranosidase from Talaromyces leycettanus JCM12802 was heterologously expressed in Pichia pastoris GS115 and characterized. The recombinant α-l-arabinofuranosidase, TlAbf51, showed an optimum temperature and pH of 55–60 °C and 3.5–4.0, respectively, and remained stable at 50 °C and pH 3.0–9.0. TlAbf51 showed a higher catalytic efficiency (5712 mM⁻¹ s⁻¹) than most fungal α-l-arabinofuranosidases towards the substrate 4-nitrophenyl-α-l-arabinofuranoside. Moreover, TlAbf51 preferentially removed 1,2- or 1,3-linked arabinofuranose residues from arabinoxylan and acted synergistically with the bifunctional xylanase/cellulase TcXyn10A at an activity ratio of 5:1. The highest yields of arabinose and xylooligosaccharides were obtained when TlAbf51 was added after TcXyn10A or when both enzymes were added simultaneously. High-performance anion-exchange chromatography analyses showed that (i) arabinose and xylooligosaccharides with low degrees of polymerization (DP1–DP5) and (ii) arabinose and xylooligosaccharides (DP1–DP3) were the major hydrolysates obtained during the hydrolysis of sodium hydroxide-pretreated cornstalk and corn bran, respectively.

Conclusions

In contrast to other fungal GH51 α-l-arabinofuranosidases, recombinant TlAbf51 showed excellent stability over a broad pH range and high catalytic efficiency. Moreover, TlAbf51 acted synergistically with another hemicellulase to digest arabino-polysaccharides. These favorable enzymatic properties make TlAbf51 attractive for biomass pretreatment and biofuel production.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1192-z) contains supplementary material, which is available to authorized users.

The modular arabinanolytic enzyme Abf43A-Abf43B-Abf43C from Ruminiclostridium josui consists of three GH43 modules classified in different subfamilies

The abnA gene from Ruminiclostridium josui encodes the large modular arabinanolytic enzyme, Abf43A-Abf43B-Abf43C, consisting of an N-terminal signal peptide, a Laminin_G_3 module, a GH43_22 module, a Laminin_G_3 module, a Big_4 module, a GH43_26 module, a GH43_34 module and a dockerin module in order with a calculated molecular weight of 204,108. Three truncated enzymes were recombinantly produced in Escherichia coli and biochemically characterized, RjAbf43A consisting of the first Laminin_G_3 module and GH43_22 module, RjAbf43B consisting of the second Laminin_G_3 module, Big_4 module and GH43_26 module, and RjAbf43C consisting of the GH43_34 module. RjAbf43A showed a strong α-l-arabinofuranosidase activity toward sugar beet arabinan, highly branched arabinan but not linear arabinan, thus it acted in the removal of arabinose side chains from sugar beet arabinan. By contrast, RjAbf43B showed a strong exo-α-1,5-l-arabinofuranosidase activity toward linear arabinan and arabinooligosaccharides whereas RjAbf43C showed low activity toward these substrates. Although RjAbf43B was activated by the presence of some metal ions such as Zn²⁺, Mg²⁺ and Ni²⁺, RjAbf43A was inhibited by these ions. RjAbf43A and RjAbf43B attacked sugar beet arabinan in a synergistic manner. By comparison, RjAbf43A-Abf43B containing both GH43_22 and GH43_26 modules showed lower hydrolytic activity toward sugar beet arabinan but higher activity toward sugar beet fiber than the sum of the individual activities of RjAbf43A and RjAbf43B, suggesting that the coexistence of two distinct GH43 modules in a single polypeptide is important for the efficient hydrolysis of an insoluble and natural polysaccharide but not a soluble substrate.

Synergistic effect of acetyl xylan esterase from Talaromyces leycettanus JCM12802 and xylanase from Neocallimastix patriciarum achieved by introducing carbohydrate-binding module-1

Wheat bran is an effective raw material for preparation xylooligosaccharides; however, current research mainly focuses on alkali extraction and enzymatic hydrolysis methods. Since ester bonds are destroyed during the alkali extraction process, xylanase and arabinofuranosidase are mainly used to hydrolyze xylooligosaccharides. However, alkali extraction costs are very high, and the method also causes pollution. Therefore, this study focuses on elucidating a method to efficiently and directly degrade destarched wheat bran. First, an acidic acetyl xylan esterase (AXE) containing a carbohydrate-binding module-1 (CBM1) domain was cloned from Talaromyces leycettanus JCM12802 and successfully expressed in Pichia pastoris. Characterization showed that the full-length acetyl xylan esterase AXE + CBM1 was similar toe uncovered AXE with an optimum temperature and pH of 55 °C and 6.5, respectively. Testing the acetyl xylan esterase and xylanase derived from Neocallimastix patriciarum in a starch-free wheat bran cooperative experiment revealed that AXE + CBM1 and AXE produced 29% and 16% reducing sugars respectively, compared to when only NPXYN11 was used. In addition, introduced the CBM1 domain into NPXYN11, and the results indicated that the CBM1 domain showed little effect on NPXYN11 properties. Finally, the systematically synergistic effects between acetyl xylan esterase and xylanase with/without the CBM1 domain demonstrated that the combined ratio of AXE + CBM1 coming in first and NPXYN11 + CBM1 s increased reducing sugars by almost 35% with AXE and NPXYN11. Furthermore, each component's proportion remained the same with respect to xylooligosaccharides, with the largest proportion (86%) containing of 49% xylobiose and 37% xylotriose.

Insight to Improve α-L-Arabinofuranosidase Productivity in Pichia pastoris and Its Application on Corn Stover Degradation

α-L-arabinofuranosidase (ARA) with enhanced specific activity and in large amounts, is needed for a variety of industrial applications. To improve ARA production with engineered methylotrophic yeast Pichia pastoris, a genetically modified ara gene from Aspergillus niger ND-1 was investigated. Through codon optimization and rational replacement of α-factor signal peptide with the native propeptide (MFSRRNLVALGLAATVSA), ARA production was improved from 2.61 ± 0.13 U/mL to 14.37 ± 0.22 U/mL in shaking flask culture (a 5.5-fold increase). Results of N-terminal sequencing showed that secreted active ARA of recombinant strain p-oARA had theoretical initial five amino acids (GPCDI) comparable to the mature sequences of α-oARA (EAEAG) and αp-oARA (NLVAL). The kinetic values have been determined for ARA of recombinant strain p-oARA (V_max = 747.55 μmol/min/mg, K_m = 5.36 mmol/L), optimal activity temperature 60°C and optimal pH 4.0. Scaling up of ARA production by p-oARA in a 7.5-L fermentor resulted in remarkably high extracellular ARA specific activity (479.50 ± 12.83 U/mg) at 168 h, and maximal production rate 164.47 ± 4.40 U/mL. In studies of corn stover degradation activity, degree of synergism for ARA and xylanase was 32.4% and enzymatic hydrolysis yield for ARA + xylanase addition was 15.9% higher than that of commercial cellulase, indicating significant potential of ARA for catalytic conversion of corn stover to fermentable sugars for biofuel production.

Two Distinct α-l-Arabinofuranosidases in Caldicellulosiruptor Species Drive Degradation of Arabinose-Based Polysaccharides

Species in the extremely thermophilic genus Caldicellulosiruptor can degrade unpretreated plant biomass through the action of multimodular glycoside hydrolases. To date, most focus with these bacteria has been on hydrolysis of glucans and xylans, while the biodegradation mechanism for arabinose-based polysaccharides remains unclear. Here, putative α-l-arabinofuranosidases (AbFs) were identified in Caldicellulosiruptor species by homology to less-thermophilic versions of these enzymes. From this screen, an extracellular XynF was determined to be a key factor in hydrolyzing α-1,2-, α-1,3-, and α-1,5-l-arabinofuranosyl residues of arabinose-based polysaccharides. Combined with a GH11 xylanase (XynA), XynF increased arabinoxylan hydrolysis more than 6-fold compared to the level seen with XynA alone, likely the result of XynF removing arabinofuranosyl side chains to generate linear xylans that were readily degraded. A second AbF, the intracellular AbF51, preferentially cleaved the α-1,5-l-arabinofuranosyl glycoside bonds within sugar beet arabinan. β-Xylosidases, such as GH39 Xyl39B, facilitated the hydrolysis of arabinofuranosyl residues at the nonreducing terminus of the arabinose-branched xylo-oligosaccharides by AbF51. These results demonstrate the separate but complementary contributions of extracellular XynF and cytosolic AbF51 in processing the bioconversion of arabinose-containing oligosaccharides to fermentable monosaccharides.IMPORTANCE Degradation of hemicellulose, due to its complex chemical structure, presents a major challenge during bioconversion of lignocellulosic biomass to biobased fuels and chemicals. Degradation of arabinose-containing polysaccharides, in particular, can be a key bottleneck in this process. Among Caldicellulosiruptor species, the multimodular arabinofuranosidase XynF is present in only selected members of this genus. This enzyme exhibited high hydrolysis activity, broad specificity, and strong synergism with other hemicellulases acting on arabino-polysaccharides. An intracellular arabinofuranosidase, AbF51, occurs in all Caldicellulosiruptor species and, in conjunction with xylosidases, processes the bioconversion of arabinose-branched oligosaccharides to fermentable monosaccharides. Taken together, the data suggest that plant biomass degradation in Caldicellulosiruptor species involves extracellular XynF that acts synergistically with other hemicellulases to digest arabino-polysaccharides that are subsequently transported and degraded further by intracellular AbF51 to produce short-chain arabino sugars.

An Acid-Adapted Endo-α-1,5-L-arabinanase for Pectin Releasing

An arabinanase gene was cloned by overlap-PCR from Penicillium sp. Y702 and expressed in Pichia pastoris. The recombinant enzyme was named AbnC702 with 20 U/mg of endo-arabinanase activity toward linear α-1,5-L-arabinan. The optimal pH and temperature of AbnC702 were 5.0 and 50 °C, respectively. The recombinant AbnC702 was highly stable at pH 5.0-7.0 and 50 °C. It could retain about 72.3 % of maximum specific activity at pH 5.0 after incubation for 2.5 h, which indicated AbnC702 was an acid-adapted enzyme. The K _m and V _max values were 24.8 ± 4.7 mg/ml and 88.5 ± 5.6 U/mg, respectively. A three-dimensional structure of AbnC702 was made by homology modeling, and the counting of acidic/basic amino residues within the region of 10 Å around the active site, as well the hydrogen bonds within the area of 5 Å around the active site, might theoretically interpret the acid adaptability of AbnC702. Analysis of hydrolysis products by thin layer chromatography (TLC) combined with high-performance liquid chromatography (HPLC) verified that the recombinant AbnC702 was an endo-1,5-α-L-arabinanase, which yielded arabinobiose and arabinotriose as major products. AbnC702 was applied in pectin extraction from apple pomace with synergistic action of α-L-arabinofuranosidase.

Secreted Alpha-N-Arabinofuranosidase B Protein Is Required for the Full Virulence of Magnaporthe oryzae and Triggers Host Defences

Rice blast disease caused by Magnaporthe oryzae is one of the most devastating fungal diseases of rice and results in a huge loss of rice productivity worldwide. During the infection process, M. oryzae secretes a large number of glycosyl hydrolase proteins into the host apoplast to digest the cell wall and facilitate fungal ingression into host tissues. In this study, we identified a novel arabinofuranosidase-B (MoAbfB) protein that is secreted by M. oryzae during fungal infection. Deletion of MoAbfB from M. oryzae resulted in reduced disease severity in rice. Biochemical assays revealed that the MoAbfB protein exhibited arabinofuranosidase activity and caused degradation of rice cell wall components. Interestingly, pre-treatment of rice with the MoAbfB protein inhibited fungal infection by priming defence gene expression. Our findings suggest that MoAbfB secretion affects M. oryzae pathogenicity by breaking down the host cell wall, releasing oligosaccharides that may be recognized by the host to trigger innate immune responses.

Novel Trifunctional Xylanolytic Enzyme Axy43A from Paenibacillus curdlanolyticus Strain B-6 Exhibiting Endo-Xylanase, β-d-Xylosidase, and Arabinoxylan Arabinofuranohydrolase Activities

The axy43A gene encoding the intracellular trifunctional xylanolytic enzyme from Paenibacillus curdlanolyticus B-6 was cloned and expressed in Escherichia coli Recombinant PcAxy43A consisting of a glycoside hydrolase family 43 and a family 6 carbohydrate-binding module exhibited endo-xylanase, β-xylosidase, and arabinoxylan arabinofuranohydrolase activities. PcAxy43A hydrolyzed xylohexaose and birch wood xylan to release a series of xylooligosaccharides, indicating that PcAxy43A contained endo-xylanase activity. PcAxy43A exhibited β-xylosidase activity toward a chromogenic substrate, p-nitrophenyl-β-d-xylopyranoside, and xylobiose, while it preferred to hydrolyze long-chain xylooligosaccharides rather than xylobiose. In addition, surprisingly, PcAxy43A showed arabinoxylan arabinofuranohydrolase activity; that is, it released arabinose from both singly and doubly arabinosylated xylose, α-l-Araf-(1→2)-d-Xylp or α-l-Araf-(1→3)-d-Xylp and α-l-Araf-(1→2)-[α-l-Araf-(1→3)]-β-d-Xylp Moreover, the combination of PcAxy43A and P. curdlanolyticus B-6 endo-xylanase Xyn10C greatly improved the efficiency of xylose and arabinose production from the highly substituted rye arabinoxylan, suggesting that these two enzymes function synergistically to depolymerize arabinoxylan. Therefore, PcAxy43A has the potential for the saccharification of arabinoxylan into simple sugars for many applications. IMPORTANCE In this study, the glycoside hydrolase 43 (GH43) intracellular multifunctional endo-xylanase, β-xylosidase, and arabinoxylan arabinofuranohydrolase (AXH) from P. curdlanolyticus B-6 were characterized. Interestingly, PcAxy43A AXH showed a new property that acted on both the C(O)-2 and C(O)-3 positions of xylose residues doubly substituted with arabinosyl, which usually obstruct the action of xylanolytic enzymes. Furthermore, the studies here show interesting properties for the processing of xylans from cereal grains, particularly rye arabinoxylan, and show a novel relationship between PcAxy43A and endo-xylanase Xyn10C from strain B-6, providing novel metabolic potential for processing arabinoxylans into xylose and arabinose.

The use of T-DNA insertional mutagenesis to improve cellulase production by the thermophilic fungus Humicola insolens Y1

Humicola insolens is an excellent producer of pH-neutral active, thermostable cellulases that find many industrial applications. In the present study, we developed an efficient Agrobacterium tumefaciens-mediated transformation system for H. insolens. We transformed plasmids carrying the promoter of the glyceraldehyde-3-phosphate dehydrogenase gene of H. insolens driving the transcription of genes encoding neomycin phosphotransferase, hygromycin B phosphotransferase, and enhanced green fluorescent protein. We optimized transformation efficiency to obtain over 300 transformants/10⁶ conidia. T-DNA insertional mutagenesis was employed to generate an H. insolens mutant library, and we isolated a transformant termed T4 with enhanced cellulase and hemicellulase activities. The FPase, endoglucanase, cellobiohydrolase, β-glucosidase, and xylanase activities of T4, measured at the end of fermentation, were 60%, 440%, 320%, 41%, and 81% higher than those of the wild-type strain, respectively. We isolated the sequences flanking the T-DNA insertions and thus identified new genes potentially involved in cellulase and hemicellulase production. Our results show that it is feasible to use T-DNA insertional mutagenesis to identify novel candidate genes involved in cellulase production. This will be valuable when genetic improvement programs seeking to enhance cellulase production are planned, and will also allow us to gain a better understanding of the genetics of the thermophilic fungus H. insolens.