Characterization of Two New Endo-β-1,4-xylanases from Eupenicillium parvum 4–14 and Their Applications for Production of Feruloylated Oligosaccharides

A novel cellulolytic/xylanolytic SbAA14 from Sordaria brevicollis with a branched chain preference and its synergistic effects with glycoside hydrolases on lignocellulose

In this study, the novel auxiliary activity (AA) family 14 lytic polysaccharide monooxygenase (LPMO) SbAA14 from Sordaria brevicollis was successfully characterized. It was active against heteroxylan, xyloglucan and cellulose in β-cellulose and released native oligosaccharides and corresponding C1- and/or C4-oxidized products. SbAA14 showed a branched chain preference, because partial removal of arabinosyl substituents from heteroxylan led to a decrease in activity. SbAA14 had synergistic effects with the debranching enzyme EpABF62C in an enzyme- and ascorbic acid-dependent manner. SbAA14 had synergistic effects with the GH10 endoxylanase EpXYN1, and the degree of synergy was greater with step-by-step addition than with simultaneous addition. SbAA14 could also synergize with Celluclast® 1.5 L on NaOH-pretreated wheat straw and on NaOH-pretreated and hydrogen peroxide-acetic acid (HPAC)-H2SO4-pretreated bamboo substrates. The greatest synergistic effect between SbAA14 and Celluclast® 1.5 L was observed for HPAC-H2SO4-200 mM pretreated bamboo, in which the degree of synergy reached approximately 1.61. The distinctive substrate preference of SbAA14 indicated that it is a novel AA14 LPMO that may act mainly on heteroxylan with numerous arabinosyl substituents between cellulose fibers rather than on recalcitrant xylan tightly associated with cellulose. These findings broaden the understanding of enigmatic AA14 LPMOs and provide new insights into the substrate specificities and biological functionalities of AA14 LPMOs in fungi.

Insights into the capability of the lignocellulolytic enzymes of Penicillium parvum 4-14 to saccharify corn bran after alkaline hydrogen peroxide pretreatment

BACKGROUND

Corn bran is a major agro-industrial byproduct from corn starch processing. It contains abundant arabinoxylan that can be converted into value-added chemicals via biotechnology. Corn bran arabinoxylan (CBAX) is one of the most recalcitrant xylans for enzymatic degradation due to its particular heterogeneous nature. The present study aimed to investigate the capability of the filamentous fungus Penicillium parvum 4-14 to enzymatically saccharify CBAX and reveal the fungal carbohydrate-active enzyme (CAZyme) repertoire by genome sequencing and secretome analysis.

RESULTS

CBAX1 and CBAX2 with different branching degrees, together with corn bran residue (CBR) were generated from corn bran after alkaline hydrogen peroxide (AHP) pretreatment and graded ethanol precipitation. The protein blends E_CBAX1, E_CBAX2, and E_CBR were produced by the fungus grown on CBAX1, CBAX2, or CBR, respectively. Under the optimal conditions, E_CBAX1 released more than 80% xylose and arabinose from CBAX1 and CBAX2. Almost complete saccharification of the arabinoxylans was achieved by combining E_CBAX1 and a commercial enzyme cocktail Cellic®CTec3. Approximately 89% glucose, 64% xylose, and 64% arabinose were liberated from CBR by E_CBR. The combination of E_CBR with Cellic®CTec3 enhanced the saccharification of CBR, with conversion ratios of 97% for glucose, 81% for xylose, and 76% for arabinose. A total of 376 CAZymes including plentiful lignocellulolytic enzymes were predicted in P. parvum based on the fungal genomic sequence (25.8 Mb). Proteomic analysis indicated that the expression of CAZymes in P. parvum varied between CBAX1 and CBR, and the fungus produced complete cellulases, numerous hemicellulases, as well as high levels of glycosidases under the culture conditions.

CONCLUSIONS

This investigation disclosed the CAZyme repertoire of P. parvum at the genomic and proteomic levels, and elaborated on the promising potential of fungal lignocellulolytic enzymes upon saccharification of corn bran biomass after AHP pretreatment.

Comparison of the Biochemical Properties and Roles in the Xyloglucan-Rich Biomass Degradation of a GH74 Xyloglucanase and Its CBM-Deleted Variant from Thielavia terrestris

Xyloglucan is closely associated with cellulose and still retained with some modification in pretreated lignocellulose; however, its influence on lignocellulose biodegradation is less understood. TtGH74 from Thielavia terrestris displayed much higher catalytic activity than previously characterized fungal GH74 xyloglucanases. The carbohydrate-binding module 1 (CBM1) deleted variant (TtGH74ΔCBM) had the same optimum temperature and pH but an elevated thermostability. TtGH74 displayed a high binding affinity on xyloglucan and cellulose, while TtGH74ΔCBM completely lost the adsorption capability on cellulose. Their hydrolysis action alone or in combination with other glycoside hydrolases on the free xyloglucan, xyloglucan-coated phosphoric acid-swollen cellulose or pretreated corn bran and apple pomace was compared. CBM1 might not be essential for the hydrolysis of free xyloglucan but still effective for the associated xyloglucan to an extent. TtGH74 alone or synergistically acting with the CBH1/EG1 mixture was more effective in the hydrolysis of xyloglucan in corn bran, while TtGH74ΔCBM showed relatively higher catalytic activity on apple pomace, indicating that the role and significance of CBM1 are substrate-specific. The degrees of synergy for TtGH74 or TtGH74ΔCBM with the CBH1/EG1 mixture reached 1.22–2.02. The addition of GH10 xylanase in TtGH74 or the TtGH74ΔCBM/CBH1/EG1 mixture further improved the overall hydrolysis efficiency, and the degrees of synergy were up to 1.50–2.16.

Functional characterization of a GH62 family α-L-arabinofuranosidase from Eupenicillium parvum suitable for monosaccharification of corncob arabinoxylan in combination with key enzymes

Corncob rich in arabinoxylan is an important raw material widely used in bio-refinery. Complete saccharification of arabinoxylan depends on the synergism of different enzymes including α-L-arabinofuranosidase (ABF). This study aimed to investigate the functional characteristics of a new ABF EpABF62A belonging to glycoside hydrolase (GH) 62 family from the fungus Eupenicillium parvum, and to explore its potential in the saccharification of corncob arabinoxylan. The recombinant EpABF62A showed high activity against wheat arabinoxylan and rye arabinoxylan, with the optimal temperature of 55 °C and pH of 4.5. The protein contains an N-terminal cellulose-binding domain family 1 (CBM_1) domain, and displayed a 59.5% absorption rate to phosphoric acid swollen cellulose. Regioselectivity analysis indicated that the enzyme selectively removed α-1,2 or α-1,3 linked arabinofuranosyl residues on mono-substituted xylose residues on arabinoxylan. Corncob arabinoxylans (CAX1 or CAX2) with different (low or high) branching degrees were extracted from the raw material by alkaline hydrogen peroxide pretreatment and graded ethanol precipitation. Single EpABF62A removed 69.5% or 67.1% arabinose from CAX1 or CAX2, respectively. EpABF62A combined with a GH10 xylanase, a GH43 β-D-xylosidase and a GH67 α-glucuronidase released 75.0% or 64.5% xylose from CAX1 or CAX2, respectively. The addition of the four hemicellulases enhanced the saccharification the solid fraction of the pretreated corncob by the commercial cellulase Cellic® CTec2, and the conversion ratios of glucose, xylose and arabinose were up to 94.0%, 91.8% and 82.6%, respectively.

A novel thermostable xylanase from Geobacillus vulcani GS90: Production, biochemical characterization, and its comparative application in fruit juice enrichment

Xylanases have great attention to act as a potential role in agro-industrial processes. In this study, production, characterization, and fruit juice application of novel xylanase from thermophilic Geobacillus vulcani GS90 (GvXyl) were performed. GvXyl was purified via acetone precipitation and gel-filtration chromatography. The results showed that GvXyl had 1,671.4 U/mg of specific activity and optimally worked at pH 8 and 55°C. It was also active in a wide pH (3-9) and temperature (30-90ºC) ranges. GvXyl was highly stable at 90ºC and relatively stable at pH 3-9. The kinetic parameters of GvXyl were obtained as K_m , V_max , and k_cat ; 10.2 mg/ml, 4,104 µmol min^-1  mg^-1 , and 3,542.6 s^-1 , respectively. GvXyl had higher action than commercial xylanase in fruit juice enrichment. These results revealed that GvXyl might possess a potential influence in fruit juice processing because of its high specific activity and great thermal stability. PRACTICAL APPLICATIONS: Polysaccharides include starch, pectin, and hemicellulose create problems by lowering fruit juice quality in beverages. To overcome this problem, various clarification processes might be applied to natural fruit juices. Even though chemicals are widely used for this purpose, recently enzymes including xylanases are preferred for obtaining high-quality products. In this study, we reported the production and biochemical characterization of novel thermostable xylanase from thermophilic G. vulcani GS90 (GvXyl). Also, apple and orange juice enrichment were performed with the novel xylanase to increase the quality in terms of yield, clarity, and reducing sugar substance. The improved quality features of apple and orange juices with GvXyl was then compared to commercially available β-1,4-xylanase. The results revealed that GvXyl might possess a potential influence in fruit juice processing because of its high specific activity and great thermal stability.

Feruloylated Arabinoxylan and Oligosaccharides: Chemistry, Nutritional Functions, and Options for Enzymatic Modification

Cereal brans and grain endosperm cell walls are key dietary sources of different types of arabinoxylan. Arabinoxylan is the main group of hemicellulosic polysaccharides that are present in the cell walls of monocot grass crops and hence in cereal grains. The arabinoxylan polysaccharides consist of a backbone of β-(1→4)-linked xylopyranosyl residues, which carry arabinofuranosyl moieties, hence the term arabinoxylan. Moreover, the xylopyranosyl residues can be acetylated or substituted by 4-O-methyl-d-glucuronic acid. The arabinofuranosyls may be esterified with a feruloyl group. Feruloylated arabinoxylo-oligosaccharides exert beneficial bioactivities via prebiotic, immunomodulatory, and/or antioxidant effects. New knowledge on microbial enzymes that catalyze specific structural modifications of arabinoxylans can help us understand how these complex fibers are converted in the gut and provide a foundation for the production of feruloylated arabinoxylo-oligosaccharides from brans or other cereal grain processing sidestreams as functional food ingredients. There is a gap between the structural knowledge, bioactivity data, and enzymology insight. Our goal with this review is to present an overview of the structures and bioactivities of feruloylated arabinoxylo-oligosaccharides and review the enzyme reactions that catalyze specific changes in differentially substituted arabinoxylans.

Biochemical characterization and enhanced production of endoxylanase from thermophilic mould Myceliophthora thermophila

Endoxylanase production from M. thermophila BJTLRMDU3 using rice straw was enhanced to 2.53-fold after optimization in solid state fermentation (SSF). Endoxylanase was purified to homogeneity employing ammonium sulfate precipitation followed by gel filtration chromatography and had a molecular mass of ~ 25 kDa estimated by SDS-PAGE. Optimal endoxylanase activity was recorded at pH 5.0 and 60 °C. Purified enzyme showed complete tolerance to n-hexane, but activity was slightly inhibited by other organic solvents. Among surfactants, Tweens (20, 60, and 80) and Triton X 100 slightly enhanced the enzyme activity. The V_max and K_m values for purified endoxylanase were 6.29 µmol/min/mg protein and 5.4 mg/ml, respectively. Endoxylanase released 79.08 and 42.95% higher reducing sugars and soluble proteins, respectively, which control after 48 h at 60 °C from poultry feed. Synergistic effect of endoxylanase (100 U/g) and phytase (15 U/g) on poultry feed released higher amount of reducing sugars (58.58 mg/feed), soluble proteins (42.48 mg/g feed), and inorganic phosphate (28.34 mg/feed) in contrast to control having 23.55, 16.98, and 10.46 mg/feed of reducing sugars, soluble proteins, and inorganic phosphate, respectively, at 60 °C supplemented with endoxylanase only.

A highly xyloglucan active lytic polysaccharide monooxygenase EpLPMO9A from Eupenicillium parvum 4-14 shows boosting effect on hydrolysis of complex lignocellulosic substrates

The recently identified lytic polysaccharide monooxygenases (LPMOs) are important auxiliary proteins which contribute to lignocellulose biodegradation by oxidatively cleaving the glycosidic bonds in cellulose and other polysaccharides. The vast differences in terms of substrate specificity and regioselectivity within LPMOs provide us new possibilities to find promising candidates for the use in enzyme cocktails in biorefinery applications. In this study, a highly xyloglucan active family AA9 lytic polysaccharide monooxygenase EpLPMO9A was identified from Eupenicillium parvum 4-14. EpLPMO9A exhibited a mixed C1/C4 oxidative cleavage activity on cellulose and xyloglucan with a broad range of pH stability and good thermal stability at 40 °C. It showed a higher boosting effect on the enzymatic saccharification of complex lignocellulosic substrates associated with xyloglucan than on the lignocellulosic substrates without xyloglucan particularly in low commercial cellulase dosage cases. The oxidative cleavage of xyloglucan by EpLPMO9A may facilitate to open up the sterical hindrance of cellulose by xyloglucan and thereby increase accessibility for cellulase to lignocellulosic substrates. The discovery of more and more hemicellulose-active LPMOs and their contribution to breaking down the barriers by oxidatively acting on hemicellulose may expand our knowledge for their functions of LPMOs in lignocellulose biodegradation.

Characterization and functional analysis of two novel thermotolerant α-L-arabinofuranosidases belonging to glycoside hydrolase family 51 from Thielavia terrestris and family 62 from Eupenicillium parvum

Abstract

Arabinofuranose substitutions on xylan are known to interfere with enzymatic hydrolysis of this primary hemicellulose. In this work, two novel α-l-arabinofuranosidases (ABFs), TtABF51A from Thielavia terrestris and EpABF62C from Eupenicillium parvum, were characterized and functionally analyzed. From sequences analyses, TtABF51A and EpABF62C belong to glycoside hydrolase (GH) families 51 and 62, respectively. Recombinant TtABF51A showed high activity on 4-nitrophenyl-α-l-arabinofuranoside (83.39 U/mg), low-viscosity wheat arabinoxylan (WAX, 39.66 U/mg), high-viscosity rye arabinoxylan (RAX, 32.24 U/mg), and sugarbeet arabinan (25.69 U/mg), while EpABF62C preferred to degrade arabinoxylan. For EpABF62C, the rate of hydrolysis of RAX (94.10 U/mg) was 2.1 times that of WAX (45.46 U/mg). The optimal pH and reaction temperature for the two enzymes was between 4.0 and 4.5 and 65 °C, respectively. Calcium played an important role in the thermal stability of EpABF62C. TtABF51A and EpABF62C showed the highest thermal stabilities at pH 4.5 or 5.0, respectively. At their optimal pHs, TtABF51A and EpABF62C retained greater than 80% of their initial activities after incubation at 55 °C for 96 h or 144 h, respectively. ¹H NMR analysis indicated that the two enzymes selectively removed arabinose linked to C-3 of mono-substituted xylose residues in WAX. Compared with the singular application of the GH10 xylanase EpXYN1 from E. parvum, co-digestions of WAX including TtABF51A and/or EpABF62C released 2.49, 3.38, and 4.81 times xylose or 3.38, 1.65, and 2.57 times of xylobiose, respectively. Meanwhile, the amount of arabinose released from WAX by TtABF51A with EpXYN1 was 2.11 times the amount with TtABF51A alone.

Key points

• Two novel α-l-arabinofuranosidases (ABFs) displayed high thermal stability.

• The thermal stability of GH62 family EpABF62C was dependent on calcium.

• Buffer pH affects the thermal stability of the two ABFs.

• Both ABFs enhance the hydrolysis of WAX by a GH10 xylanase.

Electronic supplementary material

The online version of this article (10.1007/s00253-020-10867-7) contains supplementary material, which is available to authorized users.

Alkaline organosolv pretreatment of different sorghum stem parts for enhancing the total reducing sugar yields and p-coumaric acid release

BACKGROUND

The sorghum stem can be divided into the pith and rind parts with obvious differences in cell type and chemical composition, thus arising the different recalcitrance to enzyme hydrolysis and demand for different pretreatment conditions. The introduction of organic solvents in the pretreatment can reduce over-degradation of cellulose and hemicellulose, but significance of organic solvent addition in pretreatment of different parts of sorghum stem is still unclear. Valorization of each component is critical for economy of sorghum biorefinery. Therefore, in this study, NaOH-ethanol pretreatment condition for different parts of the sorghum stem was optimized to maximize p-coumaric acid release and total reducing sugar recovery.

RESULT

Ethanol addition improved p-coumaric acid release and delignification efficiency, but significantly reduced hemicellulose deconstruction in NaOH-ethanol pretreatment. Optimization using the response surface methodology revealed that the pith, rind and whole stem require different NaOH-ethanol pretreatment conditions for maximal p-coumaric acid release and xylan preservation. By respective optimal NaOH-ethanol pretreatment, the p-coumaric acid release yields reached 94.07%, 97.24% and 95.05% from pith, rind and whole stem, which increased by 8.16%, 8.38% and 8.39% compared to those of NaOH-pretreated samples. The xylan recoveries of pith, rind and whole stem reached 76.80%, 88.46% and 85.01%, respectively, which increased by 47.75%, 15.11% and 35.97% compared to NaOH pretreatment. Adding xylanase significantly enhanced the enzymatic saccharification of pretreated residues. The total reducing sugar yields after respective optimal NaOH-ethanol pretreatment and enzymatic hydrolysis reached 84.06%, 82.29% and 84.09% for pith, rind and whole stem, respectively, which increased by 29.56%, 23.67% and 25.56% compared to those of NaOH-pretreated samples. Considering the separation cost of the different stem parts, whole sorghum stem can be directly used as feedstock in industrial biorefinery.

CONCLUSION

These results indicated that NaOH-ethanol is effective for the efficient fractionation and pretreatment of sorghum biomass. This work will help to understand the differences of different parts of sorghum stem under NaOH-ethanol pretreatment, thereby improving the full-component utilization of sorghum stem.

Highly Efficient Extraction of Ferulic Acid from Cereal Brans by a New Type A Feruloyl Esterase from Eupenicillium parvum in Combination with Dilute Phosphoric Acid Pretreatment

Feruloyl esterase (FAE) is a critical enzyme in bio-extraction of ferulic acid (FA) from plant cell wall. A new FAE (EpFAE1) encoding gene was isolated from Eupenicillium parvum and heterologously expressed in Pichia pastoris cells. Based on phylogenetic tree analysis, the protein EpFAE1 belongs to type A of the seventh FAE subfamily. Using methyl ferulate as substrate, the optimum temperature and pH for the catalytic activity of EpFAE1 were 50 °C and 5.5, respectively. The enzyme exhibited high stability at 50 °C, in a wide pH range (3.0-11.0), or in the presence of 2 M of NaCl. Together with the endo-xylanase EpXYN1, EpFAE1 released 72.32% and 4.00% of the alkali-extractable FA from de-starched wheat bran (DSWB) or de-starched corn bran (DSCB), respectively. Meanwhile, the substrates were pretreated with 1.75% (for DSWB) or 1.0% (for DSCB) of phosphoric acid (PA) at 90 °C for 12 h, followed by enzymatic hydrolysis of the soluble and insoluble fractions. The release efficiencies of FA were up to 84.64% for DSWB and 66.73% for DSCB. Combined dilute PA pretreatment with enzymatic hydrolysis is a low-cost and highly efficient method for the extraction of FA from cereal brans.