A novel thermostable β-1,3-1,4-glucanase from Thermoascus aurantiacus and its application in oligosaccharide production from oat bran

Biochemical properties and application of a multi-domain β-1,3-1,4-glucanase from Fibrobacter sp

A novel glycoside hydrolase (GH) family 16 multi-domain β-1,3-1,4-glucanase (FsGlc16A) from Fibrobacter sp. UWP2 was identified, heterogeneously expressed, and its enzymatic properties, protein structure and application potential were characterized. Enzymological characterization showed that FsGlc16A performed the optimal catalytic activity at pH 4.5 and 50 °C with a specific activity of 3263 U/mg. FsGlc16A exhibited the substrate specificity towards oat β-glucan, barley β-glucan and lichenan, and in addition, it hydrolyzed oat β-glucan and lichenan into different β-glucooligosaccharides with polymerization degrees of 3-4, which further illustrated that it belonged to the endo-type β-1,3-1,4-glucanase. FsGlc16A was classified in subfamily25 of GH16. A 'PXSSSS' repeats domain was identified at the C-terminus of FsGlc16A, which was distinct from the typical GH family 16 β-1,3-1,4-glucanases. Removing the 'PXSSSS' repeats domain affected the binding of the substrate to FsGlc16A and reduced the enzyme activity. FsGlc16A displayed good potential for the applications, which hydrolyzed oat bran into β-glucooligosaccharides, and reduced filtration time (18.89 %) and viscosity (3.64 %) in the saccharification process. This study investigated the enzymatic properties and domain function of FsGlc16A, providing new ideas and insights into the study of β-1,3-1,4-glucanase.

Identification and Characterization of Two Novel Extracellular β-Glucanases from Chaetomium globosum against Fusarium sporotrichioides

Chaetomium globosum can inhibit the growth of fusarium by means of their extracellular proteins. Two novel β-glucanases, designated Cgglu17A and Cgglu16B, were separated from the supernatant of C. globosum W7 and verified to have the ability to hydrolyze cell walls of Fusarium sporotrichioides MLS-19. Cgglu17A (397 amino acids) was classified as glycoside hydrolase family 17 while Cgglu16B belongs to the family16 (284 amino acids). Recombinant protein Cgglu17A was successfully expressed in Escherichia coli, and the enzymes were purified by affinity chromatography. Maximum activity of Cgglu17A appeared at the pH 5.5 and temperature 50 °C, but Cgglu16B shows the maximum activity at the pH 5.0 and temperature 50 °C. Most of heavy metal ions had inhibition effect on the two enzymes, but Cgglu17A and Cgglu16B were respectively activated by Ba2+ and Mn2+. Cgglu17A exhibited high substrate specificity, almost only catalyzing the cleavage of β-1,3-glycosidic bond, in various polysaccharose, to liberate glucose. However, Cgglu16B showed high catalytic activities to both β-1,3-glycosidic and β-1,3-1,4-glycosidic bonds. Cgglu17A was an exo-glucanase, but Cgglu16B was an endo-glucanase based on hydrolytic properties assay. Both of two enzymes showed potential antifungal activity, and the synergistic effect was observed in the germination experiment of pathogenic fungus. In conclusion, Cgglu17A (exo-1,3-β-glucanase) and Cgglu16B (endo-1,3(4)-β-glucanase) were confirmed to play a key role in the process of C. globosum controlling fusarium and have potential application value on industry and agriculture for the first time.

Investigation of the nutritional and functional roles of a combinational use of xylanase and β-glucanase on intestinal health and growth of nursery pigs

BACKGROUND

Xylanase and β-glucanase combination (XG) hydrolyzes soluble non-starch polysaccharides that are anti-nutritional compounds. This study aimed to evaluate the effects of increasing levels of XG on intestinal health and growth performance of nursery pigs.

METHODS

Forty pigs (6.5 ± 0.4 kg) were assigned to 5 dietary treatments and fed for 35 d in 3 phases (11, 9, and 15 d, respectively). Basal diets mainly included corn, soybean meal, and corn distiller's dried grains with solubles, contained phytase (750 FTU/kg), and were supplemented with 5 levels of XG at (1) 0, (2) 280 TXU/kg xylanase and 125 TGU/kg β-glucanase, (3) 560 and 250, (4) 840 and 375, or (5) 1,120 and 500, respectively. Growth performance was measured. On d 35, all pigs were euthanized and jejunal mucosa, jejunal digesta, jejunal tissues, and ileal digesta were collected to determine the effects of increasing XG levels and XG intake on intestinal health.

RESULTS

Increasing XG intake tended to quadratically decrease (P = 0.059) viscosity of jejunal digesta (min: 1.74 mPa·s at 751/335 (TXU/TGU)/kg). Increasing levels of XG quadratically decreased (P < 0.05) Prevotellaceae (min: 0.6% at 630/281 (TXU/TGU)/kg) in the jejunal mucosa. Increasing XG intake quadratically increased (P < 0.05) Lactobacillaceae (max: 40.3% at 608/271 (TXU/TGU)/kg) in the jejunal mucosa. Increasing XG intake quadratically decreased (P < 0.05) Helicobacteraceae (min: 1.6% at 560/250 (TXU/TGU)/kg) in the jejunal mucosa. Increasing levels of XG tended to linearly decrease (P = 0.073) jejunal IgG and tended to quadratically increase (P = 0.085) jejunal villus height to crypt depth ratio (max: 2.62 at 560/250 (TXU/TGU)/kg). Increasing XG intake tended to linearly increase the apparent ileal digestibility of dry matter (P = 0.087) and ether extract (P = 0.065). Increasing XG intake linearly increased (P < 0.05) average daily gain.

CONCLUSIONS

A combinational use of xylanase and β-glucanase would hydrolyze the non-starch polysaccharides fractions, positively modulating the jejunal mucosa-associated microbiota. Increased intake of these enzyme combination possibly reduced digesta viscosity and humoral immune response in the jejunum resulting in improved intestinal structure, and ileal digestibility of nutrients, and finally improving growth of nursery pigs. The beneficial effects were maximized at a combination of 550 to 800 TXU/kg xylanase and 250 to 360 TGU/kg β-glucanase.

New insights into endophytic fungi diversity and their potential correlation with polyphyllin levels of Paris polyphylla var. yunnanensis

Endophytes confer fitness advantages to host plants. However, the ecological communities of endophytic fungi in the different tissues (rhizomes, stems, and leaves) of Paris polyphylla and the relationship of their endophytic fungi with polyphyllin levels remain unclear. In this study, the community diversity and differences of endophytic fungi in the rhizomes, stems, and leaves of P. polyphylla var. yunnanensis were investigated, and a comprehensively diverse community of endophytic fungi was represented, including 50 genera, 44 families, 30 orders, 12 classes, and 5 phyla. Distributions of endophytic fungi differed greatly across the three tissues, with six genera common to all tissues, and 11, 5, and 4 genera specific to the rhizomes, stems, and leaves, respectively. Seven genera showed a significantly positive correlation to polyphyllin contents, indicating their potential roles in polyphyllin accumulation. This study provides valuable information for further research of the ecological and biological functions of endophytic fungi of P. polyphylla.

Distinct roles of carbohydrate-binding modules in multidomain β-1,3-1,4-glucanase on polysaccharide degradation

Lam16A is a novel GH16 β-1,3-1,4-lichenase isolated from the genus Caldicellulosiruptor which can utilize untreated carbohydrate components of plant cell walls. Its catalytic module has been characterized that the six carbohydrate-binding modules (CBMs) were queued in the C-terminus, but their roles were still unclear. Here, full-length and CBM-truncated mutants of Lam16A were purified and characterized through heterologous expression in Escherichia coli. The profiles of these proteins, including the enzyme activity, degrading efficiency, substrate-binding affinity, and thermostability, were explored. Full-length Lam16A with six CBMs showed excellent thermostability and the highest activity against barley β-glucan and laminarin with optimum pH of 6.5. The CBMs stimulated degrading ability of the catalytic module, especially against β-1,3(4)-glucan-based polysaccharides. The released products from β-1,3-1,4-glucan by Lam16A or its truncated mutants revealed an endo-type glycoside hydrolase. Lam16As exhibited strong binding affinities to the insoluble polysaccharides, especially Lam16A-1CBM. The degradation of yeast cell walls by Lam16A enzyme solution relative to the control reduced the absorbance values at OD₈₀₀ by ~ 85% ± 1.2, enabling the release of up to ~ 0.057 ± 0.0039 µg/mL of the cytoplasmic protein into the supernatant, lowering the viability of the cells by ~ 70.3% ± 6.9, thus causing significant damage in the cell wall structure. Taken together, CBMs could influence the substrate specificity, thermal stability, and binding affinity of β-1,3-1,4-glucanase. These results demonstrate the great potential of these enzymes to promote the bioavailability of β-1,3-glucan oligosaccharides for health benefits. KEY POINTS: • Carbohydrate-binding modules strongly influenced the enzyme activity and binding affinity, and further impacted glycoside hydrolase activity. • Lam16A enzymes have sufficient ability to hydrolyze β-1,3-1,4-glucan-based polysaccharides. • Lam16As provide a powerful tool to promote the bioavailability of β-1,3-glucan oligosaccharides.

Purification, characterization, immobilization and applications of an enzybiotic β-1,3-1,4-glucanase produced from halotolerant marine Halomonas meridiana ES021

Extracellular β-1,3-1,4-glucanase-producing strain Halomonas meridiana ES021 was isolated from Gabal El-Zeit off shore, Red Sea, Egypt. The Extracellular enzyme was partially purified by precipitation with 75% acetone followed by anion exchange chromatography on DEAE-cellulose, where a single protein band was determined with molecular mass of approximately 72 kDa. The K_m value was 0.62 mg β-1,3-1,4-glucan/mL and V_max value was 7936 U/mg protein. The maximum activity for the purified enzyme was observed at 40 °C, pH 5.0, and after 10 min of the reaction. β-1,3-1,4-glucanase showed strong antibacterial effect against Bacillus subtilis, Streptococcus agalactiae and Vibrio damsela. It also showed antifungal effect against Penicillium sp. followed by Aspergillus niger. No toxicity was observed when tested on Artemia salina. Semi-purified β-1,3-1,4-glucanase was noticed to be effective in clarification of different juices at different pH values and different time intervals. The maximum clarification yields were 51.61% and 66.67% on mango juice at 40 °C and pH 5.3 for 2 and 4 h, respectively. To our knowledge, this is the first report of β-1,3-1,4-glucanase enzyme from halotolerant Halomonas species.

Characterization of Paenibacillus sp. GKG Endo-β-1, 3-Glucanase, a Member of Family 81 Glycoside Hydrolases

Paenibacillus sp. GKG was isolated based on its ability to produce hydrolysis zones on agar plates containing yeast cell wall substrate as the single carbon source. The extracellular enzymes secreted into the culture medium were identified by LC-MS/MS proteomics. Endo-β-1,3-glucanase PsLam81A containing GH81 catalytic and the CBM56 carbohydrate-binding modules was selected for heterologous expression in Escherichia coli. The identity of the recombinant PsLam81A was confirmed by LC-MS/MS proteomics. The PsLam81A showed the highest activity at 60 °C, and the optimal pH range was between 6.5 and 8.0. The analysis of the full-length PsLam81A and truncated PsLam81AΔCBM56 enzymes showed that the CBM56 module improved the hydrolytic activity towards linear β-1,3-glucans—curdlan and pachyman but had no effect on hydrolysis of β-1,3/β1,6-branched glucans—laminarin and yeast β-glucan. The characterization of PsLam81A enzyme broadens current knowledge on the biochemical properties and substrate specificity of family 81 glycoside hydrolases and allows prediction of the necessity of CBM56 module in the process of designing new truncated or chimeric glycosidases.

Microwave-assisted degradation of β-D-glucan from Ganoderma lucidum and the structural and immunoregulatory properties of oligosaccharide fractions

Microwave-assisted degradation of β-(1 → 3,1 → 6)-D-glucan from Ganoderma lucidum and correlated immunoregulatory activities were investigated in this study. The optimal temperature and degradation time for microwave hydrothermal hydrolysis were 140 °C and 40 min, respectively. Under these conditions, a high yield of degradation rate (98.4 %) and abundant β-oligosaccharide products (GLOS) with different degrees of polymerization (DP 2-24) were obtained. Four fractions including F1 (DP 2-8), F2 (DP 6-19), F3 (DP 8-24) and F4 (high DPs) with different average ratios of β-(1 → 3) to β-(1 → 6)-linked glucose units were isolated from GLOS. The structures of oligosaccharides with DP (2-6) in F1 were identified as linear β-(1 → 3)-linked glucooligosaccharides without or with β-(1 → 6)-linked glucose residues based on MS/MS analysis. The immunoregulation activity of β-glucooligosaccharides was correlated with their DPs and the average ratios of β-(1 → 3) to β-(1 → 6)-linked glucose units. F4 fraction with high DPs and ratio of 3.29:1 exhibited higher immunoenhancing activity on inducing NF-κB activation through binding to dectin-1. Surface plasmon resonance (SPR) analysis indicated that β-glucooligosaccharides could bind to Dectin-1 directly and the binding affinity increased with the increase of DPs and the ratios of β-(1 → 3)-linked glucose.

Characterization of a Thermostable Lichenase from Bacillus subtilis B110 and Its Effects on β-Glucan Hydrolysis

Lichenase is an enzyme mainly implicated in the degradation of polysaccharides in the cell walls of grains. Emerging evidence shows that a highly efficient expression of a thermostable recombinant lichenase holds considerable promise for application in the beer-brewing and animal feed industries. Herein, we cloned a lichenase gene (CelA203) from Bacillus subtilis B110 and expressed it in E. coli. This gene contains an ORF of 729 bp, encoding a protein with 242 amino acids and a calculated molecular mass of 27.3 kDa. According to the zymogram results, purified CelA203 existed in two forms, a monomer, and a tetramer, but only the tetramer had potent enzymatic activity. CelA203 remained stable over a broad pH and temperature range and retained 40% activity at 70°C for 1 h. The K_m and V_max of CelA203 towards barley β-glucan and lichenan were 3.98 mg/ml, 1017.17 U/mg, and 2.78 mg/ml, 198.24 U/mg, respectively. Furthermore, trisaccharide and tetrasaccharide were the main products obtained from CelA203-mediated hydrolysis of deactivated oat bran. These findings demonstrate a promising role for CelA203 in the production of oligosaccharides in animal feed and brewing industries.

Advances in research on solid-state fermented feed and its utilization: The pioneer of private customization for intestinal microorganisms

With sustainable development of biotechnology, increasing attention has been placed on utilization of solid-state fermented feed (SFF). Solid-state fermented feed has been a candidate strategy to alleviate the contradiction between supply and demand of feed resources, ensure food hygiene safety, promoting energy conservation, and emission reduction. In production of SFF, a variety of organic acids, enzymes, vitamins, peptides, and other unknown growth factors are produced, which could affect performance of animals. Solid-state fermented feed produced by different fermentation techniques has great instability on different physiological stages of different animals, which hinders the application and standardized production of SFF. Herein, we summarize the current advances in the role of the characteristics of SFF prepared by different manufacturing technique and its research progress in animal experiments on growth performance, gastrointestinal ecology, and immune system, so as to provide references for further acquiring a relatively perfect set of SFF production and evaluation systems.

Structural and biochemical insights into the substrate-binding mechanism of a glycoside hydrolase family 12 β-1,3-1,4-glucanase from Chaetomium sp

β-1,3-1,4-Glucanases are a type of hydrolytic enzymes capable of catalyzing the strict cleavage of β-1,4 glycosidic bonds adjacent to β-1,3 linkages in β-D-glucans and have exhibited great potential in food and feed industrials. In this study, a novel glycoside hydrolase (GH) family 12 β-1,3-1,4-glucanase (CtGlu12A) from the thermophilic fungus Chaetomium sp. CQ31 was identified and biochemically characterized. CtGlu12A was most active at pH 7.5 and 65 °C, respectively, and exhibited a high specific activity of 999.9 U mg^-1 towards lichenin. It maintained more than 80% of its initial activity in a wide pH range of 5.0-11.0, and up to 60 °C after incubation at 55 °C for 60 min. Moreover, the crystal structures of CtGlu12A with gentiobiose and tetrasccharide were resolved. CtGlu12A had a β-jellyroll fold, and performed retaining mechanism with two glutamic acids severing as the catalytic residues. In the complex structure, cellobiose molecule showed two binding modes, occupying subsites -2 to -1 and subsites + 1 to + 2, respectively. The concave cleft made mixed β-1,3-1,4-glucan substrates maintain a bent conformation to fit into the active site. Overall, this study is not only helpful for the understanding of the substrate-binding model and catalytic mechanism of GH 12 β-1,3-1,4-glucanases, but also provides a basis for further enzymatic engineering of β-1,3-1,4-glucanases.

An Aspergillus nidulans endo-β-1,3-glucanase exhibited specific catalytic features and was used to prepare 3-O-β-cellobiosyl-d-glucose and 3-O-β-gentiobiosyl-d-glucose with high antioxidant activity from barley β-glucan and laminarin, respectively

An endo-β-1,3(4)-glucanase AnENG16A from Aspergillus nidulans shows distinctive catalytic features for hydrolysis of β-glucans. AnENG16A hydrolyzed Eisenia bicyclis laminarin to mainly generate 3-O-β-gentiobiosyl-d-glucose and hydrolyzed barley β-glucan to mainly produce 3-O-β-cellobiosyl-d-glucose. Using molecular exclusion chromatography, we isolated and purified 3-O-β-cellobiosyl-d-glucose and 3-O-β-gentiobiosyl-d-glucose, respectively, from AnENG16A-hydrolysate of barley β-glucan and E. bicyclis laminarin. Further study reveals that 3-O-β-cellobiosyl-d-glucose had 8.99-fold higher antioxidant activity than barley β-glucan and 3-O-β-gentiobiosyl-d-glucose exhibited 43.0% higher antioxidant activity than E. bicyclis laminarin. Notably, 3-O-β-cellobiosyl-d-glucose and 3-O-β-gentiobiosyl-d-glucose exhibited 148.9% and 116.0% higher antioxidant activity than laminaritriose, respectively, indicating that β-1,4-linkage or -1,6-linkage at non-reducing end of β-glucotrioses had enhancing effect on antioxidant activity compared to β-1,3-linkage. Furthermore, 3-O-β-cellobiosyl-d-glucose showed 237.9% higher antioxidant activity than cellotriose, and laminarin showed 5.06-fold higher antioxidant activity than barley β-glucan, indicating that β-1,4-linkage at reducing end of β-glucans or oligosaccharides resulted in decrease of antioxidant activity compared to β-1,3-linkage.

Enhanced hydrolytic efficiency of an engineered CBM11-glucanase enzyme chimera against barley β-d-glucan extracts

The β-d-glucans are abundant cell wall polysaccharides in many cereals and contain both (1,3)- and (1,4)-bonds. The β-1,3-1,4-glucanases (EC 3.2.1.73) hydrolyze β-(1,4)-d-glucosidic linkages in glucans, and have applications in both animal and human food industries. A chimera between the family 11 carbohydrate-binding module from Ruminoclostridium (Clostridium)thermocellumcelH (RtCBM11), with the β-1,3-1,4-glucanase from Bacillus subtilis (BglS) was constructed by end-to-end fusion (RtCBM11-BglS) to evaluate the effects on the catalytic function and its application in barley β-glucan degradation for the brewing industry. The parental and chimeric BglS presented the same optimum pH (6.0) and temperature (50 °C) for maximum activity. The RtCBM11-BglS showed increased thermal stability and 30% higher hydrolytic efficiency against purified barley β-glucan, and the rate of hydrolysis of β-1,3-1,4-glucan in crude barley extracts was significantly increased. The enhanced catalytic performance of the RtCBM11-BglS may be useful for the treatment of crude barley extracts in the brewing industry.

High cellulolytic potential of the Ktedonobacteria lineage revealed by genome-wide analysis of CAZymes

Traditionally, filamentous fungi and actinomycetes are well-known cellulolytic microorganisms that have been utilized in the commercial production of cellulase enzyme cocktails for industrial-scale degradation of plant biomass. Noticeably, the Ktedonobacteria lineage (phylum Chloroflexi) with actinomycetes-like morphology was identified and exhibited diverse carbohydrate utilization or degradation abilities. In this study, we performed genome-wide profiling of carbohydrate-active enzymes (CAZymes) in the filamentous Ktedonobacteria lineage. Numerous CAZymes (153-290 CAZymes, representing 63-131 glycoside hydrolases (GHs) per genome), including complex mixtures of endo- and exo-cellulases, were predicted in 15 available Ktedonobacteria genomes. Of note, 4-28 CAZymes were predicted to be extracellular enzymes, whereas 3-29 CAZymes were appended with carbohydrate-binding modules (CBMs) that may promote their binding to insoluble carbohydrate substrates. This number far exceeded other Chloroflexi lineages and were comparable to the cellulolytic actinomycetes. Six multi-modular extracellular GHs were cloned from the thermophilic Thermosporothrix hazakensis SK20-1^T strain and heterologously expressed. The putative endo-glucanases of ThazG5-1, ThazG9, and ThazG12 exhibited strong cellulolytic activity, whereas the putative exo-glucanases ThazG6 and ThazG48 formed weak but observable halos on carboxymethyl cellulose plates, indicating their potential biotechnological application. The purified recombinant ThazG12 had near-neutral pH (optimal 6.0), high thermostability (60°C), and broad specificity against soluble and insoluble polysaccharide substrates. It also represented described a novel thermostable bacterial β-1,4-glucanase in the GH12 family. Together, this research revealed the underestimated cellulolytic potential of the Ktedonobacteria lineage and highlighted its potential biotechnological utility as a promising microbial resource for the discovery of industrially useful cellulases.