Characterization of a glucose-stimulated β-glucosidase from Microbulbifer sp. ALW1

Polymer degrading marine Microbulbifer bacteria: an un(der)utilized source of chemical and biocatalytic novelty

Microbulbifer is a genus of halophilic bacteria that are commonly detected in the commensal marine microbiomes. These bacteria have been recognized for their ability to degrade polysaccharides and other polymeric materials. Increasingly, Microbulbifer genomes indicate these bacteria to be an untapped reservoir for novel natural product discovery and biosynthetic novelty. In this review, we summarize the distribution of Microbulbifer bacteria, activities of the various polymer degrading enzymes that these bacteria produce, and an up-to-date summary of the natural products that have been isolated from Microbulbifer strains. We argue that these bacteria have been hiding in plain sight, and contemporary efforts into their genome and metabolome mining are going to lead to a proliferation of Microbulbifer-derived natural products in the future. We also describe, where possible, the ecological interactions of these bacteria in marine microbiomes.

Characterization of a novel cold-adapted GH1 β-glucosidase from Psychrobacillus glaciei and its application in the hydrolysis of soybean isoflavone glycosides

The novel β-glucosidase gene (pgbgl1) of glycoside hydrolase (GH) family 1 from the psychrotrophic bacterium Psychrobacillus glaciei sp. PB01 was successfully expressed in Escherichia coli BL21 (DE3). The deduced PgBgl1 contained 447 amino acid residues with a calculated molecular mass of 51.4 kDa. PgBgl1 showed its maximum activity at pH 7.0 and 40 °C, and still retained over 10% activity at 0 °C, suggesting that the recombinant PgBgl1 is a cold-adapted enzyme. The substrate specificity, Km, Vmax, and Kcat/Km for the p-Nitrophenyl-β-D-glucopyranoside (pNPG) as the substrate were 1063.89 U/mg, 0.36 mM, 1208.31 U/mg and 3871.92/s, respectively. Furthermore, PgBgl1 demonstrated remarkable stimulation of monosaccharides such as glucose, xylose, and galactose, as well as NaCl. PgBgl1 also demonstrated a high capacity to convert the primary soybean isoflavone glycosides (daidzin, genistin, and glycitin) into their respective aglycones. Overall, PgBgl1 exhibited high catalytic activity towards aryl glycosides, suggesting promising application prospects in the food, animal feed, and pharmaceutical industries.

Microbial β-glucosidases: Recent advances and applications

The global β-glucosidase market is currently estimated at ∼400 million USD, and it is expected to double in the next six years; a trend that is mainly ascribed to the demand for the enzyme for biofuel processing. Microbial β-glucosidase, particularly, has thus garnered significant attention due to its ease of production, catalytic efficiency, and versatility, which have all facilitated its biotechnological potential across different industries. Hence, there are continued efforts to screen, produce, purify, characterize and evaluate the industrial applicability of β-glucosidase from actinomycetes, bacteria, fungi, and yeasts. With this rising demand for β-glucosidase, various cost-effective and efficient approaches are being explored to discover, redesign, and enhance their production and functional properties. Thus, this present review provides an up-to-date overview of advancements in the utilization of microbial β-glucosidases as "Emerging Green Tools" in 21st-century industries. In this regard, focus was placed on the use of recombinant technology, protein engineering, and immobilization techniques targeted at improving the industrial applicability of the enzyme. Furthermore, insights were given into the recent progress made in conventional β-glucosidase production, their industrial applications, as well as the current commercial status-with a focus on the patents.

Biochemical and in silico structural properties of a thermo-acid stable β-glucosidase from Beauveria bassiana

β-glucosidase hydrolyses the glycosidic bonds in cellobiose and cello-oligosaccharides, a critical step in the saccharification for biofuel production. Hence, the aim of this study was to gain insights into the biochemical and structural properties of a β-glucosidase from Beauveria bassiana, an entomopathogenic fungus. The β-glucosidase was purified to homogeneity using salt precipitation, ultrafiltration, and chromatographic techniques, attaining a specific activity of 496 U/mg. The molecular mass of the enzyme was then estimated via SDS-PAGE to be 116 kDa, while its activity pattern was confirmed by zymography using 4-methylumbelliferyl-β-d-glucopyranoside. Furthermore, the pH optima and temperature of the enzyme were found to be pH 5.0 and 60 °C respectively; its activity was significantly enhanced by Mg2+ and Na+ and was found to be relatively moderate in the presence of ethanol and dichloromethane. Molecular docking of the modelled B. bassiana β-glucosidase structure with the substrates, viz., 4-nitrophenyl β-d-glucopyranoside and cellobiose, revealed the binding affinity energies of -7.2 and -6.2 (kcal mol-1), respectively. Furthermore, the computational study predicted Lys-657, Asp-658, and Arg-1000 as the core amino acid residues in the catalytic site of the enzyme. This is the first investigation into a purified β-glucosidase from B. bassiana, providing valuable insights into the functional properties of carbohydrases from entomopathogenic fungal endophytes.

Screening, cloning, immobilization and application prospects of a novel β-glucosidase from the soil metagenome

The soil environment for straw return is a rich and valuable library containing many microorganisms and proteins. In this study, we aimed to screen a high-quality β-glucosidase (BGL) from the soil metagenomic library and to overcome the limitation of the low extraction rate of resveratrol in Polygonum cuspidatum. This includes the construction of a soil metagenomic library, screening of BGL, bioinformatics analysis, cloning, expression, immobilization, enzymatic property analysis, and application for the transformation of polydatin. The results showed that the soil metagenomic library of straw return was successfully constructed, and a novel BGL was screened. The identified 1356 bp long BGL belonged to the glycoside hydrolase 1 (GH1) family and was named Bgl1356. After successful cloning and expression of Bgl1356, it was immobilized using chitosan. The optimum temperature of immobilized Bgl1356 was 50 °C, and the pH was 5. It exhibited good tolerance for various metal ions (CO2+, Ni2+, Cu2+, Mn2+, Na2+, Ca2+, and Ag+) and organic solvents (DMSO, Triton-X-10, and ethanol). Enzymatic kinetics assays showed that Bgl1356 had good affinity for the substrate, and the specific enzyme activity was 234.03 U/mg. The conversion rate of polydatin by immobilized Bgl1356 was 95.70 ± 1.08%, facilitating the production of high amounts of resveratrol. Thus, this paper reports a novel temperature-, organic solvent-, and metal ion-tolerant BGL that has good application prospects in the pharmaceutical industry.

Microbial production and applications of β-glucosidase-A review

β-Glucosidase exists in all areas of living organisms, and microbial β-glucosidase has become the main source of its production because of its unique physicochemical properties and the advantages of high-yield production by fermentation. With the rise of the green circular economy, the production of enzymes through the fermentation of waste as the substrate has become a popular trend. Lignocellulosic biomass is an easily accessible and sustainable feedstock that exists in nature, and the production of biofuels from lignocellulosic biomass requires the involvement of β-glucosidase. This review proposes ways to improve β-glucosidase yield and catalytic efficiency. Optimization of growth conditions and purification strategies of enzymes can increase enzyme yield, and enzyme immobilization, genetic engineering, protein engineering, and whole-cell catalysis provide solutions to enhance the catalytic efficiency and activity of β-glucosidase. Besides, the diversified industrial applications, challenges and prospects of β-glucosidase are also described.

Exploring the partial degradation of polysaccharides: Structure, mechanism, bioactivities, and perspectives

Polysaccharides are promising biomolecules with lowtoxicity and diverse bioactivities in food processing and clinical drug development. However, an essential prerequisite for their applications is the fine structure characterization. Due to the complexity of polysaccharide structure, partial degradation is a powerful tool for fine structure analysis, which can effectively provide valid information on the structure of backbone and branching glycosidic fragments of complex polysaccharides. This review aims to conclude current methods of partial degradation employed for polysaccharide structural characterization, discuss the molecular mechanisms, and describe the molecular structure and solution properties of degraded polysaccharides. In addition, the effects of polysaccharide degradation on the conformational relationships between the molecular structure and bioactivities, such as antioxidant, antitumor, and immunomodulatory activities, are also discussed. Finally, we summarize the prospects and current challenges for the partial degradation of polysaccharides. This review will be of great value for the scientific elucidation of polysaccharide fine structures and potential applications.

Recent Advances in β-Glucosidase Sequence and Structure Engineering: A Brief Review

β-glucosidases (BGLs) play a crucial role in the degradation of lignocellulosic biomass as well as in industrial applications such as pharmaceuticals, foods, and flavors. However, the application of BGLs has been largely hindered by issues such as low enzyme activity, product inhibition, low stability, etc. Many approaches have been developed to engineer BGLs to improve these enzymatic characteristics to facilitate industrial production. In this article, we review the recent advances in BGL engineering in the field, including the efforts from our laboratory. We summarize and discuss the BGL engineering studies according to the targeted functions as well as the specific strategies used for BGL engineering.

Identification of LncRNAs and Functional Analysis of ceRNA Related to Fatty Acid Synthesis during Flax Seed Development

Flax is a flowering plant cultivated for its oil and contains various unsaturated fatty acids. Linseed oil is known as the "deep-sea fish oil" of plants, and is beneficial to brain and blood lipids, among other positive effects. Long non-coding RNAs (lncRNAs) play an important role in plant growth and development. There are not many studies assessing how lncRNAs are related to the fatty acid synthesis of flax. The relative oil contents of the seeds of the variety Heiya NO.14 (for fiber) and the variety Macbeth (for oil) were determined at 5 day, 10 day, 20 day, and 30 day after flowering. We found that 10-20 day is an important period for ALA accumulation in the Macbeth variety. The strand-specific transcriptome data were analyzed at these four time points, and a series of lncRNAs related to flax seed development were screened. A competing endogenous RNA (ceRNA) network was constructed and the accuracy of the network was verified using qRT-PCR. MSTRG.20631.1 could act with miR156 on the same target, squamosa promoter-binding-like protein (SPL), to influence fatty acid biosynthesis through a gluconeogenesis-related pathway during flax seed development. This study provides a theoretical basis for future studies assessing the potential functions of lncRNAs during seed development.

Characterization of a New Glucose-Tolerant GH1 β-Glycosidase from Aspergillus fumigatus with Transglycosylation Activity

Concern over environmental impacts has spurred many efforts to replace fossil fuels with biofuels such as ethanol. However, for this to be possible, it is necessary to invest in other production technologies, such as second generation (2G) ethanol, in order to raise the levels of this product and meet the growing demand. Currently, this type of production is not yet economically feasible, due to the high costs of the enzyme cocktails used in saccharification stage of lignocellulosic biomass. In order to optimize these cocktails, the search for enzymes with superior activities has been the goal of several research groups. For this end, we have characterized the new β-glycosidase AfBgl1.3 from A. fumigatus after expression and purification in Pichia pastoris X-33. Structural analysis by circular dichroism revealed that increasing temperature destructured the enzyme; the apparent T_m value was 48.5 °C. The percentages of α-helix (36.3%) and β-sheet (12.4%) secondary structures at 25 °C were predicted. Biochemical characterization suggested that the optimal conditions for AfBgl1.3 were pH 6.0 and temperature of 40 °C. At 30 and 40 °C, the enzyme was stable and retained about 90% and 50% of its activity, respectively, after pre-incubation for 24 h. In addition, the enzyme was highly stable at pH between 5 and 8, retaining over 65% of its activity after pre-incubation for 48 h. AfBgl1.3 co-stimulation with 50-250 mM glucose enhanced its specific activity by 1.4-fold and revealed its high tolerance to glucose (IC₅₀ = 2042 mM). The enzyme was active toward the substrates salicin (495.0 ± 49.0 U mg^-1), pNPG (340.5 ± 18.6 U mg^-1), cellobiose (89.3 ± 5.1 U mg^-1), and lactose (45.1 ± 0.5 U mg^-1), so it had broad specificity. The V_max values were 656.0 ± 17.5, 706.5 ± 23.8, and 132.6 ± 7.1 U mg^-1 toward p-nitrophenyl-β-D-glucopyranoside (pNPG), D-(-)-salicin, and cellobiose, respectively. AfBgl1.3 displayed transglycosylation activity, forming cellotriose from cellobiose. The addition of AfBgl1.3 as a supplement at 0.9 FPU/g of cocktail Celluclast^® 1.5L increased carboxymethyl cellulose (CMC) conversion to reducing sugars (g L^-1) by about 26% after 12 h. Moreover, AfBgl1.3 acted synergistically with other Aspergillus fumigatus cellulases already characterized by our research group-CMC and sugarcane delignified bagasse were degraded, releasing more reducing sugars compared to the control. These results are important in the search for new cellulases and in the optimization of enzyme cocktails for saccharification.

Characterization of a bifunctional and endolytic alginate lyase from Microbulbifer sp. ALW1 and its application in alginate oligosaccharides production from Laminaria japonica

The diverse biological activities of alginate oligosaccharides attracted extensive exploration of alginate lyases with various substrate specificity and enzymatic properties. In this study, an alginate lyase from Microbulbifer sp. ALW1, namely AlgL7, was phylogenetically classified into the polysaccharide lyase family 7 (PL7). The conserved amino acid residues Tyr606 and His499 in AlgL7 were predicted to act as the general acid/base catalysts. The enzyme was enzymatically characterized after heterologous expression and purification in E. coli. AlgL7 displayed optimal activity at 40 °C and pH 7.0. It had good stability at temperature below 35 °C and within a pH range of 5.0-10.0. AlgL7 exhibited good stability against the reducing reagent β-ME and the surfactants of Tween-20 and Triton X-100. The degradation profiles of alginate indicated AlgL7 was a bifunctional endolytic alginate lyase generating alginate oligosaccharides with the degrees of polymerization 2-4. The degradation products of sodium alginate exhibited stronger antioxidant activities than the untreated polysaccharide. In addition, AlgL7 could directly digest Laminaria japonica to produce alginate oligosaccharides. These characteristics of AlgL7 offer a great potential of its application in high-value utilization of brown algae resources.

Characterisation of marine bacterium Microbulbifer sp. ALW1 with Laminaria japonica degradation capability

Marine bacterium Microbulbifer sp. ALW1 was revealed to be able to effectively degrade Laminaria japonica thallus fragments into fine particles. Polysaccharide substrate specificity analysis indicated that ALW1 could produce extracellular alginate lyase, laminarinase, fucoidanase and cellulase. Based on alignment of the 16 S rRNA sequence with other reference relatives, ALW1 showed the closest relationship with Microbulbifer aggregans CCB-MM1T. The cell morphology and some basic physiological and biochemical parameters of ALW1 cells were characterised. ALW1 is a Gram-negative, rod- or oval-shaped, non-spore-forming and non-motile bacterium. The DNA–DNA relatedness values of ALW1 with type strains of M. gwangyangensis (JCM 17,800), M. aggregans (JCM 31,875), M. maritimus (JCM 12,187), M. okinawensis (JCM 16,147) and M. rhizosphaerae (DSM 28,920) were 28.9%, 43.3%, 41.2%, 35.4% and 45.6%, respectively. The major cell wall sugars of ALW1 were determined to be ribose and galactose, which differed from other closely related species. These characteristics indicated that ALW1 could be assigned to a separate species of the genus Microbulbifer. The complete genome of ALW1 contained one circular chromosome with 4,682,287 bp and a GC content of 56.86%. The putative encoded proteins were categorised based on their functional annotations. Phenotypic, physiological, biochemical and genomic characterisation will provide insights into the many potential industrial applications of Microbulbifer sp. ALW1.

Key points.

Crystal structure of metagenomic β-glycosidase MeBglD2 in complex with various saccharides

Metagenomic MeBglD2 is a glycoside hydrolase family 1 (GH1) β-glycosidase that has β-glucosidase, β-fucosidase, and β-galactosidase activities, and is highly activated in the presence of monosaccharides and disaccharides. The β-glucosidase activity of MeBglD2 increases in a cellobiose concentration-dependent manner and is not inhibited by a high concentration of D-glucose or cellobiose. Previously, we solved the crystal structure of MeBglD2 and designed a thermostable mutant; however, the mechanism of substrate recognition of MeBglD2 remains poorly understood. In this paper, we report the X-ray crystal structures of MeBglD2 complexed with various saccharides, such as D-glucose, D-xylose, cellobiose, and maltose. The results showed that subsite - 1 of MeBglD2, which contained two catalytic glutamate residues (a nucleophilic Glu356 and an acid/base Glu170) was common to other GH1 enzymes, but the positive subsites (+ 1 and + 2) had different binding modes depending on the type of sugar. Three residues (Glu183, Asn227, and Asn229), located at the positive subsites of MeBglD2, were involved in substrate specificity toward cellobiose and/or chromogenic substrates in the presence of additive sugars. The docking simulation of MeBglD2-cellobiose indicated that Asn229 and Trp329 play important roles in the recognition of + 1 D-glucose in cellobiose. Our findings provide insights into the unique substrate recognition mechanism of GH1, which can incorporate a variety of saccharides into its positive subsites. KEY POINTS: • Metagenomic glycosidase, MeBglD2, recognizes various saccharides • Structures of metagenomic MeBglD2 complexed with various saccharides are determined • MeBglD2 has a unique substrate recognition mechanism at the positive subsites.

Study on the Biochemical Characterization and Selectivity of Three β-Glucosidases From Bifidobacterium adolescentis ATCC15703

Three β-glucosidases from Bifidobacterium adolescentis ATCC15703, namely, BaBgl1A, BaBgl3A, and BaBgl3B, were overexpressed in Escherichia coli. The recombinant β-glucosidases were sufficiently purified using Ni²⁺ affinity chromatography, and BaBgl1A exhibited the best purification efficiency with a purification factor of 2.3-fold and specific activity of 71.2 U/mg. Three recombinant β-glucosidases acted on p-nitrophenyl-β-glucopyranoside (pNPβGlc) at around pH 7.0 and 30–50°C. The results of the substrate specificity assay suggested that BaBgl1A acted exclusively as β-1,2-glucosidase, while BaBgl3A and BaBgl3B acted mostly as β-1,3-glucosidase and β-1,4-glucosidase, respectively. The substrate specificity of the three recombinant enzymes was further studied using the ginsenosides Rb1 and Rd as substrates. The results of thin-layer chromatography and high-performance liquid chromatography analyses showed that BaBgl1A exhibited the highest bioconversion ability on Rb1 and Rd, where it hydrolyzed the outer C-3 glucose moieties of Rb1 and Rd into the rare ginsenosides Gypenoside XVII and F₂; BaBgl3A exhibited medium bioconversion ability on Rb1, where it hydrolyzed both the outer C-3 and C-20 glucose moieties of Rb1 into Gyp XVII and Rd; and BaBgl3B was not active on Rb1 and Rd. These β-glucosidases will act as new biocatalytic tools for transforming ginsenosides and preparing active glycosides and aglycone.