Production and Characterization of Highly Thermostable β-Glucosidase during the Biodegradation of Methyl Cellulose by Fusarium oxysporum

Novel melanin-derived stationary phase for immobilized metal ion affinity chromatography in recombinant His-tagged protein purification

The matrix of the stationary phase is a crucial element in affinity chromatography for protein purification. Various materials, including polymer or magnetic materials, have been employed as the matrix in the purification of His-tagged protein. Here, for the first time, we utilized a combination of melanin and alginate, both natural polymer materials, to synthesize Ni-melanin/alginate (Ni-M/A) beads for His-tagged protein purification. We investigated the binding of His-tagged Mpro on the Ni-M/A beads, referred to as Ni-M/A-Mpro, and assessed the elution efficiency of Mpro from the beads. Our examination involved FTIR, EDS, XRD, SDS-PAGE, and Western blotting methods. FTIR spectra revealed notable changes in the stretching patterns and intensities of hydroxyl, amine, carbonyl, imine and amide chemical groups, when Mpro protein was present in the Ni-M/A sample. XRD spectra demonstrated the occurrence of two Nickel peaks at 35-40 deg and 40-45 deg in Ni-M/A, but only one nickel peak at 35-40 deg in Ni-M/A-Mpro, indicating the binding of Mpro on the Nickel ions. EDS analysis reported a decrease in the concentration of Nickel on the surface of Ni-M/A from 16% to 7% when Mpro protein was loaded into the stationary phase. Importantly, our data indicated that the purity of the His-tagged protein Mpro after purification reached 97% after just one-step purification using the Ni-M/A stationary phase. Moreover, the binding capacity of Ni-M/A for Mpro was approximately 5.2 mg/g with recovery efficiency of 40%. Our results suggested Ni-M/A as a highly potential solid phase for affinity chromatography in the purification of His-tagged protein.

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.

Differential scanning calorimetry (DSC) as a tool for studying thermal properties of a crude cellulase cocktail

Abstract

Differential scanning calorimetry (DSC) was used as an efficient and rapid tool in studying the conformational transitions between the folded and unfolded structures of cellulolytic enzymes. The thermal properties of two crude hydrolytic enzyme cocktails containing extracellular cellulases from Trichoderma longibrachiatum DIBAF-10 were analyzed and compared with three commercial cellulase preparations. Differences in the thermal behavior of fungal cellulases in the liquid phase, freeze-dried state, liquid formulations in sodium citrate buffer (pH 4.8), and contact with cellulose, carboxymethyl cellulose, and cellobiose were evaluated. DSC profiles of cellulases from the DIBAF-10 strain provided important thermodynamic information about the thermal stability of the included proteins. Crude enzyme cocktails underwent a reproducible and irreversible exothermic aggregation phenomenon at 52.45 ± 0.90 °C like commercial β-glucosidase. Freeze-dried and resuspended in a sodium citrate buffer, cellulases from T. longibrachiatum showed an endothermic peak dependent on buffer and enzyme concentration. In the enzyme-substrates systems, a shift of the same peak was recorded for all substrates tested. The thermal analysis of freeze-dried cellulase samples in the range of 20–150 °C gave information on the denaturation process. In conclusion, we demonstrated that DSC is a cost-effective tool for obtaining "conformational fingerprinting" of crude fungal cellulase preparations.

Graphical abstract

Study on the interaction mechanism between Crocus sativus and Fusarium oxysporum based on dual RNA-seq

The saffron phenylpropane synthesis pathway and Fusarium oxysporum cell wall-degrading enzymes play key roles in their early interactions. Saffron (Crocus sativus) is a highly important crop with diverse medicinal properties. F. oxysporum is a widely-distributed soil-borne fungus, causing the serious saffron rot disease. Currently, there is no effective management strategy to control this disease because of no resistant cultivars and limited information about the resistance and pathogenic mechanisms. In this study, we first characterized the infection process and physiological responses of saffron infected by F. oxysporum. The molecular mechanism of these infection interactions was revealed by dual RNA-seq analysis. On the 3rd day of infection, the hyphae completely entered, colonized and spread in the corm cells; while on the 6th day of infection, hyphae had appeared in the xylem cells, blocking these vessels. Transcriptome results indicate that within the host, phenylpropanoid metabolism, plant hormone signal transduction and plant pathogen interaction pathways were activated during infection. These pathways were conducive to the enhancement of cell wall, the occurrence of hypersensitivity, and the accumulation of various antibacterial proteins and phytoantitoxins. Meanwhile, in the fungus, many up-regulated genes were related to F. oxysporum cell wall degrading enzymes, toxin synthesis and pathogenicity gene, showing its strong pathogenicity. This study provides new ideas for the control of saffron corm rot, and also provides a theoretical basis for mining the key functional genes.

Cellulolytic and Xylanolytic Enzymes from Yeasts: Properties and Industrial Applications

Lignocellulose, the main component of plant cell walls, comprises polyaromatic lignin and fermentable materials, cellulose and hemicellulose. It is a plentiful and renewable feedstock for chemicals and energy. It can serve as a raw material for the production of various value-added products, including cellulase and xylanase. Cellulase is essentially required in lignocellulose-based biorefineries and is applied in many commercial processes. Likewise, xylanases are industrially important enzymes applied in papermaking and in the manufacture of prebiotics and pharmaceuticals. Owing to the widespread application of these enzymes, many prokaryotes and eukaryotes have been exploited to produce cellulase and xylanases in good yields, yet yeasts have rarely been explored for their plant-cell-wall-degrading activities. This review is focused on summarizing reports about cellulolytic and xylanolytic yeasts, their properties, and their biotechnological applications.

A Comprehensive Network Integrating Signature Microbes and Crucial Soil Properties During Early Biological Soil Crust Formation on Tropical Reef Islands

Biological soil crusts (BSCs/biocrusts), which are distributed across various climatic zones and well-studied in terrestrial drylands, harbor polyextremotolerant microbial topsoil communities and provide ecological service for local and global ecosystem. Here, we evaluated BSCs in the tropical reef islands of the South China Sea. Specifically, we collected 41 BSCs, subsurface, and bare soil samples from the Xisha and Nansha Archipelagos. High-throughput amplicon sequencing was performed to analyze the bacterial, fungal, and archaeal compositions of these samples. Physicochemical measurement and enzyme activity assays were conducted to characterize the soil properties. Advanced computational analysis revealed 47 biocrust-specific microbes and 10 biocrust-specific soil properties, as well as their correlations in BSC microbial community. We highlighted the previously underestimated impact of manganese on fungal community regulation and BSC formation. We provide comprehensive insight into BSC formation networks on tropical reef islands and established a foundation for BSC-directed environmental restoration.

Cloning, biochemical characterization and molecular docking of novel thermostable β-glucosidase BglA9 from Anoxybacillus ayderensis A9 and its application in de-glycosylation of Polydatin

This study reports a novel BglA9 gene of 1345 bp encoding β-glucosidase from Anoxybacillus ayderensis A9, which was amplified and expressed in E. coli BL21 (DE3): pLysS cells, purified with Ni-NTA column having molecular weight of 52.6 kDa and was used in the bioconversion of polydatin to resveratrol. The kinetic parameters values using pNPG as substrate were K_m (0.28 mM), V_max (43.8 μmol/min/mg), k_cat (38.43 s^-1) and k_cat/K_m (135.5 s^-1 mM^-1). The BglA9 was active in a broad pH range and had an activity half-life around 24 h at 50 °C. The de-glycosylation efficiency of BglA9 for polydatin was determined by estimating the amount of glucose released after enzymatic reaction by a dinitrosalicylic acid (DNS) assay. The kinetic parameters of BglA9 for polydatin were 5.5 mM, 20.84 μmol/min/mg, 18.28 s^-1and 3.27 s^-1 mM^-1 for K_m, V_max, k_cat, and k_cat/K_m values, respectively. The K_i value for glucose was determined to be 1.7 M. The residues Gln19, His120, Glu355, Glu409, Glu178, Asn222 may play a crucial role in the deglycosylation as revealed by the 3D structure of enzyme docked with polydatin.

Functional properties and potential application of ethanol tolerant β-glucosidases from Pichia ofunaensis and Trichosporon multisporum yeasts

β-Glucosidases have been extensively investigated to integrate the enzyme complex for cellulose fiber saccharification and for improving the aroma of wine. To produce these enzymes, greater attention has been given to filamentous fungi and bacteria, and few investigations have targeted the potential applications of enzymes secreted by yeasts. Addressing this issue, in this study, β-glucosidases were produced by the Pichia ofunaensis and Trichosporon multisporum yeasts, via solid state fermentation with wheat bran as a substrate. When using p-Nitrophenyl β-d-glucopyranoside (pNPG) as an enzyme substrate, maximum β-glucosidase activities were detected at pH 5.5-6.0 and 50-60 °C for P. ofunaensis, and pH 5-6 and 55 °C for T. multisporum. Both enzymes were able to hydrolyze cellobiose and exhibited stability over a wide range of pH (3.5-9.0) for 24 h at 4 °C, thermostability up to 50 °C for 1 h and tolerance to 10 mM phenolic compounds. Negative modulation on enzyme activity was observed in the presence of Cu2+, Fe3+, Zn2+, Al3+ and Hg2+, while both β-glucosidases were tolerant to 30% methanol, isopropanol and acetone. In the presence of ethanol and glucose, enzymes from P. ofunaensis were the more active and stable of the two. These enzymes, especially the P. ofunaensis β-glucosidases, could be tested in enology for improving the aroma of wine and for integrating a cellulolytic complex to produce 2G ethanol.

Glycoside Hydrolases and Glycosyltransferases from Hyperthermophilic Archaea: Insights on Their Characteristics and Applications in Biotechnology

Hyperthermophilic Archaea colonizing unnatural habitats of extremes conditions such as volcanoes and deep-sea hydrothermal vents represent an unmeasurable bioresource for enzymes used in various industrial applications. Their enzymes show distinct structural and functional properties and are resistant to extreme conditions of temperature and pressure where their mesophilic homologs fail. In this review, we will outline carbohydrate-active enzymes (CAZymes) from hyperthermophilic Archaea with specific focus on the two largest families, glycoside hydrolases (GHs) and glycosyltransferases (GTs). We will present the latest advances on these enzymes particularly in the light of novel accumulating data from genomics and metagenomics sequencing technologies. We will discuss the contribution of these enzymes from hyperthermophilic Archaea to industrial applications and put the emphasis on newly identifed enzymes. We will highlight their common biochemical and distinct features. Finally, we will overview the areas that remain to be explored to identify novel promising hyperthermozymes.

Target of rapamycin controls hyphal growth and pathogenicity through FoTIP4 in Fusarium oxysporum

Fusarium oxysporum is the causal agent of the devastating Fusarium wilt by invading and colonizing the vascular system in various plants, resulting in substantial economic losses worldwide. Target of rapamycin (TOR) is a central regulator that controls intracellular metabolism, cell growth, and stress responses in eukaryotes, but little is known about TOR signalling in F. oxysporum. In this study, we identified conserved FoTOR signalling pathway components including FoTORC1 and FoTORC2. Pharmacological assays showed that F. oxysporum is hypersensitive to rapamycin in the presence of FoFKBP12 while the deletion mutant strain ΔFofkbp12 is insensitive to rapamycin. Transcriptomic data indicated that FoTOR signalling controls multiple metabolic processes including ribosome biogenesis and cell wall-degrading enzymes (CWDEs). Genetic analysis revealed that FoTOR1 interacting protein 4 (FoTIP4) acts as a new component of FoTOR signalling to regulate hyphal growth and pathogenicity of F. oxysporum. Importantly, transcript levels of genes associated with ribosome biogenesis and CWDEs were dramatically downregulated in the ΔFotip4 mutant strain. Electrophoretic mobility shift assays showed that FoTIP4 can bind to the promoters of ribosome biogenesis- and CWDE-related genes to positively regulate the expression of these genes. These results suggest that FoTOR signalling plays central roles in regulating hyphal growth and pathogenicity of F. oxysporum and provide new insights into FoTOR1 as a target for controlling and preventing Fusarium wilt in plants.

Thermostable cellulose saccharifying microbial enzymes: Characteristics, recent advances and biotechnological applications

Cellulases play a promising role in the bioconversion of renewable lignocellulosic biomass into fermentable sugars which are subsequently fermented to biofuels and other value-added chemicals. Besides biofuel industries, they are also in huge demand in textile, detergent, and paper and pulp industries. Low titres of cellulase production and processing are the main issues that contribute to high enzyme cost. The success of ethanol-based biorefinery depends on high production titres and the catalytic efficiency of cellulases functional at elevated temperatures with acid/alkali tolerance and the low cost. In view of their wider application in various industrial processes, stable cellulases that are active at elevated temperatures in the acidic-alkaline pH ranges, and organic solvents and salt tolerance would be useful. This review provides a recent update on the advances made in thermostable cellulases. Developments in their sources, characteristics and mechanisms are updated. Various methods such as rational design, directed evolution, synthetic & system biology and immobilization techniques adopted in evolving cellulases with ameliorated thermostability and characteristics are also discussed. The wide range of applications of thermostable cellulases in various industrial sectors is described.

Effect of liquid volume and microflora source on degradation rate and microbial community in corn stover degradation

Degradation is the bottleneck in the utilization of crop straw. In this paper, we screened the microbial consortia degrading corn stover from straw degrading consortia MC1 (M), sheep feces (Y), and mixtures (Q) of M, Y, and cattle feces. The effects of microflora source and liquid volume (representing dissolved oxygen) on the microbial community and degradation rate of corn stover were investigated. The results showed that the degradation rate and cellulase activity of a 200 mL liquid volume (L2) were significantly higher than that of 100 mL (L1). Microflora source had a significant effect on bacterial and fungal diversity, composition and taxa. Q and Y had higher bacterial and fungal α-diversity than that of M. The degradation rate was significantly correlated with cellulase activity but not with microbial diversity. This indicated that liquid volume had a significant effect on degradation rate while microflora source had a significant effect on microbial community in corn stover degradation.

How Carbon Source and Degree of Oligosaccharide Polymerization Affect Production of Cellulase-Degrading Enzymes by Fusarium oxysporum f. sp. lycopersici

Cellulases are a group of enzymes responsible for the degradation of cellulose, which is one of the most abundant polymers on Earth. The three main groups of cellulases are endoglucosidases, exoglucosidases, and β-glucosidases; however, the mechanism of induction of these enzymes remains poorly characterized. Cellooligosaccharides are among the main inducers of these enzymes in filamentous fungi, yet it is not clear how their degree of polymerization may affect the strength of induction. In the present study, we investigated the effect of different carbohydrate-based inducers, such as lactose, sophorose, cellooligosaccharides, and xylooligosacharides, characterized by different concentrations and degree of polymerization, on cellulases production by the fungus Fusarium oxysporum f. sp. lycopersici, which is one of the most studied lignocellulose degrading fungi with the ability to consume both cellulose and hemicellulose. Moreover, the effect of carbon source on cellulase induction was assessed by growing the biomass on sucrose or glycerol. Results showed a correlation between induction efficiency and the cellooligosaccharides' concentration and size, as well as the carbon source available. Specifically, cellotetraose was a better inducer when sucrose was the carbon source, while cellobiose yielded a better result on glycerol. These findings can help optimize industrial cellulase production.

Optimization of extracellular ethanol-tolerant β-glucosidase production from a newly isolated Aspergillus sp. DHE7 via solid state fermentation using jojoba meal as substrate: purification and biochemical characterization for biofuel preparation

BACKGROUND

The increasing demand and the continuous depletion in fossil fuels have persuaded researchers to investigate new sources of renewable energy. Bioethanol produced from cellulose could be a cost-effective and a viable alternative to petroleum. It is worth note that β-glucosidase plays a key role in the hydrolysis of cellulose and therefore in the production of bioethanol. This study aims to investigate a simple and standardized method for maximization of extracellular β-glucosidase production from a novel fungal isolate under solid-state fermentation using agro-industrial residues as the sole source of carbon and nitrogen. Furthermore, purification and characterization of β-glucosidase were performed to determine the conditions under which the enzyme displayed the highest performance.

RESULTS

A fungus identified genetically as a new Aspergillus sp. DHE7 was found to exhibit the highest extracellular β-glucosidase production among the sixty fungal isolates tested. Optimization of culture conditions improved the enzyme biosynthesis by 2.1-fold (174.6 ± 5.8 U/g of dry substrate) when the fungus grown for 72 h at 35 °C on jojoba meal with 60% of initial substrate moisture, pH 6.0, and an inoculum size of 2.54 × 107 spores/mL. The enzyme was purified to homogeneity through a multi-step purification process. The purified β-glucosidase is monomeric with a molecular mass of 135 kDa as revealed by the SDS-PAGE analysis. Optimum activity was observed at 60 °C and pH of 6.0, with a remarkable pH and thermal stability. The enzyme retained about 79% and 53% of its activity, after 1 h at 70 °C and 80 °C, respectively. The purified β-glucosidase hydrolysed a wide range of substrates but displaying its greater activity on p-nitrophenyl-β-D-glucopyranoside and cellobiose. The values of Km and Vmax on p-nitrophenyl β-D-glucopyranoside were 0.4 mM and 232.6 U/mL, respectively. Purified β-glucosidase displayed high catalytic activity (improved by 25%) in solutions contained ethanol up to 15%.

CONCLUSION

β-glucosidase characteristics associated with its ability to hydrolyse cellobiose, underscore its utilization in improving the quality of food and beverages. In addition, taking into consideration that the final concentration of ethanol produced by the conventional methods is about 10%, suggests its use in ethanol-containing industrial processes and in the saccharification processes for bioethanol production.

Structural aspects of β-glucosidase of Myceliophthora thermophila (MtBgl3c) by homology modelling and molecular docking

Cellulases are the enzymes with diverse range of industrial applications. Cellulases degrade cellulose into monomeric glucose units by hydrolysing β-1,4-glycosidic bonds. There are three components of cellulases: a) endoglucanase, b) exoglucanase and c) β-glucosidase which act synergistically in cellulose bioconversion. The cellulases are the third largest industrial enzymes with a great potential in bioethanol production. In this investigation, a β-glucosidase of a thermophilic fungus Myceliophthora thermophila (MtBgl3c) was analysed for its structural characterization using in silico approaches. The protein structure of MtBgl3c is unknown, therefore an attempt has been made to model 3D structure using Modeller 9.23 software. The MtBgl3c protein model generated was validated from Verify 3D and ERRAT scores of 89.37% and 71.25%, respectively derived from SAVES. Using RAMPAGE the Ramachandran plot was generated, which predicted the accuracy of the 3D model with 91.5% amino acid residues in the favored region. The ion binding and N-glycosylation sites were also predicted. The generated model was docked with cellobiose to predict the most favorable binding sites of MtBgl3c. The key amino acid residues involved in cellobiose bonding are Val88, Asp106, Asp287, Tyr255, Arg170, Glu514. The catalytic conserved amino residues of MtBgl3c were identified. The dock score of cellobiose with MtBgl3c is much lower (-6.46 kcal/mol) than that of glucose (-5.61 kcal/mol), suggesting its high affinity for cellobiose. The docking data of MtBgl3c with glucose illustrate its tolerance to glucose. The present study provides insight into structural characteristics of the MtBgl3c which can be further validated by experimental data. Highlights3D structure of β-glucosidase (MtBgl3c) of Myceliophthora thermophila is being proposed based on computational analysesThe amino acid residues Asp106, Asp287, Tyr255, Arg170 and Glu514 have been identified to play catalytically important role in substrate bindingDocking and interaction of MtBgl3c with cellobiose and glucose has been confirmedDocking analysis of MtBgl3c with glucose suggested its glucose toleranceThe data would be useful in engineering enzymes for attaining higher catalytic efficiencyCommunicated by Ramaswamy H. Sarma.

Molecular modeling, docking and simulation dynamics of β-glucosidase reveals high-efficiency, thermo-stable, glucose tolerant enzyme in Paenibacillus lautus BHU3 strain

The enzyme β-glucosidase mediates the rate limiting step of conversion of cellobiose to glucose and thus plays a vital role in the process of cellulose degradation. The present study deals with analysis of the effective novel strain of Paenibacillus lautus BHU3 for identifying high-efficiency thermostable, glucose tolerant β-glucosidases. Seven counterparts with elevated T_m values ranging from 64.6 to 75.8 °C with high thermo-stability, were revealed through this analysis. The blind molecular docking of the model enzymes structures with cellobiose and pNPG gave high negative interaction energies ranging from -11.33 to -13.29 and -6.43 to -9.054 (kcal mol^-1), respectively. The enzyme WP_096774744.1 effectively formed 5 hydrogen bonds with the highest interaction energy (-13.29 kcal mol^-1) with cellobiose at its catalytic site. Molecular dynamics simulation analysis performed for the WP_096774744.1-pNPG complex predicted Glu5, Arg7, Lue68, Gly69 and Phe325 as the major contributing residues for accomplishing hydrolysis of β-1-4-linkage. Further, the molecular docking of WP_096774744.1 enzyme with glucose revealed a distinct glucose-binding site distant from the substrate-binding site, thus confirming the deficient competitive inhibition by glucose. Hence, WP_096774744.1 β-glucosidase appears to be an efficient enzyme with enhanced activity to biodegrade the cellulosic materials and highly relevant for waste management and various industrial applications.

Synergistic Action of a Lytic Polysaccharide Monooxygenase and a Cellobiohydrolase from Penicillium funiculosum in Cellulose Saccharification under High-Level Substrate Loading

Lytic polysaccharide monooxygenases (LPMOs) are crucial industrial enzymes required in the biorefinery industry as well as in the natural carbon cycle. These enzymes, known to catalyze the oxidative cleavage of glycosidic bonds, are produced by numerous bacterial and fungal species to assist in the degradation of cellulosic biomass. In this study, we annotated and performed structural analysis of an uncharacterized LPMO from Penicillium funiculosum (PfLPMO9) based on computational methods in an attempt to understand the behavior of this enzyme in biomass degradation. PfLPMO9 exhibited 75% and 36% sequence identities with LPMOs from Thermoascus aurantiacus (TaLPMO9A) and Lentinus similis (LsLPMO9A), respectively. Furthermore, multiple fungal genetic manipulation tools were employed to simultaneously overexpress LPMO and cellobiohydrolase I (CBH1) in a catabolite-derepressed strain of Penicillium funiculosum, PfMig1⁸⁸ (an engineered variant of P. funiculosum), to improve its saccharification performance toward acid-pretreated wheat straw (PWS) at 20% substrate loading. The resulting transformants showed improved LPMO and CBH1 expression at both the transcriptional and translational levels, with ∼200% and ∼66% increases in ascorbate-induced LPMO and Avicelase activities, respectively. While the secretome of PfMig⁸⁸ overexpressing LPMO or CBH1 increased the saccharification of PWS by 6% or 13%, respectively, over the secretome of PfMig1⁸⁸ at the same protein concentration, the simultaneous overexpression of these two genes led to a 20% increase in saccharification efficiency over that observed with PfMig1⁸⁸, which accounted for 82% saccharification of PWS under 20% substrate loading.IMPORTANCE The enzymatic hydrolysis of cellulosic biomass by cellulases continues to be a significant bottleneck in the development of second-generation biobased industries. While increasing efforts are being made to obtain indigenous cellulases for biomass hydrolysis, the high production cost of this enzyme remains a crucial challenge affecting its wide availability for the efficient utilization of cellulosic materials. This is because it is challenging to obtain an enzymatic cocktail with balanced activity from a single host. This report describes the annotation and structural analysis of an uncharacterized lytic polysaccharide monooxygenase (LPMO) gene in Penicillium funiculosum and its impact on biomass deconstruction upon overexpression in a catabolite-derepressed strain of P. funiculosum Cellobiohydrolase I (CBH1), which is the most important enzyme produced by many cellulolytic fungi for the saccharification of crystalline cellulose, was further overexpressed simultaneously with LPMO. The resulting secretome was analyzed for enhanced LPMO and exocellulase activities and the corresponding improvement in saccharification performance (by ∼20%) under high-level substrate loading using a minimal amount of protein.

Assessment and evaluation of cellulase production using ragi (Eleusine coracana) husk as a substrate from thermo-acidophilic Aspergillus fumigatus JCM 10253

The cellulase production by filamentous fungi Aspergillus fumigatus JCM 10253 was carried out using agro-industrial waste ragi husk as a substrate in the microbial fermentation. The effect of the process parameters such as temperature, substrate concentration, pH, and incubation process time and their interdependence was studied using response surface methodology. The optimum cellulase activities were obtained at 50 °C under the conditions with 1-2% of substrate concentration at pH 2-4 for the incubation period of 7-8 days. The maximum carboxymethyl cellulase (CMCase) and β-glucosidase activities with optimized process variables were 95.2 IU/mL and 0.174 IU/mL, respectively. The morphological characterization of fungus by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) revealed the presence of secondary protein structures. Furthermore, this study demonstrated that the application of ragi husk could be a promising feedstock for value-added industrial products. The thermo-acidophilic nature of isolated strain Aspergillus fumigatus JCM 10253 possessed a significant potential for higher titer of cellulase production that could be further employed for lignocellulosic bioethanol production.

Production and characterization of an enzyme extract with cellulase activity produced by an indigenous strain of Fusarium verticillioides ITV03 using sweet sorghum bagasse

OBJECTIVES

To evaluate a strain of Fusarium verticillioides ITV03 isolated from wood residues in the Veracruz region of Mexico. Endoglucanase and β-glucosidase production by submerged fermentation was optimized using a Box-Behnken design, where the independent variables were urea, ammonium sulfate and yeast extract.

RESULTS

After optimization, an endoglucanase activity of 0.27 U/mL was achieved; subsequently, three carbon sources were evaluated (carboxymethyl cellulose, sweet sorghum bagasse cellulose and delignified sweet sorghum bagasse (DSSB). The results showed that DSSB yielded the greatest endoglucanase (0.28 U/mL) and β-glucosidase (0.12 U/mL) activities. Both enzymatic activities were characterized for the effect of pH, temperature and thermostability. The optimal parameters of β-glucosidase and endoglucanase activity were pH 5 and 4 respectively, the optimum temperature 60 °C. These enzymes were stable at 50 °C for 150.68 h and 8.54 h, with an activation energy (E_a(day)) of 265.55 kJ/mol and 44.40 kJ/mol respectively, for β-glucosidase and endoglucanase.

CONCLUSION

The present work shows that a native strain like F. verticillioides ITV03 using DSSB supplemented with nitrogen has a great potential as a producer of cellulase for lignocellulosic residue hydrolysis.

Heterologous secretory expression of β-glucosidase from Thermoascus aurantiacus in industrial Saccharomyces cerevisiae strains

The use of plant biomass for biofuel production will require efficient utilization of the sugars in lignocellulose, primarily cellobiose, because it is the major soluble by-product of cellulose and acts as a strong inhibitor, especially for cellobiohydrolase, which plays a key role in cellulose hydrolysis. Commonly used ethanologenic yeast Saccharomyces cerevisiae is unable to utilize cellobiose; accordingly, genetic engineering efforts have been made to transfer β-glucosidase genes enabling cellobiose utilization. Nonetheless, laboratory yeast strains have been employed for most of this research, and such strains may be difficult to use in industrial processes because of their generally weaker resistance to stressors and worse fermenting abilities. The purpose of this study was to engineer industrial yeast strains to ferment cellobiose after stable integration of tabgl1 gene that encodes a β-glucosidase from Thermoascus aurantiacus (TaBgl1). The recombinant S. cerevisiae strains obtained in this study secrete TaBgl1, which can hydrolyze cellobiose and produce ethanol. This study clearly indicates that the extent of glycosylation of secreted TaBgl1 depends from the yeast strains used and is greatly influenced by carbon sources (cellobiose or glucose). The recombinant yeast strains showed high osmotolerance and resistance to various concentrations of ethanol and furfural and to high temperatures. Therefore, these yeast strains are suitable for ethanol production processes with saccharified lignocellulose.

The Statistical Optimisation of Recombinant β-glucosidase Production through a Two-Stage, Multi-Model, Design of Experiments Approach

β-glucosidases are a class of enzyme that are widely distributed in the living world, with examples noted in plants, fungi, animals and bacteria. They offer both hydrolysis and synthesis capacity for a wide range of biotechnological processes. However, the availability of native, or the production of recombinant β-glucosidases, is currently a bottleneck in the widespread industrial application of this enzyme. In this present work, the production of recombinant β-glucosidase from Streptomyces griseus was optimised using a Design of Experiments strategy, comprising a two-stage, multi-model design. Three screening models were comparatively employed: Fractional Factorial, Plackett-Burman and Definitive Screening Design. Four variables (temperature, incubation time, tryptone, and OD_{600 nm}) were experimentally identified as having statistically significant effects on the production of S.griseus recombinant β-glucosidase in E. coli BL21 (DE3). The four most influential variables were subsequently used to optimise recombinant β-glucosidase production, employing Central Composite Design under Response Surface Methodology. Optimal levels were identified as: OD_{600 nm}, 0.55; temperature, 26 °C; incubation time, 12 h; and tryptone, 15 g/L. This yielded a 2.62-fold increase in recombinant β-glucosidase production, in comparison to the pre-optimised process. Affinity chromatography resulted in homogeneous, purified β-glucosidase that was characterised in terms of pH stability, metal ion compatibility and kinetic rates for p-nitrophenyl-β-D-glucopyranoside (pNPG) and cellobiose catalysis.

Identification and characterization of a novel β-glucosidase via metagenomic analysis of Bursaphelenchus xylophilus and its microbial flora

β-glucosidases catalyze the final step of cellulose hydrolysis and are essential in cellulose degradation. A β-glucosidase gene, cen502, was identified and isolated from a metagenomic library from Bursaphelenchus xylophilus via functional screening. Analyses indicated that cen502 encodes a 465 amino acid polypeptide that contains a catalytic domain belonging to the glycoside hydrolase family 1 (GH1). Cen502 was heterologously expressed, purified, and biochemically characterized. Recombinant Cen502 displayed optimum enzymatic activity at pH 8.0 and 38 °C. The enzyme had highest specific activity to p-nitrophenyl-β-D-glucopyranoside (pNPG; 180.3 U/mg) and had K_m and V_max values of 2.334 mol/ml and 9.017 μmol/min/mg, respectively. The addition of Fe²⁺ and Mn²⁺ significantly increased Cen502 β-glucosidase activity by 60% and 50%, respectively, while 10% and 25% loss of β-glucosidase activity was induced by addition of Pb²⁺ and K⁺, respectively. Cen502 exhibited activity against a broad array of substrates, including cellobiose, lactose, salicin, lichenan, laminarin, and sophorose. However, Cen502 displayed a preference for the hydrolysis of β-1,4 glycosidic bonds rather than β-1,3, β-1,6, or β-1,2 bonds. Our results indicate that Cen502 is a novel β-glucosidase derived from bacteria associated with B. xylophilus and may represent a promising target to enhance the efficiency of cellulose bio-degradation in industrial applications.

Multifunctional carbon dots for highly luminescent orange-emissive cellulose based composite phosphor construction and plant tissue imaging

A new class of carbon dot (CD) grafted cellulose hybrid phosphors has been prepared in a facile and fast process. The reddish-orange emissive CDs can be effectively dispersed in cellulose matrices through hydrogen binding, and thus highly efficient orange-emissive CD-based phosphors were successfully obtained with a quantum yield of 44%. Moreover, the affinity of CDs for binding cellulose provides them the feasibility for fluorescence mapping of cellulosic plant cell walls. Several model plant tissues have been employed to investigate the pathway of CDs. Confocal analysis demonstrated that plant tissues can readily absorb CDs from aqueous solutions and bind them with cellulose-rich structures. These studies may open up new avenues for the exploration of CDs in long-wavelength emissive solid-state lighting and plant tissue imaging.

Synchronized purification and immobilization of his-tagged β-glucosidase via Fe3O4/PMG core/shell magnetic nanoparticles

In this paper, an efficient and convenient Fe₃O₄/PMG/IDA-Ni²⁺ nanoparticles that applied to purify and immobilize his-tagged β-glucosidase was synthesized, in which, Fe₃O₄/PMG (poly (N, N’-methylenebisacrylamide-co-glycidyl methacrylate) core/shell microspheres were synthesized firstly using distillation-precipitation polymerization, then iminodiacetic acid (IDA) was used to open epoxy rings on the shell of microspheres to the combination of Ni²⁺. The gene of β-glucosidase that was from Coptotermes formosanus Shiraki was amplified, cloned into the expression vector pET28a with an N-terminal His-tag, and expressed in E.coli BL21. The nanoparticles showed the same purification efficiency as commercial nickel column which was a frequently used method in the field of purifying his-tagged proteins from crude cell lysates. The results indicated that Fe₃O₄/PMG/IDA-Ni²⁺ nanoparticles can be considered as an excellent purification material. β-glucosidase was immobilized on the surface of Fe₃O₄/PMG/IDA-Ni²⁺ to form Fe₃O₄/PMG/IDA-β-glucosidase by means of covalent bound with imidazolyl and Ni²⁺. The immobilized β-glucosidase exhibited excellent catalytic activity and stabilities compared with free β-glucosidase. In addition, immobilized β-glucosidase can be recycled for many times and retain more than 65% of the original activity. The materials display enormous potential in the aspect of purifying and immobilizing enzyme.