Production, immobilization and characterization of beta-glucosidase for application in cellulose degradation from a novel Aspergillus versicolor

Beta-glucosidase (EC 3.2.1.21) catalyzes the hydrolysis of cellobiose and cellooligosaccharides containing (1 → 4)-beta-glycosidic bonds to glucose, which is crucial in cellulosic ethanol production. In this study, Aspergillus versicolor, a novel highly productive beta-glucosidase strain, was first isolated from Camptotheca acuminata seeds. The highest beta-glucosidase activity with 812.86 U/mL was obtained by using the response surface methodology, and a 14.4-fold has increased compared to the control. The beta-glucosidase was then purified to homogeneity with recovery yield and specific activity of 25.98% and 499.15 U/mg, respectively. To enhance its stability and recyclability, the purified beta-glucosidase was first immobilized onto magnetic MnO₂ by electrostatic adsorption. The immobilized materials were characterized by FR-IT, TEM and FE-SEM. Compared with the free beta-glucosidase, the immobilized enzyme exhibited enhanced thermal stability (1.5-fold raise in half-life at 50 °C), and reusability (holding over 60% activity after eight cycles), besides, the optimum pH has increased to 6.0. Substrate specificity research suggested that the enzyme had high hydrolytic activity on cellobiose. It also had a hydrolysis effect on (1 → 3) and (1 → 6)-beta-glycosidic linkages. Application trials in cellulose hydrolysis revealed that the immobilized enzyme was comparatively more effective. Our results suggested this novel immobilized beta-glucosidase makes a promising alternative for the cellulosic ethanol production.

Enzymatic hydrolysis of lignocellulosic biomass using native cellulase produced by Aspergillus niger ITV02 under liquid state fermentation

The objective of this work was to evaluate the biochemical characteristics of an enzymatic extract obtained from autochthonous fungus Aspergillus niger ITV02 and its application in the enzymatic hydrolysis of wheat straw and corn stubble pretreated by steam explosion. The enzymatic extract was obtained by submerged fermentation using delignified sweet sorghum bagasse as a carbon source. The results obtained showed that the enzymatic extract had β-glucosidase and endoglucanase activities. The effects of pH and temperature on cellulase activity were evaluated and its thermostability was determined. The optimal parameters of the β-glucosidase and endoglucanase activities obtained were pH 5 and 70 °C. The enzymatic extract of A. niger ITV02 was used to hydrolyze wheat straw and corn stubble, and the hydrolysis yields were compared with those obtained by a commercial cellulase (Celluclast 1.5L NS 50013) and CellicCTec3. The results showed that with the use the mixture of Celluclast 1.5L-A. niger ITV02 and CellicCTec3-A. niger ITV02 in the hydrolysis, conversions of 86.36% and 67.8% were obtained, respectively. Glucose production for the mixture extract increased 2.15 times more than when the enzyme was used independently alone. The present work shows that A. niger ITV02 has a potential as an enzyme producer for lignocellulosic hydrolysis.

Microbial Beta Glucosidase Enzymes: Recent Advances in Biomass Conversation for Biofuels Application

The biomass to biofuels production process is green, sustainable, and an advanced technique to resolve the current environmental issues generated from fossil fuels. The production of biofuels from biomass is an enzyme mediated process, wherein β-glucosidase (BGL) enzymes play a key role in biomass hydrolysis by producing monomeric sugars from cellulose-based oligosaccharides. However, the production and availability of these enzymes realize their major role to increase the overall production cost of biomass to biofuels production technology. Therefore, the present review is focused on evaluating the production and efficiency of β-glucosidase enzymes in the bioconversion of cellulosic biomass for biofuel production at an industrial scale, providing its mechanism and classification. The application of BGL enzymes in the biomass conversion process has been discussed along with the recent developments and existing issues. Moreover, the production and development of microbial BGL enzymes have been explained in detail, along with the recent advancements made in the field. Finally, current hurdles and future suggestions have been provided for the future developments. This review is likely to set a benchmark in the area of cost effective BGL enzyme production, specifically in the biorefinery area.

Purification and characterization of a novel -glucosidase from Aspergillus flavus and its application in saccharification of soybean meal

Aspergillus flavus has been regarded as a potential candidate for its production of industrial enzymes, but the details of β-glucosidase from this strain is very limited. In herein, we first reported a novel β-glucosidase (AfBglA) with the molecular mass of 94.2 kDa from A. flavus. AfBglA was optimally active at pH 4.5 and 60 °C and is stable between pH 3.5 and 9.0 and at a temperature of up to 55 °C for 30 min remaining more than 90% of its initial activity. It showed an excellent tolerance to Trypsin, Pepsin, Compound Protease, and Flavourzyme and its activity was not inhibited by specific certain cations. AfBglA displayed broad substrate specificity, it acted on all tested pNP-glycosides and barley glucan, indicating this novel β-glucosidase exhibited a β-1, 3-1, 4-glucanase activity. Moreover, the AfBglA could effectively hydrolyze the soybean meal suspension into glucose and exhibit a strong tolerance to the inhibition of glucose at a concentration of 20.0 g/L during the saccharification. The maximum amount of the glucose obtained by AfBglA corresponded to 67.0 g/kg soybean meal. All of these properties mentioned above indicated that the AfBglA possibly attractive for food and feed industry and saccharification of cellulolytic materials.

Discovery of a Novel Fungus with an Extraordinary β-Glucosidase and Potential for On-Site Production of High Value Products

Among cellulases, β-glucosidases play a key role in the final conversion of cellulose into glucose as well as they boost the performance of the other cellulases, in particular cellobiohydrolases in relieving product inhibition. This chapter serves as case example from screening for novel fungal cellulases focusing on β-glucosidases to identifying a gene encoding the key β-glucosidase in the fungus with highest activity. In the case example, the β-glucosidase-producing fungus showed to belong to an unknown fungal species, Aspergillus saccharolyticus, not previously described. The gene was expressed in Trichoderma reesei, which has low indigenous β-glucosidase activity, and the activity of the purified enzyme was assessed in hydrolysis of various pretreated lignocellulosic biomasses. The potential of using the natural producing strain for on-site production of β-glucosidases using lignocellulosic biorefinery waste streams as substrates is discussed. Finally, the potential of the fungus for consolidated bioprocessing of waste streams into valuable compounds, such as organic acids is highlighted.

Transcriptomic and evolutionary analyses of white pear (Pyrus bretschneideri) β-amylase genes reveals their importance for cold and drought stress responses

β-amylase (BAM) genes play essential roles in plant abiotic stress responses. Although the genome of Chinese white pear (Pyrus bretschneideri) has recently been made available, knowledge regarding the BAM family in pear, including gene function, evolutionary history and patterns of gene expression remains limited. In this study, we identified 17 PbBAMs in the pear genome. Of these, 12 PbBAM members were mapped onto 9 chromosomes and 5 PbBAM genes were located on scaffold contigs. Based on gene structure, protein motif analysis, and the topology of the phylogenetic tree of the PbBAM family, we classified member genes into 4 groups. All PbBAM genes were found to contain typical glycosyl hydrolysis 14 domain motifs. Interfamilial comparisons revealed that the phylogenetic relationships of BAM genes in other Rosaceae species were similar those found in pear. We also found that whole-genome duplication (WGD)/segmental duplication events played critical roles in the expansion of the BAM family. Next, we used transcriptomic data to study gene expression during the response of drought and low temperate responses, and found that genes in Group B were related to drought and cold stress. We identified four PbBAM genes associated with abiotic stress in Pear. Finally, by analyzing co-expression networks and co-regulatory genes, we found that PbBAM1a and PbBAM1b were associated with the pear abiotic stress response.

Investigation of inter- and intraspecies variation through genome sequencing of Aspergillus section Nigri

Aspergillus section Nigri comprises filamentous fungi relevant to biomedicine, bioenergy, health, and biotechnology. To learn more about what genetically sets these species apart, as well as about potential applications in biotechnology and biomedicine, we sequenced 23 genomes de novo, forming a full genome compendium for the section (26 species), as well as 6 Aspergillus niger isolates. This allowed us to quantify both inter- and intraspecies genomic variation. We further predicted 17,903 carbohydrate-active enzymes and 2,717 secondary metabolite gene clusters, which we condensed into 455 distinct families corresponding to compound classes, 49% of which are only found in single species. We performed metabolomics and genetic engineering to correlate genotypes to phenotypes, as demonstrated for the metabolite aurasperone, and by heterologous transfer of citrate production to Aspergillus nidulans. Experimental and computational analyses showed that both secondary metabolism and regulation are key factors that are significant in the delineation of Aspergillus species.

Homology Modeling for Enzyme Design

Homology modeling is a very powerful tool in the absence of atomic structures for understanding the general fold of the enzyme, conserved residues, catalytic tunnel/pocket as well as substrate and product binding sites. This information is useful for structure-assisted enzyme design approach for the development of robust enzymes especially for industrial applications.

Characterization of two extracellular β-glucosidases produced from the cellulolytic fungus Aspergillus sp. YDJ216 and their potential applications for the hydrolysis of flavone glycosides

A cellulolytic fungus YDJ216 was isolated from a compost and identified as an Aspergillus sp. strain. Two extracellular β-glucosidases, BGL1 and BGL2, were purified using ultrafiltration, ammonium sulfate fractionation, and High-Q chromatography. Molecular masses of BGL1 and BGL2 were estimated to be 97 and 45 kDa, respectively, by SDS-PAGE. The two enzymes eluted as one peak at 87 kDa by Sephacryl S-200 chromatography, and located at similar positions in a zymogram after intact gel electrophoresis, suggesting BGL1 and BGL2 might be monomeric and dimeric, respectively. Both enzymes showed similar enzymatic properties; they were optimally active at pH 4.0-4.5 and 60 °C, and had similar half-lives at 70 °C. Two enzymes also preferred p-nitrophenyl glucose (pNPG) with the same K_m and hardly hydrolyzed cellobiose, suggesting both enzymes are aryl β-glucosidases. However, V_max for pNPG of BGL1 (953.2 U/mg) was much higher than those of BGL2 (66.5U/mg) and other β-glucosidases reported. When tilianin (a flavone glycoside of acacetin) was reacted with both enzymes, inhibitory activity for monoamine oxidase, relating to oxidation of neurotransmitter amines, was increased closely to the degree obtained by acacetin. These results suggest that BGL1 and BGL2 could be used to hydrolyze flavone glycosides to improve their inhibitory activities.

Expression and characterization of a glucose-tolerant β-1,4-glucosidase with wide substrate specificity from Cytophaga hutchinsonii

Cytophaga hutchinsonii is a gram-negative bacterium that can efficiently degrade crystalline cellulose by a novel strategy without cell-free cellulases or cellulosomes. Genomic analysis implied that C. hutchinsonii had endoglucanases and β-glucosidases but no exoglucanases which could processively digest cellulose and produce cellobiose. In this study, BglA was functionally expressed in Escherichia coli and found to be a β-glucosidase with wide substrate specificity. It can hydrolyze pNPG, pNPC, cellobiose, and cellodextrins. Moreover, unlike most β-glucosidases whose activity greatly decreases with increasing length of the substrate chains, BglA has similar activity on cellobiose and larger cellodextrins. The K _m values of BglA on cellobiose, cellotriose, and cellotetraose were calculated to be 4.8 × 10^-2, 5.6 × 10^-2, and 5.3 × 10^-2 mol/l, respectively. These properties give BglA a great advantage to cooperate with endoglucanases in C. hutchinsonii in cellulose degradation. We proposed that C. hutchinsonii could utilize a simple cellulase system which consists of endoglucanases and β-glucosidases to completely digest amorphous cellulose into glucose. Moreover, BglA was also found to be highly tolerant to glucose as it retained 40 % activity when the concentration of glucose was 100 times higher than that of the substrate, showing potential application in the bioenergy industry.

Fungal Beta-glucosidases: a bottleneck in industrial use of lignocellulosic materials

Profitable biomass conversion processes are highly dependent on the use of efficient enzymes for lignocellulose degradation. Among the cellulose degrading enzymes, beta-glucosidases are essential for efficient hydrolysis of cellulosic biomass as they relieve the inhibition of the cellobiohydrolases and endoglucanases by reducing cellobiose accumulation. In this review, we discuss the important role beta-glucosidases play in complex biomass hydrolysis and how they create a bottleneck in industrial use of lignocellulosic materials. An efficient beta-glucosidase facilitates hydrolysis at specified process conditions, and key points to consider in this respect are hydrolysis rate, inhibitors, and stability. Product inhibition impairing yields, thermal inactivation of enzymes, and the high cost of enzyme production are the main obstacles to commercial cellulose hydrolysis. Therefore, this sets the stage in the search for better alternatives to the currently available enzyme preparations either by improving known or screening for new beta-glucosidases.