Abstract
BackgroundThe 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. ResultsA 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%. Conclusionβ-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. Graphical abstract▪
Highlights
The increasing demand and the continuous depletion in fossil fuels have persuaded researchers to investigate new sources of renewable energy
The efficient degradation and hydrolysis of the cellulosic material to glucose requires the synergistic action of specific enzymes namely; endo-glucanases (E C 3.2.1.4) that internally hydrolyze the cellulosic chains and decrease in turn their polymerization level, exo-glucanases (E C 3.2.1.91), which attack non-reducing and reducing cellulose extremities, releasing cellobiose units from the molecule ends, and β-glucosidases (E C 3.2.1.21), a member of the glycosyl hydrolase groups, that hydrolyse cellobiose to glucose and other cello-dextrins, preventing its accumulation, which is considered as a strong inhibitor of endo-and exo-glucanases [3]
Screening of various fungal isolates for the production of extracellular β-glucosidase Sixty isolated filamentous fungi were screened for their abilities to produce extracellular β-glucosidases under solid-state fermentation (SSF) after 96 h using wheat bran as a substrate
Summary
The increasing demand and the continuous depletion in fossil fuels have persuaded researchers to investigate new sources of renewable energy. The ability of β-glucosidase to use various glycosidic substrates makes it appropriate for a variety of industrial processes, such as the enzymatic hydrolysis of cellulose for the production of fermentable sugars and the production of soy-derived functional foods. Β-glucosidases are utilized in a number of biotechnological processes, including the manufacture of new carbohydrate products, alcohol-based fuels, and the modification of flavonoids' shape and properties [5]. They play an essential role in several biological processes, such as cyanide-based biodefense (CN released from cyano-glucoside) and the degradation of different harmful metabolites. Β-glucosidases may be used in the synthesis of alkyl and aryl glycosides from natural polysaccharides and alcohols by reverse hydrolysis or trans-glycosylation, resulting in pharmaceutical products, detergent, and cosmetic industries [6]
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