Biochemical characterization of a novel thermo-halo-tolerant GH5 endoglucanase from a thermal spring metagenome

Discovery of two bifunctional/multifunctional cellulases by functional metagenomics

Cellulases are widely used in industry, and the usage in bioconversion of biofuels makes cellulases more valuable. In this study, two tandem genes that encoded cellulases ZF994-1 and ZF994-2, respectively, were identified on a cosmid from a soil metagenomic library. Phylogenetic analysis indicated that ZF994-1 and ZF994-2 belonged to glycoside hydrolase family 12 (GH12), and GH3, respectively. Based on the substrate specificity analysis, the recombinant ZF994-1 exhibited weak endoglucanase activity, moderate β-1,3-glucanase and β-1,4-mannanase activities, and strong β-glucosidase activity, while the recombinant ZF994-2 exhibited moderate endoglucanase activity and strong β-glucosidase activity. More than 45% β-glucosidase activity of the recombinant ZF994-1 retained in the buffer containing 3 M glucose, indicating the good tolerance against glucose. The recombinant ZF994-2 showed high activity in the presence of metal ions and organic reagents, exhibiting potential industrial applications.

A thermo-alkali stable and detergent compatible processive β-1,4-glucanase from Himalayan Bacillus sp. PCH94

Present study reports a novel and robust GH9 processive endoglucanase β-1,4-glucanase from Bacillus sp. PCH94 (EGaseBL) with thermo-alkali stable properties. The EGaseBL gene was cloned in pET-28b(+) and expressed in Escherichia coli BL21(DE3) cells. The recombinant protein was purified 94-fold with a yield of 67.8%. The biochemical characterization revealed an active enzyme at a wide pH (4.0–10.0) and temperature (4–100°C). It showed a Km and Vmax of 1.10 mg/ml and 208.24 IU/mg, respectively, using β-glucan as a substrate. The EGaseBL showed dual activities for endoglucanase (134.17 IU/mg) and exoglucanase (28.76 IU/mg), assayed using substrates β-glucan and Avicel, respectively. The enzyme is highly stable in neutral and alkaline pH and showed a half-life of 11.29 h, and 8.31 h in pH 7.0 and 9.0, respectively. The enzyme is also compatible with commercial detergents (Tide, Surf, Ghadi, Raj, and Healing tree) of the Indian market and retained > 85% enzyme activity. Concisely, robustness, extreme functionality, and detergent compatibility endorse EGaseBL as a potential bioresource for the detergent industry, in addition to its implications for the bioethanol industry.

Characterization of a novel thermophilic metagenomic GH5 endoglucanase heterologously expressed in Escherichia coli and Saccharomyces cerevisiae

Background

Endoglucanases from thermophilic microorganisms are a valuable resource as they can be used in a wide variety of biotechnological applications including the valorisation of biomass and the production of biofuels. In the present work we analysed the metagenome from the hot spring Muiño da Veiga, located in the northwest of Spain (in the Galicia region), in search for novel thermostable endoglucanases.

Results

Sequence analysis of the metagenome revealed a promising enzyme (Cel776). Predictions on protein structure and conserved amino acid sequences were conducted, as well as expression in heterologous systems with Escherichia coli and Saccharomyces cerevisiae as the host. Cel776Ec was correctly expressed and purified by taking advantage of the His-Tag system, with a yield of 0.346 U/mL in the eluted fraction. Cel776Sc was expressed extracellulary and was easily recovered from the supernatant without the need of further purification, requiring only a concentration step by ultrafiltration, with a significantly higher yield of 531.95 U/mL, revealing a much more suitable system for production of large amounts of the enzyme. Their biochemical characterization revealed biotechnologically interesting enzymes. Both Cel776Ec and Cel776Sc had an optimal temperature of 80 °C and optimal pH of 5. Cel776Ec exhibited high thermostability maintaining its activity for 24 h at 60 °C and maintained its activity longer than Cel776Sc at increasing incubation temperatures. Moreover, its substrate specificity allowed the degradation of both cellulose and xylan. Whereas Cel776Ec was more active in the presence of calcium and magnesium, manganese was found to increase Cel776Sc activity. A stronger inhibitory effect was found for Cel776Ec than Cel776Sc adding detergent SDS to the reaction mix, whereas EDTA only significantly affected Cel776Sc activity.

Conclusions

Our study reports the discovery of a new promising biocatalyst for its application in processes, such as the production of biofuel and the saccharification of plant biomass, due to its bifunctional enzymatic activity as an endoglucanase and as a xylanase, as well as highlights the advantages of a yeast expression system over bacteria.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02172-4.

Recent advancements in prebiotic oligomers synthesis via enzymatic hydrolysis of lignocellulosic biomass

Interest in functional food, such as non-digestible prebiotic oligosaccharides is increasing day by day and their production is shifting toward sustainable manufacturing. Due to the presence of high carbohydrate content, lignocellulosic biomass (LCB) is the most-potential, cost-effective and sustainable substrate for production of many useful products, including lignocellulose-derived prebiotic oligosaccharides (LDOs). These have the same worthwhile properties as other common oligosaccharides, such as short chain carbohydrates digestible to the gut flora but not to humans mainly due to their resistance to the low pH and high temperature and their demand is constantly increasing mainly due to increased awareness about their potential health benefits. Despite several advantages over the thermo-chemical route of synthesis, comprehensive and updated information on the conversion of lignocellulosic biomass to prebiotic oligomers via controlled enzymatic saccharification is not available in the literature. Thus, the main objective of this review is to highlight recent advancements in enzymatic synthesis of LDOs, current challenges, and future prospects of sustainably producing prebiotic oligomers via enzymatic hydrolysis of LCB substrates. Enzyme reaction engineering practices, custom-made enzyme preparations, controlled enzymatic hydrolysis, and protein engineering approaches have been discussed with regard to their applications in sustainable synthesis of lignocellulose-derived oligosaccharide prebiotics. An overview of scale-up aspects and market potential of LDOs has also been provided.