A Thermophilic GH5 Endoglucanase from Aspergillus fumigatus and Its Synergistic Hydrolysis of Mannan-Containing Polysaccharides

Xinxi Gu,Lijuan Zhang,Haiqiang Lu,Xiangchen Meng

doi:10.3390/catal11070862

Xinxi Gu, Lijuan Zhang + Show 2 more

Open Access

https://doi.org/10.3390/catal11070862

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Abstract

In this study, we isolated and identified a thermophilic strain of Aspergillus fumigatus from the “Daqu” samples. Transcriptomic analysis of A. fumigatus identified 239 carbohydrate-active enzymes (CAZy)-encoding genes, including 167 glycoside hydrolase (GH)-encoding genes, 58 glycosyltransferase (GT)-encoding genes, 2 polysaccharide lyase (PLs)-encoding genes and 12 carbohydrate esterase (CEs)-encoding genes, which indicates that the strain has a strong potential for application for enzyme production. Furthermore, we also identified a novel endoglucanase gene (AfCel5A), which was expressed in Pichia pastoris and characterized. The novel endoglucanase AfCel5A exhibited the highest hydrolytic activity against CMC-Na and the optimal activity at 80 °C and pH 4.0 and also showed good stability at pH 3.0–11.0 and below 70 °C. The Km and Vmax values of AfCel5 were 0.16 ± 0.05 mg·mL−1 and 7.23 ± 0.33 mol mg−1·min−1, respectively, using CMC-Na as a substrate. Further, the endoglucanase exhibited a high tolerance toward NaCl as well as glucose. In addition, the finding that the endoglucanase AfCel5A in combination with β-mannanse (ManBK) clearly increased the release of total reducing sugars of glucomannan by up to 74% is significant.

Highlights

Lignocellulose is the richest renewable source for the industrial production of fuels and chemicals and is comprised of lignin, cellulose and hemicellulose [1,2,3]
The endoglucanase EC 3.2.1.4 plays a significant role in lignocellulose hydrolysis, as it can break down lignocellulose into cellobiose and glucose [6]
Endoglucanases are often known as cellulase, which is widely used in feed additives, pulp and biofuel industries [7,8]

Summary

Introduction

Lignocellulose is the richest renewable source for the industrial production of fuels and chemicals and is comprised of lignin, cellulose and hemicellulose [1,2,3]. The endoglucanase EC 3.2.1.4 plays a significant role in lignocellulose hydrolysis, as it can break down lignocellulose into cellobiose and glucose [6]. Endoglucanases are often known as cellulase, which is widely used in feed additives, pulp and biofuel industries [7,8]. Endoglucanases can be isolated from bacteria and fungi, the Trichoderma and Aspergillus spp. The optimum pH of endoglucanases from fungi is between pH 3.0 and 6.0, and the optimum temperature is in the range of 40–60 ◦C [11]. Circumventing the poor tolerance and the low catalytic efficiency of endoglucanases remains a significant research focus

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