AUTHOR=Yin Yi-Rui , Sang Peng , Xian Wen-Dong , Li Xin , Jiao Jian-Yu , Liu Lan , Hozzein Wael N. , Xiao Min , Li Wen-Jun 

TITLE=Expression and Characteristics of Two Glucose-Tolerant GH1 β-glucosidases From Actinomadura amylolytica YIM 77502T for Promoting Cellulose Degradation

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.03149

DOI=10.3389/fmicb.2018.03149

ISSN=1664-302X

ABSTRACT=<p>The bioconversion of lignocellulose in various industrial processes, such as biofuel production, requires the degradation of cellulose. <italic>Actinomadura amylolytica</italic> YIM 77502<sup>T</sup> is an aerobic, Gram-positive actinomycete that can efficiently degrade crystalline cellulose by extracellular cellulases. Genomic analysis of <italic>A. amylolytica</italic> identified 9 cellulase and 11 β-glucosidase genes that could potentially encode proteins that digest cellulose. Extracellular proteome characterization of <italic>A. amylolytica</italic> cell-free culture supernatant by liquid chromatography tandem mass spectrometry analysis revealed that 4 of these cellulases and 2 of these β-glucosidases functioned during cellulose hydrolysis. Thin-layer chromatography analysis revealed extracellular β-glucosidases play a major role in carboxyl methyl cellulose (CMC) degradation of products in culture supernatants. In this study, 2 of the identified secreted β-glucosidases, AaBGL1 and AaBGL2, were functionally expressed in <italic>Escherichia coli</italic> and found to have β-glucosidase activity with wide substrate specificities, including for <italic>p</italic>-nitrophenyl β-<sc>D</sc>-glucopyranoside (pNPG), <italic>p</italic>-nitrophenyl-beta-<sc>D</sc>-cellobioside (pNPC), and cellobiose. Moreover, AaBGL1 and AaBGL2 had high tolerances for glucose. After adding these β-glucosidases to commercial cellulases, the degradation rates of CMC, Avicel, birch sawdust, and corncob powder increased by 37, 42, 33, and 9%, respectively. Overall, this work identifies an alternative potential source of β-glucosidases with potential applications in commercial cellulose utilization and the bioenergy industry.</p>