Abstract
SummaryThe success of second‐generation (2G) ethanol technology relies on the efficient transformation of hemicellulose into monosaccharides and, particularly, on the full conversion of xylans into xylose for over 18% of fermentable sugars. We sought new hemicellulases using ruminal liquid, after enrichment of microbes with industrial lignocellulosic substrates and preparation of metagenomic libraries. Among 150 000 fosmid clones tested, we identified 22 clones with endoxylanase activity and 125 with β‐xylosidase activity. These positive clones were sequenced en masse, and the analysis revealed open reading frames with a low degree of similarity with known glycosyl hydrolases families. Among them, we searched for enzymes that were thermostable (activity at > 50°C) and that operate at high rate at pH around 5. Upon a wide series of assays, the clones exhibiting the highest endoxylanase and β‐xylosidase activities were identified. The fosmids were sequenced, and the corresponding genes cloned, expressed and proteins purified. We found that the activity of the most active β‐xylosidase was at least 10‐fold higher than that in commercial enzymatic fungal cocktails. Endoxylanase activity was in the range of fungal enzymes. Fungal enzymatic cocktails supplemented with the bacterial hemicellulases exhibited enhanced release of sugars from pretreated sugar cane straw, a relevant agricultural residue.
Highlights
Rising energy consumption, depletion of fossil fuels and increased environmental concern have placed the focus of energy generation on the production of liquid biofuels from agricultural residues and municipal solid wastes, and in particular, large efforts have been devoted to the production of bioethanol, this ethanol is known as 2G ethanol in contrast with ethanol produced from grain or sugarcane known as 1G (Dashtban et al, 2009; Ramos et al, 2016; Valdivia et al, 2016)
The success of second-generation (2G) ethanol technology relies on the efficient transformation of hemicellulose into monosaccharides and, on the full conversion of xylans into xylose for over 18% of fermentable sugars
Fungal enzymatic cocktails supplemented with the bacterial hemicellulases exhibited enhanced release of sugars from pretreated sugar cane straw, a relevant agricultural residue
Summary
Depletion of fossil fuels and increased environmental concern have placed the focus of energy generation on the production of liquid biofuels from agricultural residues and municipal solid wastes, and in particular, large efforts have been devoted to the production of bioethanol, this ethanol is known as 2G ethanol in contrast with ethanol produced from grain or sugarcane known as 1G (Dashtban et al, 2009; Ramos et al, 2016; Valdivia et al, 2016). Efficient hydrolysis of lignocellulosic material requires intensive pretreatments (physical, chemical or a combination of both) to make cellulose and hemicellulose available for enzymatic hydrolysis (Bothast and Saha, 1997; Alvarez et al, 2016; Valdivia et al, 2016). Degradation of pretreated lignocellulosic residues requires the synergistic action of several enzymes to breakdown cellulose and hemicellulose. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.
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