In muro deacetylation of xylan affects lignin properties and improves saccharification of aspen wood
Journal article, 2017
Background: Lignocellulose from fast growing hardwood species is a preferred source of polysaccharides for advanced biofuels and "green" chemicals. However, the extensive acetylation of hardwood xylan hinders lignocellulose saccharification by obstructing enzymatic xylan hydrolysis and causing inhibitory acetic acid concentrations during microbial sugar fermentation. To optimize lignocellulose for cost-effective saccharification and biofuel production, an acetyl xylan esterase AnAXE1 from Aspergillus niger was introduced into aspen and targeted to cell walls. Results: AnAXE1-expressing plants exhibited reduced xylan acetylation and grew normally. Without pretreatment, their lignocellulose yielded over 25% more glucose per unit mass of wood (dry weight) than wild-type plants. Glucose yields were less improved (+7%) after acid pretreatment, which hydrolyses xylan. The results indicate that AnAXE1 expression also reduced the molecular weight of xylan, and xylan-lignin complexes and/or lignin co-extracted with xylan, increased cellulose crystallinity, altered the lignin composition, reducing its syringyl to guaiacyl ratio, and increased lignin solubility in dioxane and hot water. Lignin-associated carbohydrates became enriched in xylose residues, indicating a higher content of xylo-oligosaccharides. Conclusions: This work revealed several changes in plant cell walls caused by deacetylation of xylan. We propose that deacetylated xylan is partially hydrolyzed in the cell walls, liberating xylo-oligosaccharides and their associated lignin oligomers from the cell wall network. Deacetylating xylan thus not only increases its susceptibility to hydrolytic enzymes during saccharification but also changes the cell wall architecture, increasing the extractability of lignin and xylan and facilitating saccharification.
Populus
Xylan
Wood
Plant-Cell Wall
Acetylation
Saccharification
Author
P. M. A. Pawar
Purdue University
Swedish University of Agricultural Sciences (SLU)
M. Derba-Maceluch
Swedish University of Agricultural Sciences (SLU)
Sun-Li Chong
Chalmers, Biology and Biological Engineering, Industrial Biotechnology
M. L. Gandla
Umeå University
S. S. Bashar
Swedish University of Agricultural Sciences (SLU)
T. Sparrman
Umeå University
P. Ahvenainen
University of Helsinki
M. Hedenstrom
Umeå University
M. Ozparpucu
Swiss Federal Laboratories for Materials Science and Technology (Empa)
Swiss Federal Institute of Technology in Zürich (ETH)
M. Ruggeberg
Swiss Federal Laboratories for Materials Science and Technology (Empa)
Swiss Federal Institute of Technology in Zürich (ETH)
R. Serimaa
University of Helsinki
M. Lawoko
Royal Institute of Technology (KTH)
M. Tenkanen
University of Helsinki
L. J. Jonsson
Umeå University
E. J. Mellerowicz
Swedish University of Agricultural Sciences (SLU)
Biotechnology for Biofuels
17546834 (ISSN) 1754-6834 (eISSN)
Vol. 10 1 Art nr 98- 98Subject Categories
Industrial Biotechnology
DOI
10.1186/s13068-017-0782-4