Open Collections

Assessment of novel accessory enzymes to enhance biomass deconstruction

University of British Columbia

The production of monomeric sugars from lignocellulosic feedstocks is challenging, partly due to the high enzyme loadings that are typically required to effectively break down biomass substrates. One pretreatment approach is to try to keep most of the sugars associated with the solid fraction where cellulose and hemicellulose degrading enzymes will be needed to both open-up the lignocellulosic matrix and hydrolyse the polymeric matrix. Past work has shown that the addition of “accessory enzymes” to the “cellulase” cocktail can enhance the hydrolytic performance of enzyme mixture while reducing the protein/enzyme loading required to hydrolyse pretreated biomass substrates. The potential of novel “hemicellulose-specific” enzymes to work synergistically with traditional (Celluclast) and more recent (CTec series) cellulase mixtures was assessed on a range of pretreated and “model” cellulosic substrates. Xyloglucanases showed a higher degree of cooperation than did mixed-linkage glucanases. However, although they generally enhanced cellulose hydrolysis, this synergistic cooperation was strongly influenced by the type of enzyme activity, substrate composition and enzyme and substrate concentration. The backbone-acting xyloglucanase from Bacteroides ovatus, BoGH5, demonstrated a broader specificity compared to other accessory enzymes, resulting in a higher degree of cooperation with cellulase enzymes and enhanced cellulose hydrolysis. Supplementing Celluclast with both backbone acting and debranching enzyme α-xylosidase, resulted in an over 10% improvement in cellulose hydrolysis for substrates with a higher hemicellulose content. This also correlated with an increase in the release of xyloglucan-derived oligomers. As a result of this enhanced synergism, it was possible to reduce the overall protein/enzyme loading by 35% when a goal of 80% cellulose hydrolysis of alkali pretreated corn stover within 72 hrs was targeted. The thesis work suggested that xyloglucan plays a role in limiting enzyme access to the cellulose and therefore the xyloglucan must be disrupted in order to facilitate effective cellulose hydrolysis. It is likely that xyloglucan acts as a physical barrier, possibly coating cellulose microfibrills and/or restraining cellulose fiber swelling.

Text

2018-05-25

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/66105

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/