Abstract
Efficient saccharification of lignocellulosic biomass requires concerted development of a pretreatment method, an enzyme cocktail and an enzymatic process, all of which are adapted to the feedstock. Recent years have shown great progress in most aspects of the overall process. In particular, increased insights into the contributions of a wide variety of cellulolytic and hemicellulolytic enzymes have improved the enzymatic processing step and brought down costs. Here, we review major pretreatment technologies and different enzyme process setups and present an in-depth discussion of the various enzyme types that are currently in use. We pay ample attention to the role of the recently discovered lytic polysaccharide monooxygenases (LPMOs), which have led to renewed interest in the role of redox enzyme systems in lignocellulose processing. Better understanding of the interplay between the various enzyme types, as they may occur in a commercial enzyme cocktail, is likely key to further process improvements.
Highlights
Industrial-scale production of cellulosic ethanol based on enzymatic saccharification of biomass was established by several companies during the past decade [17, 298]
A more recent report by Merino and Cherry [238] from Novozymes Inc. showed that engineering the production strain for Celluclast 1.5L to express a BG from A. oryzae led to significant improvement in both the conversion yield and rate of cellulose saccharification by the cellulase preparation
Detailed studies have confirmed that the type of pretreatment impacts the efficiency of individual enzyme components, such as the CBH TrCel7A from Hypocrea jecorina [159] and the lytic polysaccharide monooxygenases (LPMOs) TaAA9A from T. aurantiacus [143], which, in turn, affects the optimal composition of the enzyme cocktail necessary for breaking down the feedstock [144]
Summary
Industrial-scale production of cellulosic ethanol based on enzymatic saccharification of biomass was established by several companies during the past decade [17, 298]. In terms of promiscuity among EGs and LPMOs, the fact that GH7 EGs (such as TrCel7B), and potentially some AA9 LPMOs, can act on both xylan and glucomannan likely contributes to their importance in enzyme cocktails for biomass breakdown [61, 168, 300, 355].
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