Abstract
BackgroundLytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that cleave polysaccharides through an oxidative mechanism. These enzymes are major contributors to the recycling of carbon in nature and are currently used in the biorefinery industry. LPMOs are commonly used in synergy with cellulases to enhance biomass deconstruction. However, there are few examples of the use of monocomponent LPMOs as a tool for cellulose fibrillation. In this work, we took advantage of the LPMO action to facilitate disruption of wood cellulose fibers as a strategy to produce nanofibrillated cellulose (NFC).ResultsThe fungal LPMO from AA9 family (PaLPMO9E) was used in this study as it displays high specificity toward cellulose and its recombinant production in bioreactor is easily upscalable. The treatment of birchwood fibers with PaLPMO9E resulted in the release of a mixture of C1-oxidized oligosaccharides without any apparent modification in fiber morphology and dimensions. The subsequent mechanical shearing disintegrated the LPMO-pretreated samples yielding nanoscale cellulose elements. Their gel-like aspect and nanometric dimensions demonstrated that LPMOs disrupt the cellulose structure and facilitate the production of NFC.ConclusionsThis study demonstrates the potential use of LPMOs as a pretreatment in the NFC production process. LPMOs weaken fiber cohesion and facilitate fiber disruption while maintaining the crystallinity of cellulose.
Highlights
Lytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that cleave polysac‐ charides through an oxidative mechanism
In P. pastoris, the use of the α-mating factor (α-MF) as signal peptide is sometimes associated with incorrect cleavage by the Ste13 protease [31]
At industrial scale, the most commonly used pretreatments are chemical or enzymatic. Chemical pretreatments, such as TEMPO-mediated oxidation or carboxymethylation, introduce negative charges on the fiber surface inducing electrostatic repulsion that improves the disintegration of cellulose fibers [18, 19, Table 2 Values of crystallinity index (CrI), hemicellulose percentage (%HC), lateral fibril dimensions (LFD) and lateral fibril aggregate dimensions (LFAD) and accessible/total fibril surface ratio (AS/(AS + inaccessible cellulose surface (IAS))), calculated from the C4-region deconvolution of the solid-state 13C Cross‐polarization/magic angle spinning (CP/MAS) NMR spectra from the starting bleached birchwood Kraft fibers (KF), PaLPMO9E-treated bleached birchwood Kraft fibers (KF-LPMO), Ultra Turrax dispersed PaLPMO9E-treated fibers (NFC0) and PaLPMO9E-treated fibers submitted to mechanical shearing (NFC1–3)
Summary
Lytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that cleave polysac‐ charides through an oxidative mechanism. NFC is obtained by mechanical delamination of the fibers as firstly reported in the early 1980s It consists in flexible fibrils with length higher than CNCs and lateral dimensions depending on the production process but ranging from few nanometers to tens of nanometers [11, 12]. Both CNC and NFC are used in many applications thanks to their amazing properties such as high mechanical strength, ability to stabilize emulsions, gas barrier, dispersing properties and others [6, 7, 13,14,15,16,17].
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