Enzyme mediated nanofibrillation of cellulose by the synergistic actions of an endoglucanase, lytic polysaccharide monooxygenase (LPMO) and xylanase

SbPL1CE8 from Segatella bryantii combines with SbGH28GH105 in a multi-enzyme cascade for pectic biomass utilization

Pectinases are useful biocatalysts for pectic biomass processing and are extensively used in the food/feed, textile and papermaking industries. Two pectinase genes, a pectate lyase (SbPL1CE8) and a polygalacturonase (SbGH28GH105) were isolated from Segatella bryantii and functionally characterized. Recombinant rSbPL1CE8 was most active against polygalacturonic acid (PGA) and pectin with a 60 % degree of esterification, with kcat/Km values of 721.18 ± 64.77 and 327.02 ± 22.44 mL/s/mg, respectively. Truncated rSbPL1 acted as a mesophilic alkaline pectate lyase, which was highly resistant to inactivation by methanol and ethanol. The rSbPL1CE8 exclusively digested PGA and pectin into unsaturated digalacturonate (uG2), which was further converted into galacturonic acid by rSbGH28GH105. The rSbPL1CE8 was highly effective for saccharification of waste materials from Zea mays, Oryza sativa and Arachis hypogaea processing, and for ramie fiber degumming. This novel pectate lyase has great potential for application in industrial pectic biomass processing.

Periodate oxidation-mediated nanocelluloses: Preparation, functionalization, structural design, and applications

In recent years, the remarkable progress in nanotechnology has ignited considerable interest in investigating nanocelluloses, an environmentally friendly and sustainable nanomaterial derived from cellulosic feedstocks. Current research primarily focuses on the preparation and applications of nanocelluloses. However, to enhance the efficiency of nanofibrillation, reduce energy consumption, and expand nanocellulose applications, chemical pre-treatments of cellulose fibers have attracted substantial interest and extensive exploration. Various chemical pre-treatment methods yield nanocelluloses with diverse functional groups. Among these methods, periodate oxidation has garnered significant attention recently, due to the formation of dialdehyde cellulose derived nanocellulose, which exhibits great promise for further modification with various functional groups. This review seeks to provide a comprehensive and in-depth examination of periodate oxidation-mediated nanocelluloses (PONCs), including their preparation, functionalization, hierarchical structural design, and applications. We believe that PONCs stand as highly promising candidates for the development of novel nano-cellulosic materials.

Enzymatic approaches for diversifying bioproducts from cellulosic biomass

Cellulosic biomass is the most abundantly available natural carbon-based renewable resource on Earth. Its widespread availability, combined with rising awareness, evolving policies, and changing regulations supporting sustainable practices, has propelled its role as a crucial renewable feedstock to meet the escalating demand for eco-friendly and renewable materials, chemicals, and fuels. Initially, biorefinery models using cellulosic biomass had focused on single-product platform, primarily monomeric sugars for biofuel. However, since the launch of the first pioneering cellulosic plants in 2014, these models have undergone significant revisions to adapt their biomass upgrading strategy. These changes aim to diversify the bioproduct portfolio and improve the revenue streams of cellulosic biomass biorefineries. Within this area of research and development, enzyme-based technologies can play a significant role by contributing to eco-design in producing and creating innovative bioproducts. This Feature Article highlights our strategies and recent progress in utilizing the biological diversity and inherent selectivity of enzymes to develop and continuously optimize sustainable enzyme-based technologies with distinct application approaches. We have advanced technologies for standalone platforms, which produce various forms of cellulose nanomaterials engineered with customized and enhanced properties and high yields. Additionally, we have tailored technologies for integration within a biorefinery concept. This biorefinery approach prioritizes designing tailored processes to establish bionanomaterials, such as cellulose and lignin nanoparticles, and bioactive molecules as part of a new multi-bioproduct platform for cellulosic biomass biorefineries. These innovations expand the range of bioproducts that can be produced from cellulosic biomass, transcending the conventional focus on monomeric sugars for biofuel production to include biomaterials biorefinery. This shift thereby contributes to strengthening the Bioeconomy strategy and supporting the achievement of several Sustainable Development Goals (SDGs) of the 2030 Agenda for Sustainable Development.

Action of AA9 lytic polysaccharide monooxygenase enzymes on different cellulose allomorphs

Lytic polysaccharide monooxygenase (LPMO)-catalyzed oxidative processes play a major role in natural biomass conversion. Despite their oxidative cleavage at the surface of polysaccharides, understanding of their mode of action, and the impact of structural patterns of the cellulose fiber on LPMO activity is still not fully understood. In this work, we investigated the action of two different LPMOs from Podospora anserina on celluloses showing different structural patterns. For this purpose, we prepared cellulose II and cellulose III allomorphs from cellulose I cotton linters, as well as amorphous cellulose. LPMO action was monitored in terms of surface morphology, molar mass changes and monosaccharide profile. Both PaLPMO9E and PaLPMO9H were active on the different cellulose allomorphs (I, II and III), and on amorphous cellulose (PASC) whereas they displayed a different behavior, with a higher molar mass decrease observed for cellulose I. Overall, the pretreatment with LPMO enzymes clearly increased the accessibility of all types of cellulose, which was quantified by the higher carboxylate content after carboxymethylation reaction on LPMO-pretreated celluloses. This work gives more insight into the action of LPMOs as a tool for deconstructing lignocellulosic biomass to obtain new bio-based building blocks.

Fungi play a crucial role in sustaining microbial networks and accelerating organic matter mineralization and humification during thermophilic phase of composting

Fungi play an important role in the mineralization and humification of refractory organic matter such as lignocellulose during composting. However, limited research on the ecological role of fungi in composting system hindered the development of efficient microbial agents. In this study, six groups of lab-scale composting experiments were conducted to reveal the role of fungal community in composting ecosystems by comparing them with bacterial community. The findings showed that the thermophilic phase was crucial for organic matter degradation and humic acid formation. The Richness index of the fungal community peaked at 1165 during this phase. PCoA analysis revealed a robust thermal stability in the fungal community. Despite temperature fluctuations, the community structure, predominantly governed by Pichia and Candida, remained largely unaltered. The stability of fungal community and the complexity of ecological networks were 1.26 times and 5.15 times higher than those observed in bacterial community, respectively. Fungi-bacteria interdomain interaction markedly enhanced network complexity, contributing to maintain microbial ecological functions. The core fungal species belonging to the family Saccharomycetaceae drove interdomain interaction during thermophilic phase. This study demonstrated the key role of fungi in the composting system, which would provide theoretical guidance for the development of high efficiency composting agents to strengthen the mineralization and humification of organic matter.

Oxidation of cellulose fibers using LPMOs with varying allomorphic substrate preferences, oxidative regioselectivities, and domain structures

Lytic polysaccharide monooxygenases (LPMOs) are excellent candidates for enzymatic functionalization of natural polysaccharides, such as cellulose or chitin, and are gaining relevance in the search for renewable biomaterials. Here, we assessed the cellulose fiber modification potential and catalytic performance of eleven cellulose-active fungal AA9-type LPMOs, including C1-, C4-, and C1/C4-oxidizing LPMOs with and without CBM1 carbohydrate-binding modules, on cellulosic substrates with different degrees of crystallinity and polymer chain arrangement, namely, Cellulose I, Cellulose II, and amorphous cellulose. The potential of LPMOs for cellulose fiber modification varied among the LPMOs and depended primarily on operational stability and substrate binding, and, to some extent, also on regioselectivity and domain structure. While all tested LPMOs were active on natural Cellulose I-type fibers, activity on the Cellulose II allomorph was almost exclusively detected for LPMOs containing a CBM1 and LPMOs with activity on soluble hemicelluloses and cello-oligosaccharides, for example NcAA9C from Neurospora crassa. The single-domain variant of NcAA9C oxidized the cellulose fibers to a higher extent than its CBM-containing natural variant and released less soluble products, indicating a more dispersed oxidation pattern without a CBM. Our findings reveal great functional variation among cellulose-active LPMOs, laying the groundwork for further LPMO-based cellulose engineering.

Molecular mechanism of cellulose depolymerization by the two-domain BlCel9A enzyme from the glycoside hydrolase family 9

Carbohydrate-active enzymes from the glycoside hydrolase family 9 (GH9) play a key role in processing lignocellulosic biomass. Although the structural features of some GH9 enzymes are known, the molecular mechanisms that drive their interactions with cellulosic substrates remain unclear. To investigate the molecular mechanisms that the two-domain Bacillus licheniformis BlCel9A enzyme utilizes to depolymerize cellulosic substrates, we used a combination of biochemical assays, X-ray crystallography, small-angle X-ray scattering, and molecular dynamics simulations. The results reveal that BlCel9A breaks down cellulosic substrates, releasing cellobiose and glucose as the major products, but is highly inefficient in cleaving oligosaccharides shorter than cellotetraose. In addition, fungal lytic polysaccharide oxygenase (LPMO) TtLPMO9H enhances depolymerization of crystalline cellulose by BlCel9A, while exhibiting minimal impact on amorphous cellulose. The crystal structures of BlCel9A in both apo form and bound to cellotriose and cellohexaose were elucidated, unveiling the interactions of BlCel9A with the ligands and their contribution to substrate binding and products release. MD simulation analysis reveals that BlCel9A exhibits higher interdomain flexibility under acidic conditions, and SAXS experiments indicate that the enzyme flexibility is induced by pH and/or temperature. Our findings provide new insights into BlCel9A substrate specificity and binding, and synergy with the LPMOs.

Biotechnological innovations in nanocellulose production from waste biomass with a focus on pineapple waste

New materials' synthesis and utilization have shown many critical challenges in healthcare and other industrial sectors as most of these materials are directly or indirectly developed from fossil fuel resources. Environmental regulations and sustainability concepts have promoted the use of natural compounds with unique structures and properties that can be biodegradable, biocompatible, and eco-friendly. In this context, nanocellulose (NC) utility in different sectors and industries is reported due to their unique properties including biocompatibility and antimicrobial characteristics. The bacterial nanocellulose (BNC)-based materials have been synthesized by bacterial cells and extracted from plant waste materials including pineapple plant waste biomass. These materials have been utilized in the form of nanofibers and nanocrystals. These materials are found to have excellent surface properties, low density, and good transparency, and are rich in hydroxyl groups for their modifications to other useful products. These materials are well utilized in different sectors including biomedical or health care centres, nanocomposite materials, supercapacitors, and polymer matrix production. This review explores different approaches for NC production from pineapple waste residues using biotechnological interventions, approaches for their modification, and wider applications in different sectors. Recent technological developments in NC production by enzymatic treatment are critically discussed. The utilization of pineapple waste-derived NC from a bioeconomic perspective is summarized in the paper. The chemical composition and properties of nanocellulose extracted from pineapple waste may have unique characteristics compared to other sources. Pineapple waste for nanocellulose production aligns with the principles of sustainability, waste reduction, and innovation, making it a promising and novel approach in the field of nanocellulose materials.

The upsurge of lytic polysaccharide monooxygenases in biomass deconstruction: characteristic functions and sustainable applications

Lytic polysaccharide monooxygenases (LPMOs) are one of the emerging classes of copper metalloenzymes that have received considerable attention due to their ability to boost the enzymatic conversion of intractable polysaccharides such as plant cell walls and chitin polymers. LPMOs catalyze the oxidative cleavage of β-1,4-glycosidic bonds using molecular O2 or H2 O2 in the presence of an external electron donor. LPMOs have been classified as an auxiliary active (AA) class of enzymes and, further based on substrate specificity, divided into eight families. Until now, multiple LPMOs from AA9 and AA10 families, mostly from microbial sources, have been investigated; the exact mechanism and structure-function are elusive to date, and recently discovered AA families of LPMOs are just scratched. This review highlights the origin and discovery of the enzyme, nomenclature, three-dimensional protein structure, substrate specificity, copper-dependent reaction mechanism, and different techniques used to determine the product formation through analytical and biochemical methods. Moreover, the diverse functions of proteins in various biological activities such as plant-pathogen/pest interactions, cell wall remodeling, antibiotic sensitivity of biofilms, and production of nanocellulose along with certain obstacles in deconstructing the complex polysaccharides have also been summarized, while highlighting the innovative and creative ways to overcome the limitations of LPMOs in hydrolyzing the biomass.

Exploring the potential of cellulose autofluorescence for optical detection of tannin in red wines

The growing demand for opto-electronic devices within an automated landscape has opened up new opportunities for harnessing sustainable cellulose materials for sensors technology. Cellulose, a versatile material, enables its combination with other materials, but in most of these applications, cellulose is typically employed as support or substrate, while its inherent autofluorescence remains largely underexplored for sensors. In light of this context, this study delves into the autofluorescence characteristics of pristine cellulose nanocrystals extracted from wood via enzymatic route for optical sensors tailored to detect tannins. By fine-tuning the experimental setup, photoluminescence (PL) emission bands were scrutinized across three distinct spectral regions, namely 300-400 nm, 400-500 nm and 550-700 nm. The proposed mechanism reveals the occurrence of dynamic fluorescence quenching, which enabled the selective monitoring of tannins in red wines across a dynamic range spanning from 10 to 1060 μg mL-1. This sensing platform provided a limit of detection (LoD) of 6.1 μg mL-1. Notably, the sensing platform's efficacy was validated with remarkable recovery rates of 99.7 % and 95.3 % when subjected to testing with cabernet sauvignon and tannat wines. These findings emphasize the sensing platform's potential for monitoring tannic acids in beverages and food products.

Bionanocomposites with Enhanced Physical Properties from Curli Amyloid Assemblies and Cellulose Nanofibrils

Proteinaceous amyloid fibrils are one of the stiffest biopolymers due to their extensive cross-β-sheet quaternary structure, whereas cellulose nanofibrils (CNFs) exhibit interesting properties associated with their nanoscale size, morphology, large surface area, and biodegradability. Herein, CNFs were supplemented with amyloid fibrils assembled from the Curli-specific gene A (CsgA) protein, the main component of bacterial biofilms. The resulting composites showed superior mechanical properties, up to a 7-fold increase compared to unmodified CNF films. Wettability and thermogravimetric analyses demonstrated high surface hydrophobicity and robust thermal tolerance. Bulk spectroscopic characterization of CNF-CsgA films revealed key insights into the molecular organization within the bionanocomposites. Atomic force microscopy and photoinduced force microscopy revealed the high-resolution location of curli assemblies into the CNF films. This novel sustainable and cost-effective CNF-based bionanocomposites supplemented with intertwined bacterial amyloid fibrils opens novel directions for environmentally friendly applications demanding high mechanical, water-repelling properties, and thermal resistance.

Functional characterization of fungal lytic polysaccharide monooxygenases for cellulose surface oxidation

BACKGROUND

Microbial lytic polysaccharide monooxygenases (LPMOs) cleave diverse biomass polysaccharides, including cellulose and hemicelluloses, by initial oxidation at C1 or C4 of glycan chains. Within the Carbohydrate-Active Enzymes (CAZy) classification, Auxiliary Activity Family 9 (AA9) comprises the first and largest group of fungal LPMOs, which are often also found in tandem with non-catalytic carbohydrate-binding modules (CBMs). LPMOs originally attracted attention for their ability to potentiate complete biomass deconstruction to monosaccharides. More recently, LPMOs have been applied for selective surface modification of insoluble cellulose and chitin.

RESULTS

To further explore the catalytic diversity of AA9 LPMOs, over 17,000 sequences were extracted from public databases, filtered, and used to construct a sequence similarity network (SSN) comprising 33 phylogenetically supported clusters. From these, 32 targets were produced successfully in the industrial filamentous fungus Aspergillus niger, 25 of which produced detectable LPMO activity. Detailed biochemical characterization of the eight most highly produced targets revealed individual C1, C4, and mixed C1/C4 regiospecificities of cellulose surface oxidation, different redox co-substrate preferences, and CBM targeting effects. Specifically, the presence of a CBM correlated with increased formation of soluble oxidized products and a more localized pattern of surface oxidation, as indicated by carbonyl-specific fluorescent labeling. On the other hand, LPMOs without native CBMs were associated with minimal release of soluble products and comparatively dispersed oxidation pattern.

CONCLUSIONS

This work provides insight into the structural and functional diversity of LPMOs, and highlights the need for further detailed characterization of individual enzymes to identify those best suited for cellulose saccharification versus surface functionalization toward biomaterials applications.

Production and Characterization of Cellulose Nanocrystals from Eucalyptus Dissolving Pulp Using Endoglucanases from Myceliophthora thermophila

Endoglucanase (EG) is a key enzyme during enzymatic preparation of cellulose nanocrystals (CNCs). Myceliophthora thermophila is a thermophilic fungus that has thermal properties and a high secretion of endoglucanases (EGs), and could serve as potential sources of EGs for the preparation of CNCs. In this work, four different GH families (GH5, GH7, GH12, and GH45) of EGs from M. thermophila were expressed and purified, and their enzymatic characteristics and feasibility of application in CNC preparation were investigated. It was shown that the MtEG5A from M. thermophila has good potential in the enzymatic preparation of CNCs using eucalyptus dissolving pulp as feedstock. It was also observed that there was a synergistic effect between the MtEG5A and other MtEGs in the preparation of CNCs, which improved the yield and properties of CNCs obtained by enzymatic hydrolysis. This study provides a reference for understanding the enzymatic characteristics of different families of EGs from M. thermophile and their potential application in nanocellulose production.

Optimized Lytic Polysaccharide Monooxygenase Action Increases Fiber Accessibility and Fibrillation by Releasing Tension Stress in Cellulose Cotton Fibers

Lytic polysaccharide monooxygenase (LPMO) enzymes have recently shaken up our knowledge of the enzymatic degradation of biopolymers and cellulose in particular. This unique class of metalloenzymes cleaves cellulose and other recalcitrant polysaccharides using an oxidative mechanism. Despite their potential in biomass saccharification and cellulose fibrillation, the detailed mode of action of LPMOs at the surface of cellulose fibers still remains poorly understood and highly challenging to investigate. In this study, we first determined the optimal parameters (temperature, pH, enzyme concentration, and pulp consistency) of LPMO action on the cellulose fibers by analyzing the changes in molar mass distribution of solubilized fibers using high performance size exclusion chromatography (HPSEC). Using an experimental design approach with a fungal LPMO from the AA9 family (PaLPMO9H) and cotton fibers, we revealed a maximum decrease in molar mass at 26.6 °C and pH 5.5, with 1.6% w/w enzyme loading in dilute cellulose dispersions (100 mg of cellulose at 0.5% w/v). These optimal conditions were used to further investigate the effect of PaLPMO9H on the cellulosic fiber structure. Direct visualization of the fiber surface by scanning electron microscopy (SEM) revealed that PaLPMO9H created cracks on the cellulose surface while it attacked tension regions that triggered the rearrangement of cellulose chains. Solid-state NMR indicated that PaLPMO9H increased the lateral fibril dimension and created novel accessible surfaces. This study confirms the LPMO-driven disruption of cellulose fibers and extends our knowledge of the mechanism underlying such modifications. We hypothesize that the oxidative cleavage at the surface of the fibers releases the tension stress with loosening of the fiber structure and peeling of the surface, thereby increasing the accessibility and facilitating fibrillation.

Hemicellulolytic enzymes in lignocellulose processing

Lignocellulosic biomass is the most abundant source of carbon-based material on a global basis, serving as a raw material for cellulosic fibers, hemicellulosic polymers, platform sugars, and lignin resins or monomers. In nature, the various components of lignocellulose (primarily cellulose, hemicellulose, and lignin) are decomposed by saprophytic fungi and bacteria utilizing specialized enzymes. Enzymes are specific catalysts and can, in many cases, be produced on-site at lignocellulose biorefineries. In addition to reducing the use of often less environmentally friendly chemical processes, the application of such enzymes in lignocellulose processing to obtain a range of specialty products can maximize the use of the feedstock and valorize many of the traditionally underutilized components of lignocellulose, while increasing the economic viability of the biorefinery. While cellulose has a rich history of use in the pulp and paper industries, the hemicellulosic fraction of lignocellulose remains relatively underutilized in modern biorefineries, among other reasons due to the heterogeneous chemical structure of hemicellulose polysaccharides, the composition of which varies significantly according to the feedstock and the choice of pretreatment method and extraction solvent. This paper reviews the potential of hemicellulose in lignocellulose processing with focus on what can be achieved using enzymatic means. In particular, we discuss the various enzyme activities required for complete depolymerization of the primary hemicellulose types found in plant cell walls and for the upgrading of hemicellulosic polymers, oligosaccharides, and pentose sugars derived from hemicellulose depolymerization into a broad spectrum of value-added products.

Comparison of the solid-state and submerged fermentation derived secretomes of hyper-cellulolytic Penicillium janthinellum NCIM 1366 reveals the changes responsible for differences in hydrolytic performance

Solid-state fermentation (SSF) and submerged fermentation (SmF) have often been compared for production of biomass hydrolyzing enzymes highlighting the superiority of the SSF produced enzymes, but the reasons for the performance differences are under-explored. Penicillium janthinellum NCIM 1366 culture extracts from SSF had better hydrolytic performance along with a higher initial rate of reaction. Secretome analyses of the SSF and SmF enzymes using LC/MS-MS, indicated that while the type of proteins secreted were similar in both modes, the abundance of specific beta glucosidases, lytic polysaccharide monooxygenases and hemicellulolytic enzymes were very high in SSF resulting in efficient initiation, low accumulation of cellobiose and high initial reaction rates. Key enzymes that catalyse lignocellulose breakdown under SSF and SmF are therefore different and the fungus may be speculated to have regulation mechanisms that aid differential expression under different cultivation modes.

BsLPMO10A from Bacillus subtilis boosts the depolymerization of diverse polysaccharides linked via β-1,4-glycosidic bonds

Lytic polysaccharide monooxygenase (LPMO) is known as an oxidatively cleaving enzyme in recalcitrant polysaccharide deconstruction. Herein, we report a novel AA10 LPMO derived from Bacillus subtilis (BsLPMO10A). A substrate specificity study revealed that the enzyme exhibited an extensive active-substrate spectrum, particularly for polysaccharides linked via β-1,4 glycosidic bonds, such as β-(Man1 → 4Man), β-(Glc1 → 4Glc) and β-(Xyl1 → 4Xyl). HPAEC-PAD and MALDI-TOF-MS analyses indicated that BsLPMO10A dominantly liberated native oligosaccharides with a degree of polymerization (DP) of 3-6 and C1-oxidized oligosaccharides ranging from DP3ox to DP6ox from mixed linkage glucans and beechwood xylan. Due to its synergistic action with a variety of glycoside hydrolases, including glucanase IDSGLUC5-38, xylanase TfXYN11-1, cellulase IDSGLUC5-11 and chitinase BtCHI18-1, BsLPMO10A dramatically accelerated glucan, xylan, cellulose and chitin saccharification. After co-reaction for 72 h, the reducing sugars in Icelandic moss lichenan, beechwood xylan, phosphoric acid swollen cellulose and chitin yielded 3176 ± 97, 7436 ± 165, 649 ± 44, and 2604 ± 130 μmol/L, which were 1.47-, 1.56-, 1.44- and 1.25-fold higher than those in the GHs alone groups, respectively (P < 0.001). In addition, the synergy of BsLPMO10A and GHs was further validated by the degradation of natural feedstuffs, the co-operation of BsLPMO10A and GHs released 3266 ± 182 and 1725 ± 107 μmol/L of reducing sugars from Oryza sativa L. and Arachis hypogaea L. straws, respectively, which were significantly higher than those produced by GHs alone (P < 0.001). Furthermore, BsLPMO10A also accelerated the liberation of reducing sugars from Celluclast® 1.5 L, a commercial cellulase cocktail, on filter paper, A. hypogaea L. and O. sativa L. straws by 49.58 % (P < 0.05), 72.19 % (P < 0.001) and 54.36 % (P < 0.05), respectively. This work has characterized BsLPMO10A with a broad active-substrate scope, providing a promising candidate for lignocellulosic biomass biorefinery.

PACER: a novel 3D plant cell wall model for the analysis of non-catalytic and enzymatic responses

Background

Substrate accessibility remains a key limitation to the efficient enzymatic deconstruction of lignocellulosic biomass. Limited substrate accessibility is often addressed by increasing enzyme loading, which increases process and product costs. Alternatively, considerable efforts are underway world-wide to identify amorphogenesis-inducing proteins and protein domains that increase the accessibility of carbohydrate-active enzymes to targeted lignocellulose components.

Results

We established a three-dimensional assay, PACER (plant cell wall model for the analysis of non-catalytic and enzymatic responses), that enables analysis of enzyme migration through defined lignocellulose composites. A cellulose/azo-xylan composite was made to demonstrate the PACER concept and then used to test the migration and activity of multiple xylanolytic enzymes. In addition to non-catalytic domains of xylanases, the potential of loosenin-like proteins to boost xylanase migration through cellulose/azo-xylan composites was observed.

Conclusions

The PACER assay is inexpensive and parallelizable, suitable for screening proteins for ability to increase enzyme accessibility to lignocellulose substrates. Using the PACER assay, we visualized the impact of xylan-binding modules and loosenin-like proteins on xylanase mobility and access to targeted substrates. Given the flexibility to use different composite materials, the PACER assay presents a versatile platform to study impacts of lignocellulose components on enzyme access to targeted substrates.

Lignocellulose degradation by Penicillium janthinellum enzymes is influenced by its variable secretome and a unique set of feedstock characteristics

Substrate characteristics and proteins that affect lignocellulose-hydrolysis by the hypercellulolytic fungus Penicillium janthinellum NCIM 1366 (PJ-1366) were investigated. The hydrolysis rate of PJ-1366 enzymes was very high, with upto 75 % of the reaction being completed in initial 4 h. Comparison of the hydrolytic efficiencies on differently pretreated biomass indicated that the greatest (negative) effect was imparted by lignin, suggesting that improving ligninase activity of the PJ-1366 enzymes may help to improve hydrolysis. Larger pore sizes and higher crystallinity of substrates, which favor enzyme penetration and processive hydrolysis, positively influenced hydrolysis efficiency. For alkali-pretreated substrates, 16 FPU/g of PJ-1366 cellulases released the sugar-equivalent of using 10 FPU/g of a commercial biomass hydrolyzing enzyme. By correlation analysis, 41 proteins, including 20 CAZymes were identified, whose abundance in the secretome positively correlated with the cellulase activities of the culture filtrate. These proteins may be considered as the primary drivers of FPase/CMCase/pNPGase/xylanase activity in PJ-1366.

Biomedical engineering aspects of nanocellulose: a review

Cellulose is one of the most abundant renewable biopolymer in nature and is present as major constituent in both plant cell walls as well as synthesized by some microorganisms as extracellular products. In both the systems, cellulose self-assembles into a hierarchical ordered architecture to form micro to nano-fibrillated structures, on basis of which it is classified into various forms. Nanocellulose (NCs) exist as rod-shaped highly crystalline cellulose nanocrystals to high aspect ratio cellulose nanofibers, micro-fibrillated cellulose and bacterial cellulose (BC), depending upon the origin, structural and morphological properties. Moreover, NCs have been processed into diversified products ranging from composite films, coatings, hydrogels, aerogels, xerogels, organogels, rheological modifiers, optically active birefringent colored films using traditional-to-advanced manufacturing techniques. With such versatility in structure-property, NCs have profound application in areas of healthcare, packaging, cosmetics, energy, food, electronics, bioremediation, and biomedicine with promising commercial potential. Herein this review, we highlight the recent advancements in synthesis, fabrication, processing of NCs, with strategic chemical modification routes to tailor its properties for targeted biomedical applications. We also study the basic mechanism and models for biosynthesis of cellulose in both plant and microbial systems and understand the structural insights of NC polymorphism. The kinetics study for both enzymatic/chemical modifications of NCs and microbial growth behavior of BC under various reactor configurations are studied. The challenges associated with the commercial aspects as well as industrial scale production of pristine and functionalized NCs to meet the growing demands of market are discussed and prospective strategies to mitigate them are described. Finally, post chemical modification evaluation of biological and inherent properties of NC are important to determine their efficacy for development of various products and technologies directed for biomedical applications.

Conversion of Cellulose and Lignin Residues into Transparent UV-Blocking Composite Films

The valorization of cellulose and lignin residues in an integrated biorefinery is of great significance to improve the overall economics but has been challenged by their structural recalcitrance, especially for lignin residue. In this work, a facile chemical conversion route to fabricating functional UV-blocking cellulose/lignin composite films through a facile dissolution-regeneration process using these biomass residues was proposed. Three representative lignin residues, i.e., aspen and poplar wood lignin, and corn stover (CS) lignin were assessed for their feasibility for the film fabrication. The UV-blocking performance of the composite films were comparatively investigated. Results showed that all these three lignin residues could enhance the UV-blocking property of the composite films, corresponding to the reduction in the optical energy band gap from 4.31 to 3.72 eV, while poplar lignin had a considerable content of chromophores and showed the best UV-blocking enhancement among these three assessing lignins. The enhancement of UV-blocking property was achieved without compromising the visible-light transparency, mechanical strength and thermal stability of the composite films even at 4% lignin loading. This work showed the high promise of integrating biomass residue conversion into lignocellulose biorefinery for a multi-production purpose.

Lytic polysaccharide monooxygenases as powerful tools in enzymatically assisted preparation of nano-scaled cellulose from lignocellulose: A review

Nanocellulose, either in the form of fibers or crystals, constitutes a renewable, biobased, biocompatible material with advantageous mechanical properties that can be isolated from lignocellulosic biomass. Enzyme-assisted isolation of nanocellulose is an attractive, environmentally friendly approach that leads to products of higher quality compared to their chemically prepared counterparts. Lytic polysaccharide monooxygenases (LPMOs) are enzymes that oxidatively cleave the β-1,4-glycosidic bond of polysaccharides upon activation of O₂ or H₂O₂ and presence of an electron donor. Their use for treatment of cellulose fibers towards the preparation of nano-scaled cellulose is related to the ability of LPMOs to create nicking points on the fiber surface, thus facilitating fiber disruption and separation. The aim of this review is to describe the mode of action of LPMOs on cellulose fibers towards the isolation of nanostructures, thus highlighting their great potential for the production of nanocellulose as a novel value added product from lignocellulose.

Two C1-oxidizing AA9 lytic polysaccharide monooxygenases from Sordaria brevicollis differ in thermostability, activity, and synergy with cellulase

Cellulolytic fungi usually have multiple genes for C1-oxidizing auxiliary activity 9 (AA9) lytic polysaccharide monooxygenases (LPMOs) in their genomes, but their potential functional differences are less understood. In this study, two C1-oxidizing AA9 LPMOs, SbLPMO9A and SbLPMO9B, were identified from Sordaria brevicollis, and their differences, particularly in terms of thermostability, reducing agent specificity, and synergy with cellulase, were explored. The two enzymes exhibited weak binding to cellulose and intolerance to hydrogen peroxide. Their oxidative activity was influenced by cellulose crystallinity and surface morphology, and both enzymes tended to oxidize celluloses of lower crystallinity and high surface area. Comparably, SbLPMO9A had much better thermostability than SbLPMO9B, which may be attributed to the presence of a carbohydrate binding module 1 (CBM1)-like sequence at its C-terminus. In addition, the two enzymes exhibited different specificities and responsivities toward electron donors. SbLPMO9A and SbLPMO9B were able to boost the catalytic efficiency of endoglucanase I (EGI) on physically and chemically pretreated substrates but with different degrees of synergy. Substrate- and enzyme-specific synergism was observed by comparing the synergistic action of SbLPMO9A or SbLPMO9B with commercial Celluclast 1.5L on three kinds of cellulosic substrates. On regenerated amorphous cellulose and PFI (Papirindustriens Forskningsinstitut)-fibrillated bleached eucalyptus pulp, SbLPMO9B showed a higher synergistic effect than SbLPMO9A, while on delignified wheat straw, the synergistic effect of SbLPMO9A was higher than that of SbLPMO9B. On account of its excellent thermostability and boosting effect on the enzymatic hydrolysis of delignified wheat straw, SbLPMO9A may have high application potential in biorefineries for lignocellulosic biomass. KEY POINTS: • C1-oxidizing SbLPMO9A displayed higher thermostability than SbLPMO9B, probably due to the presence of a CBM1-like module. • The oxidative activity of the two SbLPMO9s on celluloses increased with decreasing cellulose crystallinity or increasing beating degree. • The two SbLPMO9s boosted the catalytic efficiency of cellulase, but the synergistic effect was substrate- and enzyme-specific.

Review on Nonconventional Fibrillation Methods of Producing Cellulose Nanofibrils and Their Applications

The production of cellulose nanofibrils (CNFs) continues to receive considerable attention because of their desirable material characteristics for a variety of consumer applications. There are, however, challenges that remain in transitioning CNFs from research to widespread adoption in the industrial sectors, including production cost and material performance. This Review covers CNFs produced from nonconventional fibrillation methods as a potential alternative solution. Pretreating biomass by biological, chemical, mechanical, or physical means can render plant feedstocks more facile for processing and thus lower energy requirements to produce CNFs. CNFs from nonconventional fibrillation methods have been investigated for various applications, including films, composites, aerogels, and Pickering emulsifiers. Continued research is needed to develop protocols to standardize the characterization (e.g., degree of fibrillation) of the lignocellulosic fibrillation processes and resulting CNF products to make them more attractive to the industry for specific product applications.

Enzymatic Fibre Modification During Production of Dissolving Wood Pulp for Regenerated Cellulosic Materials

The production of regenerated cellulosic fibres, such as viscose, modal and lyocell, is based mainly on the use of dissolving wood pulp as raw material. Enzymatic processes are an excellent alternative to conventional chemical routes in the production of dissolving pulp, in terms of energy efficiency, reagent consumption and pulp yield. The two main characteristics of a dissolving pulp are the cellulose purity and the molecular weight, both of which can be controlled with the aid of enzymes. A purification process for paper-grade kraft pulp has been proposed, based on the use of xylanases in combination with hot and cold caustic extraction, without the conventional pre-hydrolysis step before kraft pulping. This enzyme aided purification allowed the production of a dissolving pulp that met the specifications for the manufacture of viscose, < 3% xylan, > 92% ISO brightness and 70% Fock's reactivity. Endoglucanases (EGs) can efficiently reduce the average molecular weight of the cellulose while simultaneously increasing the pulp reactivity for viscose production. It is shown in this study that lytic polysaccharide monooxygenases act synergistically with EGs in the modification of bleached dissolving pulp.

Impact of the Enzyme Charge on the Production and Morphological Features of Cellulose Nanofibrils

The available research does not allow specific relationships to be established between the applied enzymatic-mechanical treatment, the degree of polymerization, and the characteristics of the cellulose nanofibrils (CNFs) produced. This work aims to establish specific relationships between the intensity of enzymatic treatment, the degree of polymerization of the cellulose, the morphology of CNFs, and the tensile strength of the CNF films. It is determined that the decrease in the degree of polymerization plays an essential role in the fibrillation processes of the cell wall to produce CNFs and that there is a linear relationship between the degree of polymerization and the length of CNFs, which is independent of the type of enzyme, enzyme charge, and intensity of the applied mechanical treatment. In addition, it is determined that the percentage of the decrease in the degree of polymerization of CNFs due to mechanical treatment is irrespective of the applied enzyme charge. Finally, it is shown that the aspect ratio is a good indicator of the efficiency of the fibrillation process, and is directly related to the mechanical properties of CNF films.

Comparison of C4-oxidizing and C1/C4-oxidizing AA9 LPMOs in substrate adsorption, H2O2-driven activity and synergy with cellulase on celluloses of different crystallinity

Two C1/C4-oxidizing AA9 lytic polysaccharide monooxygenases (AA9 LPMOs), AoLPMO9A and AoLPMO9B, and one C4-oxidizing AoLPMO9C from Aspergillus oryzae, were characterized and compared with the well-studied C4-oxidizing NcLPMO9C. NcLPMO9C and AoLPMO9C harboring carbohydrate-binding module 1 (CBM1) exhibited much stronger adsorption capacity than AoLPMO9A and B without CBM1. The binding affinity is crucial for the efficacy of H₂O₂ as cosubstrate and oxidative activity of AA9 LPMOs on crystalline cellulose. C4-oxidizing AA9 LPMOs had a striking boosting effect on cellobiohydrolase I (CBHI), while C1/C4-oxidizing AA9 LPMOs boosted CBHII and endoglucanase I (EGI) activity. Our results indicated that two types of AA9 LPMOs with different modularities and regioselectivities varied in cellulose adsorption, H₂O₂-driven activity and synergy with cellulase on celluloses of different crystallinity which could complement each other in lignocellulose degradation. C4-oxidizing AA9 LPMOs with CBM1 were particularly essential in cellulase cocktail due to high H₂O₂-driven activity and a striking boosting effect on CBHI.

Cellulose fibers deconstruction by twin-screw extrusion with in situ enzymatic hydrolysis via bioextrusion

The aim of this work was to study the cellulose fibers deconstruction by twin-screw extrusion with in situ enzymatic hydrolysis via bioextrusion, for cellulose nanofibrils (CNF) production. Cellulose pulp was extruded with an optimized screw profile, with or without (reference) the addition of an enzymatic solution. An increase of crystallinity index from 67.0% to 73.7% and decrease of DP from 1003 to 419 were observed with bioextrusion. Direct activity measurements of the enzyme confirmed its activity during the process (sugar content increasing from 0.07 ± 0.004 to 2.38 ± 0.003 mg/mL) and after the process (specific activities around 0.20 CMCU/mL). Enzymes were not deactivated during bioextrusion and could be recycled. CNF properties were higher with bioextrusion compared to reference (respective quality indices of 55.5 ± 2.7 and 39.8 ± 2.8), with a lower energy consumption. This proof of concept could be optimized for the industrial production of highly concentrated CNF.

Lipase-Immobilized Cellulosic Capsules with Water Absorbency for Enhanced Pickering Interfacial Biocatalysis

Lipase-immobilized cellulosic capsules consisting of hydrophobic ethyl cellulose (EC) and hydrophilic carboxymethyl cellulose (CMC) were developed with a promising interfacial activity and water absorbency for the enhanced Pickering interfacial biocatalysis. Lipase was physically immobilized with water-absorbent materials (CMC) via hydrogen bonding and electrostatic interactions and acted as the interior catalytic core of the capsule. The interfacially active EC worked as the exterior shell, enabling capsules to stabilize the oil-in-water Pickering emulsion for the subsequent Pickering interfacial catalysis. The capsules with CMC created interior water-rich conditions to improve the conformational and enzymatic activity of the immobilized lipase. Compared with capsules without water-absorbent materials, the capsules with CMC enhanced the efficiency of the Pickering interfacial catalysis for the esterification of oleic acid and 1-octanol by 12%. Immobilized with a small amount of lipase (0.0625 g/g), the cellulosic capsules with water absorbency could convert 50.8% of the reactants after 10 h under room temperature, significantly higher than that by the same amount of free lipase in the biphasic system (15%) and a Pickering emulsion (24.1%) stabilized by empty capsules (without lipase). Moreover, the cellulosic capsules could be recycled by simple centrifugation while retaining their high relative catalytic activity for at least eight cycles, demonstrating their sustainable catalytic performance.

New thermostable endoglucanase from Spirochaeta thermophila and its mutants with altered substrate preferences

Endoglucanases are key elements in several industrial applications, such as cellulosic biomass hydrolysis, cellulose fiber modification for the production paper and composite materials, and in nanocellulose production. In all of these applications, the desired function of the endoglucanase is to create nicks in the amorphous regions of the cellulose. However, endoglucanase can be diverted from its activity on the fibers by other substrates-soluble oligosaccharides. This issue was addressed in the current study using enzyme engineering and an enzyme evolution approach. To this end, a hypothetical endoglucanase from a thermostable bacterium Spirochaeta thermophila was for the first time cloned and characterized. The wild-type enzyme was used as a starting point for mutagenesis and molecular evolution toward a preference for the higher molecular weight substrates. The best of the evolved enzymes was more active than the wild-type enzyme toward high molecular weight substrate at temperatures below 45 °C (3-fold more active at 30 °C) and showed little or no activity with low molecular weight substrates. These findings can be instrumental in bioeconomy sectors, such as second-generation biofuels and biomaterials from lignocellulosic biomass. KEY POINTS: • A new thermostable endoglucanase was characterized. • The substrate specificity of this endoglucanase was changed by means of genetic engineering. • A mutant with a preference for long molecular weight substrate was obtained and proposed to be beneficial for cellulose fiber modification.

Moulding of micropatterned nanocellulose films and their application in fluid handling

HYPOTHESIS

Well-controlled micropatterned nanocellulose films are able to be fabricated via spray coating onto a micropatterned impermeable moulded surface. The micropattern size is able control the directionality of wicking fluid flow.

EXPERIMENTS

Using photolithography and etching techniques, silicon moulds with channel widths of 5-500 µm and depths of 6, 12 and 18 µm were fabricated. Micropatterned nanocellulose sheets were formed by spray coating nanofibre suspensions onto the moulds. We also investigate the effect the dimensions of these micropatterned nanocellulose films have on wicking fluids.

FINDINGS

Micropatterns were imparted on the surface of nanocellulose films which resulted in three well-defined regimes of conformation with the moulds: full, partial and no conformation. These regimes were driven by the aspect ratio (channel depth/width) of the moulds. Achieved channel widths and depths were compared to those possible with other micropattern fabrication techniques. The directionality of the wicking water droplets can be controlled with the micropatterned channel. Channels within the full conformation regime resulted in increased directionality of fluid flow compared with those not within this regime. This research demonstrates the industrially scalable process of spray coating has potential to serve as the foundation for a new generation of paper-based microfluidic devices.

Water-soluble chlorophyll-binding proteins from Brassica oleracea allow for stable photobiocatalytic oxidation of cellulose by a lytic polysaccharide monooxygenase

BACKGROUND

Lytic polysaccharide monooxygenases (LPMOs) are indispensable redox enzymes used in industry for the saccharification of plant biomass. LPMO-driven cellulose oxidation can be enhanced considerably through photobiocatalysis using chlorophyll derivatives and light. Water soluble chlorophyll binding proteins (WSCPs) make it is possible to stabilize and solubilize chlorophyll in aqueous solution, allowing for in vitro studies on photostability and ROS production. Here we aim to apply WSCP-Chl a as a photosensitizing complex for photobiocatalysis with the LPMO, TtAA9.

RESULTS

We have in this study demonstrated how WSCP reconstituted with chlorophyll a (WSCP-Chl a) can create a stable photosensitizing complex which produces controlled amounts of H2O2 in the presence of ascorbic acid and light. WSCP-Chl a is highly reactive and allows for tightly controlled formation of H2O2 by regulating light intensity. TtAA9 together with WSCP-Chl a shows increased cellulose oxidation under low light conditions, and the WSCP-Chl a complex remains stable after 24 h of light exposure. Additionally, the WSCP-Chl a complex demonstrates stability over a range of temperatures and pH conditions relevant for enzyme activity in industrial settings.

CONCLUSION

With WSCP-Chl a as the photosensitizer, the need to replenish Chl is greatly reduced, enhancing the catalytic lifetime of light-driven LPMOs and increasing the efficiency of cellulose depolymerization. WSCP-Chl a allows for stable photobiocatalysis providing a sustainable solution for biomass processing.

Enzymatic processing of lignocellulosic biomass: principles, recent advances and perspectives

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.

Cellulose Nanofibrils-based Hydrogels for Biomedical Applications: Progresses and Challenges

Background:

Cellulose Nanofibrils (CNFs) are natural nanomaterials with nanometer dimensions. Compared with ordinary cellulose, CNFs own good mechanical properties, large specific surface areas, high Young's modulus, strong hydrophilicity and other distinguishing characteristics, which make them widely used in many fields. This review aims to introduce the preparation of CNFs-based hydrogels and their recent biomedical application advances.

Methods:

By searching the recent literatures, we have summarized the preparation methods of CNFs, including mechanical methods and chemical mechanical methods, and also introduced the fabrication methods of CNFs-based hydrogels, including CNFs cross-linked with metal ion and with polymers. In addition, we have summarized the biomedical applications of CNFs-based hydrogels, including scaffold materials and wound dressings.

Results:

CNFs-based hydrogels are new types of materials that are non-toxic and display a certain mechanical strength. In the tissue scaffold application, they can provide a micro-environment for the damaged tissue to repair and regenerate it. In wound dressing applications, it can fit the wound surface and protect the wound from the external environment, thereby effectively promoting the healing of skin tissue.

Conclusion:

By summarizing the preparation and application of CNFs-based hydrogels, we have analyzed and forecasted their development trends. At present, the research of CNFs-based hydrogels is still in the laboratory stage. It needs further exploration to be applied in practice. The development of medical hydrogels with high mechanical properties and biocompatibility still poses significant challenges.

Nanocellulose Production: Exploring the Enzymatic Route and Residues of Pulp and Paper Industry

Increasing environmental and sustainability concerns, caused by current population growth, has promoted a raising utilization of renewable bio-resources for the production of materials and energy. Recently, nanocellulose (NC) has been receiving great attention due to its many attractive features such as non-toxic nature, biocompatibility, and biodegradability, associated with its mechanical properties and those related to its nanoscale, emerging as a promising material in many sectors, namely packaging, regenerative medicine, and electronics, among others. Nanofibers and nanocrystals, derived from cellulose sources, have been mainly produced by mechanical and chemical treatments; however, the use of cellulases to obtain NC attracted much attention due to their environmentally friendly character. This review presents an overview of general concepts in NC production. Especial emphasis is given to enzymatic hydrolysis processes using cellulases and the utilization of pulp and paper industry residues. Integrated process for the production of NC and other high-value products through enzymatic hydrolysis is also approached. Major challenges found in this context are discussed along with its properties, potential application, and future perspectives of the use of enzymatic hydrolysis as a pretreatment in the scale-up of NC production.

A trimodular bacterial enzyme combining hydrolytic activity with oxidative glycosidic bond cleavage efficiently degrades chitin

Findings from recent studies have indicated that enzymes containing more than one catalytic domain may be particularly powerful in the degradation of recalcitrant polysaccharides such as chitin and cellulose. Some known multicatalytic enzymes contain several glycoside hydrolase domains and one or more carbohydrate-binding modules (CBMs). Here, using bioinformatics and biochemical analyses, we identified an enzyme, Jd1381 from the actinobacterium Jonesia denitrificans, that uniquely combines two different polysaccharide-degrading activities. We found that Jd1381 contains an N-terminal family AA10 lytic polysaccharide monooxygenase (LPMO), a family 5 chitin-binding domain (CBM5), and a family 18 chitinase (Chi18) domain. The full-length enzyme, which seems to be the only chitinase produced by J. denitrificans, degraded both α- and β-chitin. Both the chitinase and the LPMO activities of Jd1381 were similar to those of other individual chitinases and LPMOs, and the overall efficiency of chitin degradation by full-length Jd1381 depended on its chitinase and LPMO activities. Of note, the chitin-degrading activity of Jd1381 was comparable with or exceeded the activities of combinations of well-known chitinases and an LPMO from Serratia marcescens Importantly, comparison of the chitinolytic efficiency of Jd1381 with the efficiencies of combinations of truncated variants-JdLPMO10 and JdCBM5-Chi18 or JdLPMO10-CBM5 and JdChi18-indicated that optimal Jd1381 activity requires close spatial proximity of the LPMO10 and the Chi18 domains. The demonstration of intramolecular synergy between LPMOs and hydrolytic enzymes reported here opens new avenues toward the development of efficient catalysts for biomass conversion.

Industrial Use of Cell Wall Degrading Enzymes: The Fine Line Between Production Strategy and Economic Feasibility

Cell Wall Degrading Enzymes (CWDEs) are a heterogeneous group of enzymes including glycosyl-hydrolases, oxidoreductases, lyases, and esterases. Microbes with degrading activities toward plant cell wall polysaccharides are the most relevant source of CWDEs for industrial applications. These organisms secrete a wide array of CWDEs in amounts strictly necessary for their own sustenance, nonetheless the production of CWDEs from wild type microbes can be increased at large-scale by using optimized fermentation strategies. In the last decades, advances in genetic engineering allowed the expression of recombinant CWDEs also in lab-domesticated organisms such as E. coli, yeasts and plants, dramatically increasing the available options for the large-scale production of CWDEs. The optimization of a CWDE-producing biofactory is a hard challenge that biotechnologists tackle by testing different expression strategies and expression-hosts. Although both the yield and production costs are critical factors to produce biomolecules at industrial scale, these parameters are often disregarded in basic research. This review presents the main characteristics and industrial applications of CWDEs directed toward the cell wall of plants, bacteria, fungi and microalgae. Different biofactories for CWDE expression are compared in order to highlight strengths and weaknesses of each production system and how these aspects impact the final enzyme cost and, consequently, the economic feasibility of using CWDEs for industrial applications.

Potential of Xylanases to Reduce the Viscosity of Micro/Nanofibrillated Bleached Kraft Pulp

The generally high viscosity of micro/nanofibrillated cellulose limits its applications in cream and fluid products. A bleached softwood Kraft (BSK) pulp was refined with increasing energy (500-2500 kWh t^-1) to produce micro/nanofibrillated cellulose (MNBSK). Subsequent xylanase treatment was shown to influence the viscosity, gel point, aspect ratio, and fiber surface morphology of the MNBSK. It was apparent that the accessibility to xylanases was increased even at low refining energies (500 kWh t^-1). Depending on the initial degree of cellulose fibrillation, xylanase treatment decreased the viscosity of the MNBSK from 4190-2030 to 681-243 Pa·s at a shear rate of 0.01 s^-1, corresponding to the reduction in the aspect ratio from 183-296 to 163-194. It was likely that the xylanases were predominantly acting on the xylan present on the fiber surfaces, reducing the cross-linking points on the cellulose fibers and consequently resulting in the reduction in MNBSK viscosity.

Comparison of mixed enzymatic pretreatment and post-treatment for enhancing the cellulose nanofibrillation efficiency

In this work, lignocellulosic nanofibrils (LCNF) produced from mechanical fibrillation with mixed enzymatic pretreatment or post-treatment were compared and the chemical composition, water retention value (WRV), average-number height and crystallinity for the obtained LCNF were evaluated. Compared to pure mechanical fibrillation, both mixed enzymatic pretreatment and post-treatment could efficiently facilitate cellulose nanofibrillation. Moreover, mixed enzymatic pretreatment was more suitable for LCNF production, resulting in a relatively higher WRV of 909% and smaller average-number height of 15 nm. These discoveries provide new insights into a more efficient biological method for the production and application of cellulose nanomaterials.

A mini review of xylanolytic enzymes with regards to their synergistic interactions during hetero-xylan degradation

This review examines the recent models describing the mode of action of various xylanolytic enzymes and how these enzymes can be applied (sequentially or simultaneously) with their distinctive roles in mind to achieve efficient xylan degradation. With respect to homeosynergy, synergism appears to be as a result of β-xylanase and/or oligosaccharide reducing-end β-xylanase liberating xylo-oligomers (XOS) that are preferred substrates of the processive β-xylosidase. With regards to hetero-synergism, two cross relationships appear to exist and seem to be the reason for synergism between the enzymes during xylan degradation. These cross relations are the debranching enzymes such as α-glucuronidase or side-chain cleaving enzymes such as carbohydrate esterases (CE) removing decorations that would have hindered back-bone-cleaving enzymes, while backbone-cleaving-enzymes liberate XOS that are preferred substrates of the debranching and side-chain-cleaving enzymes. This interaction is demonstrated by high yields in co-production of xylan substituents such as arabinose, glucuronic acid and ferulic acid, and XOS. Finally, lytic polysaccharide monooxygenases (LPMO) have also been implicated in boosting whole lignocellulosic biomass or insoluble xylan degradation by glycoside hydrolases (GH) by possibly disrupting entangled xylan residues. Since it has been observed that the same enzyme (same Enzyme Commission, EC, classification) from different GH or CE and/or AA families can display different synergistic interactions with other enzymes due to different substrate specificities and properties, in this review, we propose an approach of enzyme selection (and mode of application thereof) during xylan degradation, as this can improve the economic viability of the degradation of xylan for producing precursors of value added products.

Cellulose Nano-Films as Bio-Interfaces

Cellulose, the most abundant polymer on earth, has enormous potential in developing bio-friendly, and sustainable technological products. In particular, cellulose films of nanoscale thickness (1-100 nm) are transparent, smooth (roughness <1 nm), and provide a large surface area interface for biomolecules immobilization and interactions. These attractive film properties create many possibilities for both fundamental studies and applications, especially in the biomedical field. The three liable-OH groups on the monomeric unit of the cellulose chain provide schemes to chemically modify the cellulose interface and engineer its properties. Here, the cellulose thin film serves as a substrate for biomolecules interactions and acts as a support for bio-diagnostics. This review focuses on the challenges and opportunities provided by engineering cellulose thin films for controlling biomolecules interactions. The first part reviews the methods for preparing cellulose thin films. These are by dispersing or dissolving pure cellulose or cellulose derivatives in a solvent to coat a substrate using the spin coating, Langmuir-Blodgett, or Langmuir-Schaefer method. It is shown how different cellulose sources, preparation, and coating methods and substrate surface pre-treatment affect the film thickness, roughness, morphology, crystallinity, swelling in water, and homogeneity. The second part analyses the bio-macromolecules interactions with the cellulose thin film interfaces. Biomolecules, such as antibodies and enzymes, are adsorbed at the cellulose-liquid interface, and analyzed dry and wet. This highlights the effect of film surface morphology, thickness, crystallinity, water intake capacity, and surface pre-treatment on biomolecule adsorption, conformation, coverage, longevity, and activity. Advance characterization of cellulose thin film interface morphology and adsorbed biomolecules interactions are next reviewed. X-ray and neutron scattering/reflectivity combined with atomic force microscopy (AFM), quartz crystal microbalance (QCM), microscopy, and ellipsometer allow visualizing, and quantifying the structural morphology of cellulose-biomolecule interphase and the respective biomolecules conformations, kinetics, and sorption mechanisms. This review provides a novel insight on the advantages and challenges of engineering cellulose thin films for biomedical applications. This is to foster the exploration at the molecular level of the interaction mechanisms between a cellulose interface and adsorbed biomolecules with respect to adsorbed molecules morphology, surface coverage, and quantity. This knowledge is to engineer a novel generation of efficient and functional biomedical devices.