Thin film of lignocellulosic nanofibrils with different chemical composition for QCM-D study

Comparative assessment on lignocellulose degrading enzymes and bioethanol production from spent mushroom substrate of Calocybe indica and Volvariella volvacea

In the current study, we compared the production of extracellular lignocellulose degrading enzymes and bioethanol from the spent mushroom substrate (SMS) of Calocybe indica and Volvariella volvacea. From SMS at different stages of the mushroom development cycle, ligninolytic and hydrolytic enzymes were analysed. The activities of lignin-degrading enzymes, including lignin peroxidase (LiP), laccase, and manganese peroxidase (MnP) were maximal in the spawn run and primordial stages, while hydrolytic enzymes including xylanase, cellobiohydrolase (CBH), and carboxymethyl cellulase (CMCase) showed higher activity during fruiting bodies development and at the end of the mushroom growth cycle. SMS of V. volvacea showed relatively lower ligninase activity than the SMS of C. indica, but had the maximum activity of hydrolytic enzymes. The enzyme was precipitated with acetone and further purified with the DEAE cellulose column. The maximum yield of reducing sugars was obtained after hydrolysis of NaOH (0.5 M) pretreated SMS with a cocktail of partially purified enzymes (50% v/v). After enzymatic hydrolysis, the total reducing sugars were 18.68 ± 0.34 g/l (SMS of C. indica) and 20.02 ± 0.87 g/l (SMS of V. volvacea). We observed the highest fermentation efficiency and ethanol productivity (54.25%, 0.12 g/l h) obtained from SMS hydrolysate of V. volvacea after 48 h at 30 ± 2 °C, using co-culture of Saccharomyces cerevisiae MTCC 11,815 and Pachysolen tannophilus MTCC 1077.

Preparation and Characterization of Polybutylene Succinate Reinforced with Pure Cellulose Nanofibril and Lignocellulose Nanofibril Using Two-Step Process

This study reports the preparation of a polybutylene succinate (PBS) film reinforced with pure cellulose nanofibril (PCNF) and lignocellulose nanofibril (LCNF) by a two-step process that consists of solvent dispersion and twin-screw extrusion. Compared to the conventional one-step process, this method offered improved mechanical properties. The addition of 5% CNF increased the tensile properties up to 18.8%. Further, the effect of the lignin content was also studied by using LCNF as a reinforcement. The LCNF was prepared with and without a deep eutectic solvent (DES) pretreatment to gain LCNF with a lignin content that varied between 5, 19, and 30%. The mechanical properties results show that a 5% addition of LCNF to the PBS matrix increased its tensile strength and elastic modulus. Further, the morphological and thermal properties of the composites were also studied in detail.

Unlocking the secret of lignin-enzyme interactions: Recent advances in developing state-of-the-art analytical techniques

Bioconversion of renewable lignocellulosics to produce liquid fuels and chemicals is one of the most effective ways to solve the problem of fossil resource shortage, energy security, and environmental challenges. Among the many biorefinery pathways, hydrolysis of lignocellulosics to fermentable monosaccharides by cellulase is arguably the most critical step of lignocellulose bioconversion. In the process of enzymatic hydrolysis, the direct physical contact between enzymes and cellulose is an essential prerequisite for the hydrolysis to occur. However, lignin is considered one of the most recalcitrant factors hindering the accessibility of cellulose by binding to cellulase unproductively, which reduces the saccharification rate and yield of sugars. This results in high costs for the saccharification of carbohydrates. The various interactions between enzymes and lignin have been explored from different perspectives in literature, and a basic lignin inhibition mechanism has been proposed. However, the exact interaction between lignin and enzyme as well as the recently reported promotion of some types of lignin on enzymatic hydrolysis is still unclear at the molecular level. Multiple analytical techniques have been developed, and fully unlocking the secret of lignin-enzyme interactions would require a continuous improvement of the currently available analytical techniques. This review summarizes the current commonly used advanced research analytical techniques for investigating the interaction between lignin and enzyme, including quartz crystal microbalance with dissipation (QCM-D), surface plasmon resonance (SPR), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), nuclear magnetic resonance (NMR) spectroscopy, fluorescence spectroscopy (FLS), and molecular dynamics (MD) simulations. Interdisciplinary integration of these analytical methods is pursued to provide new insight into the interactions between lignin and enzymes. This review will serve as a resource for future research seeking to develop new methodologies for a better understanding of the basic mechanism of lignin-enzyme binding during the critical hydrolysis process.

Assessment of Bleached and Unbleached Nanofibers from Pistachio Shells for Nanopaper Making

Cellulose and lignocellulose nanofibrils were extracted from pistachio shells utilizing environmentally friendly pulping and totally chlorine-free bleaching. The extracted nanofibers were used to elaborate nanopaper, a continuous film made by gravimetric entanglement of the nanofibers and hot-pressed to enhance intramolecular bonding. The elaborated nanopapers were analyzed through their mechanical, optical, and surface properties to evaluate the influence of non-cellulosic macromolecules on the final properties of the nanopaper. Results have shown that the presence of lignin augmented the viscoelastic properties of the nanopapers by ≈25% compared with fully bleached nanopaper; moreover, the hydrophobicity of the lignocellulose nanopaper was achieved, as the surface free energy was diminished from 62.65 to 32.45 mNm⁻¹ with an almost non-polar component and a water contact angle of 93.52°. On the other hand, the presence of lignin had an apparent visual effect on the color of the nanopapers, with a ΔE of 51.33 and a ΔL of −44.91, meaning a substantial darkening of the film. However, in terms of ultraviolet transmittance, the presence of lignin resulted in a practically nonexistent transmission in the UV spectra, with low transmittance in the visible wavelengths. In general, the presence of lignin resulted in the enhancement of selected properties which are desirable for packaging materials, which makes pistachio shell nano-lignocellulose an attractive option for this field.

Changes in the Dimensions of Lignocellulose Nanofibrils with Different Lignin Contents by Enzymatic Hydrolysis

Changes in the dimensions of lignocellulose nanofibrils (LCNFs) with different lignin contents from betung bamboo (Dendrocalamus asper) by enzymatic hydrolysis using endoglucanase (EG) were investigated. Lignin contents were adjusted from 3% to 27% by NaClO₂/acetic acid treatment, and LCNFs were prepared using a wet disk-mill (WDM). The dimensions of the LCNFs significantly decreased with decreasing lignin content and increasing EG addition. With increasing EG content, the average diameter of the LCNFs significantly decreased, even though they contained parts of hemicellulose and lignin. The crystal structure showed the typical cellulose I structure in all samples, but the intensity of the diffraction peak slightly changed depending on the lignin and EG contents. The crystallinity index (CrI) values of the LCNFs increased a maximum of 23.8% (LCNF-L27) under increasing EG addition, regardless of the lignin content. With the EG addition of three times the LCNF amount, LCNF-L3 showed the highest CrI value (59.1%). By controlling the composition and structure of LCNFs, it is expected that the wide range of properties of these materials can extend the property range available for existing materials.

Cellulose-Nanofiber-Mediated Sorption-Benefitting Holed Silicalite-1 Crystals

Silicalite-1-type zeolites with unique intracrystal holes or cracks were successfully prepared using a cellulose nanofiber (CNF) as an additional mediating material, and their vapor phase adsorption properties toward methyl tert-butyl ether (MTBE) and n-nitrosodimethylamine (NDMA) were examined. It was found that the mixing protocol of CNF and structure-directing agents (SDAs), the addition amount of CNF, and the CNF/SDAs amount ratio play important roles in forming the holed silicalite-1. The synthesis route that preliminarily mixes CNF with SDAs in a series of controlled conditions is particularly beneficial for the formation of the holed silicalite-1 with mesoporosity and larger pores because the CNF-SDAs composite structure benefits the zeolite growth closely encompassing CNF inside the crystal structure. It also promotes the preferential formation of the orthorhombic phase vicinal to the CNF surface, namely, the surface of the formed internal holes or cracks, with the twin-type crystal size reduced as compared to the non-CNF-templated sample. On the contrary, the synthesis route that mixes CNF with SDAs-silicate composite ions tends to modify the twin-type crystal shape at the same time to form small but uniform well-crystallized particles with less holes or cracks and a dominative monoclinic phase. It was considered that both the inter-subunit structural defect and silanol defect whose content is increased with CNF addition influence the adsorptivity of MTBE and NDMA. Owing to the small twin-type crystal size, the smaller crystal subunits, and the favored short path from the surface of internal holes or cracks, the holed silicalite-1 derived from the CNF and SDA premixture assures the easiest access of adsorbate molecules to the most energetically favored sites and is most appropriate for the adsorption of both MTBE and NDMA among the examined zeolites.

Enhanced enzymatic hydrolysis by adding long-chain fatty alcohols using film as a structure model

Many positive effects of additives on enzymatic hydrolysis of lignocellulosic materials have been investigated, but limited information has been reported on the use of long-chain fatty alcohols (LFAs) for enzymatic hydrolysis by biospired models. In this study, effects of LFAs on enzymatic hydrolysis were evaluated using biomimetic film asa structure model. LFAs clearly improved the digestibility of cellulose film from 65.1% to 77.9%, which was higher than that the digestibility of lignin-cellulose film from 53.9% to 66.2%. Further study indicated that the promotion ascribed to the effect of LFAs, which might provide more active points of chemical reaction and keep the stability of cellulase. Moreover, the digestibility of lignin-cellulose film increased by 12.3%, which might because the denaturation and nonproductive adsorption of cellulase were well prevented by supplementation of LFAs. An efficient strategy was developed to improve the enzymatic hydrolysis efficiency in the study of lignocellulosic bioconversion.

Lignin Films from Spruce, Eucalyptus, and Wheat Straw Studied with Electroacoustic and Optical Sensors: Effect of Composition and Electrostatic Screening on Enzyme Binding

Lignins were isolated from spruce, wheat straw, and eucalyptus by using the milled wood lignin (MWL) method. Functional groups and compositional analyses were assessed via 2D NMR and ³¹P NMR to realize their effect on enzyme binding. Films of the lignins were fabricated and ellipsometry, atomic force microscopy, and water contact angle measurements were used for their characterization and to reveal the changes upon enzyme adsorption. Moreover, lignin thin films were deposited on quartz crystal microgravimetry (QCM) and surface plasmon (SPR) resonance sensors and used to gain further insights into the lignin-cellulase interactions. For this purpose, a commercial multicomponent enzyme system and a monocomponent Trichoderma reesei exoglucanase (CBH-I) were considered. Strong enzyme adsorption was observed on the various lignins but compared to the multicomponent cellulases, CBH-I displayed lower surface affinity and higher binding reversibility. This resolved prevalent questions related to the affinity of this enzyme with lignin. Remarkably, a strong correlation between enzyme binding and the syringyl/guaiacyl (S/G) ratio was found for the lignins, which presented a similar hydroxyl group content (³¹P NMR): higher protein affinity was determined on isolated spruce lignin (99% G units), while the lowest adsorption occurred on isolated eucalyptus lignin (70% S units). The effect of electrostatic interactions in enzyme adsorption was investigated by SPR, which clearly indicated that the screening of charges allowed more extensive protein adsorption. Overall, this work furthers our understanding of lignin-cellulase interactions relevant to biomass that has been subjected to no or little pretreatment and highlights the widely contrasting effects of the nature of lignin, which gives guidance to improve lignocellulosic saccharification and related processes.

Hydrolysis of model cellulose films by cellulosomes: Extension of quartz crystal microbalance technique to multienzymatic complexes

Bacterial cellulosomes contain highly efficient complexed cellulases and have been studied extensively for the production of lignocellulosic biofuels and bioproducts. A surface measurement technique, quartz crystal microbalance with dissipation (QCM-D), was extended for the investigation of real-time binding and hydrolysis of model cellulose surfaces from free fungal cellulases to the cellulosomes of Clostridium thermocellum (Ruminiclostridium thermocellum). In differentiating the activities of cell-free and cell-bound cellulosomes, greater than 68% of the cellulosomes in the crude cell broth were found to exist unattached to the cell across multiple growth stages. The initial hydrolysis rate of crude cell broth measured by QCM was greater than that of cell-free cellulosomes, but the corresponding frequency drop (a direct measure of the mass of enzyme adsorbed to the film) of crude cell broth was less than that of the cell-free cellulosomes, consistent with the underestimation of the cell mass adsorbed using QCM. Inhibition of hydrolysis by cellobiose (0-10g/L), which is similar for crude cell broth and cell-free cellulosomes, demonstrates the sensitivity of the QCM to environmental perturbations of multienzymatic complexes. QCM measurements using multienzymatic complexes may be used to screen and optimize hydrolysis conditions and to develop mechanistic, surface-based models of enzymatic cellulose deconstruction.

Cellulases: Classification, Methods of Determination and Industrial Applications

Microbial cellulases have been receiving worldwide attention, as they have enormous potential to process the most abundant cellulosic biomass on this planet and transform it into sustainable biofuels and other value added products. The synergistic action of endoglucanases, exoglucanases, and β-glucosidases is required for the depolymerization of cellulose to fermentable sugars for transformation in to useful products using suitable microorganisms. The lack of a better understanding of the mechanisms of individual cellulases and their synergistic actions is the major hurdles yet to be overcome for large-scale commercial applications of cellulases. We have reviewed various microbial cellulases with a focus on their classification with mechanistic aspects of cellulase hydrolytic action, insights into novel approaches for determining cellulase activity, and potential industrial applications of cellulases.

The dual effects of lignin content on enzymatic hydrolysis using film composed of cellulose and lignin as a structure model

The degree of delignification during pretreatment is a critical question for economic conversion of biomass to sugar platform. Many models have been used to study the optimum lignin content in biomass, but few of them are able to study without disturbances, such as the complex component and structure of biomass. A novel film model composed of only cellulose and lignin was used to investigate the effect of lignin on enzymatic hydrolysis. High lignin-cellulose proportion (10.00-31.25%) hindered enzymatic hydrolysis, whereas low lignin-cellulose proportion (2.00-8.00%) showed a notable potential to promote enzymatic hydrolysis. The enzymatic hydrolysis rate of lignin-cellulose (6.00%) film was 11.5% higher than that of pure cellulose films. Further study indicated that the promotion was due to the enhancement of film porosity and roughness by residual lignin. Thus, based on the biomimetic model, excessive delignification is not recommended in view of efficient conversion and economy.

Surface Stiffness--a Parameter for Sensing the Chirality of Saccharides

Surface stiffness is considered a key parameter for designing high-performance implantable materials and artificial extracellular matrices because of its substantial effects on cell behavior. How to transform biomolecule recognition events, particularly chiral recognition, into stiffness change on material surfaces is biologically essential but very challenging for chemists. Here, we report a chirality-triggered stiffness transition on a smart polymer film, which consists of flexible polyethylenimine (PEI) main chains grafted with dipeptide units capable of discriminating chiral monosaccharides. The polymer film became substantially softer after interacting with L-ribose and became more rigid after interacting with D-ribose (the basic building block of DNA and RNA). This chiral effect provides a new method for determining the enantiomeric purity of an L/D-ribose mixture and facilitates the chiral separation of deoxyribose racemates as well as the separation of diverse mono-, di-, and oligosaccharides. These are three puzzle problems in carbohydrate chemistry. Furthermore, taking advantage of the significant differences in the surface stiffness, the proliferation of fibroblast cells on the polymeric surfaces can also be regulated by chiral biomolecules.

Contribution of a family 1 carbohydrate-binding module in thermostable glycoside hydrolase 10 xylanase from Talaromyces cellulolyticus toward synergistic enzymatic hydrolysis of lignocellulose

BACKGROUND

Enzymatic removal of hemicellulose components such as xylan is an important factor for maintaining high glucose conversion from lignocelluloses subjected to low-severity pretreatment. Supplementation of xylanase in the cellulase mixture enhances glucose release from pretreated lignocellulose. Filamentous fungi produce multiple xylanases in their cellulase system, and some of them have modular structures consisting of a catalytic domain and a family 1 carbohydrate-binding module (CBM1). However, the role of CBM1 in xylanase in the synergistic hydrolysis of lignocellulose has not been investigated in depth.

RESULTS

Thermostable endo-β-1,4-xylanase (Xyl10A) from Talaromyces cellulolyticus, which is recognized as one of the core enzymes in the fungal cellulase system, has a modular structure consisting of a glycoside hydrolase family 10 catalytic domain and CBM1 at the C-terminus separated by a linker region. Three recombinant Xyl10A variants, that is, intact Xyl10A (Xyl10Awt), CBM1-deleted Xyl10A (Xyl10AdC), and CBM1 and linker region-deleted Xyl10A (Xyl10AdLC), were constructed and overexpressed in T. cellulolyticus. Cellulose-binding ability of Xyl10A CBM1 was demonstrated using quartz crystal microbalance with dissipation monitoring. Xyl10AdC and Xyl10AdLC showed relatively high catalytic activities for soluble and insoluble xylan substrates, whereas Xyl10Awt was more effective in xylan hydrolysis of wet disc-mill treated rice straw (WDM-RS). The enzyme mixture of cellulase monocomponents and intact or mutant Xyl10A enhanced the hydrolysis of WDM-RS glucan, with the most efficient synergism found in the interactions with Xyl10Awt. The increased glucan hydrolysis yield exhibited a linear relationship with the xylan hydrolysis yield by each enzyme. This relationship revealed significant hydrolysis of WDM-RS glucan with lower supplementation of Xyl10Awt.

CONCLUSIONS

Our results suggest that Xyl10A CBM1 has the following two roles in synergistic hydrolysis of lignocellulose by Xyl10A and cellulases: enhancement of lignocellulosic xylan hydrolysis by binding to cellulose, and the efficient removal of xylan obstacles that interrupt the cellulase activity (because of similar binding target of CBM1). The combination of CBM-containing cellulases and xylanases in a fugal cellulase system could contribute to reduction of the enzyme loading in the hydrolysis of pretreated lignocelluloses.

Advancing lignocellulose bioconversion through direct assessment of enzyme action on insoluble substrates

Microbial utilization of lignocellulose from plant cell walls is integral to carbon cycling on Earth. Correspondingly, secreted enzymes that initiate lignocellulose depolymerization serve a crucial step in the bioconversion of lignocellulosic biomass to fuels and chemicals. Genome and metagenome sequencing efforts that span the past decade reveal the diversity of enzymes that have evolved to transform lignocellulose from wood, herbaceous plants and grasses. Nevertheless, there are relatively few examples where 'omic' technologies have identified novel enzyme activities or combinations thereof that dramatically improve the economics of lignocellulose bioprocessing and utilization. A likely factor contributing to the discrepancy between sequence-based enzyme discovery and enzyme application is the common practice to screen enzyme candidates based on activity measurements using soluble model compounds. In this context, the development and application of imaging, physicochemical, and spectromicroscopic techniques that allow direct assessment of enzyme action on relevant lignocellulosic substrates is reviewed.