Magnetic nickel nanostructure as cellulase immobilization surface for the hydrolysis of lignocellulosic biomass

Immobilized Cellulase on NH2-MIL-88(Fe) and Its Performance as a Biocatalyst

To broaden pH range and improve thermal stability, reusability, storage stability, and organic solvent tolerance of natural enzymes, a magnetic material (NH2-MIL-88(Fe)) was synthesized as a new material to immobilize cellulase. The results showed that the optimal temperature and pH of cellulase immobilized on NH2-MIL-88(Fe) showed a wider range compared to free cellulase, and 74% and 83% of the initial activity could be retained after 10 cycles and storage for 49 days, respectively. Moreover, the tolerance for organic solvents was improved compared with free enzyme. The reducing sugar yields from sodium carboxymethylcellulose (CMC) and corn cob hydrolyzed with cellulase immobilized on NH2-MIL-88(Fe) were higher than observed with the free enzyme, which demonstrated the better biocatalytic performance of cellulase immobilized on NH2-MIL-88(Fe).

Reversible immobilization of cellulase on gelatin for efficient insoluble cellulose hydrolysis

Immobilized enzymes are one of the most common tools used in enzyme engineering, as they can substantially reduce the cost of enzyme isolation and use. However, efficient catalysis of solid substrates using immobilized enzymes is challenging, hydrolysis of insoluble cellulose by immobilized cellulases is a typical example of this problem. In this study, inspired by bees and honeycombs, we prepared gelatin-modified cellulase (BEE) and gelatin hydrogels (HONEYCOMB) to achieve reversible recycling versus release of cellulase through temperature-responsive changes in the triple-stranded helix-like interactions between BEE and HONEYCOMB. At elevated temperatures, BEE was released from HONEYCOMB and participated in hydrolytic saccharification. After 24 h, the glucose yields of both the free enzyme and BEE reached the same level. When the temperature was decreased, BEE recombined with HONEYCOMB to facilitate the effective separation and recycling of BEE from the system. The enzymatic system retained >70 % activity after four reuse cycles. In addition, this system showed good biocompatibility and environmental safety. This method increases the mass transfer capacity and enables easy recovery of immobilized cellulase, thereby serving as a valuable strategy for the immobilization of other enzymes.

A Bibliometric Analysis: Current Perspectives and Potential Trends of Enzyme Thermostability from 1991-2022

Thermostability is considered a crucial parameter to evaluate the viability of enzymes in industrial applications. Over the past 31 years, many studies have been reported on the thermostability of enzymes. However, there is no systematic bibliometric analysis of publications on the thermostability of enzymes. In this study, 16,035 publications related to the thermostability of enzymes were searched and collected, showing an increasing annual trend. China contributed the most publications, while the United States had the highest citation count. International Journal of Biological Macromolecules is the most productive journal in the research field. Moreover, Chinese acad sci and Khosro Khajeh are the most active institutions and prolific authors in the field, respectively. Analysis of references with the strongest citation bursts and keyword co-occurrences, magnetic nanoparticles, metal-organic frameworks, molecular dynamics, and rational design are current hot spots and significant future research directions. This study is the first comprehensive bibliometric analysis summarizing trends and developments in enzyme thermostability research. Our findings could provide scholars with an understanding of the fundamental knowledge framework of the field and identify recent potential hotspots and research trends that could facilitate the discovery of collaboration opportunities.

An overview on the current status and future prospects in Aspergillus cellulase production

Cellulase is a new research point besides glucoamylase, amylase, and protease in the enzyme industry. Cellulase can decompose lignocellulosic biomass into small-molecule sugars, which facilitates microbial utilization; thus, it has a vast market potential in the field of feed, food, energy, and chemistry. The Aspergillus was the first strain used in cellulase preparation because of its safety and non-toxicity, strong growth ability, and high enzyme yield. This review provides the latest research and advances on preparing cellulase from Aspergillus. The metabolic mechanisms of cellulase secretion by Aspergillus, the selection of fermentation substrates, the comparison of the fermentation modes, and the effect of fermentation conditions have been discussed in this review. Also, the subsequent separation and purification techniques of Aspergillus cellulase, including salting out, organic solvent precipitation, ultrafiltration, and chromatography, have been declared. Further, bottlenecks in Aspergillus cellulase preparation and corresponding feasible approaches, such as genetic engineering, mixed culture, and cellulase immobilization, have also been proposed in this review. This paper provides theoretical support for the efficient production and application of Aspergillus cellulase.

Cellulase immobilization to enhance enzymatic hydrolysis of lignocellulosic biomass: An all-inclusive review

Cellulase-mediated lignocellulosic biorefinery plays a crucial role in the production of high-value biofuels and chemicals, with enzymatic hydrolysis being an essential component. The advent of cellulase immobilization has revolutionized this process, significantly enhancing the efficiency, stability, and reusability of cellulase enzymes. This review offers a thorough analysis of the fundamental principles underlying immobilization, encompassing various immobilization approaches such as physical adsorption, covalent binding, entrapment, and cross-linking. Furthermore, it explores a diverse range of carrier materials, including inorganic, organic, and hybrid/composite materials. The review also focuses on emerging approaches like multi-enzyme co-immobilization, oriented immobilization, immobilized enzyme microreactors, and enzyme engineering for immobilization. Additionally, it delves into novel carrier technologies like 3D printing carriers, stimuli-responsive carriers, artificial cellulosomes, and biomimetic carriers. Moreover, the review addresses recent obstacles in cellulase immobilization, including molecular-level immobilization mechanism, diffusion limitations, loss of cellulase activity, cellulase leaching, and considerations of cost-effectiveness and scalability. The knowledge derived from this review is anticipated to catalyze the evolution of more efficient and sustainable biocatalytic systems for lignocellulosic biomass conversion, representing the current state-of-the-art in cellulase immobilization techniques.

Synthesis of bifunctional thermal response promoters for improved high-solids enzymatic hydrolysis of corncob residues

The enzymatic hydrolysis cost of lignocellulose can be reduced by improving enzymatic hydrolysis and recycling cellulase by adding additives. A series of copolymers P(SSS-co-SPE) (PSSPs) were synthesized using sodium p-styrene sulfonate (SSS) and sulfobetaine (SPE) as monomers. PSSP exhibited upper critical solution temperature response. PSSP with high molar ratio of SSS displayed more significant improved hydrolysis performance. When 10.0 g/L PSSP5 was added to the hydrolysis system of corncob residues, and substrate enzymatic digestibility at 72 h (SED@72 h) increased by 1.4 times. PSSP with high molecular weight and moderate molar ratio of SSS, had significant temperature response, enhanced hydrolysis, and recovering cellulase properties. For high-solids hydrolysis of corncob residues, SED@48 h increased by 1.2 times with adding 4.0 g/L of PSSP3. Meanwhile, 50% of cellulase amount was saved at the room temperature. This work provides a new idea for reducing the hydrolysis cost of lignocellulose-based sugar platform technology.

Effect of Fenton oxidized lignin support on immobilized β-glucosidase activity

In this study, the Fenton oxidized lignin was prepared to investigate the effect of Fenton oxidation modification on the activity of lignin immobilized β-glucosidase (β-GL). The results demonstrated that Fenton oxidation could significantly improve the activity and stability of immobilized β-GL. This is because the Fenton oxidation increased the electrostatic, hydrogen bonding, and hydrophobic forces between lignin and β-GL, resulting in increased lignin adsorption onto β-GL. The Fenton oxidation also changed the chemical structure of lignin, altering the lignin-β-GL binding site and reducing the negative effect of lignin on the β-GL catalytic domain. This research will improve understanding of the effect of Fenton lignin oxidation on immobilized β-GL activity and expand the use of lignin in enzyme immobilization.

Mesoporous Polymeric Ionic Liquid via Confined Polymerization for Laccase Immobilization towards Efficient Degradation of Phenolic Pollutants

Laccase immobilization is a promising method that can be used for the recyclable treatment of refractory phenolic pollutants (e.g., chlorophenols) under mild conditions, but the method is still hindered by the trade-off limits of supports in terms of their high specific surface area and rich functional groups. Herein, confined polymerization was applied to create abundant amino-functionalized polymeric ionic liquids (PILs) featuring a highly specific surface area and mesoporous structure for chemically immobilizing laccase. Benefiting from this strategy, the specific surface area of the as-synthesized PILs was significantly increased by 60-fold, from 5 to 302 m2/g. Further, a maximum activity recovery of 82% towards laccase was recorded. The tolerance and circulation of the immobilized laccase under harsh operating conditions were significantly improved, and the immobilized laccase retained more than 84% of its initial activity after 15 days. After 10 cycles, the immobilized laccase was still able to maintain 80% of its activity. Compared with the free laccase, the immobilized laccase exhibited enhanced stability in the biodegradation of 2,4-dichlorophenol (2,4-DCP), recording around 80% (seven cycles) efficiency. It is proposed that the synergistic effect between PILs and laccase plays an important role in the enhancement of stability and activity in phenolic pollutant degradation. This work provides a strategy for the development of synthetic methods for PILs and the improvement of immobilized laccase stability.

Towards enhancement of fungal hydrolytic enzyme cocktail using waste algal biomass of Oscillatoria obscura and enzyme stability investigation under the influence of iron oxide nanoparticles

Development of low-cost and economic cellulase production is among the key challenges due to its broad industrial applications. One of the main topics of research pertaining to sustainable biomass waste based biorefinaries is the development of economic cellulase production strategies. The main cause of the increase in cellulase production costs is the use of commercial substrates; as a result, the cost of any cellulase-based bioprocess can be decreased by employing a productive, low-cost substrate. The goal of the current study is to develop low-cost cellulase using the carbohydrate-rich, renewable, and widely accessible cyanobacteria algae Oscillatoria obscura as the production substrate. Maximum cellulase was produced utilising the fungus Rhizopus oryzae at substrate concentration of 7.0 g among various tested concentrations of algal biomass. Maximum production rates of 22 IU/gds FP, 105 IU/gds BGL, and 116 IU/gds EG in 72 h were possible under optimal conditions and substrate concentration. Further investigations on the crude enzyme's stability in the presence of iron oxide nanoparticles (IONPs) revealed that it was thermally stable at 60 °C for up to 8 h. Additionally, the crude enzyme demonstrated pH stability by maintaining its complete activity at pH 6.0 for 8 h in the presence of the optimal dose of 15 mg IONPs. The outcomes of this research may be used to investigate the possibility of producing such enzymes in large quantities at low cost for industrial use.

Boosting Hydrolysis of Cellulose at High Temperature by β-Glucosidase Induced Metal-Organic Framework In-Situ Co-Precipitation Encapsulation

Due to the poor enzyme thermal stability, the efficient conversion of high crystallinity cellulose into glucose in aqueous phase over 50 °C is challenging. Herein, an enzyme-induced MOFs encapsulation of β-glucosidase (β-G) strategy was proposed for the first time. By using various methods, including SEM, XRD, XPS, NMR, FTIR and BET, the successful preparation of a porous channel-type flower-like enzyme complex (β-G@MOFs) was confirmed. The prepared enzyme complex (β-G@MOFs) materials showed improved thermal stability (from 50 °C to 100 °C in the aqueous phase) and excellent resistance to ionic liquids (the reaction temperature was as high as 110 °C) compared to the free enzyme (β-G). Not only the catalytic hydrolysis of cellulose by single enzyme (β-G) in ionic liquid was realized, but also the high-temperature continuous reaction performance of the enzyme was significantly improved. Benefiting from the significantly improved heat resistance, the β-G@MOFs exhibited 32.1 times and 34.2 times higher enzymatic hydrolysis rate compared to β-G for cellobiose and cellulose substrates, respectively. Besides, the catalytic activity of β-G@MOFs was retained up to 86 % after five cycles at 110 °C. This was remarkable because the fixation of the enzyme by the MOFs ensured that the folded structure of the enzyme would not expand at high temperatures, allowing the native conformation of the encapsulated protein well-maintained. Furthermore, we believe that this structural stability was caused by the confinement of flower-like porous MOFs.

Cellulase Immobilization on Nanostructured Supports for Biomass Waste Processing

Nanobiocatalysts, i.e., enzymes immobilized on nanostructured supports, received considerable attention because they are potential remedies to overcome shortcomings of traditional biocatalysts, such as low efficiency of mass transfer, instability during catalytic reactions, and possible deactivation. In this short review, we will analyze major aspects of immobilization of cellulase-an enzyme for cellulosic biomass waste processing-on nanostructured supports. Such supports provide high surface areas, increased enzyme loading, and a beneficial environment to enhance cellulase performance and its stability, leading to nanobiocatalysts for obtaining biofuels and value-added chemicals. Here, we will discuss such nanostructured supports as carbon nanotubes, polymer nanoparticles (NPs), nanohydrogels, nanofibers, silica NPs, hierarchical porous materials, magnetic NPs and their nanohybrids, based on publications of the last five years. The use of magnetic NPs is especially favorable due to easy separation and the nanobiocatalyst recovery for a repeated use. This review will discuss methods for cellulase immobilization, morphology of nanostructured supports, multienzyme systems as well as factors influencing the enzyme activity to achieve the highest conversion of cellulosic biowaste into fermentable sugars. We believe this review will allow for an enhanced understanding of such nanobiocatalysts and processes, allowing for the best solutions to major problems of sustainable biorefinery.