Enzyme Storage and Recycling: Nanoassemblies of α-Amylase and Xylanase Immobilized on Biomimetic Magnetic Nanoparticles

Optimization of newly isolated Bacillus cereus α-amylase production using orange peels and crab shells and application in wastewater treatment

A newly isolated amylolytic strain was identified as Bacillus cereus spH1 based on 16S and 16-23S gene sequencing (Accession numbers OP811441.1 and OP819558, respectively), optimization strategies, using one variable at time (OVAT) and Plackett-Burman design, were employed to improve the alpha-amylase (α-amylase) production. Condition inferred revealed that the optimal physical parameters for maximum enzyme production were 30 °C, pH 7.5, and 12 h of incubation, using tryptone, malt extract, orange (Citrus sinensis) peels, crab (Portunus segnis) shells, calcium, and sodium chloride (NaCl) as culture medium. The full factorial design (FFD) model was observed to possess a predicted R2 and adjusted R2 values of 0.9788 and 0.9862, respectively, and it can effectively predict the response variables (p = 0). Following such efforts, α-amylase activity was increased 141.6-folds, ranging from 0.06 to 8.5 U/mL. The ideal temperature and pH for the crude enzyme activity were 65 °C and 7.5, respectively. The enzyme exhibited significant stability, with residual activity over 90% at 55 °C. The maltose was the only product generated during the starch hydrolysis. Moreover, the Bacillus cereus spH1 strain and its α-amylase were used in the treatment of effluents from the pasta industry. Germination index percentages of 143% and 139% were achieved when using the treated effluent with α-amylase and the strain, respectively. This work proposes the valorization of agro-industrial residues to improve enzyme production and to develop a green and sustainable approach that holds great promise for environmental and economic challenges.

Hollow Hierarchical Porous and Antihydrolytic Spherical Zeolitic Imidazolate Frameworks for Enzyme Encapsulation and Biocatalysis

The creation of a new metal-organic framework (MOF) with a hollow hierarchical porous structure has gained significant attention in the realm of enzyme immobilization. The present work employed a novel, facile, and effective combinatorial technique to synthesize modified MOF (N-PVP/HZIF-8) with a hierarchically porous core-shell structure, allowing for the preservation of the structural integrity of the encapsulated enzyme molecules. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, confocal laser scanning microscopy, and other characterization tools were used to fully explore the changes of morphological structure and surface properties in different stages of the preparation of immobilization enzyme CRL-N-PVP/HZIF-8, thus showing the superiority of N-PVP/HZIF-8 as an enzyme immobilization platform and the logic of the immobilization process on the carrier. Additionally, the maximum enzyme loading was 216.3 mg mL-1, the relative activity of CRL-N-PVP/HZIF-8 increased by 15 times compared with the CRL@ZIF-8 immobilized in situ, and exhibited quite good thermal, chemical, and operational stability. With a maximal conversion of 88.8%, CRL-N-PVP/HZIF-8 demonstrated good catalytic performance in the biosynthesis of phytosterol esters as a proof of concept. It is anticipated that this work will offer fresh concepts from several perspectives for the creation of MOF-based immobilized enzymes for biotechnological uses.

Challenges and prospects of microbial α-amylases for industrial application: a review

α-Amylases are essential biocatalysts representing a billion-dollar market with significant long-term global demand. They have varied applications ranging from detergent, textile, and food sectors such as bakery to, more recently, biofuel industries. Microbial α-amylases have distinct advantages over their plant and animal counterparts owing to generally good activities and better stability at temperature and pH extremes. With the scope of applications expanding, the need for new and improved α-amylases is ever-growing. However, scaling up microbial α-amylase technology from the laboratory to industry for practical applications is impeded by several issues, ranging from mass transfer limitations, low enzyme yields, and energy-intensive product recovery that adds to high production costs. This review highlights the major challenges and prospects for the production of microbial α-amylases, considering the various avenues of industrial bioprocessing such as culture-independent approaches, nutrient optimization, bioreactor operations with design improvements, and product down-streaming approaches towards developing efficient α-amylases with high activity and recyclability. Since the sequence and structure of the enzyme play a crucial role in modulating its functional properties, we have also tried to analyze the structural composition of microbial α-amylase as a guide to its thermodynamic properties to identify the areas that can be targeted for enhancing the catalytic activity and thermostability of the enzyme through varied immobilization or selective enzyme engineering approaches. Also, the utilization of inexpensive and renewable substrates for enzyme production to isolate α-amylases with non-conventional applications has been briefly discussed.

Preparation of water-insoluble lignin nanoparticles by deep eutectic solvent and its application as a versatile and biocompatible support for the immobilization of α-amylase

As one of the most abundant biopolymers, lignin is a widely available resource. However, its potential largely remains untapped, with most of it ending up as waste from industries like paper production, pulp processing, and bio-refining. The research undertaken in this study focused on the extraction of lignin from agroforestry waste using a deep eutectic solvent (DES) as a carrier for α-amylase immobilization, resulting in high stability and reusability. Several techniques, including Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and the Brunauer-Emmett-Teller (BET) method were employed to examine the structure and morphology of both the extracted lignin and the immobilized enzyme. The temperature used to recover lignin by DES would affect immobilization efficiency and enzyme loading by influencing its specific surface area, pore size, and volume distribution. Investigations using Nuclear Overhauser Effect Spectroscopy (NOESY) uncovered that the hydroxyl groups in G, H, and S units and the β-O-4 structure of lignin primarily serve as binding sites for enzyme molecules. Immobilized α-amylase demonstrated a higher pH and thermal stability level, with an optimal pH of 7.0 and temperature of 100 °C, compared to the free enzyme, which exhibited optimal activity at a pH of 6.5 and temperature of 90 °C. Importantly, immobilized α-amylase retained >80 % of its initial activity even after 28 days at room temperature, and it maintained 70 % of its activity after being reused 12 times. These findings strongly suggest that lignin derived from agroforestry residues holds promising potential as a future versatile immobilization material, a prospect integral to society's sustainable development.

Nanoassemblies of acetylcholinesterase and β-lactamase immobilized on magnetic nanoparticles as biosensors to detect pollutants in water

The use of enzymes immobilized on magnetic nanoparticles to detect contaminants in aqueous samples has gained interest, since it allows the magnetic control, concentration and reuse of the enzymes. In this work, the detection of trace amounts of organophosphate pesticides (chlorpyrifos) and antibiotics (penicillin G) in water was attained by developing a nanoassembly formed by either inorganic or biomimetic magnetic nanoparticles used as substrates to immobilize acetylcholinesterase (AChE) and β-lactamase (BL). Other than the substrate, the optimization of the nanoassembly was done by testing enzyme immobilization both through electrostatic interaction (also reinforced with glutaraldehyde) and covalent bonds (by carbodiimide chemistry). Temperature (25 °C), ionic strength (150 mM NaCl) and pH (7) were set to ensure enzymatic stability and to allow both the nanoparticles and the enzymes to present ionic charges that would allow electrostatic interaction. Under these conditions, the enzyme load on the nanoparticles was ⁓0.1 mg enzyme per mg nanoparticles, and the preserved activity after immobilization was 50-60% of the specific activity of the free enzyme, being covalent bonding the one which yielded better results. Covalent nanoassemblies could detect trace concentrations of pollutants down to 1.43 nM chlorpyrifos and 0.28 nM penicillin G. They even permitted the quantification of 14.3 μM chlorpyrifos and 2.8 μM penicillin G. Also, immobilization conferred higher stability to AChE (⁓94% activity after 20 days storage at 4 °C) and allowed to reuse the BL up to 12 cycles.

Emerging nanoparticle designs against bacterial infections

The rise of antibiotic resistance has caused the prevention and treatment of bacterial infections to be less effective. Therefore, researchers turn to nanomedicine for novel and effective antibacterial therapeutics. The effort resulted in the first-generation antibacterial nanoparticles featuring the ability to improve drug tolerability, circulation half-life, and efficacy. Toward developing the next-generation antibacterial nanoparticles, researchers have integrated design elements that emphasize physical, broad-spectrum, biomimetic, and antivirulence mechanisms. This review highlights four emerging antibacterial nanoparticle designs: inorganic antibacterial nanoparticles, responsive antibacterial nanocarriers, virulence nanoscavengers, and antivirulence nanovaccines. Examples in each design category are selected and reviewed, and their structure-function relationships are discussed. These emerging designs open the door to nontraditional antibacterial nanomedicines that rely on mechano-bactericidal, function-driven, nature-inspired, or virulence-targeting mechanisms to overcome antibiotic resistance for more effective antibacterial therapy. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Stability Enhancement of Aldehyde Dehydrogenase from Anoxybacillus geothermalis Strain D9 Immobilized onto Seplite LX120

Enzyme stability is regarded as an important criterion for an industrial biocatalyst. Aldehyde dehydrogenase (ALDH) from A. geothermalis strain D9 was previously reported to exhibit good thermostability. However, this enzyme is still not suited to use in harsh environments. In this current work, we aim to see the viability of ALDH in terms of stability when immobilized into Seplite LX120. The purified ALDH was successfully immobilized via physical adsorption at 4 h with 1.25 mg/mL enzyme loading. The immobilized ALDH exhibited improved stability compared to free ALDH as the optimum temperature increased up to 80 °C and was stable with temperatures ranging from 30 to 90 °C. It was also stable in broad pH, ranging from pH 4 to pH 12. Moreover, more than 50% of the immobilized ALDH activity was retained after being stored at 25 °C and 4 °C for 9 and 11 weeks, respectively. The reusability of immobilized ALDH is up to seven cycles. The corroboration of ALDH immobilized on the Seplite LX120 was verified via Fourier-transform infrared spectroscopy, scanning electron microscopy, and a reduction in the surface area. The improved features of immobilized ALDH, especially in enzyme stability, are important for future applications.

Designing multifunctional biocatalytic cascade system by multi-enzyme co-immobilization on biopolymers and nanostructured materials

In recent decades, enzyme-based biocatalytic systems have garnered increasing interest in industrial and applied research for catalysis and organic chemistry. Many enzymatic reactions have been applied to sustainable and environmentally friendly production processes, particularly in the pharmaceutical, fine chemicals, and flavor/fragrance industries. However, only a fraction of the enzymes available has been stepped up towards industrial-scale manufacturing due to low enzyme stability and challenging separation, recovery, and reusability. In this context, immobilization and co-immobilization in robust support materials have emerged as valuable strategies to overcome these inadequacies by facilitating repeated or continuous batch operations and downstream processes. To further reduce separations, it can be advantageous to use multiple enzymes at once in one pot. Enzyme co-immobilization enables biocatalytic synergism and reusability, boosting process efficiency and cost-effectiveness. Several studies on multi-enzyme immobilization and co-localization propose kinetic advantages of the enhanced turnover number for multiple enzymes. This review spotlights recent progress in developing versatile biocatalytic cascade systems by multi-enzyme co-immobilization on environmentally friendly biopolymers and nanostructured materials and their application scope in the chemical and biotechnological industries. After a succinct overview of carrier-based and carrier-free immobilization/co-immobilizations, co-immobilization of enzymes on a range of biopolymer and nanomaterials-based supports is thoroughly compiled with contemporary and state-of-the-art examples. This study provides a new horizon in developing effective and innovative multi-enzymatic systems with new possibilities to fully harness the adventure of biocatalytic systems.

The application of conventional or magnetic materials to support immobilization of amylolytic enzymes for batch and continuous operation of starch hydrolysis processes

In the production of ethanol, starches are converted into reducing sugars by liquefaction and saccharification processes, which mainly use soluble amylases. These processes are considered wasteful operations as operations to recover the enzymes are not practical economically so immobilizations of amylases to perform both processes appear to be a promising way to obtain more stable and reusable enzymes, to lower costs of enzymatic conversions, and to reduce enzymes degradation/contamination. Although many reviews on enzyme immobilizations are found, they only discuss immobilizations of α-amylase immobilizations on nanoparticles, but other amylases and support types are not well informed or poorly stated. As the knowledge of the developed supports for most amylase immobilizations being used in starch hydrolysis is important, a review describing about their preparations, characteristics, and applications is herewith presented. Based on the results, two major groups were discovered in the last 20 years, which include conventional and magnetic-based supports. Furthermore, several strategies for preparation and immobilization processes, which are more advanced than the previous generation, were also revealed. Although most of the starch hydrolysis processes were conducted in batches, opportunities to develop continuous reactors are offered. However, the continuous operations are difficult to be employed by magnetic-based amylases.

Biomimetic Nanomaterials: Diversity, Technology, and Biomedical Applications

Biomimetic nanomaterials (BNMs) are functional materials containing nanoscale components and having structural and technological similarities to natural (biogenic) prototypes. Despite the fact that biomimetic approaches in materials technology have been used since the second half of the 20th century, BNMs are still at the forefront of materials science. This review considered a general classification of such nanomaterials according to the characteristic features of natural analogues that are reproduced in the preparation of BNMs, including biomimetic structure, biomimetic synthesis, and the inclusion of biogenic components. BNMs containing magnetic, metal, or metal oxide organic and ceramic structural elements (including their various combinations) were considered separately. The BNMs under consideration were analyzed according to the declared areas of application, which included tooth and bone reconstruction, magnetic and infrared hyperthermia, chemo- and immunotherapy, the development of new drugs for targeted therapy, antibacterial and anti-inflammatory therapy, and bioimaging. In conclusion, the authors’ point of view is given about the prospects for the development of this scientific area associated with the use of native, genetically modified, or completely artificial phospholipid membranes, which allow combining the physicochemical and biological properties of biogenic prototypes with high biocompatibility, economic availability, and scalability of fully synthetic nanomaterials.

Metal Azolate Coordination Polymer-Enabled High Payload and Non-Destructive Enzyme Immobilization for Biocatalysis and Biosensing

The biomineralized metal-organic frameworks (MOFs) as protective layers help enhance the robustness of enzymes for biocatalysis. Despite great efforts, it is still challenging to develop a recyclable system with high payload and tolerance to harsh conditions. Here, we report a facile surface charge-independent strategy based on Zn-based coordination polymer (ZnCP) for nondestructive immobilization of enzyme. The ZnCP outcompetes most of the previously reported MOFs, in terms of high-payload enzyme packaging. Moreover, benefiting from the hydrophilicity of ZnCP, the entrapped enzymes (e.g., positive cytochrome C and negative glucose oxidase) maintained high catalytic activity, resembling their native counterparts. Notably, compared with ZIF-8, such enzyme-incorporated ZnCP (enzyme@ZnCP) is more tolerant to acidic pH, which imparts the enzyme with good recyclability, even in acid species-generated catalytic reactions, thus broadening its application in biocatalysis. The feasibility of enzyme@ZnCP for protein packaging, enzyme cascade catalysis, and biosensing was also validated. Altogether, enzyme@ZnCP demonstrates high enzyme payload, operational stability, and preservation of enzymatic activity, affording a versatile platform to accommodate bioactive enzyme for biocatalysis and biosensing.

Programming an Orthogonal Self-Assembling Protein Cascade Based on Reactive Peptide-Protein Pairs for In Vitro Enzymatic Trehalose Production

Trehalose is an important rare sugar that protects biomolecules against environmental stress. We herein introduce a dual enzyme cascade strategy that regulates the proportion of cargos and scaffolds, to maximize the benefits of enzyme immobilization. Based upon the self-assembling properties of the shell protein (EutM) from the ethanolamine utilization (Eut) bacterial microcompartment, we implemented the catalytic synthesis of trehalose from soluble starch with the coimmobilization of α-amylase and trehalose synthase. This strategy improved enzymatic cascade activity and operational stability. The cascade system enabled the efficient production of trehalose with a yield of ∼3.44 g/(L U), 1.5 times that of the free system. Moreover, its activity was maintained over 12 h, while the free system was almost completely inactivated after 4 h, demonstrating significantly enhanced thermostability. In conclusion, an attractive self-assembly coimmobilization platform was developed, which provides an effective biological process for the enzymatic synthesis of trehalose in vitro.

Facile Cellulase Immobilisation on Bioinspired Silica

Cellulases are enzymes with great potential for converting biomass to biofuels for sustainable energy. However, their commercial use is limited by their costs and low reusability. Therefore, the scientific and industrial sectors are focusing on finding better strategies to reuse enzymes and improve their performance. In this work, cellulase from Aspergillus niger was immobilised through in situ entrapment and adsorption on bio-inspired silica (BIS) supports. To the best of our knowledge, this green effect strategy has never been applied for cellulase into BIS. In situ entrapment was performed during support synthesis, applying a one-pot approach at mild conditions (room temperature, pH 7, and water solvent), while adsorption was performed after support formation. The loading efficiency was investigated on different immobilisation systems by Bradford assay and FTIR. Bovine serum albumin (BSA) was chosen as a control to optimize cellulase loading. The residual activity of cellulase was analysed by the dinitro salicylic acid (DNS) method. Activity of 90% was observed for the entrapped enzyme, while activity of ~55% was observed for the adsorbed enzyme. Moreover, the supported enzyme systems were recycled five times to evaluate their reuse potential. The thermal and pH stability tests suggested that both entrapment and adsorption strategies can increase enzyme activity. The results highlight that the entrapment in BIS is a potentially useful strategy to easily immobilise enzymes, while preserving their stability and recycle potential.

Hierarchical micro- and mesoporous ZIF-8 with core-shell superstructures using colloidal metal sulfates as soft templates for enzyme immobilization

Metal-organic frameworks (MOFs), with large specific surface area and tunable porosity, have gained lots of attention for immobilizing enzymes. However, the intrinsic open channels of most reported MOFs are generally smaller than 2 nm, which significantly prevents the passage of enzymes, and the diffusion efficiency of substrates and products. Here we report a new hierarchical micro-mesoporous zeolitic imidazolate framework-8 (ZIF-8) with core-shell superstructure (HZIF-8) using colloidal hydrated zinc sulfate (ZnSO₄·7H₂O) as a soft template for enzyme immobilization. The ZnSO₄·7H₂O forms an aggregation of colloids due to the self-conglobation effect in methanol, which affords a soft template for the formation of HZIF-8. Cytochrome C (Cyt C) was immobilized in interior of HZIF-8 through entrapment during the formation of HZIF-8. The resultant immobilized Cyt C (Cyt C@HZIF-8) exhibited 4-fold and 3-fold higher activity than free Cyt C and Cyt C encapsulated in conventional microporous ZIF-8 (Cyt C@ZIF-8), respectively. Meanwhile, the Km value of Cyt C@HZIF-8 significantly decreased due to the presence of mesopores compared with Cyt C@ZIF-8, indicating enhanced substrate affinity. After 7 cycles, Cyt C@HZIF-8 still maintained 70% of its initial activity whereas Cyt C@ZIF-8 only retained 10% of its initial activity. Moreover, the obtained HZIF-8 showed outstanding performance in co-immobilization of multi-enzyme for the detection of glucose.