Immobilization of recombinant Escherichia coli cells expressing glucose isomerase using modified diatomite as a carrier for effective production of high fructose corn syrup in packed bed reactor

Xylose isomerase: From fundamental research to applied enzyme technology

Xylose isomerases (XI, EC 5.3.1.5) are key enzymes for the metabolism of pentoses by microorganisms. The importance of XIs goes beyond academic biochemical research and the catalysis of aldo-ketose conversion by XIs is among the most successful examples of industrial enzyme technology in a market that generates multibillion dollar annual revenues. Here we present an in-depth review of how structural information has contributed to the current understanding of XI catalysis, and discuss topics related to the ongoing efforts to elucidate key aspects of the catalytic mechanism. An overview of XI immobilization is also provided that illustrates how the discoveries in basic enzyme technology research can generate opportunities for novel uses of XI, and we review not only historical aspects but also more recent applications in HFCS, biofuels and other applications. The systems biology revolution will impact all aspects of XI research and application, and we finalize by reviewing the contemporary efforts of metabolic and protein engineering using XI and the future roles of the enzyme in the expanding bioeconomy.

Keratin-reinforced encapsulation of whole cells expressing glucose isomerase: Development of robust and reusable biocatalyst microbeads

Glucose isomerase (GI) is crucial in high-fructose corn syrup production. This study introduces a novel approach to enhance GI stability and reusability through whole-cell encapsulation of Streptomyces olivochromogenes PTCC 1457 in hybrid microbeads, utilizing keratin as a multifunctional stabilizer and cross-linker. Optimal bead formation was achieved using 2 % alginate, 2-3 % CaCl2, and 2.5 % keratin at pH 7.0 and 37-40 °C. Keratin played a vital role in forming a robust and flexible matrix. Immobilization in keratin-alginate-biomass beads maintained GI activity (655 GIU·g-1) comparable to free enzyme (650 GIU·g-1), while silicate incorporation reduced activity to 234 GIU·g-1. The immobilized enzyme exhibited enhanced stability over a wider pH (6-9) and temperature (4-60 °C) range compared to the free enzyme. Importantly, the immobilized GI maintained 80 % of its initial activity after 20 reaction cycles. Thermogravimetric analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, and tensile testing confirmed the formation of hybrid beads with improved thermal and mechanical stability. This novel immobilization strategy, leveraging keratin's unique properties, offers a promising approach for enhancing GI stability, reusability, and storage longevity, potentially improving its industrial applicability in high-fructose corn syrup production.

An Overview of Microorganisms Immobilized in a Gel Structure for the Production of Precursors, Antibiotics, and Valuable Products

Using free microorganisms for industrial processes has some limitations, such as the extensive consumption of substrates for growth, significant sensitivity to the microenvironment, and the necessity of separation from the product and, therefore, the cyclic process. It is widely acknowledged that confining or immobilizing cells in a matrix or support structure enhances enzyme stability, facilitates recycling, enhances rheological resilience, lowers bioprocess costs, and serves as a fundamental prerequisite for large-scale applications. This report summarizes the various cell immobilization methods, including several synthetic (polyvinylalcohol, polyethylenimine, polyacrylates, and Eudragit) and natural (gelatin, chitosan, alginate, cellulose, agar-agar, carboxymethylcellulose, and other polysaccharides) polymeric materials in the form of thin films, hydrogels, and cryogels. Advancements in the production of well-known antibiotics like penicillin and cephalosporin by various strains were discussed. Additionally, we highlighted cutting-edge research related to strain producers of peptide-based antibiotics (polymyxin B, Subtilin, Tyrothricin, varigomycin, gramicidin S, friulimicin, and bacteriocin), glusoseamines, and polyene derivatives. Crosslinking agents, especially covalent linkers, significantly affect the activity and stability of biocatalysts (penicillin G acylase, penicillinase, deacetoxycephalosporinase, L-asparaginase, β-glucosidase, Xylanase, and urease). The molecular weight of polymers is an important parameter influencing oxygen and nutrient diffusion, the kinetics of hydrogel formation, rigidity, rheology, elastic moduli, and other mechanical properties crucial for long-term utilization. A comparison of stability and enzymatic activity between immobilized enzymes and their free native counterparts was explored. The discussion was not limited to recent advancements in the biopharmaceutical field, such as microorganism or enzyme immobilization, but also extended to methods used in sensor and biosensor applications. In this study, we present data on the advantages of cell and enzyme immobilization over microorganism (bacteria and fungi) suspension states to produce various bioproducts and metabolites-such as antibiotics, enzymes, and precursors-and determine the efficiency of immobilization processes and the optimal conditions and process parameters to maximize the yield of the target products.

Enhanced High-Fructose Corn Syrup Production: Immobilizing Serratia marcescens Glucose Isomerase on MOF (Co)-525 Reduces Co2+ Dependency in Glucose Isomerization to Fructose

The escalating demand for processed foods has led to the widespread industrial use of glucose isomerase (GI) for high-fructose corn syrup (HFCS) production. This reliance on GIs necessitates continual Co2+ supplementation to sustain high catalytic activity across multiple reaction cycles. In this study, Serratia marcescens GI (SmGI) was immobilized onto surfaces of the metal-organic framework (MOF) material MOF (Co)-525 to generate MOF (Co)-525-GI for use in catalyzing glucose isomerization to generate fructose. Examination of MOF (Co)-525-GI structural features using scanning electron microscopy-energy dispersive spectroscopy, Fourier-transform infrared spectroscopy, and ultraviolet spectroscopy revealed no structural changes after SmGI immobilization and the addition of Co2+. Notably, MOF (Co)-525-GI exhibited optimal catalytic activity at pH 7.5 and 70 °C, with a maximum reaction rate (Vmax) of 37.24 ± 1.91 μM/min and Km value of 46.25 ± 3.03 mM observed. Remarkably, immobilized SmGI exhibited sustained high catalytic activity over multiple cycles without continuous Co2+ infusion, retaining its molecular structure and 96.38% of its initial activity after six reaction cycles. These results underscore the potential of MOF (Co)-525-GI to serve as a safer and more efficient immobilized enzyme technology compared to traditional GI-based food-processing technologies.

Isomerase and epimerase: overview and practical application in production of functional sugars

The biosynthesis of functional sugars has gained significant attention due to their potential health benefits and increasing demand in the food industry. Enzymatic synthesis has emerged as a promising approach, offering high catalytic efficiency, chemoselectivity, and stereoselectivity. However, challenges such as poor thermostability, low catalytic efficiency, and food safety concerns have limited the commercial production of functional sugars. Protein engineering, including directed evolution and rational design, has shown promise in overcoming these barriers and improving biocatalysts for large-scale production. Furthermore, enzyme immobilization has proven effective in reducing costs and facilitating the production of functional sugars. To ensure food safety, the use of food-grade expression systems has been explored. However, downstream technologies, including separation, purification, and crystallization, still pose challenges in terms of efficiency and cost-effectiveness. Addressing these challenges is crucial to optimize the overall production process. Despite the obstacles, the future outlook for functional sugars is promising, driven by increasing awareness of their health benefits and continuous technological advancements. With further research and technological breakthroughs, industrial-scale production of functional sugars through biosynthesis will become a reality, leading to their widespread incorporation in various industries and products.

Microbial glucoamylases: structural and functional properties and biotechnological uses

Glucoamylases (GAs) are one of the principal groups of enzymes involved in starch hydrolysis and belong to the glycosylhydrolase family. They are classified as exo-amylases due to their ability to hydrolyze α-1,4 glycosidic bonds from the non-reducing end of starch, maltooligosaccharides, and related substrates, releasing β-D-glucose. Structurally, GAs possess a characteristic catalytic domain (CD) with an (α/α)6 fold and exhibit five conserved regions within this domain. The CD may or may not be linked to a non-catalytic domain with variable functions depending on its origin. GAs are versatile enzymes with diverse applications in food, biofuel, bioplastic and other chemical industries. Although fungal GAs are commonly employed for these purposes, they have limitations such as their low thermostability and an acidic pH requirement. Alternatively, GAs derived from prokaryotic organisms are a good option to save costs as they exhibit greater thermostability compared to fungal GAs. Moreover, a group of cold-adapted GAs from psychrophilic organisms demonstrates intriguing properties that make them suitable for application in various industries. This review provides a comprehensive overview of the structural and sequential properties as well as biotechnological applications of GAs in different industrial processes.

Fabrication of a Floatable Micron-Sized Enzyme Device Using Diatom Frustules

Immobilization of enzymes has been widely reported due to their reusability, thermal stability, better storage abilities, and so on. However, there are still problems that immobilized enzymes do not have free movements to react to substrates during enzyme reactions and their enzyme activity becomes weak. Moreover, when only the porosity of support materials is focused, some problems such as enzyme distortion can negatively affect the enzyme activity. Being a solution to these problems, a new function "floatability" of enzyme devices has been discussed. A "floatable" micron-sized enzyme device was fabricated to enhance the free movements of immobilized enzymes. Diatom frustules, natural nanoporous biosilica, were used to attach papain enzyme molecules. The floatability of the frustules, evaluated by macroscopic and microscopic methods, was significantly better than that of four other SiO2 materials, such as diatomaceous earth (DE), which have been widely used to fabricate micron-sized enzyme devices. The frustules were fully suspended at 30 °C for 1 h without stirring, although they settled at room temperature. When enzyme assays were performed at room temperature, 37, and 60 °C with or without external stirring, the proposed frustule device showed the highest enzyme activity under all conditions among papain devices similarly prepared using other SiO2 materials. It was confirmed by the free papain experiments that the frustule device was active enough for enzyme reactions. Our data indicated that the high floatability of the reusable frustule device, and its large surface area, is effective in maximizing enzyme activity due to the high probability to react to substrates.

Study of the Effects on Mn, Pb, and Zn Solidification in Soil by a Mixed Curing Agent of Modified Diatomite

In order to improve the application scale of diatomite in the remediation of heavy metal-contaminated soil in non-ferrous metal mining areas, the preparation of the modified diatomite-combined curing agent and its stabilizing effect on manganese (Mn), lead (Pb), and zinc (Zn) were systematically studied in non-ferrous metal tailing soil in this paper. The results showed that compared with that in natural diatomite (DE), the contents of available Mn in soil treated by acid- and alkali-modified diatomite samples (C-D and Na-D) were 18.82 and 25.93% lower, respectively, and the content of available Zn in Na-D was significantly lower, 6.71%, than that in DE. Further research showed that modified diatomite combined with quicklime (CaO) and hydroxyapatite (HAP) could significantly improve the solidification effect of soil heavy metals. Compared with that in single modified diatomite, the contents of available Mn, Pb, and Zn in the mixed curing agent-treated soil decreased by 23.59-46.32, 5.88-47.93, and 5.37-10.68%, respectively. The final pot test showed that the mixed curing agent of modified diatomite had no significant effect on the growth of plants, but it could reduce the Mn, Pb, and Zn accumulation in the upper and lower parts of plants, which is because the acid-soluble and reducible heavy metals in soil transform into an oxidizable and residual state, which reduces the mobility of heavy metals.

Enhanced catalytic efficiency and thermostability of glucose isomerase from Thermoanaerobacter ethanolicus via site-directed mutagenesis

Glucose isomerase (GI) is a key enzyme in the preparation of high fructose corn syrup (HFCS). In this study, a mutant TEGI-M-L38 M/V137 L (TEGI-M2) of glucose isomerase (TEGI-M) originated from Thermoanaerobacter ethanalicus CCSD1 was obtained by site-directed mutagenesis. The TEGI-M2 showed an optimal activity at 85 ℃ and pH 6.5 with the divalent cations Co²⁺ and Mg²⁺. The structural differences between TEGI-M and TEGI-M2 were investigated based on the homology modeling and molecular docking, to elucidate the mechanism of improvement in the enzymatic properties. Compared with the original enzyme, the TEGI-M2 showed a 2.0-fold increased enzyme activity and a decreased K_m from 234.2 mM to 85.9 mM. Finally, the application of mutant TEGI-M2 in HFCS one-step biosynthesis was attempted, resulting in a d-fructose yield of 67.3 %, which was 14.3 % higher than that of TEGI-M. This improved catalytic performance of TEGI-M2 was of great importance for the industrial preparation of d-fructose in one-step process.