Catalases as biocatalysts in technical applications: current state and perspectives

Catalase-associated immune responses in plant-microbe interactions: A review

Catalase, an enzyme central to maintaining redox balance and combating oxidative stress in plants, has emerged as a key player in plant defense mechanisms and interactions with microbes. This review article provides a comprehensive analysis of catalase-associated immune responses in plant-microbe interactions. It underscores the importance of catalase in plant defense mechanisms, highlights its influence on plant susceptibility to pathogens, and discusses its implications for understanding plant immunity and host-microbe dynamics. This review contributes to the growing body of knowledge on catalase-mediated immune responses and offers insights that can aid in the development of strategies for improved plant health and disease resistance.

Catalase immobilization: Current knowledge, key insights, applications, and future prospects - A review

Catalase (CAT), a ubiquitous enzyme in all oxygen-exposed organisms, effectively decomposes hydrogen peroxide (H2O2), a harmful by-product, into water and oxygen, mitigating oxidative stress and cellular damage, safeguarding cellular organelles and tissues. Therefore, CAT plays a crucial role in maintaining cellular homeostasis and function. Owing to its pivotal role, CAT has garnered considerable interest. However, many challenges arise when used, especially in multiple practical processes. "Immobilization", a widely-used technique, can help improve enzyme properties. CAT immobilization offers numerous advantages, including enhanced stability, reusability, and facilitated downstream processing. This review presents a comprehensive overview of CAT immobilization. It starts with discussing various immobilization mechanisms, support materials, advantages, drawbacks, and factors influencing the performance of immobilized CAT. Moreover, the review explores the application of the immobilized CAT in various industries and its prospects, highlighting its essential role in diverse fields and stimulating further research and investigation. Furthermore, the review highlights some of the world's leading companies in the field of the CAT industry and their substantial potential for economic contribution. This review aims to serve as a discerning, source of information for researchers seeking a comprehensive cutting-edge overview of this rapidly evolving field and have been overwhelmed by the size of publications.

A novel highly thermostable and stress resistant ROS scavenging metalloprotein from Paenibacillus

Reactive oxygen species (ROS) are unstable metabolites produced during cellular respiration that can cause extensive damage to the body. Here we report a unique structural metalloprotein called RSAPp for the first time, which exhibits robust ROS-scavenging activity, high thermostability, and stress resistance. RSAPp is a previously uncharacterized DUF2935 (domain of unknown function, accession number: cl12705) family protein from Paenibacillus, containing a highly conserved four-helix bundle with binding sites for variable-valence metal ions (Mn2+/Fe2+/Zn2+). Enzymatic characterization results indicated that RSAPp displays the functionality of three different antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). In particular, RSAPp exhibits a significant SOD-like activity that is remarkably effective in eliminating superoxide radicals (up to kcat/KM = 2.27 × 1011 mol-1 s-1), and maintains the catalytical active in a wide range of temperatures (25-100 °C) and pH (pH 2.0-9.0), as well as resistant to high temperature, alkali and acidic pH, and 55 different concentrations of detergent agents, chemical solvents, and inhibitors. These properties make RSAPp an attractive candidate for various industrial applications, including cosmetics, food, and pharmaceuticals.

Assessing the molluscicidal and biochemical activities of New-Fort®, an inorganic fertilizer against Theba pisana snails

Terrestrial snails are a significant issue in agricultural production worldwide. The use of nitrogen - phosphorus - potassium (NPK) based fertilizers played an important role in meeting the food demand throughout the world, so its effectiveness against land snails needs to be investigated. This study was conducted to evaluate toxic lethal effect of New-Fort®, an inorganic NPK based fertilizer, in the field for 3, 7 and 10 days and in the laboratory for 24, 48 and 72 h against Theba pisana snails. Also, the impact of its sub-lethal doses (1/10, 1/5, 1/4 and 1/2 of 48 h-LD50) on biochemical parameters were determined under laboratory conditions. The results showed that the snails percent reduction in the field were 21.4, 61.0 and 80.0 % after 10 days' application of quarter, half and one field rate and the values of LD50 in the laboratory were 4.94, 4.56 and 4.24 mg/g b.w at 24, 48 and 72 h, respectively. New-Fort® sub-lethal doses caused a significant inhibition in catalase, γ-glutamyl transferase and acetylcholinesterase activities. It also elicited a significant elevation in glutathione S-transferase activity post exposure to 1/10 and 1/5 of LD50, whereas an opposite effect was occurred after exposure to 1/4 and 1/2 of LD50. Lipid peroxidation level was reduced in snails treated with 1/10 and 1/5 of LD50, whereas it increased in 1/4 and 1/2 of LD50- treated snails. Moreover, a significant inhibition in alkaline phosphatase activity at all tested doses, with the exception of 1/2 of LD50 was observed. An increase in alanine aminotransferase and aspartate aminotransferase activities were occurred after all tested doses exposure. Our findings highlighted on how biochemical changes can be exploited to better understand the mechanisms underlying New-Fort® fertilizer toxicity against the land snail, T. pisana, as well as how to benefit from NPK fertilizers application in snail control.

Determination of Taxonomic Affiliation and Assessment of Biotechnological Potential of an Indigenous Strain of Gram-Positive Spore-Forming Bacteria

The search for new effective strains-producers of enzymes and biologically active substances for the development of new environmentally friendly plant protection products against phytopathogens is a very urgent task for the greening of agriculture. In our work, we used active strains of gram-positive spore-forming bacteria isolated from soil near the roadside zone of the Belgorod region to assess their antagonistic activity to phytopathogens and biotechnological potential. In the course of molecular genetic studies of the 16S rRNA gene of the isolated native strain, a complete similarity of the target with Bacillus subtilis was revealed. When studying morphological and cultural characteristics, it was determined that the cells of the target strain are rod-shaped, arranged singly or in pairs.The conditions of cultivation of the bacterium were revealed, which shows high growth in the composition of the medium containing 3% peptone for 20 hours, the specific increase in biomass exceeded 96%. When evaluating the antagonistic activity, it was revealed that the isolated strain suppresses the growth of cultures of Escherichia coli O157:H7, Aspergillus unguis VKM F-1754 and bacteria of the genus Ralstonia.

Biodegradation of environmental pollutants using catalase-based biocatalytic systems

The synergistic combination of biocatalysts and nanomaterials provides a new interface of a robust biocatalytic system that can effectively remediate environmental pollutants. Enzymes, such as catalase-based constructs, impart the desired candidature for catalytic transformation processes and are potential alternatives to replace conventional remediation strategies that have become laborious and somewhat inefficient. Furthermore, the controlled or uncontrolled discharge of various emerging pollutants (EPs) into water bodies is equally proportional to the fast-growing population and extensive urbanization. EPs affect the entire living being and continuously deteriorate the environmental system, directly or indirectly. The occurrence of EPs (even released after partial treatments, but still in bioactive forms) disturbs ecological integrity. Due to the ineffectiveness of in-practice traditional remediation processes, new and robust treatment measures as effective and sustainable remediation have become a meaningful goal. In this context, special attention has been shifted to engineering an enzyme (catalase)-based biodegradation system with immense prospects in environmental cleanup. The unique synergistic combination of nanomaterials (having multifunctional attributes) with enzymes of interest makes them a state-of-the-art interface that can further ameliorate bio-catalysis and biodegradation performance. This review covers current research and scientific advancement in developing and deploying catalase-based biocatalytic systems to mitigate several EPs from the environment matrices. The biocatalytic features of catalase, along with the mechanistic insight into H₂O₂ neutralization, several nano-based materials loaded with catalase, including nanoparticles (NPs), carbon nanotubes (CNTs), metal-organic frameworks (MOFs), polymeric-based composites, oxime-functionalized cryo-gel disks, electro-spun nanofibrous membranes, and other hybrid materials have also been discussed with suitable examples.

Role of C-terminal domain in a manganese-catalase from Geobacillus thermopakistaniensis

Catalases catalyze the decomposition of hydrogen peroxide into water and oxygen. We have characterized two manganese-catalases from Geobacillus thermopakistaniensis, Cat_Gt and Cat-II_Gt, which exhibited significant variation in their sequence, structure and properties. There was only 23% sequence identity between the two. The striking structural difference was the presence of an extended C-terminal domain in Cat_Gt. Molecular modelling and docking studies revealed that deletion of the C-terminal domain removes non-specific binding, which results in increased substrate affinity. To verify experimentally, a C-terminal truncated version of Cat_Gt, named as Cat_Gt-ΔC, was produced in Escherichia coli and effects of deletion were analyzed. There was no significant difference in optimal pH, optimal temperature and substrate specificity of Cat_Gt and Cat_Gt-ΔC. However, K_m value was reduced from 259 to 157 mM and Cat_Gt-ΔC exhibited ∼1.5-fold higher catalytic efficiency as compared to Cat_Gt. Furthermore, removal of the C-terminal domain converted the tetrameric nature to monomeric, and reduced the thermostability of the truncated protein. These results demonstrate that C-terminal domain of Cat_Gt might have little role in maintaining enzyme function but provides additional structural stability to the protein, which is a desired property for industrial applications.

From the Discovery of Extremozymes to an Enzymatic Product: Roadmap Based on Their Applications

With the advent of the industrial revolution, the use of toxic compounds has grown exponentially, leading to a considerable pollution of the environment. Consequently, the development of more environmentally conscious technologies is an urgent need. Industrial biocatalysis appears as one potential solution, where a higher demand for more robust enzymes aims to replace toxic chemical catalysts. To date, most of the commercially available enzymes are of mesophilic origin, displaying optimal activity in narrow ranges of temperature and pH (i.e., between 20°C and 45°C, neutral pH), limiting their actual application under industrial reaction settings, where they usually underperform, requiring larger quantities to compensate loss of activity. In order to obtain novel biocatalysts better suited for industrial conditions, an efficient solution is to take advantage of nature by searching and discovering enzymes from extremophiles. These microorganisms and their macromolecules have already adapted to thrive in environments that present extreme physicochemical conditions. Hence, extremophilic enzymes stand out for showing higher activity, stability, and robustness than their mesophilic counterparts, being able to carry out reactions at nonstandard conditions. In this brief research report we describe three examples to illustrate a stepwise strategy for the development and production of commercial extremozymes, including a catalase from an Antarctic psychrotolerant microorganism, a laccase from a thermoalkaliphilic bacterium isolated from a hot spring and an amine-transaminase from a thermophilic bacterium isolated from a geothermal site in Antarctica. We will also explore some of their interesting biotechnological applications and comparisons with commercial enzymes.

Extremophilic Oxidoreductases for the Industry: Five Successful Examples With Promising Projections

In a global context where the development of more environmentally conscious technologies is an urgent need, the demand for enzymes for industrial processes is on the rise. Compared to conventional chemical catalysts, the implementation of biocatalysis presents important benefits including higher selectivity, increased sustainability, reduction in operating costs and low toxicity, which translate into cleaner production processes, lower environmental impact as well as increasing the safety of the operating staff. Most of the currently available commercial enzymes are of mesophilic origin, displaying optimal activity in narrow ranges of conditions, which limits their actual application under industrial settings. For this reason, enzymes from extremophilic microorganisms stand out for their specific characteristics, showing higher stability, activity and robustness than their mesophilic counterparts. Their unique structural adaptations allow them to resist denaturation at high temperatures and salinity, remain active at low temperatures, function at extremely acidic or alkaline pHs and high pressure, and participate in reactions in organic solvents and unconventional media. Because of the increased interest to replace chemical catalysts, the global enzymes market is continuously growing, with hydrolases being the most prominent type of enzymes, holding approximately two-third share, followed by oxidoreductases. The latter enzymes catalyze electron transfer reactions and are one of the most abundant classes of enzymes within cells. They hold a significant industrial potential, especially those from extremophiles, as their applications are multifold. In this article we aim to review the properties and potential applications of five different types of extremophilic oxidoreductases: laccases, hydrogenases, glutamate dehydrogenases (GDHs), catalases and superoxide dismutases (SODs). This selection is based on the extensive experience of our research group working with these particular enzymes, from the discovery up to the development of commercial products available for the research market.

Catalase biosensor based on the PAni/cMWCNT support for peroxide sensing

Polymeric-based composites can contribute to enhancing the detection, stability, and performance of enzymatic biosensors, due to their high structural stability, conductivity, and biocompatibility. This work presents the fabrication of a nanocomposite of polyaniline (PAni)/gold nanoparticles (AuNP)/carboxylated multiwalled carbon nanotubes (cMWCNT) as functional support for covalently linked catalase (CAT) enzyme. PAni was electropolymerized on a screen-printed carbon electrode (SPCE) and decorated with AuNP to improve charge transfer properties. CAT was bonded through amide formation using the carboxylic groups of cMWCNT, resulting in PAni/AuNP/cMWCNT/CAT biosensor. The structural and electroactive characteristics of the nanocomposite were studied by SEM, FT-IR, and cyclic voltammetry. The optimal performance was achieved after CAT immobilization over PAni/AuNP/cMWCNT/nanocomposite, showing improved analytical features such as a fast amperometric response of 1.28 s, a wide detection range from 0.01 to 6.8 mM, a correlation coefficient (R 2) of 0.9921, a low detection limit of 2.34 µM, and an average recovery rate of 99.6% when evaluated in milk samples. Additionally, the bioelectrode showed excellent selectivity and retained bioactivity after 30 days of storage. Such remarkable performance proved the synergistic effects of both the high surface area of the cMWCNT and AuNP and the inherent PAni electroactivity, yielding direct electron transfer from CAT.

Biocatalytic oxidation of fatty alcohols into aldehydes for the flavors and fragrances industry

From Egyptian mummies to the Chanel n°5 perfume, fatty aldehydes have long been used and keep impacting our senses in a wide range of foods, beverages and perfumes. Natural sources of fatty aldehydes are threatened by qualitative and quantitative variability while traditional chemical routes are insufficient to answer the society shift toward more sustainable and natural products. The production of fatty aldehydes using biotechnologies is therefore the most promising alternative for the flavors and fragrances industry. In this review, after drawing the portrait of the origin and characteristics of fragrant fatty aldehydes, we present the three main classes of enzymes that catalyze the reaction of fatty alcohols oxidation into aldehydes, namely alcohol dehydrogenases, flavin-dependent alcohol oxidases and copper radical alcohol oxidases. The constraints, challenges and opportunities to implement these oxidative enzymes in the flavors and fragrances industry are then discussed. By setting the scene on the biocatalytic production of fatty aldehydes, and providing a critical assessment of its potential, we expect this review to contribute to the development of biotechnology-based solutions in the flavors and fragrances industry.

Catalase-Loaded Silica Nanoparticles Formulated via Direct Surface Modification as Potential Oxygen Generators for Hypoxia Relief

Enzymes are biological catalysts that have many potential industrial and biomedical applications. However, the widespread use of enzymes in the industry has been limited by their instability and poor recovery. In biomedical applications, systemic administration of enzymes has faced two main challenges: limited bioactivity mostly due to rapid degradation by proteases and immunogenic activity, since most enzymes are from nonhuman sources. Herein, we propose a robust enzyme-encapsulation strategy to mitigate these limitations. Catalase (CAT) was encapsulated in nanoporous silica nanoparticles (CAT-SiNPs) by first chemically modifying the enzyme surface with a silica precursor, followed by silica growth and finally poly(ethylene glycol) (PEG) conjugation. The formulation was carried out in mild aqueous conditions and yielded nanoparticles (NPs) with a mean diameter of 230 ± 10 nm and a concentration of 1.3 ± 0.8 × 10¹² NPs/mL. CAT-SiNPs demonstrated high enzyme activity, optimal protection from proteolysis by proteinase K and trypsin, and excellent stability over time. In addition, a new electrochemical assay was developed to measure CAT activity in a rapid, simple, and accurate manner without interference from chromophore usually present in biological samples. Concentrations of 2.5 × 10¹⁰ to 80 × 10¹⁰ CAT-SiNPs/mL not only proved to be nontoxic in cell cultures using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay but also conferred cell protection when cells were exposed to 1 mM hydrogen peroxide (H₂O₂). Finally, the ability of CAT-SiNPs to release oxygen (O₂) when exposed to H₂O₂ was demonstrated in vivo using a rat model. Following the direct injection of CAT-SiNPs in the left kidney, partial pressure of oxygen (pO₂) increased by more than 30 mmHg compared to the contralateral control kidney during the systemic infusion of safe levels of H₂O₂. This pilot study highlights the potential of CAT-SiNPs to generate O₂ to relieve hypoxia in tissues and potentially sensitize tumors against radiation therapy.

Electrocatalysis by Heme Enzymes—Applications in Biosensing

Heme proteins take part in a number of fundamental biological processes, including oxygen transport and storage, electron transfer, catalysis and signal transduction. The redox chemistry of the heme iron and the biochemical diversity of heme proteins have led to the development of a plethora of biotechnological applications. This work focuses on biosensing devices based on heme proteins, in which they are electronically coupled to an electrode and their activity is determined through the measurement of catalytic currents in the presence of substrate, i.e., the target analyte of the biosensor. After an overview of the main concepts of amperometric biosensors, we address transduction schemes, protein immobilization strategies, and the performance of devices that explore reactions of heme biocatalysts, including peroxidase, cytochrome P450, catalase, nitrite reductase, cytochrome c oxidase, cytochrome c and derived microperoxidases, hemoglobin, and myoglobin. We further discuss how structural information about immobilized heme proteins can lead to rational design of biosensing devices, ensuring insights into their efficiency and long-term stability.

Co-Immobilization and Co-Localization of Oxidases and Catalases: Catalase from Bordetella Pertussis Fused with the Zbasic Domain

Oxidases catalyze selective oxidations by using molecular oxygen as an oxidizing agent. This process promotes the release of hydrogen peroxide, an undesirable byproduct. The instantaneous elimination of hydrogen peroxide can be achieved by co-immobilization and co-localization of the oxidase and an auxiliary catalase inside the porous structure of solid support. In this paper, we proposed that catalase from Bordetella pertussis fused with a small domain (Zbasic) as an excellent auxiliary enzyme. The enzyme had a specific activity of 23 U/mg, and this was almost six-fold higher than the one of the commercially available catalases from bovine liver. The Zbasic domain was fused to the four amino termini of this tetrameric enzyme. Two domains were close in one hemisphere of the enzyme molecule, and the other two were close in the opposite hemisphere. In this way, each hemisphere contained 24 residues with a positive charge that was very useful for the purification of the enzyme via cationic exchange chromatography. In addition to this, each hemisphere contained 10 Lys residues that were very useful for a rapid and intense multipoint covalent attachment on highly activated glyoxyl supports. In fact, 190 mg of the enzyme was immobilized on one gram of glyoxyl-10% agarose gel. The ratio catalase/oxidase able to instantaneously remove more than 93% of the released hydrogen peroxide was around 5–6 mg of catalase per mg of oxidase. Thirty milligrams of amine oxidase and 160 mg of catalase were co-immobilized and co-localized per gram of glyoxyl-agarose 10BCL (10% beads cross-linked) support. This biocatalyst eliminated biogenic amines (putrescine) 80-fold faster than a biocatalyst of the same oxidase co-localized with the commercial catalase from bovine liver.

New Method of Determining Kinetic Parameters for Decomposition of Hydrogen Peroxide by Catalase

The presented study investigates the kinetic properties of catalase during hydrogen peroxide decomposition reaction. A novel and simple method is hereby proposed for the determination of the enzyme deactivation rate constant (kd) and the decomposition of H2O2 reaction rate constant (kr). Available methods allow the kd constant to be determined only based on previously experimentally determined kr. The presented method differs from the conventional procedure. Known initial and final concentrations of hydrogen peroxide enable determination of both constants at the same time based on data from only one experiment. The correctness of the new method proposed here in determining the reaction rate constant was checked by comparing the obtained constant values with the calculated values according to the commonly used Aebi method. The method was used to analyze in detail the effect of pH (3–10) and temperature (10–45 °C) of the reaction medium on kinetic constants. The value of the constant kd increases together with the value of pH and temperature. In addition, the activation energy for decomposition reaction and deactivation reaction was found to be Er = 14 kJ mol−1 and Ed = 56.8 kJ mol−1 respectively.

Isolation of a Psychrotolerant and UV-C-Resistant Bacterium from Elephant Island, Antarctica with a Highly Thermoactive and Thermostable Catalase

Microorganisms present in Antarctica have to deal not only with cold temperatures but also with other environmental conditions, such as high UV radiation, that trigger the generation of reactive oxygen species. Therefore, Antarctic microorganisms must have an important antioxidant defense system to prevent oxidative damage. One of these defenses are antioxidant enzymes, such as catalase, which is involved in the detoxification of hydrogen peroxide produced under oxidative conditions. Here, we reported the isolation and partial characterization of an Antarctic bacterium belonging to the Serratia genus that was resistant to UV-C radiation and well-adapted to cold temperatures. This microorganism, denominated strain I1P, was efficient at decreasing reactive oxygen species levels produced after UV-C irradiation. Genomic and activity assays suggested that the enzymatic antioxidant defense mechanisms of strain I1P, especially its catalase enzyme, may confer UV resistance. This catalase was active in a wide range of temperatures (20-70 °C), showing optimal activity at 50 °C (at pH 7.0), a remarkable finding considering its psychrotolerant origin. In addition, this enzyme was thermostable, retaining around 60% of its activity after 6 h of incubation at 50 °C. The antioxidant defense systems of strain I1P, including its surprisingly thermoactive and thermostable catalase enzyme, make this microorganism a good source of biocompounds with potential biotechnological applications.

Facile generation of a biotechnologically-relevant catalase showcases the efficacy of a blue-green algal biomass as a suitable bioresource for protein overproduction

Here, we show the utility of a cyanobacterial biomass for overproduction and easy downstream processing of the thermostable protein KatB (a Mn-catalase). The nitrogen-fixing blue-green alga, Anabaena, was bioengineered to overexpress the KatB protein (An-KatB). Interestingly, pure An-KatB could be isolated from Anabaena by a simple physical process, obviating the need of expensive resins or chromatographic steps. An-KatB was an efficient H₂O₂-detoxifying protein that retained all the properties of Mn-catalases. Surprisingly, the purified An-KatB showed improved characteristics than the corresponding KatB (Ec-KatB) protein purified after over-expression in E. coli. An-KatB was unaffected by exposure to high temperature (85 °C), whereas a commercially procured heme-catalase showed an appreciable drop in activity beyond 50 °C. These data convincingly demonstrate the utility of Anabaena as a competent microbial bioresource for overproduction of proteins and further highlight the advantage of An-KatB over heme-catalases in bioprocesses where H₂O₂ is to be decomposed at elevated temperatures.

Design of stable magnetic hybrid nanoparticles of Si-entrapped HRP

Hybrid and composite nanoparticles represent an attractive material for enzyme integration due to possible synergic advantages of the structural builders in the properties of the nanobiocatalyst. In this study, we report the synthesis of a new stable hybrid nanobiocatalyst formed by biomimetic silica (Si) nanoparticles entrapping both Horseradish Peroxidase (HRP) (EC 1.11.1.7) and magnetic nanoparticles (MNPs). We have demonstrated that tailoring of the synthetic reagents and post immobilization treatments greatly impacted physical and biocatalytic properties such as an unprecedented ~280 times increase in the half-life time in thermal stability experiments. The optimized nanohybrid biocatalyst that showed superparamagnetic behaviour, was effective in the batch conversion of indole-3-acetic acid, a prodrug used in Direct Enzyme Prodrug Therapy (DEPT). Our system, that was not cytotoxic per se, showed enhanced cytotoxic activity in the presence of the prodrug towards HCT-116, a colorectal cancer cell line. The strategy developed proved to be effective in obtaining a stabilized nanobiocatalyst combining three different organic/inorganic materials with potential in DEPT and other biotechnological applications.

Encapsulated catalase from Serratia genus for H2O2 decomposition in food applications

The recombinant catalase isolated from a psychrotolerant microorganism belonging to Serratia genus exhibits a high activity in a wide range of pH. Due to a great catalytic potential in operational conditions, it can be used in various industrial applications whereby it acts as a hydrogen peroxide scavenger. To reduce the cost of biocatalyst the enzyme encapsulation into a hydrogel structure was proposed. The obtained results showed a high activity of encapsulated catalase in acidic conditions (pH in range 4.4 - 6.6) and at low temperatures (6-15°C). Moreover, immobilized catalase exhibited a high stability in natural media, especially in milk. Its activity during peroxide decomposition in milk, the possibility of re-using, as well as the fixed bed reactor performance confirmed wide application possibilities. High values of enzyme and substrate concentrations led to the beads burst due to rapid oxygen diffusion from the capsules, thus they are limited.

Recent advances in enzymatic oxidation of alcohols

Enzymatic alcohol oxidation plays an important role in chemical synthesis. In the past two years, new alcohol oxidation enzymes were developed through genome-mining and protein engineering, such as new copper radical oxidases with broad substrate scope, alcohol dehydrogenases with altered cofactor preference and a flavin-dependent alcohol oxidase with enhanced oxygen coupling. New cofactor recycling methods were reported for alcohol dehydrogenase-catalyzed oxidation with photocatalyst and coupled glutaredoxin-glutathione reductase as promising examples. Different alcohol oxidation systems were used for the oxidation of primary and secondary alcohols, especially in the cascade conversion of alcohols to lactones, lactams, chiral amines, chiral alcohols and hydroxyketones. Among them, biocatalyst with low enantioselectivity demonstrated an interesting feature for complete conversion of racemic secondary alcohols through non-enantioselective oxidation.

Oriented Coimmobilization of Oxidase and Catalase on Tailor-Made Ordered Mesoporous Silica

Mesoporous silica materials are promising carriers for enzyme immobilization in heterogeneous biocatalysis applications. By tailoring their pore structural framework, these materials are designable for appropriate enzyme binding capacity and internal diffusivity. To supply O₂ efficiently to solid-supported immobilized enzymes represents a core problem of heterogeneously catalyzed oxidative biotransformations. In this study, therefore, we synthesized and compared three internally well-ordered and two amorphous silica materials as enzyme carriers, each of those with pore sizes of ≥10 nm, to enable the coimmobilization of d-amino-acid oxidase (79 kDa) and catalase (217 kDa). Both enzymes were fused to the silica-binding module Z_basic2 to facilitate their selective and oriented immobilization directly from crude protein mixtures on native silica materials. Analyzing the effects of varied pore architecture and internal surface area on the performance of the immobilized bienzymatic system, we showed that a uniform pore structural framework was beneficial for enzyme loading (≥70 mg protein/g carrier), immobilization yield (≥90%), surface and pore volume filling without hindered adsorption, and catalytic effectiveness (≥60%) of the coimmobilizate. Using the best carrier LP-SBA-15, we obtained a solid oxidase-catalase preparation with an activity of 2000 μmol/(min g_material) that was recyclable and stable during oxidation of d-methionine. These results affirm a strategy of optimizing immobilized O₂-dependent enzymes via tunable internal structuring of the silica material used as carrier. They thus make a significant advance toward the molecular design of heterogeneous oxidation biocatalysts on mesoporous silica supports.

Microbial response to environmental stresses: from fundamental mechanisms to practical applications

Environmental stresses are usually active during the process of microbial fermentation and have significant influence on microbial physiology. Microorganisms have developed a series of strategies to resist environmental stresses. For instance, they maintain the integrity and fluidity of cell membranes by modulating their structure and composition, and the permeability and activities of transporters are adjusted to control nutrient transport and ion exchange. Certain transcription factors are activated to enhance gene expression, and specific signal transduction pathways are induced to adapt to environmental changes. Besides, microbial cells also have well-established repair mechanisms that protect their macromolecules against damages inflicted by environmental stresses. Oxidative, hyperosmotic, thermal, acid, and organic solvent stresses are significant in microbial fermentation. In this review, we summarize the modus operandi by which these stresses act on cellular components, as well as the corresponding resistance mechanisms developed by microorganisms. Then, we discuss the applications of these stress resistance mechanisms on the production of industrially important chemicals. Finally, we prospect the application of systems biology and synthetic biology in the identification of resistant mechanisms and improvement of metabolic robustness of microorganisms in environmental stresses.

Hydrogen Peroxide-Resistant CotA and YjqC of Bacillus altitudinis Spores Are a Promising Biocatalyst for Catalyzing Reduction of Sinapic Acid and Sinapine in Rapeseed Meal

For the more efficient detoxification of phenolic compounds, a promising avenue would be to develop a multi-enzyme biocatalyst comprising peroxidase, laccase and other oxidases. However, the development of this multi-enzyme biocatalyst is limited by the vulnerability of fungal laccases and peroxidases to hydrogen peroxide (H2O2)-induced inactivation. Therefore, H2O2-resistant peroxidase and laccase should be exploited. In this study, H2O2-stable CotA and YjqC were isolated from the outer coat of Bacillus altitudinis SYBC hb4 spores. In addition to the thermal and alkali stability of catalytic activity, CotA also exhibited a much higher H2O2 tolerance than fungal laccases from Trametes versicolor and Trametes trogii. YjqC is a sporulation-related manganese (Mn) catalase with striking peroxidase activity for sinapic acid (SA) and sinapine (SNP). In contrast to the typical heme-containing peroxidases, the peroxidase activity of YjqC was also highly resistant to inhibition by H2O2 and heat. CotA could also catalyze the oxidation of SA and SNP. CotA had a much higher affinity for SA than B. subtilis CotA. CotA and YjqC rendered from B. altitudinis spores had promising laccase and peroxidase activities for SA and SNP. Specifically, the B. altitudinis spores could be regarded as a multi-enzyme biocatalyst composed of CotA and YjqC. The B. altitudinis spores were efficient for catalyzing the degradation of SA and SNP in rapeseed meal. Moreover, efficiency of the spore-catalyzed degradation of SA and SNP was greatly improved by the presence of 15 mM H2O2. This effect was largely attributed to synergistic biocatalysis of the H2O2-resistant CotA and YjqC toward SA and SNP.

Heterologous expression and characterization of a new heme-catalase in Bacillus subtilis 168

Reactive oxygen species (ROS) is an inherent consequence to all aerobically living organisms that might lead to the cells being lethal and susceptible to oxidative stress. Bacillus pumilus is characterized by high-resistance oxidative stress that stimulated our interest to investigate the heterologous expression and characterization of heme-catalase as potential biocatalyst. Results indicated that recombinant enzyme significantly exhibited the high catalytic activity of 55,784 U/mg expressed in Bacillus subtilis 168 and 98.097 µmol/min/mg peroxidatic activity, the apparent K  m of catalytic activity was 59.6 ± 13 mM with higher turnover rate (K  cat = 322.651 × 103 s−1). The pH dependence of catalatic and peroxidatic activity was pH 7.0 and pH 4.5 respectively with temperature dependence of 40 °C and the recombinant heme-catalase exhibited a strong Fe2+ preference. It was further revealed that catalase KatX2 improved the resistance oxidative stress of B. subtilis. These findings suggest that this B. pumilus heme-catalase can be considered among the industrially relevant biocatalysts due to its exceptional catalytic rate and high stability and it can be a potential candidate for the improvement of oxidative resistance of industrially produced strains.

Performance comparison of immobilized enzyme on the titanate nanotube surfaces modified by poly(dopamine) and poly(norepinephrine)

In this study, the performance of immobilized enzyme on the titanate nanotube surfaces modified by poly(dopamine) and poly(norepinephrine) are specifically compared.