Heterologous codA Gene Expression Leads to Mitigation of Salt Stress Effects and Modulates Developmental Processes

Transgenic tobacco plants overexpressing the choline oxidase gene from A. globiformis showed an increase in resistance at the level of primary and secondary biosynthesis of metabolites, removing the damage characteristic of salinity and stabilizing the condition of plants. We used 200 mM NaCl, which inhibits the growth of tobacco plants at all stages of development. Leaves of transgenic and wild-type (WT) plants Nicotiána tabácum were used for biochemical, cytological and molecular biological analysis. However, for transgenic lines cultivated under normal conditions (without salinity), we noted juvenile characteristics, delay in flowering, and slowing down of development, including the photosynthetic apparatus. This caused changes in the amount of chlorophyll, a delay in the plastid grana development with the preservation of prolamellar bodies. It also caused changes in the amount of sugars and indirectly downstream processes. A significant change in the activity of antioxidant enzymes and a change in metabolism is probably compensated by the regulation of a number of genes, the expression level of which was also changed. Thus, the tolerance of transgenic tobacco plants to salinity, which manifested itself as a result of the constitutive expression of codA, demonstrates an advantage over WT plants, but in the absence of salinity, transgenic plants did not have such advantages due to juvenilization.

Immobilization of a Broad Range of Polypeptides on the Frustule of the Diatom Thalassiosira pseudonana

Proteins immobilized on biosilica which have superior reactivity and specificity and are innocuous to natural environments could be useful biological materials in industrial processes. One recently developed technique, living diatom silica immobilization (LiDSI), has made it possible to immobilize proteins, including multimeric and redox enzymes, via a cellular excretion system onto the silica frustule of the marine diatom Thalassiosira pseudonana. However, the number of application examples so far is limited, and the type of proteins appropriate for the technique is still enigmatic. Here, we applied LiDSI to six industrially relevant polypeptides, including protamine, metallothionein, phosphotriesterase, choline oxidase, laccase, and polyamine synthase. Protamine and metallothionein were successfully immobilized on the frustule as protein fusions with green fluorescent protein (GFP) at the N terminus, indicating that LiDSI can be used for polypeptides which are rich in arginine and cysteine. In contrast, we obtained mutants for the latter four enzymes in forms without green fluorescent protein. Immobilized phosphotriesterase, choline oxidase, and laccase showed enzyme activities even after the purification of frustule in the presence of 1% (wt/vol) octylphenoxy poly(ethyleneoxy)ethanol. An immobilized branched-chain polyamine synthase changed the intracellular polyamine composition and silica nanomorphology. These results illustrate the possibility of LiDSI for industrial applications. IMPORTANCE Proteins immobilized on biosilica which have superior reactivity and specificity and are innocuous to natural environments could be useful biological materials in industrial processes. Living diatom silica immobilization (LiDSI) is a recently developed technique for in vivo protein immobilization on the diatom frustule. We aimed to explore the possibility of using LiDSI for industrial applications by successfully immobilizing six polypeptides: (i) protamine (Oncorhynchus keta), a stable antibacterial agent; (ii) metallothionein (Saccharomyces cerevisiae), a metal adsorption molecule useful for bioremediation; (iii) phosphotriesterase (Sulfolobus solfataricus), a scavenger for toxic organic phosphates; (iv) choline oxidase (Arthrobacter globiformis), an enhancer for photosynthetic activity and yield of plants; (v) laccase (Bacillus subtilis), a phenol oxidase utilized for delignification of lignocellulosic materials; and (vi) branched-chain polyamine synthase (Thermococcus kodakarensis), which produces branched-chain polyamines important for DNA and RNA stabilization at high temperatures. This study provides new insights into the field of applied biological materials.

Choline Oxidase-Integrated Copper Metal-Organic Frameworks as Cascade Nanozymes for One-Step Colorimetric Choline Detection

Choline is an important factor for regulating human health and is widely present in various foods. In this work, a sensor strategy based on a choline oxidase-integrated copper(II) metal-organic framework with peroxidase-like activity is constructed for one-step cascade detection of choline. The one-step cascade strategy can avoid intermediate product transferring in general multi-step reactions, and the multi-enzyme activities can be well exerted under one condition, thus exhibiting excellent catalytic activity and enhanced stability. In the integrated system, choline is catalyzed by ChO_x to produce betaine and H₂O₂, which eventually got converted to hydroxyl radicals by the peroxidase nanozyme, oxidized the chromogenic substrate ABTS, and produced an observable absorption peak at 420 nm. A new choline detection method was thus established and showed a satisfactory linear relationship at 6-300 μM, which has been used for the choline analysis in milk.

Freeform 3D Bioprinting Involving Ink Gelation by Cascade Reaction of Oxidase and Peroxidase: A Feasibility Study Using Hyaluronic Acid-Based Ink

Freeform bioprinting, realized by extruding ink-containing cells into supporting materials to provide physical support during printing, has fostered significant advances toward the fabrication of cell-laden soft hydrogel constructs with desired spatial control. For further advancement of freeform bioprinting, we aimed to propose a method in which the ink embedded in supporting materials gelate through a cytocompatible and rapid cascade reaction between oxidase and peroxidase. To demonstrate the feasibility of the proposed method, we extruded ink containing choline, horseradish peroxidase (HRP), and a hyaluronic acid derivative, cross-linkable by HRP-catalyzed reaction, into a supporting material containing choline oxidase and successfully obtained three-dimensional hyaluronic acid-based hydrogel constructs with good shape fidelity to blueprints. Cytocompatibility of the bioprinting method was confirmed by the comparable growth of mouse fibroblast cells, released from the printed hydrogels through degradation on cell culture dishes, with those not exposed to the printing process, and considering more than 85% viability of the enclosed cells during 10 days of culture. Owing to the presence of derivatives of the various biocompatible polymers that are cross-linkable through HRP-mediated cross-linking, our results demonstrate that the novel 3D bioprinting method has great potential in tissue engineering applications.

A Crosstalk- and Interferent-Free Dual Electrode Amperometric Biosensor for the Simultaneous Determination of Choline and Phosphocholine

Choline (Ch) and phosphocholine (PCh) levels in tissues are associated to tissue growth and so to carcinogenesis. Till now, only highly sophisticated and expensive techniques like those based on NMR spectroscopy or GC/LC- high resolution mass spectrometry permitted Ch and PCh analysis but very few of them were capable of a simultaneous determination of these analytes. Thus, a never reported before amperometric biosensor for PCh analysis based on choline oxidase and alkaline phosphatase co-immobilized onto a Pt electrode by co-crosslinking has been developed. Coupling the developed biosensor with a parallel sensor but specific to Ch, a crosstalk-free dual electrode biosensor was also developed, permitting the simultaneous determination of Ch and PCh in flow injection analysis. This novel sensing device performed remarkably in terms of sensitivity, linear range, and limit of detection so to exceed in most cases the more complex analytical instrumentations. Further, electrode modification by overoxidized polypyrrole permitted the development of a fouling- and interferent-free dual electrode biosensor which appeared promising for the simultaneous determination of Ch and PCh in a real sample.

A sensitive amperometric detection of neurotransmitter acetylcholine using carbon dot-modified carbon paste electrode

Acetylcholine is a neurotransmitter, which is located at the intersections of the nerve and muscles in the lymph nodes of the internal organs motor systems and in various parts of the central nervous system. A decrease of acetylcholine in brain is associated with Alzheimer's disease. That is why it is an important agent for this disease. In this study, a bienzymatic biosensor system with acetylcholine esterase and choline oxidase was prepared with carbon paste electrode modified with carbon nano Dot-(3-Aminopropyl) triethoxysilane (CDs-APTES) for determination of the amount of acetylcholine. Acetylcholine esterase and choline oxidase enzymes were immobilized onto a modified carbon paste electrode by cross-linking with glutaraldehyde. Determination of acetylcholine was carried out by the oxidation of enzymatically produced H₂ O₂ at 0.4 V versus Ag/AgCl. The effect of temperature, pH, and substrate concentration on the acetylcholine response of the prepared biosensor was investigated. In addition, the optimum CDs-APTES amount, the linear operating range of the biosensor, and the interference effect were also investigated.

Natural Deep Eutectic Solvents as Multifunctional Media for the Valorization of Agricultural Wastes

The use of natural deep eutectic solvents (NADES) as multifunctional solvents for limonene bioprocessing was reported. NADES were used for the extraction of limonene from orange peel wastes, as solvent for the chemoenzymatic epoxidation of limonene, and as sacrificial electron donor for the in situ generation of H2 O2 to promote the epoxidation reaction. The proof-of-concept for this multifunctional use was provided, and the scope and current limitations of the concept were outlined.

Surface Functionalization by Stimuli-Sensitive Microgels for Effective Enzyme Uptake and Rational Design of Biosensor Setups

We highlight microgel/enzyme thin films that were deposited onto solid interfaces via two sequential steps, the adsorption of temperature- and pH-sensitive microgels, followed by their complexation with the enzyme choline oxidase, ChO. Two kinds of functional (ionic) microgels were compared in this work in regard to their adsorptive behavior and interaction with ChO, that is, poly(N-isopropylacrylamide-co-N-(3-aminopropyl)methacrylamide), P(NIPAM-co-APMA), bearing primary amino groups, and poly(N-isopropylacrylamide-co-N-[3-(dimethylamino) propyl]methacrylamide), P(NIPAM-co-DMAPMA), bearing tertiary amino groups. The stimuli-sensitive properties of the microgels in the solution were characterized by potentiometric titration, dynamic light scattering (DLS), and laser microelectrophoresis. The peculiarities of the adsorptive behavior of both the microgels and the specific character of their interaction with ChO were revealed by a combination of surface characterization techniques. The surface charge was characterized by electrokinetic analysis (EKA) for the initial graphite surface and the same one after the subsequent deposition of the microgels and the enzyme under different adsorption regimes. The masses of wet microgel and microgel/enzyme films were determined by quartz crystal microbalance with dissipation monitoring (QCM-D) upon the subsequent deposition of the components under the same adsorption conditions, on a surface of gold-coated quartz crystals. Finally, the enzymatic responses of the microgel/enzyme films deposited on graphite electrodes to choline were tested amperometrically. The presence of functional primary amino groups in the P(NIPAM-co-APMA) microgel enables a covalent enzyme-to-microgel coupling via glutar aldehyde cross-linking, thereby resulting in a considerable improvement of the biosensor operational stability.

An Amperometric Biosensor for the Determination of Bacterial Sepsis Biomarker, Secretory Phospholipase Group 2-IIA Using a Tri-Enzyme System

A tri-enzyme system consisting of choline kinase/choline oxidase/horseradish peroxidase was used in the rapid and specific determination of the biomarker for bacterial sepsis infection, secretory phospholipase Group 2-IIA (sPLA2-IIA). These enzymes were individually immobilized onto the acrylic microspheres via succinimide groups for the preparation of an electrochemical biosensor. The reaction of sPLA2-IIA with its substrate initiated a cascading enzymatic reaction in the tri-enzyme system that led to the final production of hydrogen peroxide, which presence was indicated by the redox characteristics of potassium ferricyanide, K₃Fe(CN)₆. An amperometric biosensor based on enzyme conjugated acrylic microspheres and gold nanoparticles composite coated onto a carbon-paste screen printed electrode (SPE) was fabricated and the current measurement was performed at a low potential of 0.20 V. This enzymatic biosensor gave a linear range 0.01–100 ng/mL (R² = 0.98304) with a detection limit recorded at 5 × 10⁻³ ng/mL towards sPLA2-IIA. Moreover, the biosensor showed good reproducibility (relative standard deviation (RSD) of 3.04% (n = 5). The biosensor response was reliable up to 25 days of storage at 4 °C. Analysis of human serum samples for sPLA2-IIA indicated that the biosensor has potential for rapid bacterial sepsis diagnosis in hospital emergency department.