Highly sensitive microbial biosensor based on recombinant Escherichia coli overexpressing catechol 2,3-dioxygenase for reliable detection of catechol

Effects of electrospun nanofiber fabrications on immobilization of recombinant Escherichia coli for production of xylitol from glucose

A suitable nanofiber sheet was formulated and developed based on its efficacy in the immobilization of recombinant Escherichia coli (E. coli) to enhance xylitol production. The effects of different types of nanofibers and solvents on cell immobilization and xylitol production were studied. The most applicable nanofiber membrane was selected via preliminary screening of four types of nanofiber membrane, followed by the selection of six different solvents. Polyvinylidene fluoride (PVDF) nanofiber sheet synthesized using dimethylformamide (DMF) solvent was found to be the most suitable carrier for immobilization and xylitol production. The thin, beaded PVDF (DMF) nanofibers were more favourable for microbial adhesion, with the number of immobilized cells as high as 96 × 106 ± 3.0 cfu/ml. The attraction force between positively charged PVDF nanofibers and the negatively charged E. coli indicates that the electrostatic interaction plays a significant role in cell adsorption. The use of DMF has also produced PVDF nanofibers biocatalyst capable of synthesizing the highest xylitol concentration (2.168 g/l) and productivity (0.090 g/l/h) and 55-69% reduction in cell lysis compared with DMSO solvent and free cells. This finding suggests that recombinant E. coli immobilized on nanofibers shows great potential as a whole-cell biocatalyst for xylitol production.

A reactive matrix for in situ chemical derivatisation and specific detection of cis-diol compounds by matrix-assisted laser desorption/ionisation mass spectrometry

Analysis of cis-diol compounds is essential, because they play important roles in cosmetics, food, pharmaceuticals, and living organisms. Herein, we describe the development of a matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) method to analyse cis-diol compounds. In this method, a 6-borono-1-methylquinoline-1-ium (BMQI) reactive matrix was designed for in situ derivatisation of cis-diol compounds based on the boronate affinity interaction between boronic acid and cis-diol groups. Compared to traditional commercial matrices and other boronic acid reagents, BMQI can significantly accelerate the desorption/ionisation process, improve reproducibility, exhibit free background interference, and enhance signal intensity in the analysis of various cis-diol compounds even for amounts as low as 1 nmol. The BMQI-assisted laser desorption/ionisation mass spectrometry (LDI-MS) was successfully applied to the rapid screening and identification of sugar alcohols in different sugar-free foods. This work provides an alternative method to the LDI-MS analysis of cis-diol-containing molecules, and the method can be extended to other food samples and biofluids.

Biopolymer Composites with Sensors for Environmental and Medical Applications

One of the biggest economic and environmental sustainability problems is the over-reliance on petroleum chemicals in polymer production. This paper presents an overview of the current state of knowledge on biopolymers combined with biosensors in terms of properties, compounding methods and applications, with a focus on medical and environmental aspects. Therefore, this article is devoted to environmentally friendly polymer materials. The paper presents an overview of the current state of knowledge on biopolymers combined with biosensors in terms of properties, compounding methods and applications, with a special focus on medical and environmental aspects. The paper presents the current state of knowledge, as well as prospects. The article shows that biopolymers made from renewable raw materials are of great interest in various fields of science and industry. These materials not only replace existing polymers in many applications, but also provide new combinations of properties for new applications. Composite materials based on biopolymers are considered superior to traditional non-biodegradable materials due to their ability to degrade when exposed to environmental factors. The paper highlights the combination of polymers with nanomaterials which allows the preparation of chemical sensors, thus enabling their use in environmental or medical applications due to their biocompatibility and sensitivity. This review focuses on analyzing the state of research in the field of biopolymer-sensor composites.

Simple, rapid, and visual electrochemiluminescence sensor for on-site catechol analysis

Environmental pollution caused by aromatic compounds such as catechol (Cat) has become a major issue for human health. However, there is no simple, rapid, and low-cost method for on-site monitoring of Cat. Here, based on ECL quenching mechanism, we develop a simple, rapid and visual mesoporous silica (MSNs)-electrochemiluminescence (ECL) sensor for on-site monitoring of Cat. The mechanism of ECL quenching is due to the interaction between Cat and Ru(bpy)₃^2+* and the interactions between the oxidation products of Cat and DBAE. MSNs films with ordered perpendicular mesopore channels exhibit an amplification effect of ECL intensity due to the negatively charged pore channel. There is a good linear relationship between ECL intensity and Cat concentration in the range of 10 ∼ 1000 μM with the limit of detection (LOD) of 9.518 μM (R² = 0.99). The on-site sensor is promising to offer new opportunities for pharmaceuticals analysis, on-site monitoring, and exposure risk assessment.

A simple, rapid and visual mesoporous silica (MSNs)-electrochemiluminescence (ECL) sensor was developed for on-site monitoring of Cat.

Simultaneous detection of acetaminophen, catechol and hydroquinone using a graphene-assisted electrochemical sensor

Simple, rapid and sensitive analysis of drug-derived pollutants is critically valuable for environmental monitoring. Here, taking acetaminophen, hydroquinone and catechol as a study example, a sensor based on an ITO/APTES/r-GO@Au electrode was developed for separate and simultaneous determination of phenolic pollutants. ITO electrodes that are modified with 3-aminopropyltriethoxysilane (APTES), graphene (GO) and Au nanoparticles (Au NPs) can significantly enhance the electronic transport of phenolic pollutants at the electrode surface. The redox mechanisms of phenolic pollutants include the electron transfer with the enhancement of r-GO@Au. The modified ITO electrode exhibits excellent electrical properties to phenolic pollutants and a good linear relationship between ECL intensity and the concentration of phenolic pollutants, with a limit of detection of 0.82, 1.41 and 1.95 μM, respectively. The separate and simultaneous determination of AP, CC and HQ is feasible with the ITO/APTES/r-GO@Au electrode. The sensor shows great promise as a low-lost, sensitive, and rapid method for simultaneous determination of drug-derived pollutants.

Simple, rapid and sensitive analysis of drug-derived pollutants is critically valuable for environmental monitoring.

A novel Bacillus ligniniphilus catechol 2,3-dioxygenase shows unique substrate preference and metal requirement

Identification of novel enzymes from lignin degrading microorganisms will help to develop biotechnologies for biomass valorization and aromatic hydrocarbons degradation. Bacillus ligniniphilus L1 grows with alkaline lignin as the single carbon source and is a great candidate for ligninolytic enzyme identification. The first dioxygenase from strain L1 was heterologously expressed, purified, and characterized with an optimal temperature and pH of 32.5 °C and 7.4, respectively. It showed the highest activity with 3-ethylcatechol and significant activities with other substrates in the decreasing order of 3-ethylcatechol > 3-methylcatechol > 3-isopropyl catechol > 2, 3-dihydroxybiphenyl > 4-methylcatechol > catechol. It did not show activities against other tested substrates with similar structures. Most reported catechol 2,3-dioxygenases (C23Os) are Fe²⁺-dependent whereas Bacillus ligniniphilus catechol 2,3-dioxygenase (BLC23O) is more Mn²⁺- dependent. At 1 mM, Mn²⁺ led to 230-fold activity increase and Fe²⁺ led to 22-fold increase. Sequence comparison and phylogenetic analyses suggested that BL23O is different from other Mn-dependent enzymes and uniquely grouped with an uncharacterized vicinal oxygen chelate (VOC) family protein from Paenibacillus apiaries. Gel filtration analysis showed that BLC23O is a monomer under native condition. This is the first report of a C23O from Bacillus ligniniphilus L1 with unique substrate preference, metal-dependency, and monomeric structure.

An electrochemical method for determination of amaranth in drinks using functionalized graphene oxide/chitosan/ionic liquid nanocomposite supported nanoporous gold

An electrochemical sensor was fabricated by modifying nanoporous gold (NPG)-coated glassy carbon electrode (NPG/GCE) with functionalized graphene oxide /chitosan/ionic liquid nanocomposites (fGO/CS/IL). The introduction of ionic liquid (IL) and chitosan (CS) induced higher dispersibility of functionalized graphene oxide (fGO), and was beneficial for the combination of fGO/CS/IL with NPG/GCE. As a result of the synergistic effect of NPG and fGO/CS/IL, the resulted functionalized graphene oxide/chitosan/ionic liquid nanocomposites/nanoporous gold /glassy carbon electrode (fGO/CS/IL/NPG/GCE) showed the highest redox peak current response signal of Amaranth (E123) due to ultrahigh surface area, electronic conductivity as well as the improvement of the surface structure. Under optimized conditions, the enhanced peak currents represented excellent analytical performance for detection of Amaranth in the concentration range from 8.0 to 1200.0 nM. Meanwhile, the fGO/CS/IL/NPG/GCE presented satisfactory sensitivity and selectivity, excellent reproducibility, and long-time stability. For practical applications, the fGO/CS/IL/NPG/GCE was validated for the determination of Amaranth in three types of drinks with satisfactory results.

Biosensors for wastewater-based epidemiology for monitoring public health

Public health is attracting increasing attention due to the current global pandemic, and wastewater-based epidemiology (WBE) has emerged as a powerful tool for monitoring of public health by analysis of a variety of biomarkers (e.g., chemicals and pathogens) in wastewater. Rapid development of WBE requires rapid and on-site analytical tools for monitoring of sewage biomarkers to provide immediate decision and intervention. Biosensors have been demonstrated to be highly sensitive and selective tools for the analysis of sewage biomarkers due to their fast response, ease-to-use, low cost and the potential for field-testing. This paper presents biosensors as effective tools for wastewater analysis of potential biomarkers and monitoring of public health via WBE. In particular, we discuss the use of sewage sensors for rapid detection of a range of targets, including rapid monitoring of community-wide illicit drug consumption and pathogens for early warning of infectious diseases outbreaks. Finally, we provide a perspective on the future use of the biosensor technology for WBE to enable rapid on-site monitoring of sewage, which will provide nearly real-time data for public health assessment and effective intervention.

3-Aminobenzeneboronic Acid Functionalized MoS2 Quantum Dot as Fluorescent Nanoprobe for the Determination of o-Dihydroxybenzene

In this work, by functionalizing MoS₂ quantum dot with 3-aminobenzeneboronic acid, a novel multifunctional quantum dot (denoted as B-MoS₂ QD) was obtained and used successfully for a fluorescence nanoprobe for detecting o-dihydroxybenzene (o-DHB). Transmission electron microscopy, fluorescence spectrum, UV-vis spectrum and fluorescence lifetime were used to investigate the prepared nanoprobe. The results show that the B-MoS₂ QD nanoprobe can exhibit strong fluorescence and excellent light fastness owing to the coupled effect from the MoS₂ QDs and boronic acid; interestingly, the vicinal diols structure from its surface can bridge covalently with o-DHB, resulting in the fluorescence quenching of B-MoS₂ QDs and selective recognition toward o-DHB. With the increasing of o-DHB concentration, the nanoprobe fluorescence would gradually decrease. By measuring the fluorescence intensity of B-MoS₂ QDs, a wide linear range from 0.1 to 200.0 μM with a low detection limit of 0.025 μM was obtained for o-DHB analysis; meanwhile, this fluorescence nanoprobe possesses excellent selectivity for the selective detection of o-DHB from its analogues.

Potentiometric polyphenol oxidase biosensor for sensitive determination of phenolic micropollutant in environmental samples

The present study demonstrates the development of polyphenol oxidase (PPO) biosensor for the detection of catechol using strontium copper oxide (SrCuO₂) and polypyrrole nanotubes (PPyNT) matrix. The SrCuO₂ micro-seeds, a perovskite compound, are synthesized by co-precipitation under pH 8.0. The as-synthesized micro-seeds are characterized by scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction spectroscopy (XRD). The proposed sensor is fabricated on pencil graphite (P-Gr) by successive deposition of PPyNT, SrCuO₂, and PPO enzyme. The developed PPO/SrCuO₂/PPyNT/P-Gr sensor is characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) techniques. The PPO/SrCuO₂/PPyNT/P-Gr displayed excellent electrocatalytic activity towards the oxidation and detection of catechol. The as-developed sensor showed sensitive response ascribing to limit of detection (LOD) of 0.15 μM and sensitivity of 15.60 μA μM^-1 cm^-2. The fabricated sensor exhibited excellent repeatability and longer shelf life. The proposed biosensor finds its application within the broad linear range of 1-50 μM. Real sample analysis of mineral water, tap water, and domestic wastewater using developed sensor showed acceptable recovery. Hence, the biosensor endeavors its application in environmental monitoring and protection.

Insights into the binding interaction of substrate with catechol 2,3-dioxygenase from biophysics point of view

This study aims to clarify the interaction mechanism of substrate with catechol 2,3-dioxygenase (C23O) through multi-technique combination. A novel C23O (named C23O-2G) was cloned, heterogeneously expressed, and identified as a new member in subfamily I.2 of extradiol dioxygenases. Based on the simulations of molecular docking and dynamics, the exact binding sites of catechol on C23O-2G were identified, and the catalytic mechanism mediated by key residues was proposed. The roles of the predicted residues during catalysis were confirmed by site-directed mutagenesis, and the mutation of Thr254 could significantly increase catalytic efficiency and substrate specificity of C23O-2G. The binding and thermodynamic parameters obtained from fluorescence spectra suggested that catechol could effectively quench the intrinsic fluorescence of C23O-2G via static and dynamic quenching mechanisms and spontaneously formed C23O-2G/catechol complex by the binding forces of hydrogen bond and van der Waals force. The results of UV-vis spectra, synchronous fluorescence, and CD spectra revealed obvious changes in the microenvironment and conformation of C23O-2G, especially for the secondary structure. The atomic force microscope images further demonstrated the changes from an appearance point of view. This study could improve our mechanistic understanding of representative dioxygenases involved in aromatic compound degradation.

Differential protein profiling of soil diazotroph Rhodococcus qingshengii S10107 towards low-temperature and nitrogen deficiency

Protein-based biomarkers can be a promising approach for identification and real-time monitoring of the bio-inoculants employed under sustainable agricultural plans. In this perspective, differential proteomics of psychrophilic diazotroph Rhodococcus qingshengii S10107 (JX173283) was performed to unravel its adaptive responses towards low-temperature nitrogen deficiency and identification of a biomarker for respective physiological conditions. LC-MS/MS-based proteome analysis mapped more than 4830 proteins including 77 up-regulated and 47 down-regulated proteins (p ≤ 0.05). Differential expression of the structural genes of nif regulon viz. nifH, nifD, and nifK along with their response regulators i.e. nifA, nifL, and nifB indicated that the nitrogenase complex was activated successfully. Besides up-regulating the biosynthesis of certain amino acids viz. Leucine, Lysine, and Alanine; the expression of the peptidoglycan synthesis proteins were also increased; while, the enzymes involved in Lipid biosynthesis were found to decrease. Furthermore, two important enzymes of the pentose phosphate pathway viz. Transketolase and Transaldolase along with Ribose import ATP-binding protein RbsA were also found to induce significantly under low temperature a nitrogen deficient condition, which suggests the cellular need for ample ribose sugar instantly. Additionally, comparative protein profiling of S10107 strain with our previous studies revealed that CowN protein was significantly up-regulated in all the cases under low-temperature nitrogen deficient conditions and therefore, can be developed as a biomarker. Conclusively, present study for the first time provides an in-depth proteome profiling of R. qingshengii S10107 and proclaims CowN as a potential protein biomarker for monitoring BNF under cold niches.

Biological Effects of C60 Fullerene Revealed with Bacterial Biosensor-Toxic or Rather Antioxidant?

Nanoparticles have been attracting growing interest for both their antioxidant and toxic effects. Their exact action on cells strongly depends on many factors, including experimental conditions, preparation, and solvents used, which have contributed to the confusion regarding their safety and possible health benefits. In order to clarify the biological effects of the most abundant fullerene C₆₀, its impact on the Escherichia coli model has been studied. The main question was if C₆₀ would have any antioxidant influence on the cell and, if yes, whether and to which extent it would be concentration-dependent. An oxidative stress induced by adding hydrogen peroxide was measured with an E. coli MG1655 pKatG-lux strain sensor, with its time evolution being recorded in the presence of fullerene C₆₀ suspensions of different concentrations. Optimal conditions for the fullerene C₆₀ solubilization in TWEEN 80 2% aqueous solution, together with resulting aggregate sizes, were determined. Results obtained for the bacterial model can be extrapolated on eukaryote mitochondria. The ability of C₆₀ to penetrate through biological membranes, conduct protons, and interact with free radicals is likely responsible for its protective effect detected for E. coli. Thus, fullerene can be considered as a mitochondria-targeted antioxidant, worth further researching as a prospective component of novel medications.

Effect of plants and their root exudate on bacterial activities during rhizobacterium-plant remediation of phenol from water

We investigated remediation of phenol from water using microbe-plant partnerships. Co-introduction of maize seedlings, Pseudomonas fluorescens rifampicin-resistant P13 and P. stutzeri P7 carrying self-transmissible TOL-like plasmids reduced phenol content in water at lower phenol concentrations (25, 50, and 75 mg/L), similar to individual introduction of the bacteria. Co-introduction of plants and bacteria significantly reduced phenol content in water at higher phenol concentrations (100, 125, and 150 mg/L) compared to using individual introduction of the bacteria. Moreover, TOL-like plasmids were transferred from P7 to P13. Addition of plants promoted the growth of both strains, leading to increased plasmid transfer. At higher phenol concentrations, addition of plants resulted in increases of catechol 2, 3-dioxygenase (C23O) activity and reduction in level of reactive oxygen species (ROS) of bacteria in the degradation experiments. Increased plasmid transfer and C23O activity and reduction in ROS level might be the major reasons why plants promote bacterial degradation of phenol at higher phenol concentrations. Furthermore, root exudate of maize seedlings and artificial root exudate (ARE) constructed using major components of the root exudate had the same effects on bacterial activities. Unlike the ARE, deletion of glucose, arabinose, or fructose or all the monosaccharides from ARE resulted in no increase in numbers of both strains and in plasmid transfer. At the higher phenol concentrations, deletion of glutamic acid, aspartic acid, alanine, or glycine or all the amino acids did not stimulate bacterial C23O activity. Deletion of fumaric, oxaloacetic or citric acids still reduced bacterial ROS level as ARE did, but, deletion of all the organic acids or DIMBOA, a hydroxamic acid, did not reduce bacterial ROS level as ARE did. The data showed that each monosaccharide might be important for sufficient numbers of plant-associated bacteria and increased plasmid transfer while each amino acid might be important for maintaining bacterial C23O activity and that DIMBOA might be responsible for the decrease in ROS levels. These results are the basis for efficient remediation of phenol from water by microbe-plant partnerships and further studies on the mechanism of rhizobacterium-plant interaction.