Immobilization of PETase enzymes on magnetic iron oxide nanoparticles for the decomposition of microplastic PET

A new colorimetric lactate biosensor based on CUPRAC reagent using binary enzyme (lactate-pyruvate oxidases)-immobilized silanized magnetite nanoparticles

A novel optical lactate biosensor is presented that utilizes a colorimetric interaction between H2O2 liberated by a binary enzymatic reaction and bis(neocuproine)copper(II) complex ([Cu(Nc)2]2+) known as CUPRAC (cupric reducing antioxidant capacity) reagent. In the first step, lactate oxidase (LOx) and pyruvate oxidase (POx) were separately immobilized on silanized magnetite nanoparticles (SiO2@Fe3O4 NPs), and thus, 2 mol of H2O2 was released per 1 mol of the substrate due to a sequential enzymatic reaction of the mixture of LOx-SiO2@Fe3O4 and POx-SiO2@Fe3O4 NPs with lactate and pyruvate, respectively. In the second step, the absorbance at 450 nm of the yellow-orange [Cu(Nc)2]+ complex formed through the color reaction of enzymatically produced H2O2 with [Cu(Nc)2]2+ was recorded. The results indicate that the developed colorimetric binary enzymatic biosensor exhibits a broad linear range of response between 0.5 and 50.0 µM for lactate under optimal conditions with a detection limit of 0.17 µM. The fabricated biosensor did not respond to other saccharides, while the positive interferences of certain reducing compounds such as dopamine, ascorbic acid, and uric acid were minimized through their oxidative removal with a pre-oxidant (NaBiO3) before enzymatic and colorimetric reactions. The fabricated optical biosensor was applied to various samples such as artificial blood, artificial/real sweat, and cow milk. The high recovery values (close to 100%) achieved for lactate-spiked samples indicate an acceptable accuracy of this colorimetric biosensor in the determination of lactate in real samples. Due to the increase in H2O2 production with the bienzymatic lactate sensor, the proposed method displays double-fold sensitivity relative to monoenzymatic biosensors and involves a neat color reaction with cupric-neocuproine having a clear stoichiometry as opposed to the rather indefinite stoichiometry of analogous redox dye methods.

Unlocking a Sustainable Future for Plastics: A Chemical-Enzymatic Pathway for Efficient Conversion of Mixed Waste to MHET and Energy-Saving PET Recycling

The heterogeneous monomers obtained from plastic waste degradation are unfavorable for PET recondensation and high-value derivative synthesis. Herein, we developed an efficient chemical-enzymatic approach to convert mixed plastic wastes into homogeneous mono-2-hydroxyethyl terephthalate (MHET) without downstream purification, benefiting from three discovered BHETases (KbEst, KbHyd, and BrevEst) in nature. Towards the mixed plastic waste, integrating the chemical K2CO3-driven glycolysis process with the BHETase depolymerization technique resulted in an MHET yield of up to 98.26 % in 40 h. Remarkably, BrevEst accomplished the highest BHET hydrolysis (~87 % efficiency in 12 h) for yielding analytical-grade MHET compared to seven state-of-the-art PET hydrolases (18 %-40 %). In an investigation combining quantum theoretical computations and experimental validations, we established a MHET-initiated PET repolymerization pathway. This shortcut approach with MHET promises to strengthen the valorization of mixed plastics, offering a substantially more efficient and energy-saving route for PET recycling.

Green nanobiocatalysts: enhancing enzyme immobilization for industrial and biomedical applications

Nanobiocatalysts (NBCs), which merge enzymes with nanomaterials, provide a potent method for improving enzyme durability, efficiency, and recyclability. This review highlights the use of eco-friendly synthesis methods to create sustainable nanomaterials for enzyme transport. We investigate different methods of immobilization, such as adsorption, ionic and covalent bonding, entrapment, and cross-linking, examining their pros and cons. The decreased environmental impact of green-synthesized nanomaterials from plants, bacteria, and fungi is emphasized. The review exhibits the various uses of NBCs in food industry, biofuel production, and bioremediation, showing how they can enhance effectiveness and eco-friendliness. Furthermore, we explore the potential impact of NBCs in biomedicine. In general, green nanobiocatalysts are a notable progression in enzyme technology, leading to environmentally-friendly and effective biocatalytic methods that have important impacts on industrial and biomedical fields.

Catalytic and biocatalytic degradation of microplastics

In recent years, there has been a surge in annual plastic production, which has contributed to growing environmental challenges, particularly in the form of microplastics. Effective management of plastic and microplastic waste has become a critical concern, necessitating innovative strategies to address its impact on ecosystems and human health. In this context, catalytic degradation of microplastics emerges as a pivotal approach that holds significant promise for mitigating the persistent effects of plastic pollution. In this article, we critically explored the current state of catalytic degradation of microplastics and discussed the definition of degradation, characterization methods for degradation products, and the criteria for standard sample preparation. Moreover, the significance and effectiveness of various catalytic entities, including enzymes, transition metal ions (for the Fenton reaction), nanozymes, and microorganisms are summarized. Finally, a few key issues and future perspectives regarding the catalytic degradation of microplastics are proposed.

Increasing the Particle Size and Magnetic Property of Iron Oxide Nanoparticles through a Segregated Nucleation and Growth Process

Iron oxide nanoparticles (IONs) with good water dispersibility were prepared by the thermal decomposition of iron acetylacetonate (Fe(acac)3) in the high-boiling organic solvent polyethylene glycol (PEG) using polyethyleneimine (PEI) as a modifier. The nucleation and growth processes of the crystals were separated during the reaction process by batch additions of the reaction material, which could inhibit the nucleation but maintain the crystal growth, and products with larger particle sizes and high saturation magnetization were obtained. The method of batch addition of the reactant prepared IONs with the largest particle size and the highest saturation magnetization compared with IONs reported using PEG as the reaction solvent. The IONs prepared by this method also retained good water dispersibility. Therefore, these IONs are potentially suitable for the magnetic separation of cells, proteins, or nucleic acids when large magnetic responses are needed.

Simulation Study of Polyethylene Terephthalate Hydrolase Adsorption on Self-Assembled Monolayers

Polyethylene terephthalate (PET) hydrolase, discovered in Ideonella sakaiensis (IsPETase), is a promising agent for the biodegradation of PET under mild reaction conditions, yet the thermal stability is poor. The efficient immobilization and orientation of IsPETase on different solid substrates are essential for its application. In this work, the combined parallel tempering Monte Carlo simulation with the all-atom molecular dynamics simulation approach was adopted to reveal the adsorption mechanism, orientation, and conformational changes of IsPETase adsorbed on charged self-assembled monolayers (SAMs), including COOH-SAM and NH2-SAM with different surface charge densities (SCDs). The results show that the protein adsorption orientation was determined not only by attraction interactions but also by repulsion interactions. IsPETase is adsorbed on the COOH-SAM surface with an "end-on" orientation, which favors the exposure of the catalyzed triplet to the solution. In addition, the entrance to the catalytic active center is larger on the COOH-SAM surface with a low SCD. This work reveals the controlled orientation and conformational information on IsPETase on charged surfaces at the atomistic level. This study would certainly promote our understanding of the mechanism of IsPETase adsorption and provide theoretical support for the design of substrates for IsPETase immobilization.

Cross-linked enzyme aggregates of polyethylene terephthalate hydrolyse (PETase) from Ideonella sakaiensis for the improvement of plastic degradation

Polyethylene terephthalate (PET) is one of the most produced plastics globally and its accumulation in the environment causes harm to the ecosystem. Polyethylene terephthalate hydrolyse (PETase) is an enzyme that can degrade PET into its monomers. However, free PETase lacks operational stabilities and is not reusable. In this study, development of cross-linked enzyme aggregate (CLEA) of PETase using amylopectin (Amy) as cross-linker was introduced to solve the limitations of free PETase. PETase-Amy-CLEA exhibited activity recovery of 81.9 % at its best immobilization condition. Furthermore, PETase-Amy-CLEA exhibited 1.37-, 2.75-, 2.28- and 1.36-fold higher half-lives than free PETase at 50 °C, 45 °C, 40 °C and 35 °C respectively. Moreover, PETase-Amy-CLEA showed broader pH stability from pH 5 to 10 and could be reused up to 5 cycles. PETase-Amy-CLEA retained >70 % of initial activity after 40 days of storage at 4 °C. In addition, lower Km of PETase-Amy-CLEA indicated better substrate affinity than free enzyme. PETase-Amy-CLEA corroded PET better and products yielded was 66.7 % higher than free PETase after 32 h of treatment. Hence, the enhanced operational stabilities, storage stability, reusability and plastic degradation ability are believed to make PETase-Amy-CLEA a promising biocatalyst in plastic degradation.

Understanding microplastic pollution: Tracing the footprints and eco-friendly solutions

Microplastics (MPs) pollution has emerged as a critical environmental issue with far-reaching consequences for ecosystems and human health. These are plastic particles measuring <5 mm and are categorized as primary and secondary based on their origin. Primary MPs are used in various products like cosmetics, scrubs, body wash, and toothpaste, while secondary MPs are generated through the degradation of plastic products. These have been detected in seas, rivers, snow, indoor air, and seafood, posing potential risks to human health through the food chain. Detecting and quantifying MPs are essential to understand their distribution and abundance in the environment. Various microscopic (fluorescence microscopy, scanning electron microscopy) and spectroscopy techniques (FTIR, Raman spectroscopy, X-ray photoelectron spectroscopy) have been reported to analyse MPs. Despite the challenges in scalable removal methods, biological systems have emerged as promising options for eco-friendly MPs remediation. Algae, bacteria, and fungi have shown the potential to adsorb and degrade MPs in wastewater treatment plants (WWTPs) offering hope for mitigating this global crisis. This review examines the sources, impacts, detection, and biological removal of MPs, highlighting future directions in this crucial field of environmental conservation. By fostering global collaboration and innovative research a path towards a cleaner and healthier planet for future generations can be promised.

Recent Advances and Challenges in Enzymatic Depolymerization and Recycling of PET Wastes

Poly (ethylene terephthalate) (PET) is one of the most commonly used plastics in daily life and various industries. Enzymatic depolymerization and recycling of post-consumer PET (pc-PET) provides a promising strategy for the sustainable circular economy of polymers. Great protein engineering efforts have been devoted to improving the depolymerization performance of PET hydrolytic enzymes (PHEs). In this review, we first discuss the mechanisms and challenges of enzymatic PET depolymerization. Subsequently, we summarize the state-of-the-art engineering of PHEs including rational design, machine learning, and directed evolution for improved depolymerization performance, and highlight the advances in screening methods of PHEs. We further discuss several factors that affect the enzymatic depolymerization efficiency. We conclude with our perspective on the opportunities and challenges in bio-recycling and bio-upcycling of PET wastes.

Environmentally Benign Fast-Degrading Conductive Composites

An environmentally benign conductive composite that rapidly degrades in the presence of warm water via enzyme-mediated hydrolysis is described. This represents the first time that hydrolytic enzymes have been immobilized onto eco-friendly conductive carbon sources with the express purpose of degrading the encapsulating biodegradable plastic. Amano Lipase (AL)-functionalized carbon nanofibers (CNF) were compounded with polycaprolactone (PCL) to produce the composite film CNFAL-PCL (thickness ∼ 600 μm; CNFAL = 20.0 wt %). To serve as controls, films of the same thickness were also produced, including CNF-AL5-PCL (CNF mixed with AL and PCL; CNF = 19.2 wt % and AL = 5.00 wt %), CNF-PCL (CNF = 19.2 wt %), ALx-PCL (AL = x = 1.00 or 5.00 wt %), and PCL. The electrical performance of the CNF-containing composites was measured, and conductivities of 14.0 ± 2, 22.0 ± 5, and 31.0 ± 6 S/m were observed for CNFAL-PCL, CNF-AL5-PCL, and CNF-PCL, respectively. CNFAL-PCL and control films were degraded in phosphate buffer (2.00 mg/mL film/buffer) at 50 °C, and their average percent weight loss (Wtavg%) was recorded over time. After 3 h CNFAL-PCL degraded to a Wtavg% of 90.0% and had completely degraded after 8 h. This was considerably faster than CNF-AL5-PCL, which achieved a total Wtavg% of 34.0% after 16 days, and CNF-PCL, which was with a Wtavg% of 7.00% after 16 days. Scanning electron microscopy experiments (SEM) found that CNFAL-PCL has more open pores on its surface and that it fractures faster during degradation experiments which exposes the interior enzyme to water. An electrode made from CNFAL-PCL was fabricated and attached to an AL5-PCL support to form a fast-degrading thermal sensor. The resistance was measured over five cycles where the temperature was varied between 15.0-50.0 °C. The sensor was then degraded fully in buffer at 50 °C over a 48 h period.

Advances in magnetic materials for microplastic separation and degradation

The widespread use of plastics in modern human society has led to severe environmental pollution with microplastics (MP/MPs). The rising consumption of plastics raises the omnipresence of microplastics in aquatic environments, which carry toxic organic matter, transport toxic chemicals, and spread through the food chain, seriously threatening marine life and human health. In this context, several advanced strategies for separating and degrading MPs from water have been developed recently, and magnetic materials and their nanostructures have emerged as promising materials for targeting, adsorbing, transporting, and degrading MPs. However, a comprehensive review of MP remediation using magnetic materials and their nanostructures is currently lacking. The present work provides a critical review of the recent advances in MP removal/degradation using magnetic materials. The focus is on the comparison and analysis of the MP's removal efficiencies of different magnetic materials, including iron/ferrite nanoparticles, magnetic nanocomposites, and micromotors, aiming to unravel the underlying roles of magnetic materials in different types of MP degradation and present the general strategies for designing them with optimal performance. Finally, the review outlines the forthcoming challenges and perspectives in the development of magnetic nanomaterials for MP remediation.

Using NIR irradiation and magnetic bismuth ferrite microparticles to accelerate the removal of polystyrene microparticles from the drinking water

Magnetic bismuth ferrite (BiFO) microparticles were employed for the first time for the removal of polystyrene (PS) nano/microplastics from the drinking water. BiFO is formed by porous agglomerates with sizes of 5-11 μm, while the PS nano/microparticles have sizes in the range of 70-11000 nm. X-ray diffraction studies demonstrated that the BiFO microparticles are composed of BiFeO3/Bi25FeO40 (the content of Bi25FeO40 is ≈ 8.6%). Drinking water was contaminated with PS nano/microparticles (1 g L-1) and BiFO microparticles were also added to the contaminated water. Later, the mixture of PS-particles + BiFO was irradiated with NIR light (980 nm). Consequently, PS nano/microparticles melted on the BiFO microparticles due to the excessive heating on their surface. At the same time, the NIR (near infrared) light generated oxidizing agents (∙OH and h+), which degraded the by-products formed during the photocatalytic degradation of PS nano/microparticles. Subsequently, the NIR irradiation was stopped, and a Neodymium magnet was utilized to separate the BiFO microparticles from the water. This last procedure also permitted the removal of PS nano/microparticles by physical adsorption. Zeta potential measurements demonstrated that the BiFO surface was positively charged, allowing the removal of the negatively charged PS nano/microparticles by electrostatic attraction. The combination of the photocatalytic process and the physical adsorption permitted a complete removal of PS nano/microparticles after only 90 min as well as a high mineralization of by-products (≈95.5% as confirmed by the total organic carbon measurements). We estimate that ≈23.6% of the PS nano/microparticles were eliminated by photocatalysis and the rest of PS particles (≈76.4%) by physical adsorption. An outstanding adsorption capacity of 195.5 mg g-1 was obtained after the magnetic separation of the BiFO microparticles from the water. Hence, the results of this research demonstrated that using photocatalysis + physical-adsorption is a feasible strategy to quickly remove microplastic contaminants from the water.

Current advances in the structural biology and molecular engineering of PETase

Poly(ethylene terephthalate) (PET) is a highly useful synthetic polyester plastic that is widely used in daily life. However, the increase in postconsumer PET as plastic waste that is recalcitrant to biodegradation in landfills and the natural environment has raised worldwide concern. Currently, traditional PET recycling processes with thermomechanical or chemical methods also result in the deterioration of the mechanical properties of PET. Therefore, it is urgent to develop more efficient and green strategies to address this problem. Recently, a novel mesophilic PET-degrading enzyme (IsPETase) from Ideonella sakaiensis was found to streamline PET biodegradation at 30°C, albeit with a lower PET-degrading activity than chitinase or chitinase-like PET-degrading enzymes. Consequently, the molecular engineering of more efficient PETases is still required for further industrial applications. This review details current knowledge on IsPETase, MHETase, and IsPETase-like hydrolases, including the structures, ligand‒protein interactions, and rational protein engineering for improved PET-degrading performance. In particular, applications of the engineered catalysts are highlighted, including metabolic engineering of the cell factories, enzyme immobilization or cell surface display. The information is expected to provide novel insights for the biodegradation of complex polymers.

Harnessing extremophilic carboxylesterases for applications in polyester depolymerisation and plastic waste recycling

The steady growth in industrial production of synthetic plastics and their limited recycling have resulted in severe environmental pollution and contribute to global warming and oil depletion. Currently, there is an urgent need to develop efficient plastic recycling technologies to prevent further environmental pollution and recover chemical feedstocks for polymer re-synthesis and upcycling in a circular economy. Enzymatic depolymerization of synthetic polyesters by microbial carboxylesterases provides an attractive addition to existing mechanical and chemical recycling technologies due to enzyme specificity, low energy consumption, and mild reaction conditions. Carboxylesterases constitute a diverse group of serine-dependent hydrolases catalysing the cleavage and formation of ester bonds. However, the stability and hydrolytic activity of identified natural esterases towards synthetic polyesters are usually insufficient for applications in industrial polyester recycling. This necessitates further efforts on the discovery of robust enzymes, as well as protein engineering of natural enzymes for enhanced activity and stability. In this essay, we discuss the current knowledge of microbial carboxylesterases that degrade polyesters (polyesterases) with focus on polyethylene terephthalate (PET), which is one of the five major synthetic polymers. Then, we briefly review the recent progress in the discovery and protein engineering of microbial polyesterases, as well as developing enzyme cocktails and secreted protein expression for applications in the depolymerisation of polyester blends and mixed plastics. Future research aimed at the discovery of novel polyesterases from extreme environments and protein engineering for improved performance will aid developing efficient polyester recycling technologies for the circular plastics economy.

Recent advances in biodegradation of emerging contaminants - microplastics (MPs): Feasibility, mechanism, and future prospects

Plastics have become an essential part of life. When it enters the environment, it migrates and breaks down to form smaller size fragments, which are called microplastics (MPs). Compared with plastics, MPs are detrimental to the environment and pose a severe threat to human health. Bioremediation is being recognized as the most environmentally friendly and cost-effective degradation technology for MPs, but knowledge about the biodegradation of MPs is limited. This review explores the various sources of MPs and their migration behavior in terrestrial and aquatic environments. Among the existing MPs removal technologies, biodegradation is considered to be the best removal strategy to alleviate MPs pollution. The biodegradation potential of MPs by bacteria, fungi and algae is discussed. Biodegradation mechanisms such as colonization, fragmentation, assimilation, and mineralization are presented. The effects of MPs characteristics, microbial activity, environmental factors and chemical reagents on biodegradation are analyzed. The susceptibility of microorganisms to MPs toxicity might lead to decreased degradation efficiency, which is also elaborated. The prospects and challenges of biodegradation technologies are discussed. Eliminating prospective bottlenecks is necessary to achieve large-scale bioremediation of MPs-polluted environment. This review provides a comprehensive summary of the biodegradability of MPs, which is crucial for the prudent management of plastic waste.

Global plastic upcycling during and after the COVID-19 pandemic: The status and perspective

Plastic pollution has become one of the most pressing environmental issues worldwide since the vast majority of post-consumer plastics are hard to degrade in the environment. The coronavirus disease (COVID-19) pandemic had disrupted the previous effort of plastic pollution mitigation to a great extent due to the overflow of plastic-based medical waste. In the post-pandemic era, the remaining challenge is how to motivate global action towards a plastic circular economy. The need for one package of sustainable and systematic plastic upcycling approaches has never been greater to address such a challenge. In this review, we summarized the threat of plastic pollution during COVID-19 to public health and ecosystem. In order to solve the aforementioned challenges, we present a shifting concept, regeneration value from plastic waste, that provides four promising pathways to achieve a sustainable circular economy: 1) Increasing reusability and biodegradability of plastics; 2) Transforming plastic waste into high-value products by chemical approaches; 3) The closed-loop recycling can be promoted by biodegradation; 4) Involving renewable energy into plastic upcycling. Additionally, the joint efforts from different social perspectives are also encouraged to create the necessary economic and environmental impetus for a circular economy.

Enzymes for microplastic-free agricultural soils

Plastic mulch films and biofertilizers (processed sewage sludge, compost or manure) have helped to increase crop yields. However, there is increasing evidence that these practices significantly contribute to microplastic contamination in agricultural soils, affecting biodiversity and soil health. Here, we draw attention to the use of hydrolase enzymes that depolymerize polyester-based plastics as a bioremediation technique for agricultural soils (in situ), biofertilizers and irrigation water (ex situ), and discuss the need for fully biodegradable plastic mulches. We also highlight the need for ecotoxicological assessment of the proposed approach and its effects on different soil organisms. Enzymes should be optimized to work effectively and efficiently under the conditions found in natural soils (typically, moist solids at an ambient temperature with low salinity). Such optimization is also necessary to ensure that already distressed ecosystems are not disrupted any further.

Receptor-based detection of microplastics and nanoplastics: Current and future

Plastic pollution is an emerging environmental concern, gaining significant attention worldwide. They are classified into microplastics (MP; defined from 1 μm to 5 mm) and smaller nanoplastics (NP; <1 μm). NPs may pose higher ecological risks than MPs. Various microscopic and spectroscopic techniques have been used to detect MPs, and the same methods have occasionally been used for NPs. However, they are not based on receptors, which provide high specificity in most biosensing applications. Receptor-based micro/nanoplastics (MNP) detection can provide high specificity, distinguishing MNPs from the environmental samples and, more importantly, identifying the plastic types. It can also offer a low limit of detection (LOD) required for environmental screening. Such receptors are expected to detect NPs specifically at the molecular level. This review categorizes the receptors into cells, proteins, peptides, fluorescent dyes, polymers, and micro/nanostructures. Detection techniques used with these receptors are also summarized and categorized. There is plenty of room for future research to test for broader classes of environmental samples and many plastic types, to lower the LOD, and to apply the current techniques for NPs. Portable and handheld MNP detection should also be demonstrated for field use since the current demonstrations primarily utilized laboratory instruments. Detection on microfluidic platforms will also be crucial in miniaturizing and automating the assay and, eventually, collecting an extensive database to support machine learning-based classification of MNP types.

Microbial engineering strategies for synthetic microplastics clean up: A review on recent approaches

Microplastics are the small fragments of the plastic molecules which find their applications in various routine products such as beauty products. Later, it was realized that it has several toxic effects on marine and terrestrial organisms. This review is an approach in understanding the microplastics, their origin, dispersal in the aquatic system, their biodegradation and factors affecting biodegradation. In addition, the paper discusses the major engineering approaches applied in microbial biotechnology. Specifically, it reviews microbial genetic engineering, such as PET-ase engineering, MHET-ase engineering, and immobilization approaches. Moreover, the major challenges associated with the plastic removal are presented by evaluating the recent reports available.

Directed Immobilization of PETase on Mesoporous Silica Enables Sustained Depolymerase Activity in Synthetic Wastewater Conditions

Microplastic accumulation in terrestrial and aquatic environments is a growing environmental challenge. Biodegradation has shown promise as an intervention strategy for reducing the spread of microplastics. The wastewater treatment system is a key intervention point in microplastic biodegradation due to its pivotal role in the water cycle at the interface between human activity and the environmental. However, the best characterized microplastic degradation enzyme, PETase, lacks the stability to perform at scale in wastewater treatment. In this work, we show that genetic fusion of PETase to a silica binding peptide enables directed immobilization of the enzyme onto silica nanoparticles. PETase activity in simulated wastewater conditions is quantified by linear regression from time zero to the time of maximum fluorescence of a fluorescent oxidized product of PETase degradation of PET microfibers. Mesoporous silica is shown to be a superior support material to nonporous silica. The resulting biocatalytic nanomaterial has up to 2.5-fold enhanced stability and 6.2-fold increased activity compared to free enzyme in unbuffered, 40 °C simulated influent (ionic strength ∼15 mM). In unbuffered, 40 °C simulated effluent (ionic strength ∼700 μM), reaction velocity and overall catalytic activity were increased by the biocatalytic material 2.1-fold relative to free PETase. All reactions were performed in 0.2 mL volumes, and enzyme concentrations were normalized across both free and immobilized samples to 9 μg/mL. Site-directed mutagenesis is shown to be a complementary technique to directed immobilization, which may aid in optimization of the biomaterial for wastewater applications. PETase stabilization in application-relevant environments as shown here enables progress toward application of PETase for microplastic biodegradation in wastewater treatment.

The application of bioremediation in wastewater treatment plants for microplastics removal: a practical perspective

Wastewater treatment plants (WWTPs) play the role of intercepting microplastics in the environment and provide a platform for bioremediation to remove microplastics. Despite, this opportunity has not been adequately studied. This paper shows the potential ways microplastics-targeted bioremediation could be incorporated into wastewater treatment through the review of relevant literature on bioaugmentation of water treatment processes for pollutants removal. Having reviewed more than 90 papers in this area, it highlights that bioremediation in WWTPs can be employed through bioaugmentation of secondary biological treatment systems, particularly the aerobic conventional activated sludge, sequencing batch reactor, membrane bioreactor and rotating biological contactor. The efficiency of microplastics removal, however, is influenced by the types and forms of microorganisms used, the polymer types and the incubation time (100% for polycaprolactone with Streptomyces thermoviolaceus and 0.76% for low-density polyethylene with Acinetobacter iwoffii). Bioaugmentation of anaerobic system, though possible, is constrained by comparatively less anaerobic microplastics-degrading microorganisms identified. In tertiary system, bioremediation through biological activated carbon and biological aerated filter can be accomplished and enzymatic membrane reactor can be added to the system for deployment of biocatalysts. During sludge treatment, bioaugmentation and addition of enzymes to composting and anaerobic digestion are potential ways to enhance microplastics breakdown. Limitations of bioremediation in wastewater treatment include longer degradation time of microplastics, incomplete biodegradation, variable efficiency, specific microbial activities and uncertainty in colonization. This paper provides important insight into the practical applications of bioremediation in wastewater treatment for microplastics removal.

Immobilization of enzymes for bioremediation: A future remedial and mitigating strategy

Over the years, extensive urbanization and industrialization have led to xenobiotics contamination of the environment and also posed a severe threat to human health. Although there are multiple physical and chemical techniques for xenobiotic pollutants management, bioremediation seems to be a promising technology from the environmental perspective. It is an eco-friendly and low-cost method involving the application of microbes, plants, or their enzymes to degrade xenobiotics into less toxic or non-toxic forms. Moreover, bioremediation involving enzymes has gained an advantage over microorganisms or phytoremediation due to better activity for pollutant degradation with less waste generation. However, the significant disadvantages associated with the application of enzymes are low stability (storage, pH, and temperature) as well as the low possibility of reuse as it is hard to separate from reaction media. The immobilization of enzymes without affecting their activity provides a possible solution to the problems and allows reusability by easing the process of separation with improved stability to various environmental factors. The present communication provides an overview of the importance of enzyme immobilization in bioremediation, carrier selection, and immobilization methods, as well as the pros and cons of immobilization and its prospects.

Immobilized enzyme/microorganism complexes for degradation of microplastics: A review of recent advances, feasibility and future prospects

Environmental prevalence of microplastics has prompted the development of novel methods for their removal, one of which involves immobilization of microplastics-degrading enzymes. Various materials including nanomaterials have been studied for this purpose but there is currently a lack of review to present these studies in an organized manner to highlight the advances and feasibility. This article reviewed more than 100 peer-reviewed scholarly papers to elucidate the latest advances in the novel application of immobilized enzyme/microorganism complexes for microplastics degradation, its feasibility and future prospects. This review shows that metal nanoparticle-enzyme complexes improve biodegradation of microplastics in most studies through creating photogenerated radicals to facilitate polymer oxidation, accelerating growth of bacterial consortia for biodegradation, anchoring enzymes and improving their stability, and absorbing water for hydrolysis. In a study, the antimicrobial property of nanoparticles retarded the growth of microorganisms, hence biodegradation. Carbon particle-enzyme complexes enable enzymes to be immobilized on carbon-based support or matrix through covalent bonding, adsorption, entrapment, encapsulation, and a combination of the mechanisms, facilitated by formation of cross-links between enzymes. These complexes were shown to improve microplastics-degrading efficiency and recyclability of enzymes. Other emerging nanoparticles and/or enzymatic technologies are fusion of enzymes with hydrophobins, polymer binding module, peptide and novel nanoparticles. Nonetheless, the enzymes in the complexes present a limiting factor due to limited understanding of the degradation mechanisms. Besides, there is a lack of studies on the degradation of polypropylene and polyvinyl chloride. Genetic bioengineering and metagenomics could provide breakthrough in this area. This review highlights the optimism of using immobilized enzymes/microorganisms to increase the efficiency of microplastics degradation but optimization of enzymatic or microbial activities and synthesis of immobilized enzymes/microorganisms are crucial to overcome the barriers to their wide application.

A minireview on the bioremediative potential of microbial enzymes as solution to emerging microplastic pollution

Accumulating plastics in the biosphere implicates adverse effects, raising serious concern among scientists worldwide. Plastic waste in nature disintegrates into microplastics. Because of their minute appearance, at a scale of <5 mm, microplastics easily penetrate different pristine water bodies and terrestrial niches, posing detrimental effects on flora and fauna. The potential bioremediative application of microbial enzymes is a sustainable solution for the degradation of microplastics. Studies have reported a plethora of bacterial and fungal species that can degrade synthetic plastics by excreting plastic-degrading enzymes. Identified microbial enzymes, such as IsPETase and IsMHETase from Ideonella sakaiensis 201-F6 and Thermobifida fusca cutinase (Tfc), are able to depolymerize plastic polymer chains producing ecologically harmless molecules like carbon dioxide and water. However, thermal stability and pH sensitivity are among the biochemical limitations of the plastic-degrading enzymes that affect their overall catalytic activities. The application of biotechnological approaches improves enzyme action and production. Protein-based engineering yields enzyme variants with higher enzymatic activity and temperature-stable properties, while site-directed mutagenesis using the Escherichia coli model system expresses mutant thermostable enzymes. Furthermore, microalgal chassis is a promising model system for "green" microplastic biodegradation. Hence, the bioremediative properties of microbial enzymes are genuinely encouraging for the biodegradation of synthetic microplastic polymers.

Monitoring protein conformational changes using fluorescent nanoantennas

Understanding the relationship between protein structural dynamics and function is crucial for both basic research and biotechnology. However, methods for studying the fast dynamics of structural changes are limited. Here, we introduce fluorescent nanoantennas as a spectroscopic technique to sense and report protein conformational changes through noncovalent dye-protein interactions. Using experiments and molecular simulations, we detect and characterize five distinct conformational states of intestinal alkaline phosphatase, including the transient enzyme-substrate complex. We also explored the universality of the nanoantenna strategy with another model protein, Protein G and its interaction with antibodies, and demonstrated a rapid screening strategy to identify efficient nanoantennas. These versatile nanoantennas can be used with diverse dyes to monitor small and large conformational changes, suggesting that they could be used to characterize diverse protein movements or in high-throughput screening applications.

Recent endeavors in microbial remediation of micro- and nanoplastics

Petrochemical plastics are frequently utilized in our daily lives for various purposes such as packaging and transportation, but their burden on the environment is considered one of the most man-made pollution crises. These pollutants are slowly fragmented in the environment into microplastics and nanoplastics by consolidated actions of abiotic and biotic factors. Microplastics and nanoplastics can easily be dispersed in the atmosphere and be harmful to all kinds of life. As a result, the remediation of micro- and nanoplastics has recently received a tremendous research impetus in the realm of an ecologically benign approach, notably microbial-based remediation. Thus, the current article looks at the formation, properties, analysis, and biological effects of micro- and nanoplastics. The content is then streamlined towards a comprehensive discussion on microbial-mediated degradation of microplastics and nanoplastics, with an emphasis on front-line bacteria and enzymes, as well as remediation mechanisms. Further, technologies for the removal of microplastics and nanoplastics from the environment are presented for possible remedial considerations. An attempt is also made to highlight the practical snags of microbial plastic degradation while aiming to alleviate the environmental burden of plastic waste.