Microbial enzymes for the recycling of recalcitrant petroleum-based plastics: how far are we?

Advances in engineering substrate scope of Pseudomonas cell factories

Most current industrial bioprocesses use well-established model microorganisms and simple sugar substrates from edible starch or molasses. To broaden and sustain bioprocesses, we need to explore new robust microbial hosts with desirable traits and ideally exploit diverse waste-derived substrates. Pseudomonas species are prime candidates for new generation of industrial biotechnology due to their resilient physiology and adaptable metabolism. However, natural isolates are not always suitable for demanding biotechnological applications. Despite pseudomonads' typically broad substrate range, their catabolism can be further enhanced through metabolic engineering, synthetic biology, and/or laboratory evolution to efficiently degrade, utilize, and valorize alternative waste substrates derived from lignocellulosic residues, synthetic plastics, C1 compounds, or their mixtures.

Interactions between nanoplastics and Tetrahymena thermophila: Low toxicity vs. potential biodegradation

Nanoplastics (NPs) are prevalent throughout the environment and have raised growing environmental concerns. Although numerous studies have examined the toxicological aspects of NPs, few have investigated their environmental fate and behavior when affected by organisms other than bacteria or fungi. Planktonic ciliates are essential components of aquatic ecosystems and play important roles in decomposing organic matter and transferring energy from the microbial food web to higher trophic levels. To investigate the interplay between NPs and the ciliate Tetrahymena thermophila, we executed a sequence of feeding experiments utilizing 50 nm polystyrene nanoplastics (PS-NPs). In the presence of sufficient nutrition, exposure to PS-NPs (even at concentrations up to 500 mg/L) did not significantly inhibit growth in Tetrahymena thermophila, indicating only a mild toxic effect of PS-NPs. When ingested by T. thermophila, the PS-NPs are repackaged into aggregates with lysosomal components in the food vacuole and finally expelled as compacted "fecal pellets". This process modifies the physical attributes of PS-NPs, including their hydrophilicity, aggregability, and buoyancy, influencing their transportation, retention, deposition dynamics, and ultimately their bioavailability within the environment. A total of 73 proteins were identified from the fecal pellets, containing various hydrolases. Gel permeation chromatography (GPC), Fourier transform infrared (FTIR), and thermogravimetric analysis (TGA) were used to identify changes in molecular weights, functional groups, and thermal stabilities of PS-NP residues in fecal pellets. The results verified the degradation of PS-NPs during the passage through the T. thermophila cell.

Can the insects Galleria mellonella and Tenebrio molitor be the future of plastic biodegradation?

Plastics have been an integral part of human lives, enhancing the functionality and safety of many everyday products, contributing significantly to our overall well-being. However, petroleum-based plastics can take hundreds or even thousands of years to decompose, resulting in an unprecedented plastic waste accumulation in the environment. Widely used conventional plastic disposal methods as landfilling and incineration are also environmentally harmful, frequently leading to soil/water contamination and the release of microplastics. To overcome these limitations, researchers have been investigating novel sustainable alternatives for plastic waste management, such as the use of microorganisms, microbial-based enzymes, and, more recently, some insect larvae, being Galleria mellonella and Tenebrio molitor the most promising ones. In this review, we explore different methods of plastic waste disposal focusing on recent discoveries regarding biological plastic degradation using insects as alternative methods. We also discuss the plastic degradation mechanisms employed by G. mellonella and T. molitor larvae known so far, as salivary enzymes and the pool of microorganisms in their gut. Finally, this review highlights key challenges in plastic biodegradation, such as standardization and experimental comparability, while proposing innovative perspectives like using insects as bioreactors and exploring unexplored research directions.

Structural and Functional Characterization of an Amidase Targeting a Polyurethane for Sustainable Recycling

Global plastic production exceeded 400 million tons in 2022, urgently demanding improved waste management and recycling strategies for a circular plastic economy. While the enzymatic hydrolysis of polyethylene terephthalate (PET) has become feasible on industrial scales, efficient enzymes targeting other hydrolyzable plastic types, such as polyurethanes (PURs), are lacking. Recently, enzymes of the amidase signature (AS) family, capable of cleaving urethane bonds in a polyether-PUR analog and a linear polyester-PUR, have been identified. Herein, we present high-resolution crystal structures of the AS enzyme UMG-SP3 in three states: ligand-free, bound with a suicidal inhibitor mimicking the transition state, and bound with a monomeric PUR degradation product. Besides revealing the conserved core and catalytic triad akin to other AS family members, the UMG-SP3 structures show remarkable flexibility of loop regions. Particularly, Arg209 in loop 3 adopts two induced-fit conformations upon ligand binding. Through structure-guided kinetic studies and enzyme engineering, we mapped structural key elements that determine the enhanced hydrolysis of urethane and amide bonds in various small molecules, including a linear PUR fragment analog. Our findings contribute critical insights into urethanase activity, aiding PUR degradation campaigns and sustainable plastic recycling efforts in the future.

Discovery of a polyester polyurethane-degrading bacterium from a coastal mudflat and identification of its degrading enzyme

Biodegradation of polyurethane (PU) plastics is a lower cost and more environmentally friendly approach to the regeneration of waste plastics than the landfill or incineration alternatives. Currently, however, the lack of efficient degradation strains and their enzymes is restricting the development of viable large-scale waste PU regeneration. In this study, a wild strain (LTX1) is isolated from a coastal mudflat, and then a mutant strain (MLTX1) with higher degradation efficiency is obtained by UV mutagenesis. Both the LTX1 and MLTX1 strains are able to achieve a more than 80 % weight loss of PU foam after 12 days treatment, making them the most efficient PU foam-degrading strains available to date. The PU foam degradation is characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). A novel gene, purh, encoding one of the cutinases is cloned using genomics and transcriptomics, and its recombinant PurH, capable of efficiently degrading PU foam, is expressed in Escherichia coli and identified. The discovery of this highly-efficient PU foam-degrading strain and its enzyme may represent a leap forward in the biological depolymerization and recycling of PU foam.

Two-step biocatalytic conversion of post-consumer polyethylene terephthalate into value-added products facilitated by genetic and bioprocess engineering

Solving the plastic crisis requires high recycling quotas and technologies that allow open loop recycling. Here a biological plastic valorization approach consisting of tandem enzymatic hydrolysis and monomer conversion of post-consumer polyethylene terephthalate into value-added products is presented. Hydrolysates obtained from enzymatic degradation of pre-treated post-consumer polyethylene terephthalate bottles in a stirred-tank reactor served as the carbon source for a batch fermentation with an engineered Pseudomonas putida strain to produce 90mg/L of the biopolymer cyanophycin. Through fed-batch operation, the fermentation could be intensified to 1.4 g/L cyanophycin. Additionally, the upcycling of polyethylene terephthalate monomers to the biosurfactants (hydroxyalkanoyloxy)alkanoates and rhamnolipids is presented. These biodegradable products hold significant potential for applications in areas such as detergents, building blocks for novel polymers, and tissue engineering. In summary, the presented bio-valorization process underscores that addressing challenges like the plastic crisis requires an interdisciplinary approach.

Streptomyces coeruleorubidus strain SALG1 derived seashore plastic bottle for the biodegradation of untreated plastic polymers

Plastic pollution has become a significant environmental concern due to the widespread use and persistence of polyethylene (PE) in various industries. In this study, soil samples containing plastic waste were collected from a public landfill site, along with plastic bottles gathered from the shore of Sidi Ali Lebher in the Bejaia region, Algeria. In total, nine strains of PE-degrading actinobacteria were isolated using PE as sole carbon source. The SALG1 strain was isolated from plastic bottles and selected for its high enzymatic potential and effectiveness in degrading PE. Selected from nine actinobacteria isolates, it was identified as Streptomyces coeruleorubidus with 98.28% similarity to Streptomyces coeruleorubidus type strain ISP 5145 T based on the 16S rRNA gene sequence analysis. The growth of SALG1 was evaluated using polyethylene glycol (PEG) as the sole carbon source, demonstrating a significant reduction in PEG concentration over a 14-day period, accompanied by biomass accumulation. Furthermore, SALG1 exhibited biosurfactant production and hydrophobicity, indicating its potential to interact with hydrophobic substrates like PE. Biodegradation experiments conducted over 2 and 6 months revealed SALG1's capability to degrade colorless and black PE (9.18% and 5.22%), as well as polystyrene (PS) and polyethylene terephthalate (PET) (0.25% and 0.42%) in both liquid and solid media. Moreover, the presence of Tween 80 enhanced degradation percentages, particularly in liquid media, suggesting its utility as a potential biostimulant. Structural changes induced by SALG1 activity in polymer films were characterized using X-ray diffraction (XRD) and infrared spectrophotometry (ATR), as well as the thermogravimetric analysis (TG/DTG) providing valuable insights into the degradation mechanism.

In-Situ Product Removal for the Enzymatic Depolymerization of Poly(ethylene terephthalate) via a Membrane Reactor

Poly(ethylene terephthalate) (PET) is a common single-use plastic and a major contributor to plastic waste. PET upcycling through enzymatic depolymerization has drawn significant interests, but lack of robust enzymes in acidic environments remains a challenge. This study investigates in-situ product removal (ISPR) of protons and monomers from enzymatic PET depolymerization via a membrane reactor, focusing on the ICCG variant of leaf branch compost cutinase. More than two-fold improvements in overall PET depolymerization and terephthalic acid yields were achieved employing ISPR for an initial PET loading of 10 mgPET mlbuffer -1. The benefit of ISPR was reduced for a lower initial loading of 1 mgPET mlbuffer -1 due to decreased need for pH stabilization of the enzyme-containing solutions. A back-of-envelop analysis suggests that at a modest dilution ratio, ISPR could help achieve savings on caustic base solutions used for pH control in a bioreactor. Our study provides valuable insights for future ISPR developments for enzymatic PET depolymerization, addressing the pressing need for more sustainable solutions towards plastic recycling and environmental conservation.

Homology modeling and thermostability enhancement of Vibrio palustris PETase via hydrophobic interactions

The quest for sustainable solutions to plastic pollution has driven research into plastic-degrading enzymes, offering promising avenues for polymer recycling applications. However, enzymes derived from natural sources often exhibit suboptimal thermostability, hindering their industrial viability. Protein engineering techniques have emerged as a powerful approach to enhance the desired properties of these biocatalysts. This study aims to conduct a comprehensive analysis of the thermostability of Vibrio palustris PETase (VpPETase) through an integrated computational approach encompassing homology modeling, site-specific molecular docking, molecular dynamics (MD) simulations, and comparative evaluation of a single-point mutation (V195F) against the wild-type enzyme. Homology modeling was used to predict VpPETase model using multiple templates. Model quality was rigorously assessed using Ramachandran plot analysis, ProSA, Verify 3D, and ERRAT. Molecular docking elucidated the catalytic region comprising residues His149, Asp117, and Ser71, while highlighting the pivotal roles of His149, Tyr1, and Ser71 in substrate binding affinity. MD simulations at various temperatures revealed higher stability at 313.15 K over a 100 ns trajectory, as evidenced by analyses of root-mean-square deviation (RMSD), radius of gyration (Rg), solvent-accessible surface area (SASA), hydrogen bonding, and root-mean-square fluctuation (RMSF). The V195F mutant exhibited a slight increase in stability compared to wild-type. While this study provides valuable insights into the thermostability of VpPETase, further investigations, including experimental validation of thermostability enhancements and in vitro characterization, are warranted to fully exploit the potential of this enzyme for industrial applications in plastic recycling.

Scalable nanoplastic degradation in water with enzyme-functionalized porous hydrogels

The prevalence of nanoplastics in water has led to significant environmental and health concerns, yet effective and scalable strategies for mitigating this contamination remain limited. Here, we report a straightforward, efficient, and scalable approach to degrade nanoplastics in water using enzyme-loaded hydrogel granules with an interconnected porous structure and adjustable properties. These porous hydrogels were synthesized via a polymerization-induced phase separation method, allowing easy scaling-up. Our results show that enzyme-functionalized porous hydrogels slightly outperform free cutinase in nanoplastic degradation. Furthermore, immobilized enzymes exhibited enhanced stability under harsh conditions, achieving a 104.1 % higher PET removal rate at pH 5 than free cutinase. Notably, the immobilized enzyme retained 39.9 % of its initial degradation activity after five cycles, demonstrating good reuse stability. This method offers a promising and practical solution for using enzymes to address nanoplastic pollution in aquatic environments.

Microbial Biodegradation of Synthetic Polyethylene and Polyurethane Polymers by Pedospheric Microbes: Towards Sustainable Environmental Management

This study attempted to isolate and identify pedospheric microbes originating in dumpsites and utilized them for the degradation of selected synthetic polymers for the first time in a cost-effective, ecologically favorable and sustainable manner. Specifically, low-density polyethylene (LDPE) and polyurethane (PUR) were converted by the isolated fungi, i.e., Aspergillus flavus, A terreus, A. clavatus, A. nigers and bacterial coccus and filamentous microbes and assessed in a biotransformative assay under simulated conditions. Commendable biodegradative potentials were exhibited by the isolated microbes against polymers that were analyzed over a span of 30 days. Among the selected fungal microbes, the highest activity was achieved by A. niger, expressing 55% and 40% conversion of LDPE and PUR, respectively. In the case of bacterial strains, 50% and 40% conversion of LDPE and PUR degradation was achieved by coccus. Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) were utilized to analyze the degradative patterns in terms of vibrational and thermal characteristics, and stereomicroscopic analysis was performed for the visual assessment of morphological variations. Profound structural transformations were detected in FT-IR spectra and TGA thermograms for the selected microbes. Stereomicroscopic analysis was also indicative of the remarkable transformation of the surface morphology of these polymers after degradation by microbes in comparison to the reference samples not treated with any pedospheric microbes. The results are supportive of the utilization of the selected pedospheric microbes as environmental remediators for the cleanup of persistent polymeric toxins. This current work can be further extended for the successful optimization of further augmented percentages by using other pedospheric microbes for the successful adoption of these biotechnological tools at a practical level.

Water-Resistant Poly(vinyl alcohol)/ZnO Nanopillar Composite Films for Antibacterial Packaging

To solve the problems that poly(vinyl alcohol) (PVA) easily breeds bacteria and swells in a humid environment, PVA and ZnO nanopillar (ZnO NP) components were composed to generate PVA/ZnO NP composite films via a simple combination process of blending and heat treatment in this study. Here, ZnO NPs endowed composite films with good antibacterial properties, and the etherification and dehydration of hydroxyl groups between PVA molecular chains induced by heat treatment resulted in the composite films having excellent water-swelling resistance. Most importantly, PVA/ZnO NP composite films revealed excellent tensile strength in both humid (52.85 MPa) and dry (74.63 MPa) environments. In addition, PVA/ZnO NP composite films showed good antibacterial and antisepsis abilities as well as preservation functions in the packaging test of half-cut apples. The current work disclosed an easy strategy for producing a PVA-based antibacterial film for packaging materials that are water-resistant and highly strong, making them suitable for applications in humid environments.

Microbial strategies for effective microplastics biodegradation: Insights and innovations in environmental remediation

Microplastics (MPs), diminutive yet ubiquitous fragments arising from the degradation of plastic waste, pervade environmental matrices, posing substantial risks to ecological systems and trophic dynamics. This review meticulously examines the origins, distribution, and biological impacts of MPs, with an incisive focus on elucidating the molecular and cellular mechanisms underpinning their toxicity. We highlight the indispensable role of microbial consortia and enzymatic pathways in the oxidative degradation of MPs, offering insights into enhanced biodegradation processes facilitated by innovative pretreatment methodologies. Central to our discourse is the interplay between MPs and biota, emphasizing the detoxification capabilities of microbial metabolisms and enzymatic functions in ameliorating MPs' deleterious effects. Additionally, we address the practical implementations of MP biodegradation in environmental remediation, advocating for intensified research to unravel the complex biodegradation pathways and to forge effective strategies for the expeditious elimination of MPs from diverse ecosystems. This review not only articulates the pervasive challenges posed by MPs but also positions microbial strategies at the forefront of remedial interventions, thereby paving the way for groundbreaking advancements in environmental conservation.

Biotechnology for the degradation and upcycling of traditional plastics

Traditional plastics, predominantly derived from petrochemicals, are extensively utilized in modern industry and daily life. However, inadequate management and disposal practices have resulted in widespread environmental contamination, with polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, and polystyrene being the most prevalent pollutants. Biological methods for plastic degradation have garnered significant attention due to their cost-effectiveness and potential for resource recovery, positioning them as promising strategies for sustainable plastic waste management. While polyethylene terephthalate, characterized by its relatively less stable C-O bonds, has been extensively studied and demonstrates significant potential for biodegradation. In contrast, the biodegradation of other plastics remains a significant challenge due to the inherent stability of their C-C backbone structures. This review comprehensively examines the state-of-the-art biotechnology for treating these traditional plastics, focusing on: (1) the roles of specific microorganisms and enzymes, their taxonomic classifications, and the metabolic pathways involved in plastic biodegradation; and (2) a proposed two-stage hybrid approach integrating physicochemical and biological processes to enhance the biodegradation or upcycling of these traditional plastics. Additionally, the review highlights the critical role of multi-omics approaches and tailored strategies in enhancing the efficiency of plastic biodegradation while examining the impact of plastic molecular structures and additives on their degradation potential. It also addresses key challenges and delineates future research directions to foster the development of innovative biological methods for the effective and sustainable management of plastic waste.

Insights into polyethylene biodegradative fingerprint of Pseudomonas citronellolis E5 and Rhodococcus erythropolis D4 by phenotypic and genome-based comparative analyses

Polyethylene (PE) is the most-produced polyolefin, and consequently, it is the most widely found plastic waste worldwide. PE biodegradation is under study by applying different (micro)organisms in order to understand the biodegradative mechanism in the majority of microbes. This study aims to identify novel bacterial species with compelling metabolic potential and strategic genetic repertoires for PE biodegradation. Pseudomonas citronellolis E5 is newly isolated from solid organic waste contaminated with plastic debris, and Rhodococcus erythropolis D4 was selected for its promising potential in biodegradable plastic determined by its genetic repertoire. P. citronellolis E5 was selected for its ability to grow on PE as the only carbon and energy source. Meaningful extracellular secreted laccase activity was also characterized for D4 during growth on PE (E5 and D4 strains have a laccase activity of (2 ± 1)×10-3 U mg-1 and (3 ± 1)×10-3 U mg-1, respectively). Despite the highest level of cell numbers recorded at 7 days of growth on PE for both strains, the patterns of the metabolic products obtained and degraded during 60 days on PE were dissimilar in the two bacteria at different sampling times. However, they mainly produced metabolites belonging to carboxylic acids and alkanes with varying numbers of carbons in the aliphatic chains. Whole-genome sequence analyses of P. citronellolis E5 compared to R. erythropolis D4 and genetic determinant prediction (by gene annotation and multiple sequence alignment with reference gene products) have been performed, providing a list of 16 and 42 gene products putatively related to different metabolic steps of PE biodegradation. Altogether, these results support insights into PE biodegradation by bacteria of the Pseudomonas and Rhodococcus genera from metabolic and genetic perspectives as a base to build up novel biotechnological platforms.

Analytical tools to assess polymer biodegradation: A critical review and recommendations

Many petroleum-derived plastic materials are highly recalcitrant and persistent in the environment, posing significant threats to human and ecological receptors due to their accumulation in ecosystems. In recent years, research efforts have focused on advancing biological methods for polymer degradation. Enzymatic depolymerization has emerged as particularly relevant for biobased plastic recycling, potentially scalable for industrial use. Biodegradation involves adsorption to the plastic solid surface, followed by an interfacial reaction, resulting in cleavage of bonds of polymer chains exposed on the surface. Here, widely varying substrate-specific kinetics are observed, with the polymer's properties possessing a significant impact on the rate of this interfacial catalysis. Thus, there is a critical need for sensitive and accurate characterization of the material surface during and after interfacial depolymerization to fully understand the reaction mechanisms. Here, we provide a critical review of a range of techniques used in the analysis of material surfaces to characterize the chemical, topological, and morphological features relevant to the study of enzymatic biocatalysis, including microscopy techniques, spectroscopic techniques (e.g., X-ray diffraction analysis, Fourier transform infrared attenuated total reflectance spectroscopy, and mass spectrometry detection of analytes associated with degradation). Techniques for evaluation of surface energy and topology in their relevancy for sensitive detection of biological surface modifications are also discussed. In addition, this paper provides an overview of the strengths of these techniques and compares their performance in both sensitivity and throughput, including emerging techniques, which can be useful, particularly for the rapid analysis of the surface properties of polymeric materials in high-throughput screening of candidate biocatalysts. This research serves as a starting point in selecting and applying appropriate methodologies that provide direct evidence to the ongoing biotic degradation of polymeric materials.

Roles of carbon dioxide in the conversion of biomass or waste plastics

Under the current trend of pursuing sustainable development and environmental protection, the important application of carbon dioxide (CO2) in the conversion process of biomass or waste plastics has become a research direction of concern. The goal of this conversion process is to achieve the efficient use of carbon dioxide, providing a process for the efficient use of biomass, and solving the environmental problems caused by plastics. Remarkable progress has been made in the study of the reaction of CO2 with other substances to produce methane, low-carbon hydrocarbons, methanol, formic acid, and its derivatives, as well as ethers, aldehydes, gasoline, low-carbon alcohols, and other chemicals. In this paper, the important role of CO2 in the conversion of alcohol, sugar, cellulose, and waste plastics was reviewed, with emphasis on the important applications of CO2 as a carbon source, reactant, reaction medium, enhancing agent, solvent, and carrier gas in the conversion of biomass or waste plastics and the basic insights of the reaction mechanism. The emerging CO2 new roles not only put forward the green application of CO2 but also have guiding significance for the utilization of biomass resources and the treatment of waste plastics.

An overview on polyurethane-degrading enzymes

Polyurethanes (PUR) are durable synthetic polymers widely used in various industries, contributing significantly to global plastic consumption. PUR pose unique challenges in terms of degradability and recyclability, as they are characterised by intricate compositions and diverse formulations. Additives and proprietary structures used in commercial PUR formulations further complicate recycling efforts, making the effective management of PUR waste a daunting task. In this review, we delve into the complex challenge of enzymatic degradation of PUR, focusing on the structural and functional attributes of both enzymes and PUR. We also present documented native enzymes with reported efficacy in hydrolysing specific bonds within PUR, analysis of these enzyme structures, reaction mechanisms, substrate specificity, and binding site architecture. Furthermore, we propose essential features for the future redesign of enzymes to optimise PUR biodegradation efficiency. By outlining prospective research directions aimed at advancing the field of enzymatic biodegradation of PUR, we aim to contribute to the development of sustainable solutions for managing PUR waste and reducing environmental pollution.

Fungal microbiota of biodamages of various polymeric materials

Data on microbial fouling of various synthetic polymer materials, including those used in space technology, are summarized. It has been established that the dominant groups of microbiota of polymer fouling are the genera of mitosporous fungi Aspergillus, Penicillium, Alternaria, Trichoderma. The enzymatic properties of fungal strains from the collection of microbial cultures of the Microbial Depository Center of the National Academy of Sciences of Armenia were studied. It has been shown that Aspergillus fumigatus, Penicillium chrysogenum, P. steckii, Juxtiphoma eupyrena and a number of other fungi have biofouling activity towards polyethylene, polyethylene terephthalate and some other synthetic polymers. New fungal kits have been developed and proposed to evaluate the fungal resistance of polymeric materials. They include fungi isolated from bio-damaged polymers used in space technology and contain 2 to 5 fungal strains instead of 7 to 9 strains in previously used kits. Taking into account the obtained data, a comparative assessment of the fungal resistance of samples of synthetic polymeric materials of various classes that passed accelerated climatic tests has been carried out. It has been established that the kits of biodegradant fungi, composed of cultures of bio-damaged space technology, generally exceeded the activity of the previously used kits, based on which one can judge the obvious advantages of strains isolated from bio-damaged space technology. In the future, these kits could find application not only for biodegradation of polymers, but also for testing the biostability of various polymers, to use for the construction of aviation and space techniques. Moreover, new optimized kits may be developed based on the strains involved in this study.

Enhancing polyethylene degradation: a novel bioprocess approach using Acinetobacter nosocomialis pseudo-resting cells

Despite the discovery of several bacteria capable of interacting with polymers, the activity of the natural bacterial isolates is limited. Furthermore, there is a lack of knowledge regarding the development of bioprocesses for polyethylene (PE) degradation. Here, we report a bioprocess using pseudo-resting cells for efficient degradation of PE. The bacterial strain Acinetobacter nosocomialis was isolated from PE-containing landfills and characterized using low-density PE (LDPE) surface oxidation when incubated with LDPE. We optimized culture conditions to generate catalytic pseudo-resting cells of A. nosocomialis that are capable of degrading LDPE films in a bioreactor. After 28 days of bioreactor operation using pseudo-resting cells of A. nosocomialis, we observed the formation of holes on the PE film (39 holes per 217 cm2, a maximum diameter of 1440 μm). This study highlights the potential of bacteria as biocatalysts for the development of PE degradation processes. KEY POINTS: • New bioprocess has been proposed to degrade polyethylene (PE). • Process with pseudo-resting cells results in the formation of holes in PE film. • We demonstrated PE degradation using A. nosocomialis as a biocatalyst.

Cutting-edge developments in plastic biodegradation and upcycling via engineering approaches

The increasing use of plastics has resulted in the production of high quantities of plastic waste that pose a serious risk to the environment. The upcycling of plastics into value-added products offers a potential solution for resolving the plastics environmental crisis. Recently, various microorganisms and their enzymes have been identified for their ability to degrade plastics effectively. Furthermore, many investigations have revealed the application of plastic monomers as carbon sources for bio-upcycling to generate valuable materials such as biosurfactants, bioplastics, and biochemicals. With the advancement in the fields of synthetic biology and metabolic engineering, the construction of high-performance microbes and enzymes for plastic removal and bio-upcycling can be achieved. Plastic valorization can be optimized by improving uptake and conversion efficiency, engineering transporters and enzymes, metabolic pathway reconstruction, and also using a chemo-biological hybrid approach. This review focuses on engineering approaches for enhancing plastic removal and the methods of depolymerization and upcycling processes of various microplastics. Additionally, the major challenges and future perspectives for facilitating the development of a sustainable circular plastic economy are highlighted.

Review of key issues and potential strategies in bio-degradation of polyolefins

Polyolefins are the most widely used plastic product and a major contributor to white pollution. Currently, studies on polyolefin degradation systems are mainly focused on microorganisms and some redox enzymes, and there is a serious black-box phenomenon. The use of polyolefin-degrading enzymes is limited because of the small number of enzymes; in addition, the catalytic efficiency of these enzymes is poor and their catalytic mechanism is unclear, which leads to the incomplete degradation of polyolefins to produce microplastics. In this review, three questions are addressed: the generation and degradation of action targets that promote the degradation of polyolefins, the different modes by which enzymes bind substrates and their application scenarios, and possible multienzyme systems in a unified system. This review will be valuable for mining or modifying polyolefin degradation enzymes and constructing polyolefins degradation systems and may provide novel ideas and opportunities for polyolefin degradation.

Applications and environmental impact of biodegradable polymers in textile industry: A review

With the increasing global population, the disposal of waste has risen, especially over the last century. The Environmental Protection Agency (EPA) reported that 11 million tons of textile-related waste were landfilled in the USA in 2018, and this amount is projected to increase to 4.5 billion tons by 2040. Bio-based polymers have gained attention due to their remarkable properties. The most important biodegradable polymers include PLA, PHA, PHB, PCL, PBS, bamboo fibers, and banana fibers. Global biopolymer production capacity is expected to rise significantly, from around 2.18 million tons in 2023 to approximately 7.43 million tons by 2028. In the textile industry, the linear waste model presents numerous challenges, such as environmental damage and resource shortages. Shifting from a linear to a circular economy is essential to address these issues. Reducing, reusing, and recycling are the three key actions and strategies that form the foundation of the circular economy. This paper presents the current state of knowledge and technological advancements in biodegradable polymers in the textile industry, along with their products and applications. The study explores the cost-effectiveness, limitations, opportunities, and advancements in their manufacturing technologies. Biodegradable polymers in the textile sector are regarded as green alternatives to non-biodegradable polymers.

PEZy-miner: An artificial intelligence driven approach for the discovery of plastic-degrading enzyme candidates

Plastic waste has caused a global environmental crisis. Biocatalytic depolymerization mediated by enzymes has emerged as an efficient and sustainable alternative for plastic treatment and recycling. However, it is challenging and time-consuming to discover novel plastic-degrading enzymes using conventional cultivation-based or omics methods. There is a growing interest in developing effective computational methods to identify new enzymes with desirable plastic degradation functionalities by exploring the ever-increasing databases of protein sequences. In this study, we designed an innovative machine learning-based framework, named PEZy-Miner, to mine for enzymes with high potential in degrading plastics of interest. Two datasets integrating information from experimentally verified enzymes and homologs with unknown plastic-degrading activity were created respectively, covering eleven types of plastic substrates. Protein language models and binary classification models were developed to predict enzymatic degradation of plastics along with confidence and uncertainty estimation. PEZy-Miner exhibited high prediction accuracy and stability when validated on experimentally verified enzymes. Furthermore, by masking the experimentally verified enzymes and blending them into homolog dataset, PEZy-Miner effectively concentrated the experimentally verified entries by 14∼30 times while shortlisting promising plastic-degrading enzyme candidates. We applied PEZy-Miner to 0.1 million putative sequences, out of which 27 new sequences were identified with high confidence. This study provided a new computational tool for mining and recommending promising new plastic-degrading enzymes.

Catalyst- and Solvent-Free Upcycling of Poly(Ethylene Terephthalate) Waste to Biodegradable Plastics

Poly(ethylene terephthalate) (PET) is an important polymer with annual output second only to polyethylene. Due to its low biodegradability, a large amount of PET is recycled for sustainable development. However, current strategies for PET recycling are limited by low added value or small product scale. It is urgent to make a breakthrough on the principle of PET macromolecular reaction and efficiently prepare products with high added value and wide applications. Here, the catalyst- and solvent-free synthesis of biodegradable plastics are reported through novel carboxyl-ester transesterification between PET waste and bio-based hydrogenated dimer acid (HDA), which can directly substitute some terephthalic acid (TPA) units in PET chain by HDA unit. This macromolecular reaction can be facilely carried out on current equipment in the polyester industry without any additional catalyst and solvent, thus enabling low-cost and large-scale production. Furthermore, the product semi-bio-based copolyester shows excellent mechanical properties, regulable flexibility and good biodegradability, which is expected to substitute poly(butylene adipate-co-terephthalate) (PBAT) plastic as high value-added biodegradable materials. This work provides an environmental-friendly and economic strategy for the large-scale upcycling of PET waste.

Anaerobic Degradation of Aromatic and Aliphatic Biodegradable Plastics: Potential Mechanisms and Pathways

Biodegradable plastics (BDPs) have been widely used as substitutes for traditional plastics, and their environmental fate is a subject of intense research interest. Compared with the aerobic degradation of BDPs, their biodegradability under anaerobic conditions in environmental engineering systems remains poorly understood. This study aimed to investigate the degradability of BDPs composed of poly(butylene adipate-co-terephthalate) (PBAT), poly(lactide acid) (PLA), and their blends, and explore the mechanism underlying their microbial degradation under conditions of anaerobic digestion (AD). The BDPs readily depolymerized under thermophilic conditions but were hydrolyzed at a slow rate under conditions of mesophilic AD. After 45 days of thermophilic AD, a decrease in the molecular weight and significant increase in the production of methane and carbon dioxide production were observed. Network and metagenomics analyses identified AD as reservoirs of plastic-degrading bacteria that produce multiple plastic-degrading enzymes. PETase was identified as the most abundant plastic-degrading enzyme. A potential pathway for the anaerobic biodegradation of BDPs was proposed herein. The polymers of high molecular weight were subjected to abiotic hydrolysis to form oligomers and monomers, enabling subsequent microbial hydrolysis and acetogenesis. Ultimately, complete degradation was achieved predominantly via the pathway involved in the conversion of acetic acid to methane. These findings provide novel insight into the mechanism underlying the anaerobic degradation of BDPs and the microbial resources crucial for the efficient degradation of BDPs.

Micro-Nanoparticle Characterization: Establishing Underpinnings for Proper Identification and Nanotechnology-Enabled Remediation

Microplastics (MPLs) and nanoplastics (NPLs) are smaller particles derived from larger plastic material, polymerization, or refuse. In context to environmental health, they are separated into the industrially-created "primary" category or the degradation derivative "secondary" category where the particles exhibit different physiochemical characteristics that attenuate their toxicities. However, some particle types are more well documented in terms of their fate in the environment and potential toxicological effects (secondary) versus their industrial fabrication and chemical characterization (primary). Fourier Transform Infrared Spectroscopy (FTIR/µ-FTIR), Raman/µ-Raman, Proton Nuclear Magnetic Resonance (H-NMR), Curie Point-Gas Chromatography-Mass Spectrometry (CP-gc-MS), Induced Coupled Plasma-Mass Spectrometry (ICP-MS), Nanoparticle Tracking Analysis (NTA), Field Flow Fractionation-Multiple Angle Light Scattering (FFF-MALS), Differential Scanning Calorimetry (DSC), Thermogravimetry (TGA), Differential Mobility Particle [Sizing] (DMPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Scanning Transmission X-ray Microspectroscopy (STXM) are reviewed as part of a suite of characterization methods for physiochemical ascertainment and distinguishment. In addition, Optical-Photothermal Infrared Microspectroscopy (O-PTIR), Z-Stack Confocal Microscopy, Mueller Matrix Polarimetry, and Digital Holography (DH) are touched upon as a suite of cutting-edge modes of characterization. Organizations, like the water treatment or waste management industry, and those in groups that bring awareness to this issue, which are in direct contact with the hydrosphere, can utilize these techniques in order to sense and remediate this plastic polymer pollution. The primary goal of this review paper is to highlight the extent of plastic pollution in the environment as well as introduce its effect on the biodiversity of the planet while underscoring current characterization techniques in this field of research. The secondary goal involves illustrating current and theoretical avenues in which future research needs to address and optimize MPL/NPL remediation, utilizing nanotechnology, before this sleeping giant of a problem awakens.

Isolation of marine polyethylene (PE)-degrading bacteria and its potential degradation mechanisms

Microbial degradation of polyethylene (PE) offers a promising solution to plastic pollution in the marine environment, but research in this field is limited. In this study, we isolated a novel marine strain of Pseudalkalibacillus sp. MQ-1 that can degrade PE. Scanning electron microscopy and water contact angle results showed that MQ-1 could adhere to PE films and render them hydrophilic. Analyses using X-ray diffraction, fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy showed a decrease in relative crystallinity, the appearance of new functional groups and an increase in the oxygen-to‑carbon ratio of the PE films, making them more susceptible to degradation. The results of gel permeation chromatography and liquid chromatography-mass spectrometry indicated the depolymerization of the long PE chains, with the detection of an intermediate, decanediol. Furthermore, genome sequencing was employed to investigate the underlying mechanisms of PE degradation. The results of genome sequencing analysis identified the genes associated with PE degradation, including cytochrome P450, alcohol dehydrogenase, and aldehyde dehydrogenase involved in the oxidative reaction, monooxygenase related to ester bond formation, and esterase associated with ester bond cleavage. In addition, enzymes involved in fatty acid metabolism and intracellular transport have been identified, collectively providing insights into the metabolic pathway of PE degradation.

Enterobacter cloacae-mediated polymer biodegradation: in-silico analysis predicts broad spectrum degradation potential by Alkane monooxygenase

Plastic pollution poses a significant environmental challenge. In this study, the strain Enterobacter cloacae O5-E, a bacterium displaying polyethylene-degrading capabilities was isolated. Over a span of 30 days, analytical techniques including x-ray diffractometry, scanning electron microscopy, optical profilometry, hardness testing and mass spectrometric analysis were employed to examine alterations in the polymer. Results revealed an 11.48% reduction in crystallinity, a 50% decrease in hardness, and a substantial 25-fold increase in surface roughness resulting from the pits and cracks introduced in the polymer by the isolate. Additionally, the presence of degradational by-products revealed via gas chromatography ascertains the steady progression of degradation. Further, recognizing the pivotal role of alkane monooxygenase in plastic degradation, the study expanded to detect this enzyme in the isolate molecularly. Molecular docking studies were conducted to assess the enzyme's affinity with various polymers, demonstrating notable binding capability with most polymers, especially with polyurethane (- 5.47 kcal/mol). These findings highlight the biodegradation potential of Enterobacter cloacae O5-E and the crucial involvement of alkane monooxygenase in the initial steps of the degradation process, offering a promising avenue to address the global plastic pollution crisis.

Structural Elucidation of a Metagenomic Urethanase and Its Engineering Towards Enhanced Hydrolysis Profiles

While plastics like polyethylene terephthalate can already be degraded efficiently by the activity of hydrolases, other synthetic polymers like polyurethanes (PUs) and polyamides (PAs) largely resist biodegradation. In this study, we solved the first crystal structure of the metagenomic urethanase UMG-SP-1, identified highly flexible loop regions to comprise active site residues, and targeted a total of 20 potential hot spots by site-saturation mutagenesis. Engineering campaigns yielded variants with single mutations, exhibiting almost 3- and 8-fold improved activity against highly stable N-aryl urethane and amide bonds, respectively. Furthermore, we demonstrated the release of the corresponding monomers from a thermoplastic polyester-PU and a PA (nylon 6) by the activity of a single, metagenome-derived urethanase after short incubation times. Thereby, we expanded the hydrolysis profile of UMG-SP-1 beyond the reported low-molecular weight carbamates. Together, these findings promise advanced strategies for the bio-based degradation and recycling of plastic materials and waste, aiding efforts to establish a circular economy for synthetic polymers.

Interfacial Reactions in Chemical Recycling and Upcycling of Plastics

Depolymerization of plastics is a leading strategy to combat the escalating global plastic waste crisis through chemical recycling, upcycling, and remediation of micro-/nanoplastics. However, critical processes necessary for polymer chain scission, occurring at the polymer-catalyst or polymer-fluid interfaces, remain largely overlooked. Herein, we spotlight the importance of understanding these interfacial chemical processes as a critical necessity for optimizing kinetics and reactivity in plastics recycling and upcycling, controlling reaction outcomes, product distributions, as well as improving the environmental sustainability of these processes. Several examples are highlighted in heterogeneous processes such as hydrogenation over solid catalysts, reaction of plastics in immiscible media, and biocatalysis. Ultimately, judicious exploitation of interfacial reactivity has practical implications in developing practical, robust, and cost-effective processes to reduce plastic waste and enable a viable post-use circular plastics economy.

Interaction of Micro- and Nanoplastics with Enzymes: The Case of Carbonic Anhydrase

Microplastics (MPs) and nanoplastics (NPs) have emerged as significant environmental pollutants with potential detrimental effects on ecosystems and human health. Several studies indicate their interaction with enzymes; this topic represents a multifaceted research field encompassing several areas of interest from the toxicological and ecotoxicological impact of MPs and NPs on humans and wildlife to the biodegradation of plastics by microbial enzymes. This review aims to provide a critical analysis of the state-of-the-art knowledge of the interaction of MPs and NPs on the enzyme carbonic anhydrase (CA), providing recent insights, analyzing the knowledge gaps in the field, and drawing future perspectives of the research and its application. CA is a widespread and crucial enzyme in various organisms; it is critical for various physiological processes in animals, plants, and bacteria. It catalyzes the reversible hydration of CO2, which is essential for respiration, acid-base balance, pH homeostasis, ion transport, calcification, and photosynthesis. Studies demonstrate that MPs and NPs can inhibit CA activity with mechanisms including adsorption to the enzyme surface and subsequent conformational changes. In vitro and in silico studies highlight the role of electrostatic and hydrophobic interactions in these processes. In vivo studies present mixed results, which are influenced by factors like particle type, size, concentration, and organism type. Moreover, the potentiality of the esterase activity of CA for plastic degradation is discussed. The complexity of the interaction between CA and MPs/NPs underscores the need for further research to fully understand the ecological and health impacts of MPs and NPs on CA activity and expression and glimpses of the potentiality and perspectives in this field.

Is Laccase derived from Pleurotus ostreatus effective in microplastic degradation? A critical review of current progress, challenges, and future prospects

Exploration of Pleurotus ostreatus as a biological agent in the degradation of persistent plastics like polyethylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate, revealing a promising avenue toward mitigating the environmental impacts of plastic pollution. Leveraging the intrinsic enzymatic capabilities of this fungus, mainly its production of laccase, presents a sustainable and eco-friendly approach to breaking down complex polymer chains into less harmful constituents. This review focused on enhancements in the strain's efficiency through genetic engineering, optimized culture conditions, and enzyme immobilization to underscore the potential for scalability and practical application of this bioremediation process. The utilization of laccase from P. ostreatus in plastic waste management demonstrates a vital step forward in pursuing sustainable environmental solutions. By using the potential of fungal bioremediation, researchers can move closer to a future in which the adverse effects of plastic pollution are significantly mitigated, benefiting the health of our planet and future generations.

Biodegradation of polyethylene terephthalate (PET) by Brucella intermedia IITR130 and its proposed metabolic pathway

Accumulation of polyethylene terephthalate (PET) polyester in ecosystems across the globe is a major pollution of concern. Microbial degradation recently generated novel insights into the biodegradation of varieties of plastics. In this study, a PET degrading bacterium Brucella intermedia IITR130 was isolated from a contaminated lake ecosystem at Pallikaranai, Chennai, India. Incubation of the bacterium along with the PET sheet (0.1 mm thickness) for 60 days resulted in 26.06% degradation, indicating a half-life of 137.8 days. Considerable changes in the surface morphology of the PET sheet were found as holes, pits, and cracks on incubation with strain IITR130, as revealed by scanning electron microscopy (SEM). After bacterial treatment of PET, the formation of new functional groups, most notably in the area of 3326 cm-1 suggestive of O-H stretch, leading to carboxylic acid and alcohol as products were suggested by fourier transform infrared (FTIR) analysis. Monomethyl terephthalate (MMT) and terephthalic acid (TPA) were identified by gas chromatography-mass spectrometry (GC-MS) analysis as PET degradation metabolites. Tributyrin clearance assay confirmed the presence of a lipase/esterase enzyme in the strain IITR130. In this study, a degradation pathway for PET by an isolated and identified bacterium Brucella intermedia IITR130 was characterized in detail.

A Valuable Source of Promising Extremophiles in Microbial Plastic Degradation

Plastics have accumulated in open environments, such as oceans, rivers, and land, for centuries, but their effect has been of concern for only decades. Plastic pollution is a global challenge at the forefront of public awareness worldwide due to its negative effects on ecological systems, animals, human health, and national economies. Therefore, interest has increased regarding specific circular economies for the development of plastic production and the investigation of green technologies for plastic degradation after use on an appropriate timescale. Moreover, biodegradable plastics have been found to contain potential new hazards compared with conventional plastics due to the physicochemical properties of the polymers involved. Recently, plastic biodegradation was defined as microbial conversion using functional microorganisms and their enzymatic systems. This is a promising strategy for depolymerizing organic components into carbon dioxide, methane, water, new biomass, and other higher value bioproducts under both oxic and anoxic conditions. This study reviews microplastic pollution, the negative consequences of plastic use, and the current technologies used for plastic degradation and biodegradation mediated by microorganisms with their drawbacks; in particular, the important and questionable role of extremophilic multi-enzyme-producing bacteria in synergistic systems of plastic decomposition is discussed. This study emphasizes the key points for enhancing the plastic degradation process using extremophiles, such as cell hydrophobicity, amyloid protein, and other relevant factors. Bioprospecting for novel mechanisms with unknown information about the bioproducts produced during the plastic degradation process is also mentioned in this review with the significant goals of CO2 evolution and increasing H2/CH4 production in the future. Based on the potential factors that were analyzed, there may be new ideas for in vitro isolation techniques for unculturable/multiple-enzyme-producing bacteria and extremophiles from various polluted environments.

Biodegradation of e-waste microplastics by Penicillium brevicompactum

Electronic and electric waste (e-waste) management strategies often fall short in dealing with the plastic constituents of printed circuit boards (PCB). Some plastic materials from PCB, such as epoxy resins, may release contaminants, but neither potential environmental impact has been assessed nor mitigation strategies have been put forward. This study assessed the biodegradation of microplastics (1-2 mm in size) from PCB by the fungus Penicillium brevicompactum over 28 days, thus contributing to the discussion of mitigation strategies for decreasing the environmental impact of such plastics in the environment. The capacity of P. brevicompactum to induce microplastic fragmentation and degradation has been determined by the increased the number of smaller-sized particles and microplastic mass reduction (up to 75 % within 14 days), respectively. The occurrence of chain scission and oxidation of microplastics exposed to P. brevicompactum when compared with the control conditions (which occurred only after 28 days of exposure) can be observed. Furthermore, Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy performed in dried biomass put in evidence an increase in the absorption intensities in regions that could be attributed to functional groups associated with carbohydrates. The results underline the potential role of the genus Penicillium, particularly P. brevicompactum, in the biodegradation of microplastics from PCB, thus providing the basis for further exploration of its potential for e-waste bioremediation and research on the underlying mechanisms for sustainable approaches to mitigate e-waste pollution.

Poly(lactic acid) Degradation by Recombinant Cutinases from Aspergillus nidulans

Poly(lactic-acid) (PLA) is a biodegradable polymer widely used as a packaging material. Its monomer, lactic acid, and its derivatives have been used in the food, cosmetic, and chemical industries. The accumulation of PLA residues leads to the development of green degrading methodologies, such as enzymatic degradation. This work evaluates the potential use of three cutinolytic enzymes codified in the Aspergillus nidulans genome to achieve this goal. The results are compared with those obtained with proteinase K from Tritirachium album, which has been reported as a PLA-hydrolyzing enzyme. The results show that all three cutinases act on the polymer, but ANCUT 1 releases the highest amount of lactic acid (25.86 mM). Different reaction conditions assayed later led to double the released lactic acid. A decrease in weight (45.96%) was also observed. The enzyme showed activity both on poly L lactic acid and on poly D lactic acid. Therefore, this cutinase offers the potential to rapidly degrade these package residues, and preliminary data show that this is feasible.

Current paradigms and future challenges in harnessing gut bacterial symbionts of insects for biodegradation of plastic wastes

The ubiquitous incorporation of plastics into daily life, coupled with inefficient recycling practices, has resulted in the accumulation of millions of metric tons of plastic waste, that poses a serious threat to the Earth's sustainability. Plastic pollution, a global problem, disrupts the ecological balance and endangers various life forms. Efforts to combat plastic pollution are underway, with a promising avenue being biological degradation facilitated by certain insects and their symbiotic gut microorganisms, particularly bacteria. This review consolidates existing knowledge on plastic degradation by insects and their influence on gut microbiota. Additionally, it delves into the potential mechanisms employed by insects in symbiosis with gut bacteria, exploring the bioconversion of waste plastics into value-added biodegradable polymers through mineralization. These insights hold significant promise for the bio-upcycling of plastic waste, opening new horizons for future biomanufacturing of high-value chemicals from plastic-derived compounds. Finally, we weigh the pros and cons of future research endeavors related to the bioprospection of plastic-degrading bacteria from underexplored insect species. We also underscore the importance of bioengineering depolymerases with novel characteristics, aiming for their application in the remediation and valorization of waste plastics.

Hotspots lurking underwater: Insights into the contamination characteristics, environmental fates and impacts on biogeochemical cycling of microplastics in freshwater sediments

The widespread presence of microplastics (MPs) in aquatic environments has become a significant concern, with freshwater sediments acting as terminal sinks, rapidly picking up these emerging anthropogenic particles. However, the accumulation, transport, degradation and biochemical impacts of MPs in freshwater sediments remain unresolved issues compared to other environmental compartments. Therefore, this paper systematically revealed the spatial distribution and characterization information of MPs in freshwater (rivers, lakes, and estuaries) sediments, in which small-size (<1 mm), fibers, transparent, polyethylene (PE), and polypropylene (PP) predominate, and the average abundance of MPs in river sediments displayed significant heterogeneity compared to other matrices. Next, the transport kinetics and drivers of MPs in sediments are summarized, MPs transport is controlled by the particle diversity and surrounding environmental variability, leading to different migration behaviors and transport efficiencies. Also emphasized the spatio-temporal evolution of MPs degradation processes and biodegradation mechanisms in sediments, different microorganisms can depolymerize high molecular weight polymers into low molecular weight biodegradation by-products via secreting hydrolytic enzymes or redox enzymes. Finally, discussed the ecological impacts of MPs on microbial-nutrient coupling in sediments, MPs can interfere with the ecological balance of microbially mediated nutrient cycling by altering community networks and structures, enzyme activities, and nutrient-related functional gene expressions. This work aims to elucidate the plasticity characteristics, fate processes, and potential ecological impact mechanisms of MPs in freshwater sediments, facilitating a better understanding of environmental risks of MPs in freshwater sediments.

Microplastics Biodegradation by Estuarine and Landfill Microbiomes

Plastic pollution poses a worldwide environmental challenge, affecting wildlife and human health. Assessing the biodegradation capabilities of natural microbiomes in environments contaminated with microplastics is crucial for mitigating the effects of plastic pollution. In this work, we evaluated the potential of landfill leachate (LL) and estuarine sediments (ES) to biodegrade polyethylene (PE), polyethylene terephthalate (PET), and polycaprolactone (PCL), under aerobic, anaerobic, thermophilic, and mesophilic conditions. PCL underwent extensive aerobic biodegradation with LL (99 ± 7%) and ES (78 ± 3%) within 50-60 days. Under anaerobic conditions, LL degraded 87 ± 19% of PCL in 60 days, whereas ES showed minimal biodegradation (3 ± 0.3%). PE and PET showed no notable degradation. Metataxonomics results (16S rRNA sequencing) revealed the presence of highly abundant thermophilic microorganisms assigned to Coprothermobacter sp. (6.8% and 28% relative abundance in anaerobic and aerobic incubations, respectively). Coprothermobacter spp. contain genes encoding two enzymes, an esterase and a thermostable monoacylglycerol lipase, that can potentially catalyze PCL hydrolysis. These results suggest that Coprothermobacter sp. may be pivotal in landfill leachate microbiomes for thermophilic PCL biodegradation across varying conditions. The anaerobic microbial community was dominated by hydrogenotrophic methanogens assigned to Methanothermobacter sp. (21%), pointing at possible syntrophic interactions with Coprothermobacter sp. (a H2-producer) during PCL biodegradation. In the aerobic experiments, fungi dominated the eukaryotic microbial community (e.g., Exophiala (41%), Penicillium (17%), and Mucor (18%)), suggesting that aerobic PCL biodegradation by LL involves collaboration between fungi and bacteria. Our findings bring insights on the microbial communities and microbial interactions mediating plastic biodegradation, offering valuable perspectives for plastic pollution mitigation.

Polyethylene Terephthalate (PET) Recycled by Catalytic Glycolysis: A Bridge toward Circular Economy Principles

Plastic pollution has escalated into a critical global issue, with production soaring from 2 million metric tons in 1950 to 400.3 million metric tons in 2022. The packaging industry alone accounts for nearly 44% of this production, predominantly utilizing polyethylene terephthalate (PET). Alarmingly, over 90% of the approximately 1 million PET bottles sold every minute end up in landfills or oceans, where they can persist for centuries. This highlights the urgent need for sustainable management and recycling solutions to mitigate the environmental impact of PET waste. To better understand PET's behavior and promote its management within a circular economy, we examined its chemical and physical properties, current strategies in the circular economy, and the most effective recycling methods available today. Advancing PET management within a circular economy framework by closing industrial loops has demonstrated benefits such as reduced landfill waste, minimized energy consumption, and conserved raw resources. To this end, we identified and examined various strategies based on R-imperatives (ranging from 3R to 10R), focusing on the latest approaches aimed at significantly reducing PET waste by 2040. Additionally, a comparison of PET recycling methods (including primary, secondary, tertiary, and quaternary recycling, along with the concepts of "zero-order" and biological recycling techniques) was envisaged. Particular attention was paid to the heterogeneous catalytic glycolysis, which stands out for its rapid reaction time (20-60 min), high monomer yields (>90%), ease of catalyst recovery and reuse, lower costs, and enhanced durability. Accordingly, the use of highly efficient oxide-based catalysts for PET glycolytic degradation is underscored as a promising solution for large-scale industrial applications.

Microplastics in Ghana: An in-depth review of research, environmental threats, sources, and impacts on ecosystems and human health

Microplastics pose significant challenges on a global scale. In Ghana, these tiny pollutants infiltrate diverse ecosystems such as coastal areas, rivers, lakes, and forests, vital to the nation's economy and social well-being. This review examines the current depth of knowledge in research and the escalating concern of microplastics, identifying significant gaps in research and understanding. The findings highlight the limited understanding of the extent and distribution of microplastic pollution across different environmental compartments, primarily focusing on coastal environments. Additionally, detection and quantification techniques for microplastics face several complexities and limitations in the Ghanaian context due to constraints such as infrastructure, resources, and expertise. Despite some research efforts, particularly along the coastline, there is still a distinct lack of attention in various regions and ecosystems within Ghana. This imbalance in research focus hinders the understanding and effective mitigation of microplastics in the country. This therefore necessitates the implementation of systematic policy frameworks, emphasizing the importance of recycling and upcycling as effective strategies to address the challenges of microplastics in Ghana with more targeted research and public engagement. This review serves as a call to action for a strategic approach to research and policy-making on microplastic research and pollution in Ghana.

Mimicking the enzymatic plant cell wall hydrolysis mechanism for the degradation of polyethylene terephthalate

Plastic pollution presents a global challenge, impacting ecosystems, wildlife, and economies. Polyethylene terephthalate (PET), widely used in products like bottles, significantly contributes to this issue due to poor waste collection. In recent years, there has been increasing interest in plant biomass-degrading enzymes for plastic breakdown, due to the structural and physicochemical similarities between natural and synthetic polymers. Filamentous fungi involved in hemicellulose degradation have developed a complex mode of action that includes not only enzymes but also biosurfactants; surface-active molecules that facilitate enzyme-substrate interactions. For this reason, this study aimed to mimic the mechanism of biomass degradation by repurposing plant cell wall degrading enzymes including a cutinase and three esterases to cooperatively contribute to PET degradation. Surfactants of different charge were also introduced in the reactions, as their role is similar to biosurfactants, altering the surface tension of the polymers and thus improving enzymes' accessibility. Notably, Fusarium oxysporum cutinase combined with anionic surfactant exhibited a 2.3- and 1.6-fold higher efficacy in hydrolyzing amorphous and semi-crystalline PET, respectively. When cutinase was combined with either of two ferulic acid esterases, it resulted in complete conversion of PET intermediate products to TPA, increasing the overall product release up to 1.9- fold in presence of surfactant. The combination of cutinase with a glucuronoyl esterase demonstrated significant potential in plastic depolymerization, increasing degradation yields in semi-crystalline PET by up to 1.4-fold. The approach of incorporating enzyme cocktails and surfactants emerge as an efficient solution for PET degradation in mild reaction conditions, with potential applications in eco-friendly plastic waste management.

Advancing sustainable agriculture: Evaluation of Poly (lactic acid) (PLA) based mulch films and identification of biodegrading microorganisms among soil microbiota

Non-biodegradable polyolefin based plastic mulch residues in agricultural fields after the end of a crop cycle have raised several concerns as an environmental pollutant in recent years. This study explores the potential of Poly (lactic acid) (PLA) and Poly (butylene adipate-co-terephthalate) (PBAT) based compostable films reactively blended with compatibilizers and chain extenders as a promising solution to environmental challenges associated with traditional plastic mulch films. Epoxidized soybean oil (ESO) and Epoxy-functionalized styrene acrylic copolymer (ESA) have been used as reactive compatibilizers and chain extenders respectively. In-depth analysis of the mechanical, thermal, and barrier properties of the developed films, revealed that the PLA/PBAT blend films at 75:25 weight ratio in the presence of 5 phr ESO and 0.5 phr ESA exhibit improved performance characteristics for application as mulch films. Furthermore, the films were subjected to 360-h UV exposure to gauge their stability under prolonged exposure, specifically investigating changes in the carbonyl index. Additionally, a rigorous real-time field trial of the mulch films spanning eight months with various crops was carried out to understand their performance in practical agricultural settings. The study also involved the identification of microorganisms responsible for the degradation of the developed mulch films employing 16S rRNA sequencing.

ANCUT1, a novel thermoalkaline cutinase from Aspergillus nidulans and its application on hydroxycinnamic acids lipophilization

One of the four cutinases encoded in the Aspergillus nidulans genome, ANCUT1, is described here. Culture conditions were evaluated, and it was found that this enzyme is produced only when cutin is present in the culture medium, unlike the previously described ANCUT2, with which it shares 62% amino acid identity. The differences between them include the fact that ANCUT1 is a smaller enzyme, with experimental molecular weight and pI values of 22 kDa and 6, respectively. It shows maximum activity at pH 9 and 60 °C under assayed conditions and retains more than 60% of activity after incubation for 1 h at 60 °C in a wide range of pH values (6-10) after incubations of 1 or 3 h. It has a higher activity towards medium-chain esters and can modify long-chain length hydroxylated fatty acids constituting cutin. Its substrate specificity properties allow the lipophilization of alkyl coumarates, valuable antioxidants and its thermoalkaline behavior, which competes favorably with other fungal cutinases, suggests it may be useful in many more applications.

Characterization of Thermotoga maritima Esterase Capable of Hydrolyzing Bis(2-hydroxyethyl) Terephthalate

The gene-encoding carboxylesterase (TM1022) from the hyperthermophilic bacterium Thermotoga maritima (T. maritima) was cloned and expressed in Escherichia coli Top10 and BL21 (DE3). Recombinant TM1022 showed the best activity at pH 8.0 and 85 °C and retained 57% activity after 8 h cultivation at 90 °C. TM1022 exhibited good stability at pH 6.0-9.0, maintaining 53% activity after incubation at pH 10.0 and 37 °C for 6 h. The esterase TM1022 exhibited the optimum thermo-alkali stability and kcat/Km (598.57 ± 19.97 s-1mM-1) for pN-C4. TM1022 hydrolyzed poly(ethylene terephthalate) (PET) degradation intermediates, such as bis(2-hydroxyethyl) terephthalate (BHET) and mono(2-hydroxyethyl) terephthalate (MHET). The Km, kcat, and kcat/Km values for BHET were 0.82 ± 0.01 mM, 2.20 ± 0.02 s-1, and 2.67 ± 0.02 mM-1 s-1, respectively; those for MHET were 2.43 ± 0.07 mM, 0.04 ± 0.001 s-1, and 0.02 ± 0.001 mM-1 s-1, respectively. When purified TM1022 was added to the cutinase BhrPETase, hydrolysis of PET from drinking water bottle tops produced pure terephthalic acids (TPA) with 166% higher yield than those obtained after 72 h of incubation with BhrPETase alone as control. The above findings demonstrate that the esterase TM1022 from T. maritima has substantial potential for depolymerizing PET into monomers for reuse.

Identification and recombinant expression of a cutinase from Papiliotrema laurentii that hydrolyzes natural and synthetic polyesters

Given the multitude of extracellular enzymes at their disposal, many of which are designed to degrade nature's polymers (lignin, cutin, cellulose, etc.), fungi are adept at targeting synthetic polyesters with similar chemical composition. Microbial-influenced deterioration of xenobiotic polymeric surfaces is an area of interest for material scientists as these are important for the conservation of the underlying structural materials. Here, we describe the isolation and characterization of the Papiliotrema laurentii 5307AH (P. laurentii) cutinase, Plcut1. P. laurentii is basidiomycete yeast with the ability to disperse Impranil-DLN (Impranil), a colloidal polyester polyurethane, in agar plates. To test whether the fungal factor involved in this clearing was a secreted enzyme, we screened the ability of P. laurentii culture supernatants to disperse Impranil. Using size exclusion chromatography (SEC), we isolated fractions that contained Impranil-clearing activity. These fractions harbored a single ~22 kD band, which was excised and subjected to peptide sequencing. Homology searches using the peptide sequences identified, revealed that the protein Papla1 543643 (Plcut1) displays similarities to serine esterase and cutinase family of proteins. Biochemical assays using recombinant Plcut1 confirmed that this enzyme has the capability to hydrolyze Impranil, soluble esterase substrates, and apple cutin. Finally, we confirmed the presence of the Plcut1 in culture supernatants using a custom antibody that specifically recognizes this protein. The work shown here supports a major role for the Plcut1 in the fungal degradation of natural polyesters and xenobiotic polymer surfaces.IMPORTANCEFungi play a vital role in the execution of a broad range of biological processes that drive ecosystem function through production of a diverse arsenal of enzymes. However, the universal reactivity of these enzymes is a current problem for the built environment and the undesired degradation of polymeric materials in protective coatings. Here, we report the identification and characterization of a hydrolase from Papiliotrema laurentii 5307AH, an aircraft-derived fungal isolate found colonizing a biodeteriorated polymer-coated surface. We show that P. laurentii secretes a cutinase capable of hydrolyzing soluble esters as well as ester-based compounds forming solid surface coatings. These findings indicate that this fungus plays a significant role in biodeterioration through the production of a cutinase adept at degrading ester-based polymers, some of which form the backbone of protective surface coatings. The work shown here provides insights into the mechanisms employed by fungi to degrade xenobiotic polymers.

Recycling and high-value utilization of polyethylene terephthalate wastes: A review

Polyethelene terephthalate (PET) is a well-known thermoplastic, and recycling PET waste is important for the natural environment and human health. This study provides a comprehensive overview of the recycling and reuse of PET waste through energy recovery and physical, chemical, and biological recycling. This article summarizes the recycling methods and the high-value products derived from PET waste, specifically detailing the research progress on regenerated PET prepared by the mechanical recycling of fiber/yarn, fabric, and composite materials, and introduces the application of PET nanofibers recycled by physical dissolution and electrospinning in fields such as filtration, adsorption, electronics, and antibacterial materials. This article explains the energy recovery of PET through thermal decomposition and comprehensively discusses various chemical recycling methods, including the reaction mechanisms, catalysts, conversion efficiencies, and reaction products, with a brief introduction to PET biodegradation using hydrolytic enzymes provided. The analysis and comparison of various recycling methods indicated that the mechanical recycling method yielded PET products with a wide range of applications in composite materials. Electrospinning is a highly promising recycling strategy for fabricating recycled PET nanofibers. Compared to other methods, physical recycling has advantages such as low cost, low energy consumption, high value, simple processing, and environmental friendliness, making it the preferred choice for the recycling and high-value utilization of waste PET.

Opportunities and challenges for plastic depolymerization by biomimetic catalysis

Plastic waste has imposed significant burdens on the environment. Chemical recycling allows for repeated regeneration of plastics without deterioration in quality, but often requires harsh reaction conditions, thus being environmentally unfriendly. Enzymatic catalysis offers a promising solution for recycling under mild conditions, but it faces inherent limitations such as poor stability, high cost, and narrow substrate applicability. Biomimetic catalysis may provide a new avenue by combining high enzyme-like activity with the stability of inorganic materials. Biomimetic catalysis has demonstrated great potential in biomass conversion and has recently shown promising progress in plastic degradation. This perspective discusses biomimetic catalysis for plastic degradation from two perspectives: the imitation of the active centers and the imitation of the substrate-binding clefts. Given the chemical similarity between biomass and plastics, relevant work is also included in the discussion to draw inspiration. We conclude this perspective by highlighting the challenges and opportunities in achieving sustainable plastic recycling via a biomimetic approach.

Cloning and characterization of FMN-dependent azoreductases from textile industry effluent identified through metagenomic sequencing

Azo dyes, when released untreated in the environment, cause detrimental effects on flora and fauna. Azoreductases are enzymes capable of cleaving commercially used azo dyes, sometimes in less toxic by-products which can be further degraded via synergistic microbial cometabolism. In this study, azoreductases encoded by FMN1 and FMN2 genes were screened from metagenome shotgun sequences generated from the samples of textile dye industries' effluents, cloned, expressed, and evaluated for their azo dye decolorization efficacy. At pH 7 and 45°C temperature, both recombinant enzymes FMN1 and FMN2 were able to decolorize methyl red at 20 and 100 ppm concentrations, respectively. FMN2 was found to be more efficient in decolorization/degradation of methyl red than FMN1. This study offers valuable insights into the possible application of azoreductases to reduce the environmental damage caused by azo dyes, with the hope of contributing to sustainable and eco-friendly practices for the environment management. This enzymatic approach offers a promising solution for the bioremediation of textile industrial effluents. However, the study acknowledges the need for further process optimization to enhance the efficacy of these enzymes in large-scale applications.Implications: The study underscores the environmental hazards associated with untreated release of azo dyes into the environment and emphasizes the potential of azoreductases, specifically those encoded by FMN1 and FMN2 genes, to mitigate the detrimental effects. The study emphasizes the ongoing commitment to refining and advancing the enzymatic approach for the bioremediation of azo dye-containing effluents, marking a positive stride toward more sustainable industrial practices.