Plastic-degrading Enzyme Research Articles

Microbes and microplastics: Community shifts along an urban coastal contaminant gradient.

Plastic substrates introduced to the environment during the Anthropocene have introduced new pathways for microbial selection and dispersal. Some plastic-colonising microorganisms have adapted phenotypes for plastic degradation (selection), while the spatial transport (dispersal) potential of plastic colonisers remains controlled by polymer-specific density, hydrography and currents. Plastic-degrading enzyme abundances have recently been correlated with concentrations of plastic debris in open ocean environments, making it critical to better understand colonisation of hydrocarbon degraders with plastic degradation potential in urbanised watersheds where plastic pollution often originates. We found that microbial colonisation by reputed hydrocarbon degraders on microplastics (MPs) correlated with a spatial contaminant gradient (New York City/Long Island waterways), polymer types, temporal scales, microbial domains and putative cell activity (DNA vs. RNA). Hydrocarbon-degrading taxa enriched on polyethylene and polyvinyl chloride substrates relative to other polymers and were more commonly recovered in samples proximal to New York City. These differences in MP colonisation could indicate phenotypic adaptation processes resulting from increased exposure to urban plastic runoff as well as differences in carbon bioavailability across polymer types. Shifts in MP community potential across urban coastal contaminant gradients and polymer types improve our understanding of environmental plastic discharge impacts toward biogeochemical cycling across the global ocean.

The effect of double (S238F/W159H) mutations on the structure and dynamics of PET degrading enzyme

Polyethylene terephthalate (PET) is one of the highly produced synthetic polymers worldwide and had acquired attention due to its impact resistance, high clarity, and light weight. PET has become the first choice in making disposable bottles, leading to massive scales of production resulting in very high utilization across various facets of our daily life. Unfortunately, PET accumulates as waste and is highly resistant to biodegradation, thus presenting a serious threat to the ecosystem. Degradation of PET by enzymatic hydrolysis is a promising strategy to depolymerize the PET into its monomers. In recent studies, a plastic-degrading enzyme known as PETase (IsPETase) from the Ideonella sakaiensis has been identified to hydrolyze PET. The wild-type enzyme from Ideonella sp., has been engineered to improve the catalytic activity. While the IsPETase and its variants have been the subject of extensive structural and biochemical studies, the corresponding computational studies to support the improved activity of the mutant enzyme is not fully understood. In this work, we employed all-atom classical molecular dynamics simulations of the wild-type and double mutant IsPETase enzymes to investigate the underlying reason for the improved catalytic activity in the double mutant by means of structure-dynamics-function relationship. Our results show that the engineered mutations reshape the active site structure, volume, and dynamics of the protein loops which is crucial for substrate binding. We also demonstrate that addition of aromatic and hydrogen bond-forming residues near catalytic site improves binding affinity. This work will enable the rational design of mutants for enhanced PET degrading activity. Communicated by Ramaswamy H. Sarma

Metagenomic exploration of microbial and enzymatic traits involved in microplastic biodegradation

Agricultural mulch films are frequently applied to achieve high yield, resulting in large quantities of microplastic (MP) pollution in agroecosystem. However, studies focusing specifically on the diversity of MP-degrading enzymes and related microbial communities have yet to be conducted. Here, we established a soil microcosmic incubation with addition of 5% (w/w) conventional (low-density polyethylene (LDPE)) and biodegradable (blend of polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT)) MPs for incubation 90 days. The DNA samples extracted from soils and plastisphere of MPs were examined by metagenomics and genome binning methods, specifically targeting carbohydrate-active enzymes (CAZymes) and plastic-degrading enzymes (PDZymes). The results revealed that plastisphere of MPs exhibited significantly distinct patterns of CAZymes and PDZymes from soils, and abundances of all examined exoenzymes were higher in plastisphere than those in soils. Plastisphere of LDPE-MPs selectively enriched proteases and alkane monooxygenase (alkB), and required families of carbohydrate-binding module (CBM) to increase the binding of CAZymes with MPs. Dissimilarly, diverse CAZymes with high abundances were observed in the plastisphere of PBAT-PLA MPs and esterases were important indicative PDZymes for PBAT-PLA degradation. The enriched exoenzymes in plastisphere of LDPE-MPs were mainly assigned to Actinobacteria while Proteobacteria with higher abundance in plastisphere of PBAT-PLA MPs containing most indicative exoenzymes. Moreover, a high-quality genome classified as Amycolatopsis japonica was reconstructed and found to contain one or more gene copies of indicative exoenzymes for polyethylene. Two novel genomes classified as Sphingomonas were selectively enriched in plastisphere of PBAT-PLA MPs and contained diverse genes encoding degrading exoenzymes. Taken together, our study highlighted the CAZymes and PDZymes can be exploited as potent microbial strategies for solving MPs pollution in croplands.

Identification of Cutinolytic Esterase from Microplastic-Associated Microbiota Using Functional Metagenomics and Its Plastic Degrading Potential.

Plastic pollution has threatened biodiversity and human health by shrinking habitats, reducing food quality, and limiting the activities of organisms. Therefore, global interest in discovering novel enzymes capable of degrading plastics has increased considerably. Within this context, the functional metagenomic approach, which allows for unlocking the functional potential of uncultivable microbial biodiversity, was used to discover a plastic-degrading enzyme. First, metagenomic libraries derived from microplastic-associated microbiota were screened for esterases capable of degrading both tributyrin and polycaprolactone. Clone KAD01 produced esterase highly active against p-nitrophenyl esters (C2-C16). The gene corresponding to the enzyme activity showed moderate identity (≤ 55.94%) to any known esterases/cutinases. The gene was extracellularly expressed with a 6× histidine tag in E. coli BL21(DE3), extracellularly. Titer of the enzyme (CEstKAD01) was raised from 21.32 to 35.17U/mL by the statistical optimization of expression conditions and media components. CEstKAD01 was most active at pH 7.0 and 30°C. It was noteworthy stable over a wide pH (6.0-10.0) and temperature (20-50°C). The enzyme was active and stable in elevated NaCl concentrations up to 12% (w/v). Pre-incubation of CEstKAD01 with Mg2+, Mn2+, and Ca2+ increased the enzyme activity. CEstKAD01 displayed an excellent tolerance against various chemicals and solvents. It was determined that 1mg of the enzyme caused the release of 5.39 ± 0.18mM fatty acids from 1g apple cutin in 120min. Km and Vmax values of CEstKAD01 against p-nitrophenyl butyrate were calculated to be 1.48mM and 20.37µmol/min, respectively. The enzyme caused 6.94 ± 0.55, 8.71 ± 0.56, 7.47 ± 0.47, and 9.22 ± 0.18% of weight loss in polystyrene, high-density polyethylene, low-density polyethylene, and polyvinyl chloride after 30-day incubation. The scanning electron microscopy (SEM) analysis indicated the formation of holes and pits on the plastic surfaces supporting the degradation. In addition, the change in chemical structure in plastics treated with the enzyme was determined by Fourier Transform Infrared Spectroscopy (FTIR) analysis. Finally, the degradation products were found to have no genotoxic potential. To our knowledge, no cutinolytic esterase with the potential to degrade polystyrene (PS), high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polyvinyl chloride (PVC) has been identified from metagenomes derived from microplastic-associated microbiota.

Identification of a plastic-degrading enzyme from Cryptococcus nemorosus and its use in self-degradable plastics.

For decades, plastic waste management has been one of the major ecological challenges of our society. Despite the introduction of biodegradable alternatives such as polylactic acid (PLA), their beneficial environmental impact is limited by the requirement of specific compost facility as biodegradation of PLA in natural environment occurs at a very slow rate. In this work, a plastic-degrading enzyme was utilized to facilitate degradation process. Genomic and proteomic tools were employed to identify a new biodegradable plastic-degrading enzyme from Cryptococcus nemorosus TBRC2959. The new enzyme, Cr14CLE, functions optimally under mild conditions with temperature range of 30 to 40°C and suffers no significant loss of enzymatic activity at pH ranging from 6 to 8. In addition to PLA, Cr14CLE is capable to degrade other types of biodegradable plastic such as polybutylene succinate (PBS) and polybutylene adipate terephthalate (PBAT) as well as composite bioplastic. Applications of Cr14CLE have been demonstrated through the preparation of enzyme-coated PLA film and laminated PLA film with enzyme layer. PLA films prepared by both approaches exhibited capability to self-degrade in water. KEY POINTS: • Novel plastic-degrading enzyme (Cr14CLE) was identified and characterized. • Cr14CLE can degrade multiple types of biodegradable plastics under mild conditions. • Applications of Cr14CLE on self-degradable plastic were demonstrated.

Modulating biofilm can potentiate activity of novel plastic-degrading enzymes

Plastic pollution is an increasing global issue desperately requiring a solution. Only 9% of all plastic waste has been recycled, and whilst recycling gives a second life to plastic, it is costly and there are limited downstream uses of recycled plastic, therefore an alternative is urgently needed. Biodegradation of plastic by microorganisms is a developing field of interest with the potential for bioreactors to be used alongside recycling to degrade plastic that may otherwise be sent to landfill. Here, we have identified two novel polyethylene terephthalate (PET) degrading enzymes through genomic mining and characterised their activity, including their ability to degrade PET. One of the main roadblocks facing the development of microbial enzymes as a plastic biodegradation solution, is that their efficiency is too low to facilitate development as bioremediation tools. In an innovative approach to tackle this roadblock, we hypothesised that enhancing a bacteria’s ability to attach to and form a biofilm on plastic could maximise the local concentration of the enzyme around the target substrate, therefore increasing the overall rate of plastic degradation. We found that increasing biofilm levels, by manipulating the levels of the second messenger, Cyclic-di-GMP, led to increased levels of polyester degradation in cells expressing novel and well characterised polyester-degrading enzymes. This indicates that modulating biofilm formation is a viable mechanism to fast track the development of bacterial plastic bioremediation solutions.

Genetic engineering approach to address microplastic environmental pollution: a review

Polymeric materials have desirable chemical and physical properties, leading to a wide range of applications in consumer industries. However, such properties, which include high hydrophobicity, crystallinity, strong chemical bonds and high molecular weight, inhibit natural biodegradation of plastics by wild-type microbes. This has led to the accumulation of microplastics and nanoplastics in the environment, which is projected to be 12 000 million metric t by the year 2050. Such accumulation bears serious health side effects on both terrestrial and marine ecosystems. Current methods used to control microplastics in the environment have proved inadequate due to high plastic production and extensive uses. Biological methods of controlling plastic pollution, which involve enzymes from various microbes, have emerged as an efficient, eco-friendly and sustainable alternative to plastic treatment and recycling. However, naturally occurring plastic-biodegrading enzymes possess limited biodegradation capacity due to low thermostability and biocatalytic activities, thus limiting large-scale applications. This review focuses on leveraged protein enzyme genetic engineering techniques intended to improve the catalytic performance of putative plastic-biodegrading enzymes and production of environmentally friendly bioplastics from natural fibres as a substitute for synthetic petroleum-based plastics. Genetically modified plastic-degrading enzymes possess boosted substrate interaction, increased hydrophobicity, better catalytic efficiency, increased thermostability and optimised plastic biodegradability.

Seek and you shall find-news on the quest for novel PET-degrading enzymes.

Plastic-degrading enzymes hold immense potential for eco-friendly recycling methods. However, the catalytic rates of current enzymes do not stack up against the mammoth task of degrading millions of tons of plastic waste per year. In the quest for more efficient polyethylene terephthalate (PET)-degrading enzymes, Zhang etal. report the discovery and characterization of PET40, a versatile PET-hydrolyzing esterase that is divergent from most characterized PETases. While PET40 has comparably low hydrolytic activity on PET, Zhang etal. demonstrate its broad activity on an expanded substrate pool. This sheds light on the potential ecological role of these esterases and suggests that PET might be only a recent addition to their substrate spectrum.

The structural and molecular mechanisms of type II PETases: a mini review.

The advent of plastics has led to significant advances for humans, although the accompanying pollution has also been a source of concern for countries globally. Consequently, a biological method to effectively degrade polyethylene terephthalate (PET) has been an area of significant scientific interest. Following the report of the highly efficient PET hydrolase from the bacterium Ideonella sakaiensis strain 201-F6 (i.e., IsPETase) in 2016, its structure has been extensively studied, showing that it belongs to the type II PETase group. Unlike type I PETases that include most known cutinases, structural investigations of type II PETases have only been conducted since 2017. Type II PETases are further divided into type IIa and IIb enzymes. Moreover, even less research has been conducted on type IIa plastic-degrading enzymes. Here, we present a review of recent studies of the structure and mechanism of type II PETases, using the known structure of the type IIa PETase PE-H from the marine bacterium Pseudomonas aestusnigri in addition to the type IIb enzyme IsPETase as representatives. These studies have provided new insights into the structural features of type II PETases that exhibit PET catalytic activity. In addition, recent studies investigating the rational design of IsPETases are reviewed and summarized alongside a discussion of controversies surrounding PETase investigations.

Machine Learning Based Prediction of Enzymatic Degradation of Plastics Using Encoded Protein Sequence and Effective Feature Representation

Enzyme biocatalysis for plastic treatment and recycling is an emerging field of growing interest. However, it is challenging and time-consuming to identify plastic-degrading enzymes with desirable functionality, given the large number of putative enzyme sequences. There is a critical need to develop an effective approach to accurately predict the enzyme activity in degrading different types of plastics. In this study, we developed a machine-learning-based plastic enzymatic degradation (PED) framework to predict the ability of an enzyme to degrade plastics of interest by exploring and recognizing hidden patterns in protein sequences. A data set integrating information from a wide range of experimentally verified enzymes and various common plastic substrates was created. A new context-aware enzyme sequence representation (CESR) mechanism was developed to learn the abundant contextual information in enzyme sequences, and feature extraction was performed for enzymes at both the amino acid level and global sequence level. Thirteen machine learning classification algorithms were compared, and XGBoost was identified as the best-performing algorithm. PED achieved an overall accuracy of 90.2% and outperformed sequence-based protein classification models from the existing literature. Furthermore, important enzyme features in plastic degradation were identified and comprehensively interpreted. This study demonstrated a new tool for the prediction and discovery of plastic-degrading enzymes.

Mechanistic studies of a lipase unveil effect of pH on hydrolysis products of small PET modules

Biocatalysis is a key technology enabling plastic recycling. However, despite advances done in the development of plastic-degrading enzymes, the molecular mechanisms that govern their catalytic performance are poorly understood, hampering the engineering of more efficient enzyme-based technologies. In this work, we study the hydrolysis of PET-derived diesters and PET trimers catalyzed by the highly promiscuous lipase B from Candida antarctica (CALB) through QM/MM molecular dynamics simulations supported by experimental Michaelis–Menten kinetics. The computational studies reveal the role of the pH on the CALB regioselectivity toward the hydrolysis of bis-(hydroxyethyl) terephthalate (BHET). We exploit this insight to perform a pH-controlled biotransformation that selectively hydrolyzes BHET to either its corresponding diacid or monoesters using both soluble and immobilized CALB. The discoveries presented here can be exploited for the valorization of BHET resulting from the organocatalytic depolymerization of PET.

Engineering the plastic degradation enzyme Ple629 from marine consortium to improve its thermal stability

Petrochemical-derived polyester plastics such as polyethylene terephthalate (PET) and polybutylene adipate terephthalate (PBAT) have been widely used. However, the difficulty to be degraded in nature (PET) or the long biodegradation cycle (PBAT) resulted in serious environmental pollution. In this connection, treating these plastic wastes properly becomes one of the challenges of environment protection. From the perspective of circular economy, biologically depolymerizing the waste of polyester plastics and reusing the depolymerized products is one of the most promising directions. Recent years have seen many reports on polyester plastics degrading organisms and enzymes. Highly efficient degrading enzymes, especially those with better thermal stability, will be conducive to their application. The mesophilic plastic-degrading enzyme Ple629 from the marine microbial metagenome is capable of degrading PET and PBAT at room temperature, but it cannot tolerate high temperature, which hampers its potential application. On the basis of the three-dimensional structure of Ple629 obtained from our previous study, we identified some sites which might be important for its thermal stability by structural comparison and mutation energy analysis. We carried out transformation design, and performed expression, purification and thermal stability determination of the mutants. The melting temperature (Tm) values of mutants V80C and D226C/S281C were increased by 5.2 ℃ and 6.9 ℃, respectively, and the activity of mutant D226C/S281C was also increased by 1.5 times compared with that of the wild-type enzyme. These results provide useful information for future engineering and application of Ple629 in polyester plastic degradation.

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.

Set of Small Molecule Polyurethane (PU) Model Substrates: Ecotoxicity Evaluation and Identification of PU Degrading Biocatalysts

Polyurethanes (PUs) are an exceedingly heterogeneous group of plastic polymers, widely used in a variety of industries from construction to medical implants. In the past decades, we have witnessed the accumulation of PU waste and its detrimental environmental impacts. PUs have been identified as one of the most toxic polymers leaching hazardous compounds derived both from the polymer itself and the additives used in production. Further environmental impact assessment, identification and characterization of substances derived from PU materials and establishing efficient degradation strategies are crucial. Thus, a selection of eight synthetic model compounds which represent partial PU hydrolysis products were synthesized and characterized both in terms of toxicity and suitability to be used as substrates for the identification of novel biocatalysts for PU biodegradation. Overall, the compounds exhibited low in vitro cytotoxicity against a healthy human fibroblast cell line and virtually no toxic effect on the nematode Caenorhabditis elegans up to 500 µg mL−1, and two of the substrates showed moderate aquatic ecotoxicity with EC50 values 53 µg mL−1 and 45 µg mL−1, respectively, on Aliivibrio fischeri. The compounds were successfully applied to study the mechanism of ester and urethane bond cleaving preference of known plastic-degrading enzymes and were used to single out a novel PU-degrading biocatalyst, Amycolatopsis mediterranei ISP5501, among 220 microbial strains. A. mediterranei ISP5501 can also degrade commercially available polyether and polyester PU materials, reducing the average molecular number of the polymer up to 13.5%. This study uncovered a biocatalyst capable of degrading different types of PUs and identified potential enzymes responsible as a key step in developing biotechnological process for PU waste treatment options.

Investigating the effects of cyclic topology on the performance of a plastic degrading enzyme for polyethylene terephthalate degradation

Agitation is a commonly encountered stress for enzymes during all stages of production and application, but investigations that aim to improve their tolerance using topological engineering have yet to be reported. Here, the plastic-degrading enzyme IsPETase was cyclized in a range of topologies including a cyclic monomer, cyclic dimer and catenane using SpyTag/SpyCatcher technologies, and their tolerance towards different stresses including mechanical agitation was investigated. The cyclic dimer and catenane topologies were less susceptible to agitation-induced inactivation resulting in enhancement of polyethylene terephthalate (PET) degradation. While contrary to conventional belief, cyclic topologies did not improve tolerance of IsPETase towards heat or proteolytic treatment, the close proximity of active sites in the dimeric and catenane variants was found to enhance PET conversion into small soluble products. Together, these findings illustrate that it is worthwhile to explore the topology engineering of enzymes used in heterogeneous catalysis as it improves factors that are often overlooked in homogeneous catalysis studies.

DeepTM: A deep learning algorithm for prediction of melting temperature of thermophilic proteins directly from sequences

Thermally stable proteins find extensive applications in industrial production, pharmaceutical development, and serve as a highly evolved starting point in protein engineering. The thermal stability of proteins is commonly characterized by their melting temperature (Tm). However, due to the limited availability of experimentally determined Tm data and the insufficient accuracy of existing computational methods in predicting Tm, there is an urgent need for a computational approach to accurately forecast the Tm values of thermophilic proteins. Here, we present a deep learning-based model, called DeepTM, which exclusively utilizes protein sequences as input and accurately predicts the Tm values of target thermophilic proteins on a dataset consisting of 7790 thermophilic protein entries. On a test set of 1550 samples, DeepTM demonstrates excellent performance with a coefficient of determination (R2) of 0.75, Pearson correlation coefficient (P) of 0.87, and root mean square error (RMSE) of 6.24 ℃. We further analyzed the sequence features that determine the thermal stability of thermophilic proteins and found that dipeptide frequency, optimal growth temperature (OGT) of the host organisms, and the evolutionary information of the protein significantly affect its melting temperature. We compared the performance of DeepTM with recently reported methods, ProTstab2 and DeepSTABp, in predicting the Tm values on two blind test datasets. One dataset comprised 22 PET plastic-degrading enzymes, while the other included 29 thermally stable proteins of broader classification. In the PET plastic-degrading enzyme dataset, DeepTM achieved RMSE of 8.25 ℃. Compared to ProTstab2 (20.05 ℃) and DeepSTABp (20.97 ℃), DeepTM demonstrated a reduction in RMSE of 58.85% and 60.66%, respectively. In the dataset of thermally stable proteins, DeepTM (RMSE=7.66 ℃) demonstrated a 51.73% reduction in RMSE compared to ProTstab2 (RMSE=15.87 ℃). DeepTM, with the sole requirement of protein sequence information, accurately predicts the melting temperature and achieves a fully end-to-end prediction process, thus providing enhanced convenience and expediency for further protein engineering.

Plastic-degrading bacteria isolated from contaminated mangrove sediment in Wonorejo, Surabaya

Plastics have become inevitable needs in modern society due to their attractive properties, including thermostability, lightweight, flexibility, superior insulation, and low cost, which have led to massive production. Their persistence and challenges in disposal have detrimental effects on the environment leading to the development of a promising degradation process which is efficient, time-saving, and cost-effective. This study focused on discovering the potential plastic-degrading bacteria isolated from plastic-contaminated mangrove sediment in the Wonorejo area. We buried a commercially available plastic bag in the polluted mangrove sediment for 16 weeks. Our results showed that indigenous bacteria formed a biofilm on the plastic surface leading to a plastic dry weight loss of up to 12%. FTIR analysis revealed obvious transmittance attenuations in the buried plastic polymer, suggesting that their chemical properties may have been interrupted due to bacterial activity. Further, bacteria isolation and biochemical screening revealed that they were primarily dominated by Bacillus. According to 16S rRNA sequencing, they were identified as Brevibacilllus (BIO-B), Stenotrophomonas (BIO-G), and Lysinibacillus (SOI-C). The three genera mentioned earlier exhibited a detectable level of plastic-degrading activity and possessed lipolytic, ligninolytic, and alkane-degrading activities. Stenotrophomonas (BIO-G) showed a degradation activity on low-density polyethylene (LDPE) represented by a plastic dry weight loss of up to 8.9% within 4 weeks. As expected, plastic treated with BIO-G showed transmittance attenuation in FTIR analysis, albeit with a lower percentage than that treated with indigenous bacteria. Moreover, SEM analysis reveals changes in the morphological surface of plastic. Together, FTIR and SEM analysis indicated that bacteria disrupt both the chemical structure and morphological appearance of plastic polymer upon degradation process. These results denote that BIO-G indeed composes the aforementioned indigenous bacteria from polluted mangrove sediment. Thus, our study suggests the indigenous bacteria isolated from contaminated areas produced plastic-degrading enzymes and secreted to the environment to break down plastic compounds.

Environmental impact and mitigation of micro(nano)plastics pollution using green catalytic tools and green analytical methods

The exponential utilization of plastics and their recalcitrant nature results in their extensive environmental accumulation, a pressing environmental problem that modern societies are currently facing. The presence of plastic waste in different environmental matrices can seriously affect life forms, ecosystems, and the economy. Furthermore, plastic wastes can break down into smaller pieces called microplastics (MPs) and nanoplastics (NPs), leading to new interactions with the environment and living organisms. Therefore, there is an urgent need to provide sustainable and cost-effective solutions for their mitigation. The first half of this review discusses the characteristics, sources, distribution, and adverse consequences of MPs and NPs. The latter half discusses mitigation strategies based on the utilization of enzymes as green catalytic tools. Enzymatic approaches outstand as effective sustainable strategies for microplastic degradation since plastic-degrading enzymes can specifically target the polymer structure for their further degradation. In addition, we have also discussed the novel approaches to enhance the performances and stability of natural enzymes including immobilization methods onto different materials and nanomaterials. Finally, possible key directions are also provided for future research considerations to find a practical, feasible, and environmentally friendly strategy to tackle the current crisis of plastic pollution.

A Review of Cross-Disciplinary Approaches for the Identification of Novel Industrially Relevant Plastic-Degrading Enzymes

The large-scale global use of plastics has led to one of the greatest environmental issues of the 21st century. The incredible durability of these polymers, whilst beneficial for a wide range of purposes, makes them hard to break down. True recycling of plastics is difficult and expensive, leading to accumulation in the environment as waste. Recently, a new field of research has developed, aiming to use natural biological processes to solve this man-made problem. Incredibly, some microorganisms are able to produce enzymes with the capacity to chemically break down plastic polymers into their monomeric building blocks. At an industrial scale, this process could allow for a circular recycling economy, whereby plastics are broken down, then built back up into novel consumer plastics. As well as providing a solution for the removal of plastics from the environment, this would also eliminate the need for the creation of virgin plastics. Analytical techniques, such as those allowing quantification of depolymerisation activity and enzyme characterization, have underpinned this field and created a strong foundation for this nascent inter-disciplinary field. Recent advances in cutting-edge ‘omics approaches such as DNA and RNA sequencing, combined with machine learning strategies, provide in-depth analysis of genomic systems involved in degradation. In particular, this can provide understanding of the specific protein sequence of the enzymes involved in the process, as well as insights into the functional and mechanistic role of the enzymes within these microorganisms, allowing for potential high-throughput discovery and subsequent exploitation of novel depolymerases. Together, these cross-disciplinary analytical techniques offer a complete pipeline for the identification, validation, and upscaling of potential enzymatic solutions for industrial deployment. In this review, we provide a summary of the research within the field to date, the analytical techniques most commonly applied for enzyme discovery and industrial upscaling, and provide recommendations for a standardised approach to allow research conducted in this field to be benchmarked to ensure focus is on the discovery and characterisation of industrially relevant enzymes.

Effects of Microplastic on Human Gut Microbiome: Detection of Plastic-Degrading Genes in Human Gut Exposed to Microplastics—Preliminary Study

Microplastics are major pollutants in the environment, and it is currently established that microplastics have already entered human food chains and been incorporated into the human body through ingestion and inhalation. Several works in animal models have already reported the adverse effect of microplastic exposure on biological systems; however, the effect of microplastic contamination on human health is still far from understood. In previous work, we reported microplastic contamination in the digestive tract of the Indonesian coastal and highland population. Using the same stool samples, we extended our previous work by investigating gut microbial composition in samples with and without microplastic contamination using next-generation sequencing. We found that microplastic contamination does not affect overall gut microbial composition and the abundance of gut-health-related genes. However, we found a negative and positive correlation between specific types of microplastics with certain bacterial taxa, especially from the genera Roseburia, Clostridium, and Prevotella. Despite the lack of a profound effect on the gut microbiome, we detected for the first time the presence of genes encoding plastic-degrading enzymes in the human gut microbiome, suggesting an adaptation of gut microbiome to microplastic contamination.