Plastics: Environmental and Biotechnological Perspectives on Microbial Degradation

Synergistic Mutations Create Bacillus Subtilisin Variants with Enhanced Poly-l-Lactic Acid Depolymerization Activity

Enzymatic recycling of poly-l-lactic acid (PLLA) plastic has recently become an area of interest; however, investigation of enzymatic mechanisms and engineering strategies to improve activity remains limited. In this study, we have identified a subtilisin from Bacillus pumilus that has the ability to depolymerize high-molecular-weight PLLA. We performed a comparative, mutational analysis of this enzyme with a less active homologue from Bacillus subtilis to determine residues favored for activity. Our results demonstrate that both enzymes contain residues favored for PLLA depolymerization, with the generation of several hyperactive variants. In silico modeling suggests that increases in activity are due to opening of the binding pockets and increased surface hydrophobicity. Combinations of hyperactive mutations have synergistic effects with the generation of subtilisin variants with 830- and 184-fold increases in activity for B. subtilis and B. pumilus subtilisins, respectively. One B. pumilus subtilisin variant can visibly dissolve high-molecular-weight PLLA films.

Implementation of the β-hydroxyaspartate cycle increases growth performance of Pseudomonas putida on the PET monomer ethylene glycol

Ethylene glycol (EG) is a promising next generation feedstock for bioprocesses. It is a key component of the ubiquitous plastic polyethylene terephthalate (PET) and other polyester fibers and plastics, used in antifreeze formulations, and can also be generated by electrochemical conversion of syngas, which makes EG a key compound in a circular bioeconomy. The majority of biotechnologically relevant bacteria assimilate EG via the glycerate pathway, a wasteful metabolic route that releases CO₂ and requires reducing equivalents as well as ATP. In contrast, the recently characterized β-hydroxyaspartate cycle (BHAC) provides a more efficient, carbon-conserving route for C2 assimilation. Here we aimed at overcoming the natural limitations of EG metabolism in the industrially relevant strain Pseudomonas putida KT2440 by replacing the native glycerate pathway with the BHAC. We first prototyped the core reaction sequence of the BHAC in Escherichia coli before establishing the complete four-enzyme BHAC in Pseudomonas putida. Directed evolution on EG resulted in an improved strain that exhibits 35% faster growth and 20% increased biomass yield compared to a recently reported P. putida strain that was evolved to grow on EG via the glycerate pathway. Genome sequencing and proteomics highlight plastic adaptations of the genetic and metabolic networks in response to the introduction of the BHAC into P. putida and identify key mutations for its further integration during evolution. Taken together, our study shows that the BHAC can be utilized as 'plug-and-play' module for the metabolic engineering of two important microbial platform organisms, paving the way for multiple applications for a more efficient and carbon-conserving upcycling of EG in the future.

Microbial Enzyme Biotechnology to Reach Plastic Waste Circularity: Current Status, Problems and Perspectives

The accumulation of synthetic plastic waste in the environment has become a global concern. Microbial enzymes (purified or as whole-cell biocatalysts) represent emerging biotechnological tools for waste circularity; they can depolymerize materials into reusable building blocks, but their contribution must be considered within the context of present waste management practices. This review reports on the prospective of biotechnological tools for plastic bio-recycling within the framework of plastic waste management in Europe. Available biotechnology tools can support polyethylene terephthalate (PET) recycling. However, PET represents only ≈7% of unrecycled plastic waste. Polyurethanes, the principal unrecycled waste fraction, together with other thermosets and more recalcitrant thermoplastics (e.g., polyolefins) are the next plausible target for enzyme-based depolymerization, even if this process is currently effective only on ideal polyester-based polymers. To extend the contribution of biotechnology to plastic circularity, optimization of collection and sorting systems should be considered to feed chemoenzymatic technologies for the treatment of more recalcitrant and mixed polymers. In addition, new bio-based technologies with a lower environmental impact in comparison with the present approaches should be developed to depolymerize (available or new) plastic materials, that should be designed for the required durability and for being susceptible to the action of enzymes.

Biotechnological methods to remove microplastics: a review

Microplastics pollution is major threat to ecosystems and is impacting abiotic and biotic components. Microplastics are diverse and highly complex contaminants that transport other contaminants and microbes. Current methods to remove microplastics include biodegradation, incineration, landfilling, and recycling. Here we review microplastics with focus on sources, toxicity, and biodegradation. We discuss the role of algae, fungi, bacteria in the biodegradation, and we present biotechnological methods to enhance degradation, e.g., gene editing tools and bioinformatics.

The complete genome sequence of Pseudomonas chengduensis BC1815 for genome mining of PET degrading enzymes

Pseudomonas chengduensis BC1815, isolated from a marine sediment sample of the Pacific Ocean, can grow in mineral medium with PET plastic as sole carbon source. Here, we present the complete genome of Pseudomonas chengduensis BC1815, which will facilitate the genome mining of PET degrading enzymes. The total length of the sequenced genome consists of 5,578,440 bases, with mean G + C content of 62.65%. A total of 5150 coding genes including 65 tRNAs and 12 rRNAs were predicted in the genome. Thirteen proteins of esterase, lipase and α/β hydrolase were taken as candidates for PET degrading enzymes, in which eight were membrane bounded and the others were secretory.

Biodegradation of macro- and micro-plastics in environment: A review on mechanism, toxicity, and future perspectives

Plastic waste has gained remarkable research attention due to its accumulation, associated environmental issues, and impact on living organisms. In order to overcome this challenge, there is an urgent need for its removal from the environment. Under this menace, finding appropriate treatment methods like biodegradation instead of typical treatment methods is of supreme importance. However, there is a limited review on bio-decomposition of plastics, existing microbial species, their degradation efficacy, and mechanism. From this point of view, this study focused on a brief overview of biodegradation such as influencing factors on biodegradation, existing species for macro- and micro-plastics, and present research gap. Degradation percentage, limitations of existing species, and future recommendations are proposed. Microbial species such as bacteria, algae, and fungi have the ability to decompose plastics but they are unable to completely mineralize the plastics. Meanwhile, there is limited knowledge about the involved enzymes in plastics degradation, especially in the case of algae. Bio-decomposition of plastics requires more stringent conditions which are usually feasible for field application. This work will be a reference for new researchers to use this effective strategy for plastic pollution removal.

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.

The Use of Mycelial Fungi to Test the Fungal Resistance of Polymeric Materials

There are two main themes in the research on the biodegradation of industrial materials by mycelial fungi. The challenge of reducing environmental pollution necessitates the creation of biodegradable polymers that allow microorganisms, including mycelial fungi, to degrade them to low-molecule soluble substances. Additionally, to minimize the biodegradation of industrial materials while they are operating in the environment, there is a need to produce fungi-resistant polymer compositions. The fungal resistance of industrial materials and products can be assessed using a specific set of mycelial fungi cultures. Test cultures selected for this purpose are supported in the All-Russian Collection of Microorganisms (VKM). This review addresses the principle of culture selection to assess the fungal resistance of industrial materials and evaluates the results of the tests using these cultures.

Discovering untapped microbial communities through metagenomics for microplastic remediation: recent advances, challenges, and way forward

Microplastics (MPs) are ubiquitous pollutants persisting almost everywhere in the environment. With the increase in anthropogenic activities, MP accumulation is increasing enormously in aquatic, marine, and terrestrial ecosystems. Owing to the slow degradation of plastics, MPs show an increased biomagnification probability of persistent, bioaccumulative, and toxic substances thereby creating a threat to environmental biota. Thus, remediation of MP-pollutants requires efficient strategies to circumvent the mobilization of contaminants leaching into the water, soil, and ultimately to human beings. Over the years, several microorganisms have been characterized by the potential to degrade different plastic polymers through enzymatic actions. Metagenomics (MGs) is an effective way to discover novel microbial communities and access their functional genetics for the exploration and characterization of plastic-degrading microbial consortia and enzymes. MGs in combination with metatranscriptomics and metabolomics approaches are a powerful tool to identify and select remediation-efficient microbes in situ. Advancement in bioinformatics and sequencing tools allows rapid screening, mining, and prediction of genes that are capable of polymer degradation. This review comprehensively summarizes the growing threat of microplastics around the world and highlights the role of MGs and computational biology in building effective response strategies for MP remediation.

Improving the activity and thermostability of PETase from Ideonella sakaiensis through modulating its post-translational glycan modification

The large-scale preparation of Polyehylene terephthalate (PET) hydrolysing enzymes in low-cost is critical for the biodegradation of PET in industry. In the present study, we demonstrate that the post-translational glycosylation of Pichia pastoris makes it a remarkable host for the heterologous expression of PETase from Ideonella sakaiensis 201-F6 (IsPETase). Taking advantage of the abundant N- and O-linked glycosylation sites in IsPETase and the efficient post-translational modification in endoplasmic reticulum, IsPETase is heavily glycosylated during secretory expression with P. pastoris, which improves the specific activity and thermostability of the enzyme dramatically. Moreover, the specific activity of IsPETase increased further after the bulky N-linked polysaccharide chains were eliminated by Endo-β-N-acetylglucosaminidase H (Endo H). Importantly, the partially deglycosylated IsPETase still maintained high thermostability because of the remaining mono- and oligo-saccharide residues on the protein molecules. Consequently, the partially deglycosylated IsPETase was able to be applied at 50 °C and depolymerized raw, untreated PET flakes completely in 2 to 3 days. This platform was also applied for the preparation of a famous variant of IsPETase, Fast-PETase, and the same result was achieved. Partially deglycosylated Fast-PETase demonstrates elevated efficiency in degrading postconsumer-PET trays under 55 °C than 50 °C, the reported optimal temperature of Fast-PETase. The present study provides a strategy to modulate thermostable IsPETase through glycosylation engineering and paves the way for promoting PET biodegradation from laboratories to factories.

Synergistic and Antagonistic Effects of the Co-Pyrolysis of Plastics and Corn Stover to Produce Char and Activated Carbon

The physicochemical properties of char and activated carbon produced from the co-pyrolysis of corn stover (CS) and plastics, polystyrene (PS) and polyethylene terephthalate (PET), were studied. Non-isothermal gas analysis of the volatiles was conducted using an online mass spectrometer to correlate the thermal degradation of gaseous byproducts to the formation of pores in the char materials. The findings determined that the addition of PS or PET promotes the formation of the solid char product with either higher than average pore sizes or surface areas compared to control samples. The addition of PET to corn stover increases the surface area of the char formed. The char formed from a CS:PET mass ratio of 1:1 produced char with a surface area of 423.8 ± 24.8 m²/g at 500 °C and a duration of 2 h. The surface area of the chars formed from CS and PET decreased as the amount of PET decreased, showing a tendency for PET to increase the surface area of the char materials synergistically. The addition of PS to corn stover promoted the formation of chars with, on average, larger pore sizes than the control char samples. The chars were chemically activated with potassium hydroxide, and the activated carbon that formed had lower surface areas but comparable surface functional groups to the control samples. Vanillin adsorption testing showed that activated carbon from corn stover performed the best at removing 95% of the vanillin after 2 h. In contrast, the activated carbon from the chars produced from the co-pyrolysis of corn stover and polystyrene or corn stover and polyethylene terephthalate removed 45% and 46% of vanillin after 2 h, respectively. The findings suggest that plastics have a synergistic relationship in producing char precursors with improved porosity but antagonistically affect the activated carbon adsorbent properties.

Microplastics Derived from Food Packaging Waste-Their Origin and Health Risks

Plastics are commonly used for packaging in the food industry. The most popular thermoplastic materials that have found such applications are polyethylene (PE), polypropylene (PP), poly(ethylene terephthalate) (PET), and polystyrene (PS). Unfortunately, most plastic packaging is disposable. As a consequence, significant amounts of waste are generated, entering the environment, and undergoing degradation processes. They can occur under the influence of mechanical forces, temperature, light, chemical, and biological factors. These factors can present synergistic or antagonistic effects. As a result of their action, microplastics are formed, which can undergo further fragmentation and decomposition into small-molecule compounds. During the degradation process, various additives used at the plastics' processing stage can also be released. Both microplastics and additives can negatively affect human and animal health. Determination of the negative consequences of microplastics on the environment and health is not possible without knowing the course of degradation processes of packaging waste and their products. In this article, we present the sources of microplastics, the causes and places of their formation, the transport of such particles, the degradation of plastics most often used in the production of packaging for food storage, the factors affecting the said process, and its effects.

Lignocellulolytic Biocatalysts: The Main Players Involved in Multiple Biotechnological Processes for Biomass Valorization

Human population growth, industrialization, and globalization have caused several pressures on the planet's natural resources, culminating in the severe climate and environmental crisis which we are facing. Aiming to remedy and mitigate the impact of human activities on the environment, the use of lignocellulolytic enzymes for biofuel production, food, bioremediation, and other various industries, is presented as a more sustainable alternative. These enzymes are characterized as a group of enzymes capable of breaking down lignocellulosic biomass into its different monomer units, making it accessible for bioconversion into various products and applications in the most diverse industries. Among all the organisms that produce lignocellulolytic enzymes, microorganisms are seen as the primary sources for obtaining them. Therefore, this review proposes to discuss the fundamental aspects of the enzymes forming lignocellulolytic systems and the main microorganisms used to obtain them. In addition, different possible industrial applications for these enzymes will be discussed, as well as information about their production modes and considerations about recent advances and future perspectives in research in pursuit of expanding lignocellulolytic enzyme uses at an industrial scale.

The PET-Degrading Potential of Global Metagenomes: From In Silico Mining to Active Enzymes

Against the background of the steadily increasing amount of plastic waste in the sea and on land, it is more important than ever to find ways out of this situation. In recent years, microorganisms have been discovered that are capable of degrading artificial polymers such as polyethylene terephthalate (PET). Even if the turnover rates of the enzymes responsible for this reaction may be too low to solve the global plastic pollution problem, it is still of great societal interest to find microorganisms that are able to degrade the polymer. The corresponding enzymes, PET esterases (PETases) can be used in biotechnological processes and could contribute to a resource-saving circular economy. In this chapter, we present a sequence-based in silico screening method to find new PETases in metagenomic datasets. This method can easily be adapted to find other enzyme classes. We also list a number of assays that can be used to test the enzymes for activity on PET as well as other substrates.

A concept for the biotechnological minimizing of emerging plastics, micro- and nano-plastics pollutants from the environment: A review

Plastics, micro- and nano-plastics pollution are undoubtedly a severe and crucial ecological threat due to the durability of plastics and their destructive impacts on humans and wildlife. Most scientific investigations have addressed the classification, types, distribution, ingestion, fate, impacts, degradation, and various adverse effect of plastics. Heretofore, scanty reports have addressed implementing strategies for the remediation and mitigation of plastics. Therefore, in this paper, we review the current studies on the degradation of plastics, micro- and nano-plastics aided by microorganisms, and explore the relevant degradation properties and mechanisms. Diverse microorganisms are classified, such as bacteria, fungi, algae, cyanobacteria, wax worms, and enzymes that can decompose various plastics. Furthermore, bio-degradation is influenced by microbial features and environmental parameters; therefore, the ecological factors affecting plastic degradation and the resulting degradation consequences are discussed. In addition, the mechanisms underlying microbial-mediated plastic degradation are carefully studied. Finally, upcoming research directions and prospects for plastics degradation employing microorganisms are addressed. This review covers a comprehensive overview of the microorganism-assisted degradation of plastics, micro- and nano-plastics, and serves as a resource for future research into sustainable plastics pollution management methods.

Assembly strategies for polyethylene-degrading microbial consortia based on the combination of omics tools and the "Plastisphere"

Numerous microorganisms and other invertebrates that are able to degrade polyethylene (PE) have been reported. However, studies on PE biodegradation are still limited due to its extreme stability and the lack of explicit insights into the mechanisms and efficient enzymes involved in its metabolism by microorganisms. In this review, current studies of PE biodegradation, including the fundamental stages, important microorganisms and enzymes, and functional microbial consortia, were examined. Considering the bottlenecks in the construction of PE-degrading consortia, a combination of top-down and bottom-up approaches is proposed to identify the mechanisms and metabolites of PE degradation, related enzymes, and efficient synthetic microbial consortia. In addition, the exploration of the plastisphere based on omics tools is proposed as a future principal research direction for the construction of synthetic microbial consortia for PE degradation. Combining chemical and biological upcycling processes for PE waste could be widely applied in various fields to promote a sustainable environment.

Physicochemical and biological ageing processes of (micro)plastics in the environment: a multi-tiered study on polyethylene

Pollution by plastic and microplastic impacts the environment globally. Knowledge on the ageing mechanisms of plastics in natural settings is needed to understand their environmental fate and their reactivity in the ecosystems. Accordingly, the study of ageing processes is gaining focus in the context of the environmental sciences. However, laboratory-based experimental research has typically assessed individual ageing processes, limiting environmental applicability. In this study, we propose a multi-tiered approach to study the environmental ageing of polyethylene plastic fragments focusing on the combined assessment of physical and biological processes in sequence. The ageing protocol included ultraviolet irradiation in air and in a range of water solutions, followed by a biofouling test. Changes in surface characteristics were assessed by Fourier transform infrared spectroscopy, scanning electron microscopy, and water contact angle. UV radiation both in air and water caused a significant increase in the density of oxidized groups (i.e., hydroxyl and carbonyl) on the plastic surface, whereby water solution chemistry influenced the process both by modulating surface oxidation and morphology. Biofouling, too, was a strong determinant of surface alterations, regardless of the prior irradiation treatments. All biofouled samples present (i) specific infrared bands of new surface functional groups (e.g., amides and polysaccharides), (ii) a further increase in hydroxyl and carbonyl groups, (iii) the diffuse presence of algal biofilm on the plastic surface, and (iv) a significant decrease in surface hydrophobicity. This suggests that biological-driven alterations are not affected by the level of physicochemical ageing and may represent, in real settings, the main driver of alteration of both weathered and pristine plastics. This work highlights the potentially pivotal role of biofouling as the main process of plastic ageing, providing useful technical insights for future experimental works. These results also confirm that a multi-tiered laboratory approach permits a realistic simulation of plastic environmental ageing in controlled conditions.

Polyurethane Foam Residue Biodegradation through the Tenebrio molitor Digestive Tract: Microbial Communities and Enzymatic Activity

Polyurethane (PU) is a widely used polymer with a highly complex recycling process due to its chemical structure. Eliminating polyurethane is limited to incineration or accumulation in landfills. Biodegradation by enzymes and microorganisms has been studied for decades as an effective method of biological decomposition. In this study, Tenebrio molitor larvae (T. molitor) were fed polyurethane foam. They degraded the polymer by 35% in 17 days, resulting in a 14% weight loss in the mealworms. Changes in the T. molitor gut bacterial community and diversity were observed, which may be due to the colonization of the species associated with PU degradation. The physical and structural biodegradation of the PU, as achieved by T. molitor, was observed and compared to the characteristics of the original PU (PU-virgin) using Fourier Transform InfraRed spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA), and Scanning Electron Microphotography (SEM).

Novel strategy in biohydrogen energy production from COVID - 19 plastic waste: A critical review

Usage of plastics in the form of personal protective equipment, medical devices, and common packages has increased alarmingly during these pandemic times. Though they have served as an excellent protection source in minimizing the coronavirus disease (COVID-19) spreading, they have still emerged as major environmental pollutants nowadays. These non-degradable COVID-19 plastic wastes (CPW) were treated through incineration and landfilling process, which may lead to either the release of harmful gases or contaminating the surrounding environment. Further, they can cause numerous health hazards to the human and animal populations. These plastic wastes can be efficiently managed through thermochemical processes like pyrolysis or gasification, which assist in degrading the plastic waste and also effectively convert them into useful energy-yielding products. The pyrolysis process promotes the formation of liquid fuels and chemicals, whereas gasification leads to syngas and hydrogen fuel production. These energy-yielding products can help to compensate for the fossil fuels depletion in the near future. There are many insights explained in terms of the types of reactors and influential factors that can be adopted for the pyrolysis and gasification process, to produce high efficient energy products from the wastes. In addition, advanced technologies including co-gasification and two-stage gasification were also reviewed.

PHA-Based Bioplastic: a Potential Alternative to Address Microplastic Pollution

Petroleum-derived plastics are linked to a variety of growing environmental issues throughout their lifecycle, including emission of greenhouse gases, accumulation in terrestrial and marine habitats, pollution, among others. There has been a lot of attention over the last decade in industrial and research communities in developing and producing eco-friendly polymers to deal with the current environmental issues. Bioplastics preferably are a fast-developing family of polymeric substances that are frequently promoted as substitutes to petroleum-derived plastics. Polyhydroxyalkanoates (PHAs) have a number of appealing properties that make PHAs a feasible source material for bioplastics, either as a direct replacement of petroleum-derived plastics or as a blend with elements derived from natural origin, fabricated biodegradable polymers, and/or non-biodegradable polymers. Among the most promising PHAs, polyhydroxybutyrates (PHBs) are the most well-known and have a significant potential to replace traditional plastics. These biodegradable plastics decompose faster after decomposing into carbon dioxide, water, and inorganic chemicals. Bioplastics have been extensively utilized in several sectors such as food-processing industry, medical, agriculture, automobile industry, etc. However, it is also associated with disadvantages like high cost, uneconomic feasibility, brittleness, and hydrophilic nature. A variety of tactics have been explored to improve the qualities of bioplastics, with the most prevalent being the development of gas and water barrier properties. The prime objective of this study is to review the current knowledge on PHAs and provide a brief introduction to PHAs, which have drawn attention as a possible potential alternative to conventional plastics due to their biological origin, biocompatibility, and biodegradability, thereby reducing the negative impact of microplastics in the environment. This review may help trigger further scientific interest to thoroughly research on PHAs as a sustainable option to greener bioplastics.

Distinct Bacterial and Fungal Communities Colonizing Waste Plastic Films Buried for More Than 20 Years in Four Landfill Sites in Korea

Plastic pollution has been recognized as a serious environmental problem, and microbial degradation of plastics is a potential, environmentally friendly solution to this. Here, we analyzed and compared microbial communities on waste plastic films (WPFs) buried for long periods at four landfill sites with those in nearby soils to identify microbes with the potential to degrade plastics. Fourier-transform infrared spectroscopy spectra of these WPFs showed that most were polyethylene and had signs of oxidation, such as carbon-carbon double bonds, carbon-oxygen single bonds, or hydrogen-oxygen single bonds, but the presence of carbonyl groups was rare. The species richness and diversity of the bacterial and fungal communities on the films were generally lower than those in nearby soils. Principal coordinate analysis of the bacterial and fungal communities showed that their overall structures were determined by their geographical locations; however, the microbial communities on the films were generally different from those in the soils. For the pulled data from the four landfill sites, the relative abundances of Bradyrhizobiaceae, Pseudarthrobacter, Myxococcales, Sphingomonas, and Spartobacteria were higher on films than in soils at the bacterial genus level. At the species level, operational taxonomic units classified as Bradyrhizobiaceae and Pseudarthrobacter in bacteria and Mortierella in fungi were enriched on the films. PICRUSt analysis showed that the predicted functions related to amino acid and carbohydrate metabolism and xenobiotic degradation were more abundant on films than in soils. These results suggest that specific microbial groups were enriched on the WPFs and may be involved in plastic degradation.

Sourcing thermotolerant poly(ethylene terephthalate) hydrolase scaffolds from natural diversity

Enzymatic deconstruction of poly(ethylene terephthalate) (PET) is under intense investigation, given the ability of hydrolase enzymes to depolymerize PET to its constituent monomers near the polymer glass transition temperature. To date, reported PET hydrolases have been sourced from a relatively narrow sequence space. Here, we identify additional PET-active biocatalysts from natural diversity by using bioinformatics and machine learning to mine 74 putative thermotolerant PET hydrolases. We successfully express, purify, and assay 51 enzymes from seven distinct phylogenetic groups; observing PET hydrolysis activity on amorphous PET film from 37 enzymes in reactions spanning pH from 4.5-9.0 and temperatures from 30-70 °C. We conduct PET hydrolysis time-course reactions with the best-performing enzymes, where we observe differences in substrate selectivity as function of PET morphology. We employed X-ray crystallography and AlphaFold to examine the enzyme architectures of all 74 candidates, revealing protein folds and accessory domains not previously associated with PET deconstruction. Overall, this study expands the number and diversity of thermotolerant scaffolds for enzymatic PET deconstruction.

Biodegradation of polyethylene by Meyerozyma guilliermondii and Serratia marcescens isolated from the gut of waxworms (larvae of Plodia interpunctella)

The widespread use of polyethylene (PE) causes a large amount of indigestible plastic waste. Waxworms (the larvae of Plodia interpunctella) can eat PE, but the degradation principle of PE under the action of intestinal microorganisms is still unclear, especially the insufficient research on key degradable PE strains. In this study, we fed waxworms with PE. Two strains with high PE degradation efficiency were isolated and purified, and the effects of single and microbial consortia on PE degradation were evaluated by water contact angle (WCA), FTIR, GC-MS, SEM and RT-qPCR. The results showed that Meyerozyma guilliermondii ZJC1 (MgZJC1) and Serratia marcescens ZJC2 (SmZJC2) could degrade PE. However, the degradation efficiency of the microbial consortium was higher, and the weight loss rate of PE was 15.87 %. In addition, the PE degradation products of MgZJC1 were C₉H₁₀O, C₂₀H₁₅NO, C₂₈H₄₄O₃ and C₁₆H₃₂O₂, and the PE degradation products of SmZJC2 were C₁₆H₁₈O, C₁₄H₁₈N₂O₇ and C₃₁H₄₈O₆. The PE degradation products of the microbial consortium were C₁₁H₂₄, C₁₉H₁₀O, C₁₅H₃₂, C₁₄H₃₀, C₁₆H₃₄, C₂₅H₅₂ and C₂₇H₅₆. RT-qPCR results showed that SmZJC2 promoted PE degradation by upregulating the expression of multiple genes, such as multicopper oxidase genes (PiSm-CueO). MgZJC1 responded to carbon deficiency by upregulating the expression of multiple genes, such as key enzyme genes in the tricarboxylic acid (TCA) cycle. This study can be used to develop an efficient microbial consortium for PE degradation and provide a basis for the reuse of PE waste. It can also provide a research basis for the joint degradation of PE by microbial consortia composed of bacteria and fungi.

Recent Advances in Micro-/Nanoplastic (MNPs) Removal by Microalgae and Possible Integrated Routes of Energy Recovery

Reliance on plastic has resulted in the widespread occurrence of micro-/nanoplastics (MNPs) in aquatic ecosystems, threatening the food web and whole ecosystem functions. There is a tight interaction between MNPs and microalgae, as dominant living organisms and fundamental constituents at the base of the aquatic food web. Therefore, it is crucial to better understand the mechanisms underlying the interactions between plastic particles and microalgae, as well as the role of microalgae in removing MNPs from aquatic ecosystems. In addition, finding a suitable route for further utilization of MNP-contaminated algal biomass is of great importance. The present review article provides an interdisciplinary approach to elucidate microalgae-MNP interactions and subsequent impacts on microalgal physiology. The degradation of plastic in the environment and differences between micro- and nanoplastics are discussed. The possible toxic effects of MNPs on microalgal growth, photosynthetic activity, and morphology, due to physical or chemical interactions, are evaluated. In addition, the potential role of MNPs in microalgae cultivation and/or harvesting, together with further safe routes for biomass utilization in biofuel production, are suggested. Overall, the current article represents a state-of-the-art overview of MNP generation and the consequences of their accumulation in the environment, providing new insights into microalgae integrated routes of plastic removal and bioenergy production.

Providing octane degradation capability to Pseudomonas putida KT2440 through the horizontal acquisition of oct genes located on an integrative and conjugative element

The extensive use of petrochemicals has produced serious environmental pollution problems; fortunately, bioremediation is considered an efficient way to fight against pollution. In line with Synthetic Biology is that robust microbial chassis with an expanded ability to remove environmental pollutants are desirable. Pseudomonas putida KT2440 is a robust lab microbe that has preserved the ability to survive in the environment and is the natural host for the self-transmissible TOL plasmid, which allows metabolism of toluene and xylenes to central metabolism. We show that the P. putida KT2440 (pWW0) acquired the ability to use octane as the sole C-source after acquisition of an almost 62-kb ICE from a microbial community that harbours an incomplete set of octane metabolism genes. The ICE bears genes for an alkane monooxygenase, a PQQ-dependent alcohol dehydrogenase and aldehyde dehydrogenase but lacks the electron donor enzymes required for the monooxygenase to operate. Host rubredoxin and rubredoxin reductase allow metabolism of octane to octanol. Proteomic assays and mutants unable to grow on octane or octanoic acid revealed that metabolism of octane is mediated by redundant host and ICE enzymes. Octane is oxidized to octanol, octanal and octanoic acid, the latter is subsequently acylated and oxidized to yield acetyl-CoA that is assimilated via the glyoxylate shunt; in fact, a knockout mutant in the aceA gene, encoding isocitrate lyase was unable to grow on octane or octanoic acid.

Environmental impacts of post-consumer plastic wastes: Treatment technologies towards eco-sustainability and circular economy

The huge amounts of plastic production (millions of tons) are carried out all around world every year and EU is one of the biggest consumers of these products. In 2021, recycling rate of plastic wastes around 32.5% in the EU and the rest end up on their journey in landfills and oceans that lead to environmental pollution which is a crucial global concern. Thus, it is important to take necessary steps to control the use of such plastic and to sustainably dispose them. One of the solutions to the problem is to use a better alternative to plastics which doesn't degrade land, water or air nor affects living organisms. Circular economy is another answer to this problem, it would ensure prevention of post-consumer plastic waste from getting formed. In addition, sustainable disposal approaches for plastic waste such as pyrolysis, plasma gasification, photocatalytic degradation, and production of value-added products from polymer waste can be explored. These recycling methods has huge potential for research and studies and can play a crucial in eliminating post-consumer plastic waste. This review paper aims to discuss the environmental effects of post-consumer plastic wastes as well as the emerging approaches for the treatment of these environmental wastes towards eco-sustainability and circular economy.

The gut microbiota, a key to understanding the health implications of micro(nano)plastics and their biodegradation

The effects of plastic debris on the environment and plant, animal, and human health are a global challenge, with micro(nano)plastics (MNPs) being the main focus. MNPs are found so often in the food chain that they are provoking an increase in human intake. They have been detected in most categories of consumed foods, drinking water, and even human feces. Therefore, oral ingestion becomes the main source of exposure to MNPs, and the gastrointestinal tract, primarily the gut, constantly interacts with these small particles. The consequences of human exposure to MNPs remain unclear. However, current in vivo studies and in vitro gastrointestinal tract models have shown that MNPs of several types and sizes impact gut intestinal bacteria, affecting gut homeostasis. The typical microbiome signature of MNP ingestion is often associated with dysbiosis and loss of resilience, leads to frequent pathogen outbreaks, and local and systemic metabolic disorders. Moreover, the small micro- and nano-plastic particles found in animal tissues with accumulated evidence of microbial degradation of plastics/MNPs by bacteria and insect gut microbiota raise the issue of whether human gut bacteria make key contributions to the bio-transformation of ingested MNPs. Here, we discuss these issues and unveil the complex interplay between MNPs and the human gut microbiome. Therefore, the elucidation of the biological consequences of this interaction on both host and microbiota is undoubtedly challenging. It is expected that microbial biotechnology and microbiome research could help decipher the extent to which gut microorganisms diversify and MNP-determinant species, mechanisms, and enzymatic systems, as well as become important to understand our response to MNP exposure and provide background information to inspire future holistic studies.

The fate of microplastic in sludge management systems

Sewage sludge (SS) from wastewater treatment plants (WWTPs) is commonly used as a soil amendment on agricultural land; however, this sludge contains microplastics (MPs) which harm soil ecosystems and can leach into aquatic environments. This review aims to assess the fate of MPs in SS systems and, in the context of a changing agricultural scene, present alternatives for sustainable SS disposal that are consistent with the practices of a clean, circular economy. Anaerobic digestion and composting, which are commonly used to stabilize SS before land application, were not reported to substantially affect MP removal, although process efficiency and the microbiome were affected by MPs. Alternatively, MPs can be destroyed or removed by mono-incineration or combustion, but unfortunately, some MPs may remain in the ash after these processes. Therefore, the most desirable solutions would prevent MPs from entering the environment and remove them before they enter the biological part of a WWTP, where they build up in SS. Additionally, the management of MP-containing sludge must be adapted to the geographical context and the local economy, and it should begin with legislation addressing MPs in SS. The information presented here will help to develop good practices in waste management for preventing or decreasing the transfer of MPs into the environment.

Critical Review on the Progress of Plastic Bioupcycling Technology as a Potential Solution for Sustainable Plastic Waste Management

Plastic production worldwide has doubled in the last two decades and is expected to reach a four-fold increase by 2050. The durability of plastic makes them a perfect material for many applications, but it is also a key limitation to their end-of-life management. The current plastic lifecycle is far from circular, with only 13% being collected for recycling and 9% being successfully recycled, indicating the failure of current recycling technology. The remaining plastic waste streams are thus incinerated, landfilled, or worse, mismanaged, leading to them leaking into the environment. To promote plastic circularity, keeping material in the loop is a priority and represents a more sustainable solution. This can be achieved through the reuse of plastic items, or by using plastic waste as a resource for new materials, instead of discarding them as waste. As the discovery of plastic-degrading/utilizing microorganisms and enzymes has been extensively reported recently, the possibility of developing biological plastic upcycling processes is opening up. An increasing amount of studies have investigated the use of plastic as a carbon source for biotechnological processes to produce high-value compounds such as bioplastics, biochemicals, and biosurfactants. In the current review, the advancements in fossil-based plastic bio- and thermochemical upcycling technologies are presented and critically discussed. In particular, we highlight the developed (bio)depolymerization coupled with bioconversion/fermentation processes to obtain industrially valuable products. This review is expected to contribute to the future development and scale-up of effective plastic bioupcycling processes that can act as a drive to increase waste removal from the environment and valorize post-consumer plastic streams, thus accelerating the implementation of a circular (plastic) economy.

Analysis of endometrial lavage microbiota reveals an increased relative abundance of the plastic-degrading bacteria Bacillus pseudofirmus and Stenotrophomonas rhizophila in women with endometrial cancer/endometrial hyperplasia

The pathogenic influences of uterine bacteria on endometrial carcinogenesis remain unclear. The aim of this pilot study was to compare the microbiota composition of endometrial lavage samples obtained from women with either endometrial hyperplasia (EH) or endometrial cancer (EC) versus those with benign uterine conditions. We hypothesized that specific microbiota signatures would distinguish between the two groups, possibly leading to the identification of bacterial species associated with endometrial tumorigenesis. A total of 35 endometrial lavage specimens (EH, n = 18; EC, n = 7; metastatic EC, n = 2; benign endometrial lesions, n = 8) were collected from 32 women who had undergone office hysteroscopy. Microbiota composition was determined by sequencing the V3−V4 region of 16S rRNA genes and results were validated by real-time qPCR in 46 patients with EC/EH and 13 control women. Surprisingly, we found that Bacillus pseudofirmus and Stenotrophomonas rhizophila – two plastic-degrading bacterial species – were over-represented in endometrial lavage specimens collected from patients with EC/EH. Using computational analysis, we found that the functional profile of endometrial microbiota in EC/EH was associated with fatty acid and amino acid metabolism. In summary, our hypothesis-generating data indicate that the plastic-degrading bacteria Bacillus pseudofirmus and Stenotrophomonas rhizophila are over-represented within the endometrial lavage microbiota of women with EC/EH living in Taiwan. Whether this may be related to plastic pollution deserves further investigation.

Microbial Fermentation of Polyethylene Terephthalate (PET) Plastic Waste for the Production of Chemicals or Electricity

Ideonella sakaiensis (I. sakaiensis) can grow on polyethylene terephthalate (PET) as the major carbon and energy source. Previous work has shown that PET conversion in the presence of oxygen released carbon dioxide and water while yielding adenosine triphosphate (ATP) through oxidative phosphorylation. This study demonstrates that I. sakaiensis is a facultative anaerobe that ferments PET to the feedstock chemicals acetate and ethanol in the absence of oxygen. In addition to PET, the pure monomer ethylene glycol (EG), the intermediate product ethanol, and the carbohydrate fermentation test substance maltose can also serve as fermenting substrates. Co-culturing of I. sakaiensis with the electrogenic and acetate-consuming Geobacter sulfurreducens produced electricity from PET or EG. This newly identified plastic fermentation process by I. sakaiensis provides thus a novel biosynthetic route to produce high-value chemicals or electricity from plastic waste streams.

Current biotechnologies on depolymerization of polyethylene terephthalate (PET) and repolymerization of reclaimed monomers from PET for bio-upcycling: A critical review

The production of polyethylene terephthalate (PET) has drastically increased in the past half-century, reaching 30 million tons every year. The accumulation of this recalcitrant waste now threatens diverse ecosystems. Despite efforts to recycle PET wastes, its rate of recycling remains limited, as the current PET downcycling is mostly unremunerative. To address this problem, PET bio-upcycling, which integrates microbial depolymerization of PET followed by repolymerization of PET-derived monomers into value-added products, has been suggested. This article critically reviews current understanding of microbial PET hydrolysis, the metabolic mechanisms involved in PET degradation, PET hydrolases, and their genetic improvement. Furthermore, this review includes the use of meta-omics approaches to search PET-degrading microbiomes, microbes, and putative hydrolases. The current development of biosynthetic technologies to convert PET-derived materials into value-added products is also comprehensively discussed. The integration of various depolymerization and repolymerization biotechnologies enhances the prospects of a circular economy using waste PET.

Interactions between bacteria and nano (micro)-sized polystyrene particles by bacterial responses and microscopy

Microorganisms play an important role in biogeochemical cycles, and are inevitably found associated with plastic debris. The interplay between microbes and plastics may change the characteristics of certain plastics over time and drive the environmental fate of plastics. In this study, we evaluated interactions of bacteria with nano- and microplastics. Here, polystyrene (PS) polymer particles of various diameters, specifically 60, 220, 430, 700, 1040, 1700, and 2260 nm, were used as the plastics. Escherichia coli (E. coli, gram-negative) and Bacillus sp. (gram-positive) were chosen as model bacteria. The effects of nano- and microPS particles on E. coli and Bacillus sp. cells were investigated by measuring the growth and viability of the cells in laboratory-scale flasks and their generation of reactive oxygen species (ROS) upon their exposure to these particles of 100 mg/L. The particles inhibited the growth and viability of both types of bacterial cells, but their inhibitory effects varied depending on the diameter of PS particle. The 60-nm-diameter PS particles were visually observed to enter the cells as well as accumulate on their surfaces and enhanced ROS generation of the cells. Unexpectedly, the 1040-nm-diameter PS particles, similar in size to the bacterial cells, inhibited the growth of both E. coli and Bacillus sp. cells the most. The E. coli and Bacillus sp. cells formed microPS-biofilm complex by secreting an extracellular polymeric substance (EPS) in response to their exposure to the ∼ 1-μm-diameter PS particles. A positive correlation between relative ROS levels and specific growth rates of the E. coli cells were observed with a Pearson correlation coefficient r value of 0.676 (p < 0.05).

Oxidative degradation of UV-irradiated polyethylene by laccase-mediator system

Polyethylene (PE) is one of the most widely used plastics. However, the chemical inertness, inefficient recycling, and random landfilling of PE waste have caused serious pollution to the natural environment. In this study, a series of laccase-mediator systems (LMS) were constructed by combination of two laccases from Botrytis aclada (BaLac) and Bacillus subtilis (BsLac) with three synthetic mediators (ABTS, HBT, and TEMPO) to oxidize LDPE films (UVPE) pretreated with high-temperature UV irradiation. Scanning electron microscopy showed aging phenomena such as etching, fragmentation, and cracking on the surface of the UVPE films after LMS incubation. The FTIR results showed that LMS-UVPE added new oxygen-containing functional groups such as -OH, -CO, and CC. High-temperature gel chromatography confirmed that the average reduction in weight-average molecular weight (Mw) was approximately 40% for the BaLac experimental group. GC-MS analysis showed the presence of oxygen-containing products, such as aldehydes, ketones, and alcohols, in the reaction mixture. To verify the oxidation process UVPE degradation by LMS, we inferred three possible pathways by combined analysis of the oxidation products of LMS on UVPE and model substrates oleic acid and squalene.

Preliminary investigation of microorganisms potentially involved in microplastics degradation using an integrated metagenomic and biochemical approach

Plastic pollution is becoming an emerging environmental issue due to inappropriate disposal at the end of the materials life cycle. When plastics are released, they undergo physical and chemical corrosion, leading to the formation of small particles, commonly referred to as microplastics. In this study, a microbial community derived from the leachate of a bioreactor containing a mixture of soil and plastic collected during a landfill mining process underwent an enrichment protocol in order to select the microbial species specifically involved in plastic degradation. The procedure was set up and tested on polyethylene, polyvinyl chloride, and polyethylene terephthalate, both in anaerobic and aerobic conditions. The evolution of the microbiome has been monitored using a combined approach based on microscopy, marker-gene amplicon sequencing, genome-centric metagenomics, degradation assays, and GC-MS analyses. This procedure permitted us to deeply investigate the metabolic pathways potentially involved in plastic degradation and to depict the route for microplastics metabolization from the enriched microbial community. Six enzymes, among the ones already identified, were found in our samples (alkane 1-monooxygenase, cutinase, feruloyl esterase, triacylglycerol lipase, medium-chain acyl-CoA dehydrogenase, and protocatechuate 4,5-dioxygenase) and new enzymes, addressed as MHETases most probably for the presence of the catalytic triad (His-Asp-Ser), were detected. Among the enzymes involved in plastics degradation, alkane 1-monooxygenase was found in high copy number (between ten and 62 copies) in the metagenomes that resulted most abundant in the microbiome enriched with polyethylene, while protocatechuate 4,5-dioxygenase was found between one and eight copies in the most abundant metagenomes of the microbial culture enriched with polyethylene terephthalate. Degradation assays, performed using both bacterial lysates and supernatants, revealed interesting results on polyethylene terephthalate degradation. Moreover, this study demonstrates to what extent different types of microplastics can affect the microbial community composition. The results obtained significantly increase the knowledge of the plastic degradation process.

Enhanced biodegradation of waste poly(ethylene terephthalate) using a reinforced plastic degrading enzyme complex

Poly(ethylene terephthalate) (PET) is synthesized via a rich ester bond between terephthalate (TPA) and ethylene glycol (EG). Because of this, PET degradation takes a long time and PET accumulates in the environment. Many studies have been conducted to improve PET degrading enzyme to increase the efficiency of PET depolymerization. However, enzymatic PET decomposition is still restricted, making upcycling and recycling difficult. Here, we report a novel PET degrading complex composed of Ideonella sakaiensis PETase and Candida antarctica lipase B (CALB) that improves degradability, binding ability and enzyme stability. The reaction mechanism of chimeric PETase (cPETase) and chimeric CALB (cCALB) was confirmed by PET and bis (2-hydroxyethyl terephthalate) (BHET). cPETase generated BHET and mono (2-hydroxyethyl terephthalate (MHET) and cCALB produced terephthalate (TPA). Carbohydrate binding module 3 (CBM3) in the scaffolding protein greatly improved PET film binding affinity. Finally, the final enzyme complex demonstrated a 6.5-fold and 8.0-fold increase in the efficiency of hydrolysis from PET with either high crystalline or waste to TPA than single enzymes, respectively. This complex could effectively break down waste PET while maintaining enzyme stability and would be applied for biological upcycling of TPA.

Microplastics in landfill and leachate: Occurrence, environmental behavior and removal strategies

Plastic wastes buried in landfill are gradually broken and decomposed into microplastics under physical, chemical and biological effects, bringing environmental risks to the exploitation of waste resources. Landfill leachate as a potential source of environmental microplastics has not good attention. Microplastics in leachate carry toxic and harmful pollutants and antibiotic resistance genes, and these vectors pose greater risks to human and environmental health without systematic treatment. Recently, the main technologies of landfill leachate treatment process include order batch activated sludge process, membrane biological reaction process, flocculation process, combined filtration process, and constructed wetland process. However, there is still little knowledge about microplastic removal of the existing leachate treatment facilities, and some technologies to alleviate the sources of such microplastics should be timely developed. This paper systematically summarizes the occurrence of plastics, microplastics and nanoplastics in leachate and their interactive pollution with other toxic pollutants. Meanwhile, the prospects of their environmental behaviors in landfill and leachate are put forward. The microplastic removal by existing leachate treatment equipment and the limitations and challenges to upgrading process of development and implementation are also discussed. The paper can provide a scientific basis for studying the fate of microplastics in landfill and leachate.

Ten decadal advances in fungal biology leading towards human well-being

Fungi are an understudied resource possessing huge potential for developing products that can greatly improve human well-being. In the current paper, we highlight some important discoveries and developments in applied mycology and interdisciplinary Life Science research. These examples concern recently introduced drugs for the treatment of infections and neurological diseases; application of -OMICS techniques and genetic tools in medical mycology and the regulation of mycotoxin production; as well as some highlights of mushroom cultivaton in Asia. Examples for new diagnostic tools in medical mycology and the exploitation of new candidates for therapeutic drugs, are also given. In addition, two entries illustrating the latest developments in the use of fungi for biodegradation and fungal biomaterial production are provided. Some other areas where there have been and/or will be significant developments are also included. It is our hope that this paper will help realise the importance of fungi as a potential industrial resource and see the next two decades bring forward many new fungal and fungus-derived products.

Genome-Based Exploration of Rhodococcus Species for Plastic-Degrading Genetic Determinants Using Bioinformatic Analysis

Plastic polymer waste management is an increasingly prevalent issue. In this paper, Rhodococcus genomes were explored to predict new plastic-degrading enzymes based on recently discovered biodegrading enzymes for diverse plastic polymers. Bioinformatics prediction analyses were conducted using 124 gene products deriving from diverse microorganisms retrieved from databases, literature data, omic-approaches, and functional analyses. The whole results showed the plastic-degrading potential of Rhodococcus genus. Among the species with high plastic-degrading potential, R. erythropolis, R. equi, R. opacus, R. qingshengii, R. fascians, and R. rhodochrous appeared to be the most promising for possible plastic removal. A high number of genetic determinants related to polyester biodegradation were obtained from different Rhodococcus species. However, score calculation demonstrated that Rhodococcus species (especially R. pyridinivorans, R. qingshengii, and R. hoagii) likely possess PE-degrading enzymes. The results identified diverse oxidative systems, including multicopper oxidases, alkane monooxygenases, cytochrome P450 hydroxylases, para-nitrobenzylesterase, and carboxylesterase, and they could be promising reference sequences for the biodegradation of plastics with C−C backbone, plastics with heteroatoms in the main chain, and polyesters, respectively. Notably, the results of this study could be further exploited for biotechnological applications in biodegradative processes using diverse Rhodococcus strains and through catalytic reactions.

Co-exposure to polystyrene microplastics and lead aggravated ovarian toxicity in female mice via the PERK/eIF2α signaling pathway

Generally, individual microplastics (MPs) or lead (Pb) exposure could initiate ovarian toxicity. However, their combined effects on the ovary and its mechanism in mammals remained unclear. Female C57BL/6 mice were used in this study to investigate the combined ovarian toxicity of polystyrene MPs (PS-MPs, 0.1 mg/d/mouse) and Pb (1 g/L) for 28 days. Results showed that co-exposure to PS-MPs and Pb increased the accumulation of Pb in ovaries, the histopathological damage in ovaries and uterus, the serum malondialdehyde levels and decreased serum superoxide dismutase and sex hormone levels significantly when compared with single PS-MPs and Pb exposure. These observations indicated that co-exposure exerted more severe toxicity to mouse ovaries and uterus. Furthermore, co-exposure to PS-MPs and Pb caused endoplasmic reticulum (ER) stress by activating the PERK/eIF2α signaling pathway in the ovary, which resulted in apoptosis. However, the oxidative and ovarian damage were alleviated, and the mRNA levels of genes related to the PERK/eIF2α signaling pathway were down-regulated to levels of the control mice in the PS-MPs and Pb co-exposed mice administered with ER stress inhibitor (Salubrinal, Sal) or the antioxidant (N-acetyl-cysteine, NAC). In conclusion, our findings suggested that the combination of PS-MPs and Pb aggravated ovarian toxicity in mice by inducing oxidative stress and activating the PERK/eIF2α signaling pathway, thereby providing a basis for future studies into the combined toxic mechanism of PS-MPs and Pb in mammals.

Microbial enzymes will offer limited solutions to the global plastic pollution crisis

Global economies depend on the use of fossil-fuel-based polymers with 360-400 million metric tons of synthetic polymers being produced per year. Unfortunately, an estimated 60% of the global production is disposed into the environment. Within this framework, microbiologists have tried to identify plastic-active enzymes over the past decade. Until now, this research has largely failed to deliver functional biocatalysts acting on the commodity polymers such as polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), ether-based polyurethane (PUR), polyamide (PA), polystyrene (PS) and synthetic rubber (SR). However, few enzymes are known to act on low-density and low-crystalline (amorphous) polyethylene terephthalate (PET) and ester-based PUR. These above-mentioned polymers represent >95% of all synthetic plastics produced. Therefore, the main challenge microbiologists are currently facing is in finding polymer-active enzymes targeting the majority of fossil-fuel-based plastics. However, identifying plastic-active enzymes either to implement them in biotechnological processes or to understand their potential role in nature is an emerging research field. The application of these enzymes is still in its infancy. Here, we summarize the current knowledge on microbial plastic-active enzymes, their global distribution and potential impact on plastic degradation in industrial processes and nature. We further outline major challenges in finding novel plastic-active enzymes, optimizing known ones by synthetic approaches and problems arising through falsely annotated and unfiltered use of database entries. Finally, we highlight potential biotechnological applications and possible re- and upcycling concepts using microorganisms.

Fate of petroleum-based and plant-based teabags exposed to environmental soil conditions for one year

Petroleum-based plastics are materials which have provided important industrial benefits from being lightweight and having low production costs. However, plastic pollution is pervasive and ubiquitous on all environments. This has led some industries to rapidly introduce the so called ‘bioplastics’ into the market by switching the conventional ones for new plant-based alternatives with similar properties. However, little is known about the fate of such alternatives especially in the open environment. In this novel study, the degradation of teabags from eight different brands was investigated, five petroleum based (cellulose-PP blend) and three plant-based (cellulose, cellulose-PLA blend and PLA). The degradation was tested under real-environmental soil conditions over a 12-month period. Fourier Transform Infrared Spectroscopy (FTIR-ATR) and Scanning Electron Microscopy (SEM) techniques were used to examine the change in polymer makeup and surface degradation of teabags at 3 weeks, 3.5, 6 and 12 months. Teabag dry weight and any retrieved fragments were measured over time. Teabags that contained a plastic blended to cellulose were brittle or degraded into smaller fragments after 3 weeks in soil. Parallel to this, the cellulose layer also degraded in this short timeline. Petroleum-based teabags produced the highest numbers of PP fragments overtime and fragmented teabags were still found after 12 months. Plant-based teabags made of cellulose only or a blend of cellulose-PLA were absent from soil samples after 3.5 months, including no fragments. Contrary to this, teabags made of PLA which were marketed as completely biodegradable, persisted completely intact in soil throughout all time points. The novel results from this study provide a perspective on plastic degradation in terrestrial sources. Based on these findings, it can be recommended that teabags mostly made of cellulose or cellulose blended with a bioplastic present in a smaller ratio, are a better alternative to petroleum-based or pure PLA plastics, in terms of rapid environmental degradation. Further studies should focus on their ecotoxicity, additive presence, microbial degradation and life cycle in order to draw a full environmental assessment.

Cytotoxicity and Genotoxicity of Polystyrene Micro- and Nanoplastics with Different Size and Surface Modification in A549 Cells

Background

Micro- and nano-sized plastics (MPs and NPs) have become an environmental issue of global concern due to their small size, strong bio-permeability and high specific surface area. However, few studies have assessed the effect of polystyrene MPs and NPs on human lung cells. In this research, we evaluated the cytotoxicity and genotoxicity of polystyrene (PS) MPs and NPs with different sizes (2 μm and 80 nm) and surface modification (carboxy and amino functionalized polystyrene, pristine polystyrene) in A549 cells.

Methods

The zeta potential and hydrodynamic particle size of five types of PS plastic solutions were measured by dynamic light scattering, and their morphology and degree of aggregation were observed by scanning electron microscopy. After incubation of the PS plastics with A549 cells, the uptake and toxicity of the cells were assessed by fluorescence microscopy, laser scanning confocal microscopy, flow cytometry, MTT, micronucleus formation assay, and reactive oxygen species.

Results

The cytotoxicity and genotoxicity of A549 cells caused by nano-level PS is more serious than that of micro-level. Compared with unmodified PS-NPs, more surface-functionalized PS-NPs were found inside the cells, especially the accumulation of PS-NH₂. Cell viability and the induction of micronuclei (MN) are appreciably impacted in a dose-dependent way. Compared with pristine PS-NPs, functionalized PS-NPs showed stronger cell viability inhibitory ability, and induced more MN scores.

Conclusion

This study shows that the intrinsic size properties and surface modification of PS plastics, the interaction between PS plastics and the receiving medium, intracellular accumulation are critical factors for evaluating the toxicological influences of PS plastics on humans.

Influence of sediment texture on HDPE microplastics recovery by density separation

Microplastics (MPs) are an emerging environmental pollutant, threatening marine and terrestrial ecosystems. Because of their properties and their widely varying size (5mm-0.1 μm), it is still difficult to define a valid and efficient method for extracting MPs from solid matrices. Among the several methods proposed, density separation is the most practical and cost-effective one. Progress is still ongoing towards a deeper understanding of the advantages and limitations related to the application of density separation for MPs extraction, the recovery yields and the factors that may influence it. In this context, we introduce the following work, which provides an early-stage insight into how the sediment texture may influence the efficiency of this extraction method, and how parameters, such as sedimentation time and extraction cycles, can be modified to always achieve the best recovery. Our focus has been directed on evaluating the extraction efficiency of HDPE MPs by density separation using NaCl, from three types of sediment: sandy (SS), sandy loam (SLS) and sandy-clay loam (SCLS). We investigated the impact of sedimentation time (1, 6, 12, 24 h) and extraction cycles (3 cycles for each sedimentation time) on MPs recovery. Finally, we determined the minimum amount of MPs (MPs g/g sediment) below which it is not possible to quantify MPs with the method used. The results have shown that the recovery efficiency of MPs from sediment is structure dependent. The highest recoveries are reached after a settling time of 1 and 6 h. Furthermore, for samples with minimum clay content (SS), only one extraction cycle is needed, whereas two extraction cycles are required for SLS and SCLS. The outcomes about the detection limit (LOD) of the method, showed the existence of an interaction MPs-clay/sediment, which allowed us to understand how far this extraction method is suitable in field, thus defining the minimum grade of MPs pollution (MPs g/g sediment) below which this method is no longer capable to extract MPs from contaminated samples.