Low density polyethylene degradation by filamentous fungi

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

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

Enhanced degradation of phototreated recycled and unused low-density polyethylene films by Pleurotus ostreatus

Polyethylene, one of the most used petroleum-derived polymers, causes serious environmental pollution. The ability of Pleurotus ostreatus to degrade UV-treated and untreated recycled and unused (new) low-density polyethylene (LDPE) films was studied. We determined the fungal biomass production, enzyme production, and enzyme yield. Changes in the chemical structure and surface morphology of the LDPE after fungal growth were analyzed using FTIR spectroscopy and SEM. Functional group indices and contact angles were also evaluated. In general, the highest Lac (6013 U/L), LiP (2432 U/L), MnP (995 U/L) and UP (6671 U/L) activities were observed in irradiated recycled LDPE (IrRPE). The contact angle of all samples was negatively correlated with fermentation time; the smaller the contact angle, the longer the fermentation time, indicating effective biodegradation. The IrRPE samples exhibited the smallest contact angle (49°) at 4 weeks, and the samples were fragmented (into two pieces) at 5 weeks. This fungus could degrade unused (new) LDPE significantly within 6 weeks. The biodegradation of LDPE proceeded faster in recycled than in unused samples, which can be enhanced by exposing LDPE to UV radiation. Enzymatic production during fungal growth suggest that LDPE degradation is initiated by laccase (Lac) followed by lignin peroxidase (LiP), whereas manganese peroxidase (MnP) and unspecific peroxygenase (UP) are involved in the final degradation process. This is the first experimental study on the fungal growth and its main enzymes involved in LDPE biodegradation. This fungus has great promise as a safe, efficient, and environmentally friendly organism capable of degrading LDPE.

Tapping into fungal potential: Biodegradation of plastic and rubber by potent Fungi

Plastic polymers are present in most aspects of routine daily life. Their increasing leakage into the environment poses a threat to environmental, animal, and human health. These polymers are often resistant to microbial degradation and are predicted to remain in the environment for tens to hundreds of years. Fungi have been shown to degrade complex polymers and are considered good candidates for bioremediation (biological pollutant reduction) of plastics. Therefore, we screened 18 selected fungal strains for their ability to degrade polyurethane (PU), polyethylene (PE), and tire rubber. As a proxy for plastic polymer mineralization, we quantified O2 consumption and CO2 production in an enclosed biodegradation system providing plastic as the sole carbon source. In contrast to most studies we demonstrated that the tested fungi attach to, and colonize the different plastic polymers without any pretreatment of the plastics and in the absence of sugars, which were suggested essential for priming the degradation process. Functional polymer groups identified by Fourier-transform infrared spectroscopy (FTIR), and changes in fungal morphology as seen in light and scanning electron microscopy (SEM) were used as indicators of fungal adaptation to growth on PU as a substrate. Thereby, SEM analysis revealed new morphological structures and deformation of the cell wall of several fungal strains when colonizing PU and utilizing this plastic polymer for cell growth. Strains of Fusarium, Penicillium, Botryotinia cinerea EN41, and Trichoderma demonstrated a high potential to degrade PU, rubber, and PE. Growing on PU, over 90 % of the O2 was consumed in <14 days with 300-500 ppm of CO2 generated in parallel. Our study highlights a high bioremediation potential of some fungal strains to efficiently degrade plastic polymers, largely dependent on plastic type.

The essential role of aggregation for the emulsifying ability of a fungal CYS-rich protein

Biosurfactants are in demand by the global market as natural commodities suitable for incorporation into commercial products or utilization in environmental applications. Fungi are promising producers of these molecules and have garnered interest also for their metabolic capabilities in efficiently utilizing recalcitrant and complex substrates, like hydrocarbons, plastic, etc. Within this framework, biosurfactants produced by two Fusarium solani fungal strains, isolated from plastic waste-contaminated landfill soils, were analyzed. Mycelia of these fungi were grown in the presence of 5% olive oil to drive biosurfactant production. The characterization of the emulsifying and surfactant capacity of these extracts highlighted that two different components are involved. A protein was purified and identified as a CFEM (common in fungal extracellular membrane) containing domain, revealing a good propensity to stabilize emulsions only in its aggregate form. On the other hand, an unidentified cationic smaller molecule exhibits the ability to reduce surface tension. Based on the 3D structural model of the protein, a plausible mechanism for the formation of very stable aggregates, endowed with the emulsifying ability, is proposed. KEY POINTS: • Two Fusarium solani strains are analyzed for their surfactant production. • A cationic surfactant is produced, exhibiting the ability to remarkably reduce surface tension. • An identified protein reveals a good propensity to stabilize emulsions only in its aggregate form.

Myco-remediation of plastic pollution: current knowledge and future prospects

To date, enumerable fungi have been reported to participate in the biodegradation of several notorious plastic materials following their isolation from soil of plastic-dumping sites, marine water, waste of mulch films, landfills, plant parts and gut of wax moth. The general mechanism begins with formation of hydrophobin and biofilm proceding to secretion of specific plastic degarding enzymes (peroxidase, hydrolase, protease and urease), penetration of three dimensional substrates and mineralization of plastic polymers into harmless products. As a result, several synthetic polymers including polyethylene, polystyrene, polypropylene, polyvinyl chloride, polyurethane and/or bio-degradable plastics have been validated to deteriorate within months through the action of a wide variety of fungal strains predominantly Ascomycota (Alternaria, Aspergillus, Cladosporium, Fusarium, Penicillium spp.). Understanding the potential and mode of operation of these organisms is thus of prime importance inspiring us to furnish an up to date view on all the presently known fungal strains claimed to mitigate the plastic waste problem. Future research henceforth needs to be directed towards metagenomic approach to distinguish polymer degrading microbial diversity followed by bio-augmentation to build fascinating future of waste disposal.

Microplastics affect soil-plant system: Implications for rhizosphere biology and fitness of sage (Salvia officinalis L.)

A mesocosm experiment was set-up to investigate the effects of low-density polyethylene (LDPE) fragments deriving from plastic film on soil ecology, rhizosphere and plant (Salvia officinalis L.) fitness. The internal transcribed spacer (ITS) and 16S metagenomic analysis was adopted to evaluate taxonomic and functional shifts of both soil and rhizosphere under the influence of microplastics (MPs). Photosynthetic parameters and enzymes involved in oxidative stress were assessed to unveil the plant physiological state. MP fragments were analysed by scanning electron microscope (SEM) and metagenomics to investigate the plastisphere. Microbial biomarkers of MPs pollution were identified in soil and rhizosphere, reinforcing the concept of molecular biomonitoring. Overall, Bacillus, Nocardioides and Streptomyces genera are bacterial biomarkers of MPs pollution in soil whereas Aspergillus, Fusarium and Trichoderma genera, and Nectriaceae family are fungal biomarkers of MPs polluted soil. The data show that the presence of MPs promotes the abundance of taxa involved in the soil N cycle, but simultaneously reduces the endophytic interaction capability and enhances pathogen related functions at the rhizosphere level. A significant decrease in chlorophyll levels and increase of oxidative stress enzymes was observed in plants grown in MPs-polluted soil. The SEM observations of MPs fragments revealed a complex colonisation, where bacteria (Bacillus in MPSo and Microvirga in MPRz) and fungi (Aspergillus in MPSo and Trichoderma in MPRz) represent the main colonisers. The results demonstrate that the presence of MPs causes changes in the soil and rhizosphere microbial community and functions leading to negative effects on plant fitness.

Biodeterioration of polyethylene by Bacillus cereus and Rhodococcus equi isolated from soil

Polyethylene (PE), a non-biodegradable plastic, is widely used in agriculture as a mulch material, which causes serious plastic pollution when it is discarded. Recent studies have described the biodeterioration of PE by bacteria, but it is difficult for a single bacterial species to effectively degrade PE plastic. We isolated two strains with PE-degrading ability, Bacillus cereus (E1) and Rhodococcus equi (E3), from the soil attached to plastic waste on the south side of Mount Tai, China, using a medium with PE plastic as the only carbon source. By clear zone area analysis, we found that E1 mixed with E3 could improve the degradation of PE plastics. The mixture of E1 and E3 was incubated for 110 days in a medium containing PE and mulch film as the only carbon source, respectively. After 110 days, a decrease in pH and mass was observed. Obvious slits and depressions were observed on the surface of the PE film and the mulch films using scanning electron microscopy. The surface hydrophobicity of both films decreased, and FTIR revealed the formation of new oxidation groups on their surfaces during the degradation process and the destruction of the original CH2 long chains of PE. Besides, we found that surface of the mulch films contained more viable bacteria than the liquid medium. In conclusion, we identified two PE-degrading strains whose mixture can effectively degrade mulch film than pure PE film. Our results provide a reference for understanding PE plastic degradation pathways and their associated degradation processes.

Are you drowned in microplastic pollution? A brief insight on the current knowledge for early career researchers developing novel remediation strategies

Microplastics (MPs) composed of different polymers with various shapes, within a vast granulometric distribution (1 μm - 5 mm) and with a wide variety of physicochemical surface and bulk characteristics spiral around the globe, with different atmospheric, oceanic, cryospheric, and terrestrial residence times, while interacting with other pollutants and biota. The challenges of microplastic pollution are related to the complex relationships between the microplastic generation mechanisms (physical, chemical, and biological), their physicochemical properties, their interactions with other pollutants and microorganisms, the changes in their properties with aging, and their small sizes that facilitate their diffusion and transportation between the air, water, land, and biota, thereby promoting their ubiquity. Early career researchers (ERCs) constitute an essential part of the scientific community committed to overcoming the challenges of microplastic pollution with their new ideas and innovative scientific perspectives for the development of remediation technologies. However, because of the enormous amount of scientific information available, it may be difficult for ERCs to determine the complexity of this environmental issue. This mini-review aims to provide a quick and updated overview of the essential insights of microplastic pollution to ERCs to help them acquire the background needed to develop highly innovative physical, chemical, and biological remediation technologies, as well as valorization proposals and environmental education and awareness campaigns. Moreover, the recommendations for the development of holistic microplastic pollution remediation strategies presented here can help ERCs propose technologies considering the environmental, social, and practical dimensions of microplastic pollution while fulfilling the current government policies to manage this plastic waste.

Setting new standards: Multiphasic analysis of microplastic mineralization by fungi

Plastic materials provide numerous benefits. However, properties such as durability and resistance to degradation that make plastic attractive for variable applications likewise foster accumulation in the environment. Fragmentation of plastics leads to the formation of potentially hazardous microplastic, of which a considerable amount derives from polystyrene. Here, we investigated the biodegradation of polystyrene by the tropical sooty mold fungus Capnodium coffeae in different experimental setups. Growth of C. coffeae was stimulated significantly when cultured in presence of plastic polymers rather than in its absence. Stable isotope tracing using 13C-enriched polystyrene particles combined with cavity ring-down spectroscopy showed that the fungus mineralized polystyrene traces. However, phospholipid fatty acid stable isotope probing indicated only marginal assimilation of polystyrene-13C by C. coffeae in liquid cultures. NMR spectroscopic analysis of residual styrene contents prior to and after incubation revealed negligible changes in concentration. Thus, this study suggests a plastiphilic life style of C. coffeae despite minor usage of plastic as a carbon source and the general capability of sooty mold fungi to stimulate polystyrene mineralization, and proposes new standards to identify and unambiguously demonstrate plastic degrading capabilities of microbes.

Effective multi-stage biodegradation of commercial bulk polyurethane by Clonostachys and Purpureocillium spp

Dealing with plastic waste in an environmentally friendly and effective manner has been a conundrum that much research has attempted to address. An attractive approach is biodegradation by microorganisms; however microorganisms that have shown such potential are generally only able to degrade surface layers of polymer materials. Herein we describe the multi-stage degradation of commercial bulk polyurethane by two strains of fungi isolated from a landfill. Moreover, we demonstrate that the mechanisms of degradation are not hydrolysis alone as is usually reported, but decarboxylation as well. The data presented here suggest that chain scission at urethane groups involves hydrolysis and decarboxylation of the terminal functional groups and the release of CO2. Two strains, Clonostachys sp. PB54 and Purpureocillium sp. PB57 were both able to decrease the mass of commercial bulk polyurethane by 40 % after 90 days. Spectroscopic analysis revealed the breakage of urethane and ester linkages but also detected variations in hydrogen bonding over time, indicating initial degradation of amorphous surface regions followed by destabilization of more ordered, crystalline layers. Subsequent Liquid Chromatography Mass Spectrometry (LCMS) analysis demonstrated that the fungi were capable of liberating monomer-equivalent molecules (4,4'-methylenedianiline) from the bulk material. In this work, these fungi are shown to be capable of significantly degrading commercial bulk polyurethane in a short period of time, producing small organic molecules and CO2, and as such, are good prospects for the development of large-scale plastic biodegradation processing.

Recent developments in bio-based polyethylene: Degradation studies, waste management and recycling

Nowadays, the tendency to replace conventional fossil-based plastics is increasing considerably; there is a growing trend towards alternatives that involve the development of plastic materials derived from renewable sources, which are compostable and biodegradable. Indeed, only 1.5 % of whole plastic production is part of the small bioplastics market, even when these materials with a partial or full composition from biomass are rapidly expanding. A very interesting field of investigation is currently being developed in which the disposal and processing of the final products are evaluated in terms of reducing environmental harm. This review presents a compilation of polyethylene (PE) types, their uses, and current problems in the waste management of PE and recycling. Particularly, this review is based on the capabilities to synthesize bio-based PE from natural and renewable sources as a replacement for the raw material derived from petroleum. In addition to recent studies in degradation on different types of PE with weight loss ranges from 1 to 47 %, the techniques used and the main changes observed after degradation. Finally, perspectives are presented in the manuscript about renewable and non-renewable polymers, depending on the non-degradable, biodegradable, and compostable behavior, including composting recent studies in PE. In addition, it contributes to the 3R approaches to responsible waste management of PE and advancement towards an environmentally friendly PE.

Poly(butylene adipate-co-terephthalate) biodegradation by Purpureocillium lilacinum strain BA1S

Poly(butylene adipate-co-terephthalate) (PBAT), a promising biodegradable aliphatic-aromatic copolyester material, can be applied as an alternative material to reduce the adverse effects of conventional plastics. However, the degradation of PBAT plastics in soil is time-consuming, and effective PBAT-degrading microorganisms have rarely been reported. In this study, the biodegradation properties of PBAT by an elite fungal strain and related mechanisms were elucidated. Four PBAT-degrading fungal strains were isolated from farmland soils, and Purpureocillium lilacinum strain BA1S showed a prominent degradation rate. It decomposed approximately 15 wt.% of the PBAT films 30 days after inoculation. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Liquid chromatography mass spectrometry (LC‒MS) were conducted to analyze the physicochemical properties and composition of the byproducts after biodegradation. In the presence of PBAT, the lipolytic enzyme activities of BA1S were remarkably induced, and its cutinase gene was also significantly upregulated. Of note, the utilization of PBAT in BA1S cells was closely correlated with intracellular cytochrome P450 (CYP) monooxygenase. Furthermore, CreA-mediated carbon catabolite repression was confirmed to be involved in regulating PBAT-degrading hydrolases and affected the degradation efficiency. This study provides new insight into the degradation of PBAT by elite fungal strains and increases knowledge on the mechanism, which can be applied to control the biodegradability of PBAT films in the future. KEY POINTS: • Purpureocillium lilacinum strain BA1S was isolated from farmland soils and degraded PBAT plastic films at a prominent rate. • The lipolytic enzyme activities of strain BA1S were induced during coculture with PBAT, and the cutinase gene was significantly upregulated during PBAT degradation. • CreA-mediated carbon catabolite repression of BA1S plays an essential role in regulating the expression of PBAT-degrading hydrolases.

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

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

Wood decay fungi show enhanced biodeterioration of low-density polyethylene in the absence of wood in culture media

The involvement of microorganisms in low-density polyethylene (LDPE) degradation is widely studied across the globe. Even though soil, landfills, and garbage dumps are reported to be promising niches for such organisms, recently the involvement of wood decay fungi in polyethylene degradation is highlighted. In light of this, 50 fungal samples isolated from decaying hardwoods were assessed for their wood degradation ability and for their depolymerization enzymatic activities. For the LDPE deterioration assay, 22 fungal isolates having wood decay ability and de-polymerization enzymatic activities were selected. Fungal cultures with LDPE sheets (2 cm x 10 cm x 37.5 μm) were incubated in the presence and in the absence of wood as the carbon source (C) for 45 days. Degradation was measured by weight loss, changes in tensile properties, reduction in contact angle, changes of functional groups in Fourier-transform infrared spectroscopy, Scanning electron microscopic imaging, and CO2 evolution by strum test. Among the isolates incubated in the absence of wood, Phlebiopsis flavidoalba out-performed the other fungal species showing the highest percentage of weight reduction (23.68 ± 0.34%), and the lowest contact angle (64.28° ± 5.01). Biodegradation of LDPE by P. flavidoalba was further supported by 46.79 ± 0.67% of the mass loss, and 3.07 ± 0.13% of CO2 emission (mg/L) in the strum test. The most striking feature of the experiment was that all the isolates showed elevated degradation of LDPE in the absence of wood than that in the presence of wood. It is clear that in the absence of a preferred C source, wood decay fungi thrive to utilize any available C source (LDPE in this case) showing the metabolic adaptability of fungi to survive under stressful conditions. A potential mechanism for LDPE degradation is also proposed.

Insights into the mechanisms involved in the fungal degradation of plastics

Fungi are considered among the most efficient microbial degraders of plastics, as they produce salient enzymes and can survive on recalcitrant compounds with limited nutrients. In recent years, studies have reported numerous species of fungi that can degrade different types of plastics, yet there remain many gaps in our understanding of the processes involved in biodegradation. In addition, many unknowns need to be resolved regarding the fungal enzymes responsible for plastic fragmentation and the regulatory mechanisms which fungi use to hydrolyse, assimilate and mineralize synthetic plastics. This review aims to detail the main methods used in plastic hydrolysis by fungi, key enzymatic and molecular mechanisms, chemical agents that enhance the enzymatic breakdown of plastics, and viable industrial applications. Considering that polymers such as lignin, bioplastics, phenolics, and other petroleum-based compounds exhibit closely related characteristics in terms of hydrophobicity and structure, and are degraded by similar fungal enzymes as plastics, we have reasoned that genes that have been reported to regulate the biodegradation of these compounds or their homologs could equally be involved in the regulation of plastic degrading enzymes in fungi. Thus, this review highlights and provides insight into some of the most likely regulatory mechanisms by which fungi degrade plastics, target enzymes, genes, and transcription factors involved in the process, as well as key limitations to industrial upscaling of plastic biodegradation and biological approaches that can be employed to overcome these challenges.

Biological Degradation of Plastics and Microplastics: A Recent Perspective on Associated Mechanisms and Influencing Factors

Plastic and microplastic pollution has caused a great deal of ecological problems because of its persistence and potential adverse effects on human health. The degradation of plastics through biological processes is of great significance for ecological health, therefore, the feasibility of plastic degradation by microorganisms has attracted a lot of attention. This study comprises a preliminary discussion on the biodegradation mechanism and the advantages and roles of different bacterial enzymes, such as PET hydrolase and PCL-cutinase, in the degradation of different polymers, such as PET and PCL, respectively. With a particular focus on their modes of action and potential enzymatic mechanisms, this review sums up studies on the biological degradation of plastics and microplastics related to mechanisms and influencing factors, along with their enzymes in enhancing the degradation of synthetic plastics in the process. In addition, biodegradation of plastic is also affected by plastic additives and plasticizers. Plasticizers and additives in the composition of plastics can cause harmful impacts. To further improve the degradation efficiency of polymers, various pretreatments to improve the efficiency of biodegradation, which can cause a significant reduction in toxic plastic pollution, were also preliminarily discussed here. The existing research and data show a large number of microorganisms involved in plastic biodegradation, though their specific mechanisms have not been thoroughly explored yet. Therefore, there is a significant potential for employing various bacterial strains for efficient degradation of plastics to improve human health and safety.

Biodegradation of different types of microplastics: Molecular mechanism and degradation efficiency

Microplastics are widely distributed and a major pollutant in our ecosystem. Microplastics (MPs) are very small size plastic (<5 mm) present in environment, which comes from industrial, agricultural and household wastes. Plastic particles are more durable due to the presence of plasticizers and chemicals or additives. These plastics pollutants are more resistant to degradation. Inadequate recycling and excessive use of plastics lead to a large amount of waste accumulating in the terrestrial ecosystem, causing a risk to humans and animals. Thus, there is an urgent need to control microplastic pollution by employing different microorganisms to overcome this hazardous issue for the environment. Biological degradation depends upon different aspects, including chemical structure, functional group, molecular weight, crystallinity and additives. Molecular mechanisms for degradation of MPs through various enzymes have not extremely studied. It is necessary to degrade the MPs and overcome this problem. This review approaches different molecular mechanisms to degrade different types of microplastics and summarize the degradation efficiency of different types of bacteria, algae and fungal strains. The present study also summarizes the potential of microorganisms to degrade different polymers and the role of different enzymes in degradation of microplastics. To the outstanding of our awareness, this is the first article devoted to the role of microorganisms with their degradation efficiency. Furthermore, it also summarizes the role of intracellular and extracellular enzymes in biological degradation mechanism of microplastics.

Biodegradation efficacy of selected marine microalgae against Low-Density Polyethylene (LDPE): An environment friendly green approach

The present study dealt with the five marine microalgae strains viz., Chloroidium saccharophilum, Picochlorum maculatum, Amphora sp., Hymenomonas globosa and Limnospira indica and their effective degradation ability of Low-Density Polyethylene for the period of 45 days. The incubation of LDPE in microalgae culture has resulted in the maximum weight loss (20.16 ± 0.14 %), higher reduction rate (0.005/day) and lower half-life (138.4 days) in the LDPE treated with P. maculatum. The SEM images of all treated LDPE revealed surface erosion and the ATR-FTIR spectra showed functional group peaks along with new peaks at 1369.35 cm^-1, 2332.96 cm^-1 and 500-726 cm^-1. Carbonyl (Keto, Ester), Vinyl and Internal double bond indices increased significantly in all the treated groups. The crystallinity was decreased (64.13 %) in P. maculatum treated LDPE than the control (71.37 %). Thermogravimetric analysis showed the reduction in thermal stability after biodegradation. This efficient microalgal degradation as a bioremediation technique will reduce the plastic pollution.

Recent advances and challenges in sustainable management of plastic waste using biodegradation approach

Versatility and desirable attributes of synthetic plastics have greatly contributed towards their wide applications. However, vast accumulation of plastic wastes in environment as a result of their highly recalcitrant nature has given rise to plastic pollution. Existing strategies in alleviating plastic wastes accumulation are inadequate, and there is a pressing need for alternative sustainable approaches in tackling plastic pollution. In this context, plastic biodegradation has emerged as a sustainable and environmental-friendly approach in handling plastic wastes accumulation, due to its milder and less energy-intensive conditions. In recent years, extensive research effort has focused on the identification of microorganisms and enzymes with plastic-degrading abilities. This review aims to provide a timely and holistic view on the current status of plastic biodegradation, focusing on recent breakthroughs and discoveries in this field. Furthermore, current challenges associated to plastic biodegradation are discussed, and the future perspectives for continuous advancement of plastic biodegradation are highlighted.

Global Situation of Bioremediation of Leachate-Contaminated Soils by Treatment with Microorganisms: A Systematic Review

This systematic review presents the current state of research in the last five years on contaminants in soils, especially in leachates from solid waste landfills, with emphasis on biological remediation. In this work, the pollutants that can be treated by microorganisms and the results obtained worldwide were studied. All the data obtained were compiled, integrated, and analyzed by soil type, pollutant type, bacterial type, and the countries where these studies were carried out. This review provides reliable data on the contamination of soils worldwide, especially soils contaminated by leachate from municipal landfills. The extent of contamination, treatment objectives, site characteristics, cost, type of microorganisms to be used, and time must be considered when selecting a viable remediation strategy. The results of this study can help develop innovative and applicable methods for evaluating the overall contamination of soil with different contaminants and soil types. These findings can help develop innovative, applicable, and economically feasible methods for the sustainable management of contaminated soils, whether from landfill leachate or other soil types, to reduce or eliminate risk to the environment and human health, and to achieve greater greenery and functionality on the planet.

Biological effects on the migration and transformation of microplastics in the marine environment

Microplastics(MPs) are ubiquitous, difficult to degrade, and potentially threatening to organisms in marine environment, so it is important to clarify the factors that affect their biogeochemical processes. The impact of biological activities on the MPs in marine environment is ubiquitous and complex, and there is currently a lack of systematic summaries. This paper reviews the effects of biological actions on the migration, distribution and degradation of MPs in marine environment from four aspects: biological ingestion and digestion, biological movement, biological colonization and biological adhesion. MPs in seawater and sediments can be closely combined with organisms through three pathways: biological ingestion, biofilm formation or adhesion to organisms, and are passed between species at different trophic levels through the food chain. The generation and degradation of faecal pellets and biofilms can alter the density of "environmental MPs", thereby affecting their vertical migration and deposition in water bodies. The movement of swimming organisms and the disturbance by benthic organisms can promote the migration of MPs in water and vertical migration and resuspension in sediments, thereby changing the distribution of MPs in local sea areas. The grinding effect of the digestive tract and the secretion of chemicals from the biofilm (such as enzymes and acids) can reduce the particle size and increase surface roughness of MPs, or even degrade them completely. Besides, biological adhesion may be an important mechanism affecting the distribution, migration and preservation of MPs. There may be complex interactions and linkages among marine dynamical processes, photochemical degradation and biological processes that collectively affect the biogeochemical processes of MPs, but their relative contributions remain to be more studied.

Microplastics and their interactions with microbiota

As a new pollutant, Microplastics (MPs) are globally known for their negative impacts on different ecosystems and living organisms. MPs are easily taken up by the ecosystem in a variety of organisms due to their small size, and cause immunological, neurological, and respiratory diseases in the impacted organism. Moreover, in the impacted environments, MPs can release toxic additives and act as a vector and scaffold for colonization and transportation of specific microbes and lead to imbalances in microbiota and the biogeochemical and nutrients dynamic. To address the concerns on controlling the MPs pollution on the microbiota and ecosystem, the microbial biodegradation of MPs can be potentially considered as an effective environment friendly approach. The objectives of the presented paper are to provide information on the toxicological effects of MPs on microbiota, to discuss the negative impacts of microbial colonization of MPs, and to introduce the microbes with biodegradation ability of MPs.

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.

Biodegradability of polyethylene mulch film by Bacillus paramycoides

Discarded polyethylene (PE) mulch film has led to persistent agricultural pollution. Biodegradation of plastic waste is considered as a promising solution that can potentially overcome environmental and economic problems. In this study, a novel bacterium (Bacillus paramycoides) was isolated from a waste mulch recycling plant and showed an extraordinary ability to customize polyethylene film. It was observed by scanning electron microscopy that a large number of pits and wrinkle cracks existed on the polyethylene, indicating that the strain used PE film as the sole carbon source. Meanwhile, the loss of weight of the film was tested continuously, and approximately 12% of the initial weight of the film was found to be lost within 45 days after coincubation with TW-2. The surface hydrophobicity of the polyethylene film decreased while the surface tension increased from 9.755 to 31.013. Fourier transform infrared (FTIR) analysis indicated that absorption peaks near 1740 cm-1 and 2760 cm-1 were attributed to the stretching vibrations of aldehyde and carboxyl groups, respectively, suggesting that hydrophilic groups were produced. This was also confirmed by XPS spectroscopy analysis. X-ray diffraction (XRD) analysis also showed that the relative crystallinity decreased from 33% to 11.51%. In addition, GPC analysis showed that the molecular weight decreased, while the proportion of low molecular weight fragments increased. These results strongly indicated that the PE film was able to be degraded to some extent by the strain. Finally, a new biodegradable mechanism for polyethylene was proposed.

Direct Polyethylene Photoreforming into Exclusive Liquid Fuel over Charge-Asymmetrical Dual Sites under Mild Conditions

Direct polyethylene photoreforming to high-energy-density C₂ fuels under mild conditions is of great significance and still faces a huge challenge, which is partly attributed to the extreme instability of *CH₂CH₂ adsorbed on the traditional catalysts with single catalytic sites. Herein, charge-asymmetrical dual sites are designed to boost the adsorption of *CH₂CH₂ for direct polyethylene photoreforming into C₂ fuels under normal temperature and pressure. As a prototype, the synthetic Zr-doped CoFe₂O₄ quantum dots with charge-asymmetrical dual metal sites realize direct polyethylene photoreforming into acetic acid, with 100% selectivity of liquid fuel and the evolution rate of 1.10 mmol g^-1 h^-1, outperforming those of most previously reported photocatalysts under similar conditions. In situ X-ray photoelectron spectra, density-functional-theory calculations, and control experiments reveal the charge-asymmetrical Zr-Fe dual sites may act as the predominate catalytic sites, which can simultaneously bond with the *CH₂CH₂ intermediates for the following stepwise oxidation to form C₂ products.

Environmental toxicity and decomposition of polyethylene

In the more than 100 years since the invention of plastics, various plastic polymers have been developed that exhibit different characteristics and have been widely used in production and life. In 2020 alone, nearly 400 million tons of plastics were produced globally. However, while plastic such as polyethylene brings us convenience, it also threatens environmental sustainability and human health. Due to insufficient recycling efficiency, millions of tons of polyethylene pollutants accumulate in terrestrial or marine environments each year. Polyethylene is elastic, chemically stable, and non-biodegradable, and the traditional disposal methods include landfilling and incineration. These methods are costly, unsustainable, and further increase the burden on the environment. Therefore, recent research has increasingly focused on the biodegradation of polyethylene. In this work, we briefly summarized polyethylene's properties and environmental toxicity. We also reviewed the recent advances in the biodegradation of polyethylene with a summary of traditional abiotic methods. Finally, we proposed a brief research direction in polyethylene study with the aspect of environmental toxicology and industrial applications of decomposition technology.

Biodeterioration of low density polyethylene by mangrove associated endolichenic fungi and their enzymatic regimes

Fungal involvement in biodeterioration of Low Density Polyethylene (LDPE) has received a great attention in recent years. Among diverse groups of fungi, Endolichenic Fungi (ELF) are adapted to thrive in resource limited conditions. Present study was designed to investigate the potential of mangrove associated ELF, in biodeterioration of LDPE and to quantify key-depolymerizing enzymes. A total of 31 ELF species, isolated from 22 lichens of mangrove ecosystems in Negombo lagoon, Sri Lanka were identified using DNA barcoding techniques. ELF were inoculated into mineral salt medium, containing LDPE strips and incubated at 28±2°C, for 21 days, under laboratory conditions. After incubation, biodeterioration was monitored based on percent reductions in weights and tensile properties, increments in degree of water absorption, changes in peaks of Infrared spectra and surface erosions using Scanning Electron Microscopy. Out of 31 species, Chaetomium globosum, Daldinia eschscholtzii, Neofusicoccum occulatum, Phanerochaete chrysosporium, Schizophyllum commune and Xylaria feejeensis showed significant changes. Production of depolymerizing enzymes by these species, were assayed qualitatively using plate-based methods and quantitatively by mass level enzyme production. Among them Phanerochaete chrysosporium showed the highest enzyme activities as (9.69±0.04)x10^-3 , (1.96±0.01)x10^-3 , (5.73±0.03)x10^-3 , (0.88±0.01), (0.64±0.06), (1.43±0.01) U ml^-1 for laccase, lignin peroxidase, manganese peroxidase, amylase, lipase and esterase, respectively.

Aspergilli series Versicolores: importance of species identification in the clinical setting

The moulds of the genus Aspergillus section Nidulantes series Versicolores are ubiquitous and particularly recurrent in indoor air. They are considered present in 70% of the bioaerosols to which we are exposed most of our time spent indoors. With the taxonomic revision proposed in 2012 and the discovery of four new species, the series Versicolores currently includes 18 species. These moulds, although considered as cryptic (except Aspergillus sydowii), are opportunistic pathogens that can exhibit increased minimal inhibitory concentrations to conventional antifungal agents. In this review, we discuss the ecology and clinical implications of each species belonging to the series Versicolores. This survey also highlights the lack of consideration for taxonomic revisions in clinical practice and in scientific studies which greatly limits the acquisition of specific knowledge on species belonging to the series Versicolores.

Fungal Enzymes Involved in Plastics Biodegradation

Plastic pollution is a growing environmental problem, in part due to the extremely stable and durable nature of this polymer. As recycling does not provide a complete solution, research has been focusing on alternative ways of degrading plastic. Fungi provide a wide array of enzymes specialized in the degradation of recalcitrant substances and are very promising candidates in the field of plastic degradation. This review examines the present literature for different fungal enzymes involved in plastic degradation, describing their characteristics, efficacy and biotechnological applications. Fungal laccases and peroxidases, generally used by fungi to degrade lignin, show good results in degrading polyethylene (PE) and polyvinyl chloride (PVC), while esterases such as cutinases and lipases were successfully used to degrade polyethylene terephthalate (PET) and polyurethane (PUR). Good results were also obtained on PUR by fungal proteases and ureases. All these enzymes were isolated from many different fungi, from both Basidiomycetes and Ascomycetes, and have shown remarkable efficiency in plastic biodegradation under laboratory conditions. Therefore, future research should focus on the interactions between the genes, proteins, metabolites and environmental conditions involved in the processes. Further steps such as the improvement in catalytic efficiency and genetic engineering could lead these enzymes to become biotechnological applications in the field of plastic degradation.

A marine fungus Alternaria alternata FB1 efficiently degrades polyethylene

Huge quantities of plastic wastes have been accumulating in the environment causing serious ecological problems and significantly impacting the global carbon cycling. Plastic pollutions have been recognized as the most common and durable marine contaminants. Consequently, the marine environment is becoming a hot spot to screen microorganisms possessing potential plastic degradation capabilities. Here, by screening hundreds of plastic waste-associated samples, we isolated a fungus (named Alternaria alternata FB1) that possessing a prominent capability of colonizing on the polyethylene (PE) film. Through Scanning Electron Microscope (SEM) observation, we found this fungus could efficiently degrade the PE film and formed numerous obvious holes in the plastic surface. Moreover, the Fourier Transform Infrared (FTIR) imaging detected absorption peak in the vicinity of 1715 cm^-1, indicating the formation of carbonyl bonds (-CO-). Through X-Ray Diffraction (XRD) analysis, we found that the PE film treated by strain FB1 for 28 days showed an evident reduced relative crystallinity degree, resulting in a decrease from 62.79% to 52.02%. Strikingly, the molecular weight of PE film decreased 95% after 120 days treatment by strain FB1. Using GC-MS, we further clarified that a four-carbon product (named Diglycolamine) accounted for 93.28% of all degradation products. We defined 153 enzymes that potentially involved in the degradation of PE through a transcriptomic method. The degradation capabilities of two representative enzymes including a laccase (with a molecular weight about 59.49 kDa) and a peroxidase (with a molecular weight about 36.7 kDa) were verified. Lastly, a complete biodegradation process of PE was proposed. Given the extreme paucity of microorganisms and enzymes for effective degradation of PE in the present time, our study provides a compelling candidate for further investigation of degradation mechanisms and development of biodegradation products of PE.

Toward Microbial Recycling and Upcycling of Plastics: Prospects and Challenges

Annually, 400 Mt of plastics are produced of which roughly 40% is discarded within a year. Current plastic waste management approaches focus on applying physical, thermal, and chemical treatments of plastic polymers. However, these methods have severe limitations leading to the loss of valuable materials and resources. Another major drawback is the rapid accumulation of plastics into the environment causing one of the biggest environmental threats of the twenty-first century. Therefore, to complement current plastic management approaches novel routes toward plastic degradation and upcycling need to be developed. Enzymatic degradation and conversion of plastics present a promising approach toward sustainable recycling of plastics and plastics building blocks. However, the quest for novel enzymes that efficiently operate in cost-effective, large-scale plastics degradation poses many challenges. To date, a wide range of experimental set-ups has been reported, in many cases lacking a detailed investigation of microbial species exhibiting plastics degrading properties as well as of their corresponding plastics degrading enzymes. The apparent lack of consistent approaches compromises the necessary discovery of a wide range of novel enzymes. In this review, we discuss prospects and possibilities for efficient enzymatic degradation, recycling, and upcycling of plastics, in correlation with their wide diversity and broad utilization. Current methods for the identification and optimization of plastics degrading enzymes are compared and discussed. We present a framework for a standardized workflow, allowing transparent discovery and optimization of novel enzymes for efficient and sustainable plastics degradation in the future.

Informal landfill contributes to the pollution of microplastics in the surrounding environment

A large amount of plastic waste is generated yearly worldwide, and landfills are commonly used for the disposal of plastic waste. However, burying in landfill does not get rid of the plastic waste but leave the problem to the future. Previous works have showed that microplastics are presented in the landfill refuse and leachate, which might be potential sources of microplastics. In this work, characteristics of microplastic pollution in an informal landfill in South China were studied. Landfill refuse, underlying soil, leachate, and groundwater samples were collected from different sites within and around the landfill. Results show that microplastics in the landfill refuse and underlying soil varied from 590 to 103,080 items/kg and from 570 to 14,200 items/kg, respectively. Most of the microplastics are fibrous, small sized, and transparent. Polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) are major polymer types. Scanning electron microscope (SEM) images and Fourier Transform Infrared (FTIR) spectra of the microplastic samples indicate varying degree of weathering. Microplastic abundances in the landfill leachate and groundwater ranged from 3 to 25 items/L and from 11 to 17 items/L, respectively. Microplastics detected in the landfill leachate and groundwater are even smaller compared with those in the refuse and underlying soil and their polymer types are more diverse. This work demonstrated that microplastics presented in an informal landfill without sufficient protection can leak out to the surrounding environment. The microplastic pollution originated from informal landfills should receive more attentions.

Recent advances on ecological effects of microplastics on soil environment

The mass production and wide application of plastics and their derivatives have led to the release of a large number of discarded plastic products into the natural environment, where they continue to accumulate due to their low recycling rate and long durability. These large pieces of plastic will gradually break into microplastics (<5 mm), which are highly persistent organic pollutants and attract worldwide attention due to their small particle size and potential threats to the ecosystem. Compared with the aquatic system, terrestrial systems such as soils, as sinks for microplastics, are more susceptible to plastic pollution. In this article, we comprehensively summarized the occurrence and sources of microplastics in terrestrial soil, and reviewed the eco-toxicological effects of microplastics in soil ecosystems, in terms of physical and chemical properties of soil, soil nutrient cycling, soil flora and fauna. The influence of microplastics on soil microbial community, and particularly the microbial community on the surface of microplastics, were examined in detail. The compound effects of microplastics and other pollutants, e.g., heavy metals and antibiotics, were addressed. Future challenges of research on microplastics include development of new techniques and standardization for the extraction and qualitative and quantitative analysis of microplastics in soils, toxic effects of microplastics at microbial or even molecular levels, the contribution of microplastics to antibiotic resistance genes migration, and unraveling microorganisms for the degradation of microplastics. This work provides as a better understanding of the occurrence, distribution and potential ecological risks of microplastics in terrestrial soil ecosystems.