Microbial and Enzymatic Degradation of Synthetic Plastics

The comparative plastisphere microbial community profile at Kung Wiman beach unveils potential plastic-specific degrading microorganisms

Background

Plastic waste is a global environmental issue that impacts the well-being of humans, animals, plants, and microorganisms. Microplastic contamination has been previously reported at Kung Wiman Beach, located in Chanthaburi province along with the Eastern Gulf of Thailand. Our research aimed to study the microbial population of the sand and plastisphere and isolate microorganisms with potential plastic degradation activity.

Methods

Plastic and sand samples were collected from Kung Wiman Beach for microbial isolation on agar plates. The plastic samples were identified by Fourier-transform infrared spectroscopy. Plastic degradation properties were evaluated by observing the halo zone on mineral salts medium (MSM) supplemented with emulsified plastics, including polystyrene (PS), polylactic acid (PLA), polyvinyl chloride (PVC), and bis (2-hydroxyethyl) terephthalate (BHET). Bacteria and fungi were identified by analyzing nucleotide sequence analysis of the 16S rRNA and internal transcribed spacer (ITS) regions, respectively. 16S and ITS microbiomes analysis was conducted on the total DNA extracted from each sample to assess the microbial communities.

Results

Of 16 plastic samples, five were identified as polypropylene (PP), four as polystyrene (PS), four as polyethylene terephthalate (PET), two as high-density polyethylene (HDPE), and one sample remained unidentified. Only 27 bacterial and 38 fungal isolates were found to have the ability to degrade PLA or BHET on MSM agar. However, none showed degradation capabilities for PS or PVC on MSM agar. Notably, Planococcus sp. PP5 showed the highest hydrolysis capacity of 1.64 ± 0.12. The 16S rRNA analysis revealed 13 bacterial genera, with seven showing plastic degradation abilities: Salipiger, Planococcus, Psychrobacter, Shewanella, Jonesia, Bacillus, and Kocuria. This study reports, for the first time of the BHET-degrading properties of the genera Planococcus and Jonesia. Additionally, The ITS analysis identified nine fungal genera, five of which demonstrated plastic degradation abilities: Aspergillus, Penicillium, Peacilomyces, Absidia, and Cochliobolus. Microbial community composition analysis and linear discriminant analysis effect size revealed certain dominant microbial groups in the plastic and sand samples that were absent under culture-dependent conditions. Furthermore, 16S and ITS amplicon microbiome analysis revealed microbial groups were significantly different in the plastic and sand samples collected.

Conclusions

We reported on the microbial communities found on the plastisphere at Kung Wiman Beach and isolated and identified microbes with the capacity to degrade PLA and BHET.

Exploring untapped bacterial communities and potential polypropylene-degrading enzymes from mangrove sediment through metagenomics analysis

The versatility of plastic has resulted in huge amounts being consumed annually. Mismanagement of post-consumption plastic material has led to plastic waste pollution. Biodegradation of plastic by microorganisms has emerged as a potential solution to this problem. Therefore, this study aimed to investigate the microbial communities involved in the biodegradation of polypropylene (PP). Mangrove soil was enriched with virgin PP sheets or chemically pretreated PP comparing between 2 and 4 months enrichment to promote the growth of bacteria involved in PP biodegradation. The diversity of the resulting microbial communities was accessed through 16S metagenomic sequencing. The results indicated that Xanthomonadaceae, unclassified Gaiellales, and Nocardioidaceae were promoted during the enrichment. Additionally, shotgun metagenomics was used to investigate enzymes involved in plastic biodegradation. The results revealed the presence of various putative plastic-degrading enzymes in the mangrove soil, including alcohol dehydrogenase, aldehyde dehydrogenase, and alkane hydroxylase. The degradation of PP plastic was determined using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), and Water Contact Angle measurements. The FTIR spectra showed a reduced peak intensity of enriched and pretreated PP compared to the control. SEM images revealed the presence of bacterial biofilms as well as cracks on the PP surface. Corresponding to the FTIR and SEM analysis, the water contact angle measurement indicated a decrease in the hydrophobicity of PP and pretreated PP surface during the enrichment.

Microplastics role in cell migration and distribution during cancer cell division

Amidst the global plastic pollution crisis, the gastrointestinal tract serves as the primary entry point for daily exposure to micro- and nanoplastics. We investigated the complex dynamics between polystyrene micro- and nanoplastics (PS-MNPs) and four distinct human colorectal cancer cell lines (HT29, HCT116, SW480, and SW620). Our findings revealed a significant size- and concentration dependent uptake of 0.25, 1, and 10 μm PS-MNPs across all cell lines, with HCT116 cells exhibiting the highest uptake rates. During cell division, particles were distributed between mother and daughter cells. Interestingly, we observed no signs of elimination from the cells. Short-term exposure to 0.25 μm particles significantly amplified cell migration, potentially leading to pro-metastatic effects. Particles demonstrated high persistence in 2D and 3D cultures, and accumulation in non-proliferating parts of spheroids, without interfering with cell proliferation or division. Our study unveils the disturbing fact of the persistence and bioaccumulation of MNPs in colorectal cancer cell lines, key toxicological traits under REACH (Regulation concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals). Our observations underscore the potential of MNPs as hidden catalysts for tumor progression, particularly through enhancing cell migration and possibly fueling metastasis - a finding that sheds light on a significant and previously underexplored area of concern.

Effects of polypropylene microplastics on carbon dioxide dynamics in intertidal mangrove sediments

Microplastics (MPs) in soil can influence CO2 dynamics by altering organic carbon (OC) and microbial composition. Nevertheless, the fluctuation of CO2 response attributed to MPs in mangrove sediments is unclear. This study explores the impact of micro-sized polypropylene (mPP) particles on the carbon dynamics of intertidal mangrove sediments. In the high-tide level sediment, after 28 days, the cumulative CO2 levels for varying mPP dosages were as follows: 496.86 ± 2.07, 430.38 ± 3.84 and 447.09 ± 1.72 mg kg-1 for 0.1%, 1% and 10% (w/w) mPP, respectively. The CO2 emissions were found to be increased with a 0.1% (w/w) mPP level and decreased with 1% and 10% (w/w) mPP at high-tide level sediment, suggesting a tide level-specific dose dependence of the CO2 emission pattern in mangrove sediments. Overall, results indicated that the presence of mPP in mangrove sediments would potentially affect intertidal total CO2 storage under given experimental conditions.

Exploring the substrate spectrum of phylogenetically distinct bacterial polyesterases

The rapid escalation of plastic waste accumulation presents a significant threat of the modern world, demanding an immediate solution. Over the last years, utilization of the enzymatic machinery of various microorganisms has emerged as an environmentally friendly asset in tackling this pressing global challenge. Thus, various hydrolases have been demonstrated to effectively degrade polyesters. Plastic waste streams often consist of a variety of different polyesters, as impurities, mainly due to wrong disposal practices, rendering recycling process challenging. The elucidation of the selective degradation of polyesters by hydrolases could offer a proper solution to this problem, enhancing the recyclability performance. Towards this, our study focused on the investigation of four bacterial polyesterases, including DaPUase, IsPETase, PfPHOase, and Se1JFR, a novel PETase-like lipase. The enzymes, which were biochemically characterized and structurally analyzed, demonstrated degradation ability of synthetic plastics. While a consistent pattern of polyesters' degradation was observed across all enzymes, Se1JFR stood out in the degradation of PBS, PLA, and polyether PU. Additionally, it exhibited comparable results to IsPETase, a benchmark mesophilic PETase, in the degradation of PCL and semi-crystalline PET. Our results point out the wide substrate spectrum of bacterial hydrolases and underscore the significant potential of PETase-like enzymes in polyesters degradation.

Assessing microbial plastic degradation requires robust methods

Plastics are versatile materials that have the potential to propel humanity towards circularity and ultimate societal sustainability. However, the escalating concern surrounding plastic pollution has garnered significant attention, leading to widespread negative perceptions of these materials. Here, we question the role microbes may play in plastic pollution bioremediation by (i) defining polymer biodegradability (i.e., recalcitrant, hydrolysable and biodegradable polymers) and (ii) reviewing best practices for evaluating microbial biodegradation of plastics. We establish recommendations to facilitate the implementation of rigorous methodologies in future studies on plastic biodegradation, aiming to push this field towards the use of isotopic labelling to confirm plastic biodegradation and further determine the molecular mechanisms involved.

Progress in polystyrene biodegradation by insect gut microbiota

Polystyrene (PS) is frequently used in the plastics industry. However, its structural stability and difficulty to break down lead to an abundance of plastic waste in the environment, resulting in micro-nano plastics (MNPs). As MNPs are severe hazards to both human and environmental health, it is crucial to develop innovative treatment technologies to degrade plastic waste. The biodegradation of plastics by insect gut microorganisms has gained attention as it is environmentally friendly, efficient, and safe. However, our knowledge of the biodegradation of PS is still limited. This review summarizes recent research advances on PS biodegradation by gut microorganisms/enzymes from insect larvae of different species, and schematic pathways of the degradation process are discussed in depth. Additionally, the prospect of using modern biotechnology, such as genetic engineering and systems biology, to identify novel PS-degrading microbes/functional genes/enzymes and to realize new strategies for PS biodegradation is highlighted. Challenges and limitations faced by the application of genetically engineered microorganisms (GEMs) and multiomics technologies in the field of plastic pollution bioremediation are also discussed. This review encourages the further exploration of the biodegradation of PS by insect gut microbes/enzymes, offering a cutting-edge perspective to identify PS biodegradation pathways and create effective biodegradation strategies.

Microbial degradation of low-density polyethylene, polyethylene terephthalate, and polystyrene by novel isolates from plastic-polluted environment

Biodegradation is an eco-friendly measure to address plastic pollution. This study screened four bacterial isolates that were capable of degrading recalcitrant polymers, i.e., low-density polyethylene, polyethylene terephthalate, and polystyrene. The unique bacterial isolates were obtained from plastic polluted environment. Dermacoccus sp. MR5 (accession no. OP592184) and Corynebacterium sp. MR10 (accession no. OP536169) from Malaysian mangroves and Bacillus sp. BS5 (accession no. OP536168) and Priestia sp. TL1 (accession no. OP536170) from a sanitary landfill. The four isolates showed a gradual increase in the microbial count and the production of laccase and esterase enzymes after 4 weeks of incubation with the polymers (independent experiment set). Bacillus sp. BS5 produced the highest laccase 15.35 ± 0.19 U/mL and showed the highest weight loss i.e., 4.84 ± 0.6% for PS. Fourier transform infrared spectroscopy analysis confirmed the formation of carbonyl and hydroxyl groups as a result of oxidation reactions by enzymes. Liquid chromatography-mass spectrometry analysis showed the oxidation of the polymers to small molecules (alcohol, ethers, and acids) assimilated by the microbes during the degradation. Field emission scanning electron microscopy showed bacterial colonization, biofilm formation, and surface erosion on the polymer surface. The result provided significant insight into enzyme activities and the potential of isolates to target more than one type of polymer for degradation.

Light-driven polymer recycling to monomers and small molecules

Only a small proportion of global plastic waste is recycled, of which most is mechanically recycled into lower quality materials. The alternative, chemical recycling, enables renewed production of pristine materials, but generally comes at a high energy cost, particularly for processes like pyrolysis. This review focuses on light-driven approaches for chemically recycling and upcycling plastic waste, with emphasis on reduced energy consumption and selective transformations not achievable with heat-driven methods. We focus on challenging to recycle backbone structures composed of mainly C‒C bonds, which lack functional groups i.e., esters or amides, that facilitate chemical recycling e.g., by solvolysis. We discuss the use of light, either in conjunction with heat to drive depolymerization to monomers or via photocatalysis to transform polymers into valuable small molecules. The structural prerequisites for these approaches are outlined, highlighting their advantages as well as limitations. We conclude with an outlook, addressing key challenges, opportunities, and provide guidelines for future photocatalyst (PC) development.

Recent advances in microbial and enzymatic engineering for the biodegradation of micro- and nanoplastics

This review examines the escalating issue of plastic pollution, specifically highlighting the detrimental effects on the environment and human health caused by microplastics and nanoplastics. The extensive use of synthetic polymers such as polyethylene (PE), polyethylene terephthalate (PET), and polystyrene (PS) has raised significant environmental concerns because of their long-lasting and non-degradable characteristics. This review delves into the role of enzymatic and microbial strategies in breaking down these polymers, showcasing recent advancements in the field. The intricacies of enzymatic degradation are thoroughly examined, including the effectiveness of enzymes such as PETase and MHETase, as well as the contribution of microbial pathways in breaking down resilient polymers into more benign substances. The paper also discusses the impact of chemical composition on plastic degradation kinetics and emphasizes the need for an approach to managing the environmental impact of synthetic polymers. The review highlights the significance of comprehending the physical characteristics and long-term impacts of micro- and nanoplastics in different ecosystems. Furthermore, it points out the environmental and health consequences of these contaminants, such as their ability to cause cancer and interfere with the endocrine system. The paper emphasizes the need for advanced analytical methods and effective strategies for enzymatic degradation, as well as continued research and development in this area. This review highlights the crucial role of enzymatic and microbial strategies in addressing plastic pollution and proposes methods to create effective and environmentally friendly solutions.

Biocatalysis: landmark discoveries and applications in chemical synthesis

Biocatalysis has become an important tool in chemical synthesis, allowing access to complex molecules with high levels of activity and selectivity and with low environmental impact. Key discoveries in protein engineering, bioinformatics, recombinant technology and DNA sequencing have contributed towards the rapid acceleration of the field. This tutorial review explores enzyme engineering strategies and high-throughput screening approaches that have been applied for the discovery and development of enzymes for synthetic application. Landmark developments in the field are discussed and have been carefully selected to highlight the diverse synthetic applications of enzymes within the pharmaceutical, agricultural, food and chemical industries. The design and development of artificial biocatalytic cascades is also examined. This tutorial review will give readers an insight into the landmark discoveries and milestones that have helped shape and grow this branch of catalysis since the discovery of the first enzyme.

Biodegradation of polystyrene and polyethylene by Microbacterium esteraromaticum SW3 isolated from soil

Plastic pollution is a common concern of global environmental pollution. Polystyrene (PS) and polyethylene (PE) account for almost one-third of global plastic production. However, so far, there have been few reports on microbial strains capable of simultaneously degrading PS and PE. In this study, Microbacterium esteraromaticum SW3, a non-pathogenic microorganism that can use PS or PE as the only carbon source in the mineral salt medium (MM), was isolated from plastics-contaminated soil and identified. The optimal growth conditions for SW3 in MM were 2% (w/v) PS or 2% (w/v) PE, 35°C and pH 6.3. A large number of bacteria and obvious damaged areas were observed on the surface of PS and PE products after inoculated with SW3 for 21 d. The degradation rates of PS and PE by SW3 (21d) were 13.17% and 5.39%, respectively. Manganese peroxidase and lipase were involved in PS and PE degradation by SW3. Through Fourier infrared spectroscopy detection, different functional groups such as carbonyl, hydroxyl and amidogen groups were produced during the degradation of PS and PE by SW3. Moreover, PS and PE were degraded into alkanes, ketones, carboxylic acids, esters and so on detected by GC-MS. Collectively, we have isolated and identified SW3, which can use PS or PE as the only carbon source in MM as well as degrade PS and PE products. This study not only provides a competitive candidate strain with broad biodegradability for the biodegradation of PS and/or PE pollution, but also provides new insights for the study of plastic biodegradation pathways.

Depolymerization within a Circular Plastics System

The societal importance of plastics contrasts with the carelessness with which they are disposed. Their superlative properties lead to economic and environmental efficiency, but the linearity of plastics puts the climate, human health, and global ecosystems at risk. Recycling is fundamental to transitioning this linear model into a more sustainable, circular economy. Among recycling technologies, chemical depolymerization offers a route to virgin quality recycled plastics, especially when valorizing complex waste streams poorly served by mechanical methods. However, chemical depolymerization exists in a complex and interlinked system of end-of-life fates, with the complementarity of each approach key to environmental, economic, and societal sustainability. This review explores the recent progress made into the depolymerization of five commercial polymers: poly(ethylene terephthalate), polycarbonates, polyamides, aliphatic polyesters, and polyurethanes. Attention is paid not only to the catalytic technologies used to enhance depolymerization efficiencies but also to the interrelationship with other recycling technologies and to the systemic constraints imposed by a global economy. Novel polymers, designed for chemical depolymerization, are also concisely reviewed in terms of their underlying chemistry and potential for integration with current plastic systems.

Potential synergy of microplastics and nitrogen enrichment on plant holobionts in wetland ecosystems

Wetland ecosystems are global hotspots for environmental contaminants, including microplastics (MPs) and nutrients such as nitrogen (N) and phosphorus (P). While MP and nutrient effects on host plants and their associated microbial communities at the individual level have been studied, their synergistic effects on a plant holobiont (i.e., a plant host plus its microbiota, such as bacteria and fungi) in wetland ecosystems are nearly unknown. As an ecological entity, plant holobionts play pivotal roles in biological nitrogen fixation, promote plant resilience and defense chemistry against pathogens, and enhance biogeochemical processes. We summarize evidence based on recent literature to elaborate on the potential synergy of MPs and nutrient enrichment on plant holobionts in wetland ecosystems. We provide a conceptual framework to explain the interplay of MPs, nutrients, and plant holobionts and discuss major pathways of MPs and nutrients into the wetland milieu. Moreover, we highlight the ecological consequences of loss of plant holobionts in wetland ecosystems and conclude with recommendations for pending questions that warrant urgent research. We found that nutrient enrichment promotes the recruitment of MPs-degraded microorganisms and accelerates microbially mediated degradation of MPs, modifying their distribution and toxicity impacts on plant holobionts in wetland ecosystems. Moreover, a loss of wetland plant holobionts via long-term MP-nutrient interactions may likely exacerbate the disruption of wetland ecosystems' capacity to offer nature-based solutions for climate change mitigation through soil organic C sequestration. In conclusion, MP and nutrient enrichment interactions represent a severe ecological risk that can disorganize plant holobionts and their taxonomic roles, leading to dysbiosis (i.e., the disintegration of a stable plant microbiome) and diminishing wetland ecosystems' integrity and multifunctionality.

Biodegradation of polyethylene terephthalate by Tenebrio molitor: Insights for polymer chain size, gut metabolome and host genes

Polyethylene terephthalate (PET or polyester) is a commonly used plastic and also contributes to the majority of plastic wastes. Mealworms (Tenebrio molitor larvae) are capable of biodegrading major plastic polymers but their degrading ability for PET has not been characterized based on polymer chain size molecular size, gut microbiome, metabolome and transcriptome. We verified biodegradation of commercial PET by T. molitor larvae in a previous report. Here, we reported that biodegradation of commercial PET (Mw 29.43 kDa) was further confirmed by using the δ13C signature as an indication of bioreaction, which was increased from - 27.50‰ to - 26.05‰. Under antibiotic suppression of gut microbes, the PET was still depolymerized, indicating that the host digestive enzymes could degrade PET independently. Biodegradation of high purity PET with low, medium, and high molecular weights (MW), i.e., Mw values of 1.10, 27.10, and 63.50 kDa with crystallinity 53.66%, 33.43%, and 4.25%, respectively, showed a mass reduction of > 95%, 86%, and 74% via broad depolymerization. Microbiome analyses indicated that PET diets shifted gut microbiota to three distinct structures, depending on the low, medium, and high MW. Metagenome sequencing, transcriptomic, and metabolic analyses indicated symbiotic biodegradation of PET by the host and gut microbiota. After PET was fed, the host's genes encoding degradation enzymes were upregulated, including genes encoding oxidizing, hydrolyzing, and non-specific CYP450 enzymes. Gut bacterial genes for biodegrading intermediates and nitrogen fixation also upregulated. The multiple-functional metabolic pathways for PET biodegradation ensured rapid biodegradation resulting in a half-life of PET less than 4 h with less negative impact by PET MW and crystallinity.

Sustainable degradation of synthetic plastics: A solution to rising environmental concerns

Plastics have a significant role in various sectors of the global economy since they are widely utilized in agriculture, architecture, and construction, as well as health and consumer goods. They play a crucial role in several industries as they are utilized in the production of diverse things such as defense materials, sanitary wares, tiles, plastic bottles, artificial leather, and various other household goods. Plastics are utilized in the packaging of food items, medications, detergents, and cosmetics. The overconsumption of plastics presents a significant peril to both the ecosystem and human existence on Earth. The accumulation of plastics on land and in the sea has sparked interest in finding ways to breakdown these polymers. It is necessary to employ suitable biodegradable techniques to decrease the accumulation of plastics in the environment. To address the environmental issues related to plastics, it is crucial to have a comprehensive understanding of the interaction between microorganisms and polymers. A wide range of creatures, particularly microbes, have developed techniques to survive and break down plastics. This review specifically examines the categorization of plastics based on their thermal and biodegradable properties, as well as the many types of degradation and biodegradation. It also discusses the various types of degradable plastics, the characterization of biodegradation, and the factors that influence the process of biodegradation. The plastic breakdown and bioremediation capabilities of these microbes make them ideal for green chemistry applications aimed at removing hazardous polymers from the ecosystem.

Molecular docking and metagenomics assisted mitigation of microplastic pollution

Microplastics, tiny, flimsy, and direct progenitors of principal and subsidiary plastics, cause environmental degradation in aquatic and terrestrial entities. Contamination concerns include irrevocable impacts, potential cytotoxicity, and negative health effects on mortals. The detection, recovery, and degradation strategies of these pollutants in various biota and ecosystems, as well as their impact on plants, animals, and humans, have been a topic of significant interest. But the natural environment is infested with several types of plastics, all having different chemical makeup, structure, shape, and origin. Plastic trash acts as a substrate for microbial growth, creating biofilms on the plastisphere surface. This colonizing microbial diversity can be glimpsed with meta-genomics, a culture-independent approach. Owing to its comprehensive description of microbial communities, genealogical evidence on unconventional biocatalysts or enzymes, genomic correlations, evolutionary profile, and function, it is being touted as one of the promising tools in identifying novel enzymes for the degradation of polymers. Additionally, computational tools such as molecular docking can predict the binding of these novel enzymes to the polymer substrate, which can be validated through in vitro conditions for its environmentally feasible applications. This review mainly deals with the exploration of metagenomics along with computational tools to provide a clearer perspective into the microbial potential in the biodegradation of microplastics. The computational tools due to their polymathic nature will be quintessential in identifying the enzyme structure, binding affinities of the prospective enzymes to the substrates, and foretelling of degradation pathways involved which can be quite instrumental in the furtherance of the plastic degradation studies.

Landfill bacteriology: Role in waste bioprocessing elevated landfill gaseselimination and heat management

This study delves into the critical role of microbial ecosystems in landfills, which are pivotal for handling municipal solid waste (MSW). Within these landfills, a complex interplay of several microorganisms (aerobic/anaerobic bacteria, archaea or methanotrophs), drives the conversion of complex substrates into simplified compounds and complete mineralization into the water, inorganic salts, and gases, including biofuel methane gas. These landfills have dominant biotic and abiotic environments where various bacterial, archaeal, and fungal groups evolve and interact to decompose substrate by enabling hydrolytic, fermentative, and methanogenic processes. Each landfill consists of diverse bio-geochemical environments with complex microbial populations, ranging from deeply underground anaerobic methanogenic systems to near-surface aerobic systems. These kinds of landfill generate leachates which in turn emerged as a significant risk to the surrounding because generated leachates are rich in toxic organic/inorganic components, heavy metals, minerals, ammonia and xenobiotics. In addition to this, microbial communities in a landfill ecosystem could not be accurately identified using lab microbial-culturing methods alone because most of the landfill's microorganisms cannot grow on a culture medium. Due to these reasons, research on landfills microbiome has flourished which has been characterized by a change from a culture-dependent approach to a more sophisticated use of molecular techniques like Sanger Sequencing and Next-Generation Sequencing (NGS). These sequencing techniques have completely revolutionized the identification and analysis of these diverse microbial communities. This review underscores the significance of microbial functions in waste decomposition, gas management, and heat control in landfills. It further explores how modern sequencing technologies have transformed our approach to studying these complex ecosystems, offering deeper insights into their taxonomic composition and functionality.

Fabrication of jamun seed starch/tamarind kernel xyloglucan bio-nanocomposite films incorporated with chitosan nanoparticles and their application on sapota (Manilkara zapota) fruits

The present work develops bio-nanocomposite packaging films by valorizing agricultural byproducts jamun seed starch (JaSS) and tamarind kernel xyloglucan (XG), and adding varying concentrations of chitosan nanoparticles (ChNPs). The blending of JaSS and XG promotes a dense polymer network in the composite films with enhanced packaging attributes. However, ChNPs incorporation significantly reduced the viscosity and dynamic moduli of the JaSS/XG film-forming solutions. The FTIR and XRD results reveal improved intermolecular interactions and crystallinity. The DSC and TGA thermograms showed improved thermal stability in the ChNP-loaded JaSS/XG films. The addition of 3 % w/w ChNPs significantly enhanced the tensile strength (20.42 MPa), elastic modulus (0.8 GPa), and contact angle (89°), along with reduced water vapor transmission rate (13.26 g/h.m2) of the JaSS/XG films. The films exhibited strong antimicrobial activity against Bacillus cereus and Escherichia coli. More interestingly, the JaSS/XG/ChNPs coating on the sapota fruits retarded the weight loss and color change up to 12 days of storage. Overall, the JaSS/XG/ChNP bio-nanocomposites are promising packaging materials.

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

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

Thermophilic bacteria from Peruvian hot springs with high potential application in environmental biotechnology

Hot springs are extreme environments in which well-adapted microorganisms with biotechnological applications can thrive naturally. These thermal environments across Peruvian territory have, until now, remained poorly investigated. In this study, two hot springs, El Tragadero and Quilcate, located in Cajamarca (Peru) were selected in order to investigate the biotechnological potential of indigenous thermophilic bacteria. Enrichment and isolation processes were carried out using microbial mats, sediments, biofilms, and plastic polymers as samples. Screening for biosurfactants and siderophores production, as well as for polyethylene terephthalate (PET) hydrolysis was done using culture-dependent techniques. After molecular identification, Bacillus was found as the most abundant genus in both hot springs. Bacillus velezensis was found producing biosurfactants under high-level temperature. Anoxybacillus species (A. salavatliensis and A. gonensis) are here reported as siderophore-producing bacteria for the first time. Additionally, Brevibacillus and the less-known bacterium Tistrella mobilis were found demonstrating PET hydrolysis activity. Our study provides the first report of thermophilic bacteria isolated from Peruvian hot springs with biotechnological potential for the bioremediation of oil-, metal- and plastic-polluted environments.

Identification of key aroma compounds and core functional microorganisms associated with aroma formation for Monascus-fermented cheese

This study aimed to analyze the key aroma compounds and core functional microorganisms of Monascus-fermented cheese (MC). 36 key aroma compounds were identified according to gas chromatograph-mass spectrometer (GC-MS), aroma extract dilution analysis (AEDA), and odor activity values (OAV) analysis. And internal standard curves were used to clarify the changes in their concentration of them during cheese ripening. Furthermore, High-throughput sequencing was used to investigate the composition and dynamic changes of bacteria and fungi in MC, respectively. Lactococcus lactis was found to be the dominant bacterium while Monascus was confirmed to be the dominant fungus. In addition, Pearson correlation analysis showed that Lactococcus lactis, Staphylococcus, Trichococcus, and Monascus were strongly associated with the 36 key aroma compounds (r > 0.80, p < 0.05). Finally, a metabolic network containing biosynthetic pathways of the key aroma compounds was constructed. This study provides deeper insights into the unique aroma of MC and the contribution of cheese microbiota.

Psychrobacter species enrichment as potential microplastic degrader and the putative biodegradation mechanism in Shenzhen Bay sediment, China

Microplastic (MP) pollution has emerged as a pressing environmental concern due to its ubiquity and longevity. Biodegradation of MPs has garnered significant attention in combatting global MP contamination. This study focused on MPs within sediments near the sewage outlet of Shenzhen Bay. The objective was to elucidate the microbial communities in sediments with varying MPs, particularly those with high MP loads, and to identify microorganisms associated with MP degradation. The results revealed varying MP abundance, ranging from 211 to 4140 items kg-1 dry weight (d. w.), with the highest concentration observed near the outfall. Metagenomic analysis confirmed the enrichment of Psychrobacter species in sediments with high MP content. Psychrobacter accounted for ∼16.71% of the total bacterial community and 41.71% of hydrocarbon degrading bacteria at the S3 site, exhibiting a higher abundance than at other sampling sites. Psychrobacter contributed significantly to bacterial function at S3, as evidenced by the Kyoto Encyclopedia of Genes and Genomes pathway and enzyme analysis. Notably, 28 enzymes involved in MP biodegradation were identified, predominantly comprising oxidoreductases, hydrolases, transferases, ligases, lyases, and isomerases. We propose a putative mechanism for MP biodegradation, involving the breakdown of long-chain plastic polymers and subsequent oxidation of short-chain oligomers, ultimately leading to thorough mineralization.

Screening putative polyester polyurethane degrading enzymes with semi-automated cell-free expression and nitrophenyl probes

Cell-free expression (CFE) has shown recent utility in prototyping enzymes for discovery efforts. In this work, CFE is demonstrated as an effective tool to screen putative polyester polyurethane degrading enzyme sequences sourced from metagenomic analysis of biofilms prospected on aircraft and vehicles. An automated fluid handler with a controlled temperature block is used to assemble the numerous 30 µL CFE reactions to provide more consistent results over human assembly. In sum, 13 putative hydrolase enzymes from the biofilm organisms as well as a previously verified, polyester-degrading cutinase were expressed using in-house E. coli extract and minimal linear templates. The enzymes were then tested for esterase activity directly in extract using nitrophenyl conjugated substrates, showing highest sensitivity to shorter substrates (4-nitrophenyl hexanoate and 4-nNitrophenyl valerate). This screen identified 10 enzymes with statistically significant activities against these substrates; however, all were lower in measured relative activity, on a CFE volume basis, to the established cutinase control. This approach portends the use of CFE and reporter probes to rapidly prototype, screen and design for synthetic polymer degrading enzymes from environmental consortia. Graphical Abstract.

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.

Effects of mesophilic and thermophilic anaerobic digestion of sewage sludge on different polymers: Perspectives on the potential of the treatment to degrade microplastics

Sewage sludge is produced during municipal wastewater treatment and can be further treated to be used for soil applications due to its high nutrient and carbon content. Anaerobic digestion is often used to manage sewage sludge. However, sewage sludge has a high load of microplastics that can be transferred to the soil, causing a burden to the environment. Some researchers suggest that anaerobic digestion could be used as a method to remove microplastics from sewage sludge, while others have shown the opposite. In this study, a variety of commodity polymers (LLDPE, HDPE, PP, PS, PET, uPVC, PA66 and SBR) are tested under mesophilic (35 °C) and thermophilic (55 °C) anaerobic digestion to evaluate their degradation after the process. As 1 mm thick sheets of polymers were used, in terms of diffusion they were considered to correspond to microplastics. Different characterization methods were used to access the visual, chemical, mechanical and thermal changes caused by anaerobic digestion. The results showed evidence of polymer degradation, for example, surface smoothening of LLDPE, HDPE and PP, embrittlement of PS and uPVC, hydrolysis of PET, plasticization of PA66, and surface cracking of SBR. However, although some changes in properties happened, anaerobic digestion could not comprehensively degrade the studied polymers. Therefore, this study suggests that anaerobic digestion of sewage sludge, at the conditions tested, is not able to be used as a method to eliminate microplastics from the sewage sludge before it is added to the soil.

Degradation of low-density polyethylene by the bacterium Rhodococcus sp. C-2 isolated from seawater

Low-density polyethylene (LDPE), which accounts for 20% of the global plastic production, is discharged in great quantities into the ocean, threatening marine life and ecosystems. Marine microorganisms have previously been reported to degrade LDPE plastics; however, the exploration of strains and enzymes that degrade LDPE is still limited. Here, an LDPE-degrading bacterium was isolated from seawater of the Changjiang Estuary, China and identified as Rhodococcus sp. C-2, the relative abundance of which was dramatically enhanced during PE-degrading microbial enrichment. The strain C-2 exhibited the degradation of LDPE films, leading to their morphological deterioration, reduced hydrophobicity and tensile strength, weight loss, as well as the formation of oxygen-containing functional groups in short-chain products. Sixteen bacterial enzymes potentially involved in LDPE degradation were screened using genomic, transcriptomic, and degradation product analyses. Thereinto, the glutathione peroxidase GPx with exposed active sites catalyzed the LDPE depolymerization with the cooperation of its dissociated superoxide anion radicals. Furthermore, an LDPE degradation model involving multiple enzymes was proposed. The present study identifies a novel PE-degrading enzyme (PEase) for polyethylene bioremediation and promotes the understanding of LDPE degradation.

Insight on recently discovered PET polyester-degrading enzymes, thermostability and activity analyses

The flexibility and the low production costs offered by plastics have made them crucial to society. Unfortunately, due to their resistance to biological degradation, plastics remain in the environment for an extended period of time, posing a growing risk to life on earth. Synthetic treatments of plastic waste damage the environment and may cause damage to human health. Bacterial and fungal isolates have been reported to degrade plastic polymers in a logistic safe approach with the help of their microbial cell enzymes. Recently, the bacterial strain Ideonella sakaiensis (201-F6) was discovered to break down and assimilate polyethylene terephthalate (PET) plastic via metabolic processes at 30 °C to 37 °C. PETase and MHETase enzymes help the bacterium to accomplish such tremendous action at lower temperatures than previously discovered enzymes. In addition to functioning at low temperatures, the noble bacterium's enzymes have amazing qualities over pH and PET plastic degradation, including a shorter period of degradation. It has been proven that using the enzyme PETase, this bacterium hydrolyzes the ester linkages of PET plastic, resulting in production of terephthalic acid (TPA), nontoxic compound and mono-2-hydroxyethyl (MHET), along with further depolymerization of MHET to release ethylene glycogen (EG) and terephthalic acid (TPA) by the second enzyme MHETase. Enzymatic plastic degradation has been proposed as an environmentally friendly and long-term solution to plastic waste in the environment. As a result, this review focuses on the enzymes involved in hydrolyzing PET plastic polymers, as well as some of the other microorganisms involved in plastic degradation.

Recycling of fiber reinforced composites: Online mass spectrometric tracing, offline physicochemical speciation and toxicological evaluation of a pilot plant pyrolytic conversion

The increasing demand for lightweight materials with exceptional stability and durability has resulted in a significant rise in fiber-reinforced plastic (FRP) production. These materials find applications in various fields. However, the exceptional properties and diverse compositional range of FRPs pose challenges to conventional recycling strategies. Pyrolysis has emerged as a highly promising approach for separating the fibers from the polymer matrix. In this study, we employed thermal analysis coupled with high-resolution mass spectrometry to investigate the pyrolysis process. Representative FRP showed a starting decomposition temperature of 300 °C and bisphenol A, styrene, alkenes, and phenols could be identified. The identified parameters were used to operate a pilot plant with a capacity of up to 50 kg/h FRP, and reactor products were directly analyzed with soft photoionization mass spectrometry. The findings demonstrated good agreement between the pilot plant results and laboratory experiments, particularly for smaller compounds (m/z<200). The non-condensable fraction showed a range of 17 to 22 MJ/m3 as lower heating value. Analysis of the recovered fibers (diameter between 6.20 and 8.05 μm) revealed residual coke, but no toxic fibers were detected, according to the World Health Organization's definition. Yet, the organic coating of the fibers contained small amounts of potentially harmful PAHs. A toxicological assessment using a multicellular in vitro model confirmed the low hazardous potential of the recovered fibers. The findings contribute to developing sustainable and environmentally friendly recycling strategies for FRP while addressing important aspects related to the safety and toxicological implications of the resulting chemicals and fibers.

Microplastics are ubiquitous and increasing in soil of a sprawling urban area, Phoenix (Arizona)

Microplastics are environmental contaminants that have been extensively studied in marine and aquatic environments; terrestrial ecosystems, where most microplastics originate and have the potential to accumulate, typically receive less attention. This study aims to investigate the spatial and temporal soil concentrations of microplastics in a large desert metropolitan area, the Central Arizona-Phoenix Long-Term Ecological Research (CAP-LTER) area. Soil samples from the Ecological Survey of Central Arizona (ESCA) surveys (2005 and 2015) were leveraged to study spatial distributions and the temporal change of microplastic abundances. The temporal soil microplastics data were supplemented by microplastics deposition fluxes in a central location within the area (Tempe, AZ) for a period of one year (Oct 5th, 2020 to Sept 22nd, 2021). Samples were processed and microplastics were counted under an optical microscope to obtain quantitative information of their distribution in soil. Results for the spatial variation of the microplastic abundances in soil samples in Phoenix and the surrounding areas of the Sonoran Desert from 2015 depict microplastics as ubiquitous and abundant in soils (122 to 1299 microplastics/kg) with no clear trends between different locations. Microplastics deposition fluxes show substantial deposition in the local area (71 to 389 microplastics/m2/day with an average deposition flux of 178 microplastics/m2/day) but the role of resuspension and redistribution by dust storms to deposition may contribute to the unclear spatial trends. Comparison between the 2005 and 2015 surveys show a systematic increase in the abundance of microplastics and a decrease in microplastics size. Micro-Raman spectroscopy identified a variety of plastics including PE, PS, PVC, PA, PES and PP. However, a majority of microplastics remained chemically unidentifiable. Polyethylene was present in 75 % of the sampling sites and was the most abundant polymer on average in all soil samples.

Metal ion and hydrogen bonding synergistically mediated carboxylated lignin/cellulose nanofibrils composite film

In order to alleviate the resource and environmental problems caused by plastic film materials, the development of biodegradable cellulose-based films is crucial. Inspired by the strengthening mechanism of cellulose-lignin network from wood, carboxylated lignin (CL) was isolated using maleic acid (MA) pretreatment catalyzed by metal chlorides. Compared with pure MA, the presence of metal ions yielded CL with high carboxyl content (0.34 mmol/g), small size and good dispersibility. CL was then composited with CNF to prepare various CL/cellulose nanofibrils (CNF) composite films. When the addition of ferric chloride was 0.3 mmol/g maleic acid, the corresponding composite films exhibited highest tensile strength (180.0 MPa), Young's modulus (13.0 GPa) and excellent ultraviolet blocking rate (97.0 %). Meanwhile, the interaction forces measured by atomic force microscope showed that the binding between CNF and various CLs (276-406 nN) was higher than that between pure CNFs (202 nN), verifying that CL enhanced the mechanical properties of composite films. In summary, this work constructs a super-strong network between CL and CNF synergistically mediated by metal ion crosslinking and hydrogen bonding, which can be a promising alternative to replace conventional plastics in multiple areas.

Biodegradation of microplastics: Advancement in the strategic approaches towards prevention of its accumulation and harmful effects

Microplastics (MPs) are plastic particles in a size ranging from 1 mm to 5 mm in diameter, and are formed by the breakdown of plastics from different sources. They are emerging environmental pollutants, and pose a great threat to living organisms. Improper disposal, inadequate recycling, and excessive use of plastic led to the accumulation of MP in the environment. The degradation of MP can be done either biotically or abiotically. In view of that, this article discusses the molecular mechanisms that involve bacteria, fungi, and enzymes to degrade the MP polymers as the primary objective. As per as abiotic degradation is concerned, two different modes of MP degradation were discussed in order to justify the effectiveness of biotic degradation. Finally, this review is concluded with the challenges and future perspectives of MP biodegradation based on the existing research gaps. The main objective of this article is to provide the readers with clear insight, and ideas about the recent advancements in MP biodegradation.

Current advances, challenges and strategies for enhancing the biodegradation of plastic waste

Due to its highly recalcitrant nature, the growing accumulation of plastic waste is becoming an urgent global problem. Biodegradation is one of the best possible approaches for the treatment of plastic waste in an environmentally friendly manner, but our current knowledge on the underlying mechanisms, as well as strategies for the development and enhancement of plastic biodegradation are still limited. This review aims to provide an updated and comprehensive overview of current research on plastic waste biodegradation, focusing on enhancement strategies with ongoing research significance, including the mining of highly efficient plastic-degrading microorganisms/enzymes, utilization of synergistic additives, novel pretreatment approaches, modification via molecular engineering, and construction of bacterial/enzyme consortia systems. Studying these strategies can (i) enrich the high-performance microbial/enzymes toolbox for plastic degradation, (ii) provide methods for recycling and upgrading plastics, as well as (iii) enable further molecular modification and functional optimization of plastic-degrading enzymes to realize economically viable biodegradation of plastics. To the best of our knowledge, this is the first review to discuss in detail strategies to enhance biodegradation of plastics. Finally, some recommendations for future research on plastic biodegradation are listed, hoping to provide the best direction for tackling the plastic waste dilemma in the future.

Polyurethane-Degrading Potential of Alkaline Groundwater Bacteria

Plastic waste is a global environmental burden and long-lasting plastic polymers, including ubiquitous and toxic polyurethanes (PUs), rapidly accumulate in the water environments. In this study, samples were collected from the three alkaline groundwater occurrences in the geotectonic regions of the Pannonian basin of northern Serbia (Torda and Slankamen Banja) and Inner Dinarides of western Serbia (Mokra Gora) with aim to isolate and identify bacteria with plastic- and lignocellulose-degrading potential, that could be applied to reduce the burden of environmental plastic pollution. The investigated occurrences belong to cold, mildly alkaline (pH: 7.6-7.9) brackish and hyperalkaline (pH: 11.5) fresh groundwaters of the SO4 - Na + K, Cl - Na + K and OH, Cl - Ca, Na + K genetic type. Full-length 16S rDNA sequencing, using Oxford Nanopore sequencing device, was performed with DNA extracted from colonies obtained by cultivation of all groundwater samples, as well as with DNA extracted directly from one groundwater sample. The most abundant genera belong to Pseudomonas, Acidovorax, Kocuria and Methylotenera. All screened isolates (100%) had the ability to grow on at least 3 of the tested plastic and lignocellulosic substrates, with 53.9% isolates degrading plastic substrate Impranil® DLN-SD (SD), a model compound for PUs degradation. Isolates degrading SD that were identified by partial 16S rDNA sequencing belong to the Stenotrophomonas, Pseudomonas, Paraburkholderia, Aeromonas, Vibrio and Acidovorax genera. Taking into account that plastics, including commonly produced PUs, are widespread in groundwater, identification of PUs-degrading bacteria may have potential applications in bioremediation of groundwater polluted with this polymer.

Microplastic pollution: Understanding microbial degradation and strategies for pollutant reduction

Microplastics are ubiquitous environmental pollutants with the potential for adverse impacts on ecosystems and human health. These particles originate from the fragmentation of larger plastic items, shedding from synthetic fibers, tire abrasions, and direct release from personal care products and industrial processes. Once released into the environment, microplastics can disrupt ecosystems, accumulate in organisms, cause physical harm, and carry chemical pollutants that pose risks to both wildlife and human health. There is an urgent need to comprehensively explore the multifaceted issue of microplastic pollution and understand microbial degradation to reduce environmental pollution caused by microplastics. This paper presents a comprehensive exploration of microplastics, including their types, composition, advantages, and disadvantages, as well as the journey and evolution of microplastic pollution. The impact of microplastics on the microbiome and microbial communities is elucidated, highlighting the intricate interactions between microplastics and microbial ecosystems. Furthermore, the microbial degradation of microplastics is discussed, including the identification, characterization, and culturing methods of microplastic-degrading microorganisms. Mechanisms of microplastic degradation and the involvement of microbial enzymes are elucidated to shed light on potential biotechnological applications. Strategies for reducing microplastic pollution are presented, encompassing policy recommendations and the importance of enhanced waste management practices. Finally, the paper addresses future challenges and prospects in the field, emphasizing the need for international collaboration, research advancements, and public engagement. Overall, this study underscores the urgent need for concerted efforts to mitigate microplastic pollution and offers valuable insights for researchers, policymakers, and stakeholders involved in environmental preservation.

Synthesis and Characterization of Poly(Butylene Sebacate-Co-Terephthalate) Copolyesters with Pentaerythritol as Branching Agent

Poly(butylene sebacate-co-terephthalate) (PBSeT) copolyesters are prepared by melt polymerization via two-step transesterification and polycondensation using pentaerythritol (PE) as a branching agent. The effects of the incorporated PE on its chemical, thermal, mechanical, and degradation properties, along with the rheological properties of its melt, are investigated. The highest molecular weight and intrinsic viscosity along with the lowest melt flow index were achieved at a PE content of 0.2 mol%, with minimal reduction in the tensile strength and the highest tear strength. The addition of PE did not significantly influence the thermal behavior and stability of the PBSeT copolyesters; however, the elongation at break decreased with increasing PE content. The sample with 0.2 mol% PE exhibited a higher storage modulus and loss modulus as well as a lower loss angle tangent than the other samples, indicating improved melt elasticity. The incorporation of more than 0.2 mol% PE enhanced the enzymatic degradation of copolyesters. In summary, including within 0.2 mol%, PE effectively improved both the processability-related characteristics and degradation properties of PBSeT copolyesters, suggesting their potential suitability for use in agricultural and packaging materials.

Microplastics in mangroves with special reference to Asia: Occurrence, distribution, bioaccumulation and remediation options

Microplastics (MPs) are a new and lesser-known pollutant that has intrigued the interest of scientists all over the world in recent decades. MP (<5mm in size) can enter marine environments such as mangrove forests in a variety of ways, interfering with the health of the environment and organisms. Mangroves are now getting increasingly exposed to microplastic contamination due to their proximity to human activities and their position as critical transitional zones between land and sea. The present study reviews the status of MPs contamination specifically in mangrove ecosystems situated in Asia. Different sources and characteristics of MPs, subsequent deposition of MPs in mangrove water and sediments, bioaccumulation in different organisms are discussed in this context. MP concentrations in sediments and organisms were higher in mangrove forests exposed to fishing, coastal tourism, urban, and industrial wastewater than in pristine areas. The distribution of MPs varies from organism to organism in mangrove ecosystems, and is significantly influenced by their morphometric characteristics, feeding habits, dwelling environment etc. Mangrove plants can accumulate microplastics in their roots, stem and leaves through absorption, adsorption and entrapment helping in reducing abundance of microplastic in the surrounding environment. Several bacterial and fungal species are reported from these mangrove ecosystems, which are capable of degrading MPs. The bioremediation potential of mangrove plants offers an innovative and sustainable approach to mitigate microplastic pollution. Diverse mechanisms of MP biodegradation by mangrove dwelling organisms are discussed in this context. Biotechnological applications can be utilized to explore the genetic potential of the floral and faunal species found in the Asian mangroves. Detailed studies are required to monitor, control, and evaluate MP pollution in sediments and various organisms in mangrove ecosystems in Asia as well as in other parts of the world.

Laccase driven biocatalytic oxidation to reduce polymeric surface hydrophobicity: An effective pre-treatment strategy to enhance biofilm mediated degradation of polyethylene and polycarbonate plastics

Plastic pollution is a major global environmental issue due to its structural complexity and poor biodegradability. Biological approaches are appropriate due to cost effectiveness and environmental friendliness, however effective polymer degradation is still in its infancy. As biological treatments are slower than physical and chemical approaches, they could be applied in conjunction with pre-treatment techniques such as photo-oxidation, heat treatment, and chemical treatments. But these processes lead to high energy consumption and hazardous secondary pollution. To address these concerns, an enzymatic pre-treatment strategy has been proposed in this study, with an aim of promoting surface oxidation on the plastics leading to improved hydrophilicity. This in turn, facilitates the surface attachment of microbes, ultimately, accelerating biodegradation. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FT-IR) spectroscopy analyses confirmed the surface oxidation of the polyethylene (PE) and polycarbonate (PC) plastics mediated by the action of laccase enzyme. Contact angle measurement witnessed the increased hydrophilicity of the treated plastics. Following, a potential biofilm forming microbial consortium has been employed for the biodegradation of enzyme treated plastics. SEM analysis indicated the increased formation of corrosive pits and surface aberrations on the enzymatically pre-treated plastics and Confocal Laser Scanning microscopy (CLSM) analysis exhibited the enhanced biofilm formation and exopolysaccharide deposition on the pre-treated PE and PC. In addition, X-ray photoelectron spectroscopy (XPS) revealed the reduction in the elemental composition of carbon with an increment in the oxygen composition of plastics. Gel permeation chromatography (GPC) further confirmed the greater reduction in the molecular weights of the plastics subjected to integrated enzymatic and biofilm treatment than only biofilm treated plastics. This is the first report on the integration of enzymatic pre-treatment with the biofilm mediated microbial degradation to achieve enhanced treatment of plastics which demonstrated to be a promising technology for the effective mitigation of plastic pollution.

Insights into the shape-dependent effects of polyethylene microplastics on interactions with organisms, environmental aging, and adsorption properties

The shape-dependent effects of microplastics have been studied in the context of ingestion but have not been considered in other environmental processes. Therefore, we investigated how the shape of polyethylene microplastics (spheres, fragments, and films) affects interactions with plants, aging, and their adsorption properties. The shape had no effect on the growth rate and chlorophyll content of duckweed Lemna minor, but the fragments strongly adhered to the plant biomass and reduced the root length. The adsorption process of the model organic compound (methylene blue dye) was described by the same kinetic model for all shapes-the experimental data best fit the pseudo-second order model. However, twice as much methylene blue was adsorbed on films as on fragments and spheres. During environmental aging, most biofilm developed on films. The biofilm on spheres contained significantly less photosynthetic microorganisms, but twice as much extracellular polymeric substances (EPS) as on fragments and films. This suggests that the attachment of microorganisms to spherical particles is limited and therefore more intensive production of EPS is required for stable biofilm formation. From the results of this study, it is evident that the shape of microplastics significantly affects not only ecotoxicity but also other environmentally relevant processes.

Microbial colonization patterns and biodegradation of petrochemical and biodegradable plastics in lake waters: insights from a field experiment

Introduction

Once dispersed in water, plastic materials become promptly colonized by biofilm-forming microorganisms, commonly known as plastisphere.

Methods

By combining DNA sequencing and Confocal Laser Scanning Microscopy (CLSM), we investigated the plastisphere colonization patterns following exposure to natural lake waters (up to 77 days) of either petrochemical or biodegradable plastic materials (low density polyethylene - LDPE, polyethylene terephthalate - PET, polylactic acid - PLA, and the starch-based MaterBi® - Mb) in comparison to planktonic community composition. Chemical composition, water wettability, and morphology of plastic surfaces were evaluated, through Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), and static contact angle analysis, to assess the possible effects of microbial colonization and biodegradation activity.

Results and Discussion

The phylogenetic composition of plastisphere and planktonic communities was notably different. Pioneering microbial colonisers, likely selected from lake waters, were found associated with all plastic materials, along with a core of more than 30 abundant bacterial families associated with all polymers. The different plastic materials, either derived from petrochemical hydrocarbons (i.e., LDPE and PET) or biodegradable (PLA and Mb), were used by opportunistic aquatic microorganisms as adhesion surfaces rather than carbon sources. The Mb-associated microorganisms (i.e. mostly members of the family Burkholderiaceae) were likely able to degrade the starch residues on the polymer surfaces, although the Mb matrix maintained its original chemical structure and morphology. Overall, our findings provide insights into the complex interactions between aquatic microorganisms and plastic materials found in lake waters, highlighting the importance of understanding the plastisphere dynamics to better manage the fate of plastic debris in the environment.

A review on cutinases enzyme in degradation of microplastics

From the surface of the earth to the depths of the ocean, microplastics are a hazard for both aquatic and terrestrial habitats. Due to their small size and vast expanse, they can further integrate into living things. The fate of microplastics in the environment depends upon the biotic components such as microorganisms which have potential enzymes to degrade the microplastics. As a result, scientists are interested in using microorganisms like bacteria, fungi, and others to remediate microplastic. These microorganisms release the cutinase enzyme, which is associated with the enzymatic breakdown of microplastics and plastic films. Yet, numerous varieties of microplastics exist in the environment and their contaminants act as a significant challenge in degrading microplastics. The review discusses the cutinases enzyme degradation strategies and potential answers to deal with existing and newly generated microplastic waste - polyethylene (PE), polyethylene terephthalate (PET), poly-ε-caprolactone (PCL), polyurethanes (PU), and polybutylene succinate (PBS), along with their degradation pathways. The potential of cutinase enzymes from various microorganisms can effectively act to remediate the global problem of microplastic pollution.

Surely you can't B. cereus: Bacillus cereus infection resulting in spontaneous pseudoaneurysm of a nonaccessed arteriovenous graft

Vascular graft infections are a well-described complication of loop arteriovenous grafts (AVGs) placed for hemodialysis access and are reported to occur in 0.5% to 6.0% of AVGs. The most common microorganisms implicated in these infections are the Staphylococcus species. We present a case of a chronically nonaccessed graft rupture caused by an indolent B. cereus colonization, which is usually a foodborne contaminant. The finding of this organism as the causal agent in an AVG infection warrants further research into the potential emergence of the Bacillus species as a contributing factor in the morbidity and mortality resulting from AVG infection.

Enzyme selection, optimization, and production toward biodegradation of post-consumer poly(ethylene terephthalate) at scale

Poly(ethylene terephthalate) (PET) is one of the world's most widely used polyester plastics. Due to its chemical stability, PET is extremely difficult to hydrolyze in a natural environment. Recent discoveries in new polyester hydrolases and breakthroughs in enzyme engineering strategies have inspired enormous research on biorecycling of PET. This study summarizes our research efforts toward large-scale, efficient, and economical biodegradation of post-consumer waste PET, including PET hydrolase selection and optimization, high-yield enzyme production, and high-capacity enzymatic degradation of post-consumer waste PET. First, genes encoding PETase and MHETase from Ideonella sakaiensis and the ICCG variant of leaf-branch compost cutinase (LCCICCG ) were codon-optimized and expressed in Escherichia coli BL21(DE3) for high-yield production. To further lower the enzyme production cost, a pelB leader sequence was fused to LCCICCG so that the enzyme can be secreted into the medium to facilitate recovery. To help bind the enzyme on the hydrophobic surface of PET, a substrate-binding module in a polyhydroxyalkanoate depolymerase from Alcaligenes faecalis (PBM) was fused to the C-terminus of LCCICCG . The resulting four different LCCICCG variants (LCC, PelB-LCC, LCC-PBM, and PelB-LCC-PBM), together with PETase and MHETase, were compared for PET degradation efficiency. A fed-batch fermentation process was developed to produce the target enzymes up to 1.2 g L-1 . Finally, the best enzyme, PelB-LCC, was selected and used for the efficient degradation of 200 g L-1 recycled PET in a well-controlled, stirred-tank reactor. The results will help develop an economical and scalable biorecycling process toward a circular PET economy.

Biodegradation of polyethylene terephthalate (PET) by diverse marine bacteria in deep-sea sediments

PET plastic waste entering the oceans is supposed to take hundreds of years to degrade and tends to accumulate in the deep sea. However, we know little about the bacteria capable of plastic degradation therein. To determine whether PET-degrading bacteria are present in deep-sea sediment, we collected the samples from the eastern central Pacific Ocean and initiated microbial incubation with PET as the carbon source. After enrichment with PET for 2 years, we gained all 15 deep-sea sediment communities at five oceanic sampling sites. Bacterial isolation for pure culture and further growth tests confirmed that diverse bacteria possess degradation ability including Alcanivorax xenomutans BC02_1_A5, Marinobacter sediminum BC31_3_A1, Marinobacter gudaonensis BC06_2_A6, Thalassospira xiamenensis BC02_2_A1 and Nocardioides marinus BC14_2_R3. Furthermore, four strains were chosen as representatives to reconfirm the PET degradation capability by SEM, weight loss and UPLC-MS. The results showed that after 30-day incubation, 1.3%-1.8% of PET was lost. De-polymerization of PET by the four strains was confirmed by the occurrence of the PET monomer of MHET and TPA as the key degradation products. Bacterial consortia possessing PET-degrading potential are prevalent and diverse and might play a key role in the removal of PET pollutants in deep oceans.

Micro (nano) plastics uptake, toxicity and detoxification in plants: Challenges and prospects

Plastic pollution has emerged as a global challenge affecting ecosystem health and biodiversity conservation. Terrestrial environments exhibit significantly higher plastic concentrations compared to aquatic systems. Micro/nano plastics (MNPs) have the potential to disrupt soil biology, alter soil properties, and influence soil-borne pathogens and roundworms. However, limited research has explored the presence and impact of MNPs on aquaculture systems. MNPs have been found to inhibit plant and seedling growth and affect gene expression, leading to cytogenotoxicity through increased oxygen radical production. The article discusses the potential phytotoxicity process caused by large-scale microplastics, particularly those unable to penetrate cell pores. It also examines the available data, albeit limited, to assess the potential risks to human health through plant uptake.

Assessing biodegradation of roadway particles via complementary mass spectrometry and NMR analyses

Roadway particles (RP) that can be collected with on-vehicle system, consist of a mixture of Tire and road wear particles (TRWP) with other traffic-derived particles (exhaust or non-exhaust) and/or biogenic compounds and represent a significant source of xenobiotics, susceptible to reach the different environmental compartments. The study of the RP fate is thus a major challenge to tackle in order to understand their degradation and impact. They offer a variety of carbon sources potentially usable by microorganisms, ranging from the tire-derived plasticizers, vulcanizing agents, protective agents and their transformation products, to other traffic, road and environmental-derived contaminants. A multi-analytical approach was implemented to characterize RP and study their biodegradation. Kinetics of RP extractions were monitored during 21 days in water, methanol, acetone and chloroform to identify leaching and extractable compounds and monitor the particle composition. The results confirmed that hundreds of readily leachable chemicals can be extracted from RP directly into water according to a dynamic process with time while additional poorly soluble compounds remain in the particles. Mass spectrometry (LC-HRMS and GC-MS) allowed us to propose 296 putative compounds using an extensive rubber database. The capacity of 6 bacterial strains, belonging to Rhodococcus, Pseudomonas and Streptomyces genera, to biodegrade RP was then evaluated over 14 days of incubation. The selected strains were able to grow on RP using various substrates. Elastomer monitoring by 1H NMR revealed a significant 12 % decrease of the extractable SBR fraction when the particles were incubated with Rhodococcus ruber. After incubation, the biodegradation of 171 compounds among leachable and extractable compounds was evaluated. Fatty acids and alkanes from rubber plasticizers and paraffin waxes were the most degraded putative compounds by the six strains tested, reaching 75 % of biodegradation for some of them.

Ecological risks of microplastics contamination with green solutions and future perspectives

The rise of plasticulture as mulching material in farming systems has raised concerns about microplastics (MPs) in the agricultural landscape. MPs are emerging pollutants in croplands and water systems with significant ecological risks, particularly over the long term. In the soil systems, MPs polymer type, thinness, shape, and size induces numerous effects on soil aggregates, dissolved organic carbon (C), rapidly oxidized organic C, microbial biomass C, microbial biomass nitrogen (N), microbial immobilization, degradation of organic matter, N cycling, and production of greenhouse gas emissions (GHGs), thereby posing a significant risk of impairing soil physical and biochemical properties over time. Further, toxic chemicals released from polyethylene mulching (PMs) might indirectly harm plant growth by affecting soil wetting-drying cycles, releasing toxic substances that interact with soil matrix, and suppressing soil microbial activity. In the environment, accumulation of MPs poses a risk to human health by accelerating emissions of GHGs, e.g., methane and carbon dioxide, or directly releasing toxic substances such as phthalic acid esters (PAEs) into the soils. Also, larger sizes MPs can adhere to root surface and block stomata could significantly change the shape of root epidermal cells resulting in arrest plant growth and development by restricting water-nutrient uptake, and gene expression and altering the biodiversity of the soil pollutants. In this review, we systematically analyzed the potential risks of MPs to the soil-plant and human body, their occurrence, abundance, and migration in agroecosystems. Further, the impacts of MPs on soil microbial function, nutrient cycling, soil C, and GHGs are mechanistically reviewed, with emphasis on potential green solutions such as organic materials amendments along with future research directions for more eco-friendly and sustainable plastic management in agroecosystems.

Microplastics in lentic environments: implications for Indian ecosystems

The paper focused on occurrence, characterization, and analytical methods of microplastic (MP) pollution in the lentic environment mainly for the Indian scenario. To understand the flow of MP from plastic waste, a material flow diagram was developed using STAN, assigning the transfer coefficients based on existing scientific literature and primary survey from local recycling facilities and industries. The quantity, morphology, and polymers of MP in the water and sediments of the lentic environment were compared for various states from 2011 to 2022. The reasons for the geographical heterogeneity in microplastics may be the migratory routes of MPs in the ecosystems like commercial uses and wastewater characteristics which possibly discharged in lentic system. Factors like particle density, water surface area, water surface depth, wind speed and direction, and water flow size mainly affect MP concentrations in the lentic water body, and mainly PHI and PLI are keys to MP risk analysis. The surface characteristics of MPs reveal that it absorbs many toxic contaminants including heavy metals. The impacts of MP on ecosystem and human health were also discussed. The impacts of socioeconomic conditions on MP concentrations for different states in India were also added. Proposed methods for plastic waste generation control also included which will help for developing policy in future to prevent MP pollution in lentic environments and also motivate future researchers to establish new standardized methods of MP analysis.

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.

Two-Step Chemo-Microbial Degradation of Post-Consumer Polyethylene Terephthalate (PET) Plastic Enabled by a Biomass-Waste Catalyst

Polyethylene terephthalate (PET) pollution has significant environmental consequences; thus, new degradation methods must be explored to mitigate this problem. We previously demonstrated that a consortium of three Pseudomonas and two Bacillus species can synergistically degrade PET in culture. The consortium more readily consumes bis(2-hydroxyethyl) terephthalate (BHET), a byproduct created in PET depolymerization, compared to PET, and can fully convert BHET into metabolically usable monomers, namely terephthalic acid (TPA) and ethylene glycol (EG). Because of its crystalline structure, the main limitation of the biodegradation of post-consumer PET is the initial transesterification from PET to BHET, depicting the need for a transesterification step in the degradation process. Additionally, there have been numerous studies done on the depolymerization reaction of PET to BHET, yet few have tested the biocompatibility of this product with a bacterial consortium. In this work, a two-step process is implemented for sustainable PET biodegradation, where PET is first depolymerized to form BHET using an orange peel ash (OPA)-catalyzed glycolysis reaction, followed by the complete degradation of the BHET glycolysis product by the bacterial consortium. Results show that OPA-catalyzed glycolysis reactions can fully depolymerize PET, with an average BHET yield of 92% (w/w), and that the reaction product is biocompatible with the bacterial consortium. After inoculation with the consortium, 19% degradation of the glycolysis product was observed in 2 weeks, for a total degradation percentage of 17% when taking both steps into account. Furthermore, the 10-week total BHET degradation rate was 35%, demonstrating that the glycolysis products are biocompatible with the consortium for longer periods of time, for a total two-step degradation rate of 33% over 10 weeks. While we predict that complete degradation is achievable using this method, further experimentation with the consortium can allow for a circular recycling process, where TPA can be recovered from culture media and reused to create new materials.