Isolation and characterization of different promising fungi for biological waste management of polyurethanes

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.

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.

Bio-based polyester-polyurethane foams: synthesis and degradability by Aspergillus niger and Aspergillus clavatus

In this article, the degradability by Aspergillus niger and Aspergillus clavatus of three bio-based polyurethane (PU) foams is compared to previous degradability studies involving a Pseudomonas sp. bacterium and similar initial materials (Spontón et al. in Int. Biodet. Biodeg. 85:85-94, 2013, https://doi.org/10.1016/j.ibiod.2013.05.019 ). First, three new polyester-polyurethane foams were prepared from mixtures of castor oil (CO), maleated castor oil (MACO), toluene diisocyanate (TDI), and water. Then, their degradation tests were carried out in an aqueous medium, and employing the two mentioned fungi, after their isolation from the environment. From the degradation tests, the following was observed: (a) the insoluble (and slightly collapsed) foams exhibited free hydroxyl, carboxyl, and amine moieties; and (b) the water soluble (and low molar mass) compounds contained amines, carboxylic acids, and glycerol. The most degraded foam contained the highest amount of MACO, and therefore the highest concentration of hydrolytic bonds. A basic biodegradation mechanism was proposed that involves hydrolysis and oxidation reactions.

Identification and characterization of a fungal cutinase-like enzyme CpCut1 from Cladosporium sp. P7 for polyurethane degradation

Plastic degradation by biological systems emerges as a prospective avenue for addressing the pressing global concern of plastic waste accumulation. The intricate chemical compositions and diverse structural facets inherent to polyurethanes (PU) substantially increase the complexity associated with PU waste management. Despite the extensive research endeavors spanning over decades, most known enzymes exhibit a propensity for hydrolyzing waterborne PU dispersion (i.e., the commercial Impranil DLN-SD), with only a limited capacity for the degradation of bulky PU materials. Here, we report a novel cutinase (CpCut1) derived from Cladosporium sp. P7, which demonstrates remarkable efficiency in the degrading of various polyester-PU materials. After 12-h incubation at 55°C, CpCut1 was capable of degrading 40.5% and 20.6% of thermoplastic PU film and post-consumer foam, respectively, while achieving complete depolymerization of Impranil DLN-SD. Further analysis of the degradation intermediates suggested that the activity of CpCut1 primarily targeted the ester bonds within the PU soft segments. The versatile performance of CpCut1 against a spectrum of polyester-PU materials positions it as a promising candidate for the bio-recycling of waste plastics.IMPORTANCEPolyurethane (PU) has a complex chemical composition that frequently incorporates a variety of additives, which poses significant obstacles to biodegradability and recyclability. Recent advances have unveiled microbial degradation and enzymatic depolymerization as promising waste PU disposal strategies. In this study, we identified a gene encoding a cutinase from the PU-degrading fungus Cladosporium sp. P7, which allowed the expression, purification, and characterization of the recombinant enzyme CpCut1. Furthermore, this study identified the products derived from the CpCut1 catalyzed PU degradation and proposed its underlying mechanism. These findings highlight the potential of this newly discovered fungal cutinase as a remarkably efficient tool in the degradation of PU materials.

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.

Mechanistic understanding on the uptake of micro-nano plastics by plants and its phytoremediation

Contaminated soil is one of today's most difficult environmental issues, posing serious hazards to human health and the environment. Contaminants, particularly micro-nano plastics, have become more prevalent around the world, eventually ending up in the soil. Numerous studies have been conducted to investigate the interactions of micro-nano plastics in plants and agroecosystems. However, viable remediation of micro-nano plastics in soil remains limited. In this review, a powerful in situ soil remediation technology known as phytoremediation is emphasized for addressing micro-nano-plastic contamination in soil and plants. It is based on the synergistic effects of plants and the microorganisms that live in their rhizosphere. As a result, the purpose of this review is to investigate the mechanism of micro-nano plastic (MNP) uptake by plants as well as the limitations of existing MNP removal methods. Different phytoremediation options for removing micro-nano plastics from soil are also described. Phytoremediation improvements (endophytic-bacteria, hyperaccumulator species, omics investigations, and CRISPR-Cas9) have been proposed to enhance MNP degradation in agroecosystems. Finally, the limitations and future prospects of phytoremediation strategies have been highlighted in order to provide a better understanding for effective MNP decontamination from soil.

Synthesis and Biodegradation Test of a New Polyether Polyurethane Foam Produced from PEG 400, L-Lysine Ethyl Ester Diisocyanate (L-LDI) and Bis-hydroxymethyl Furan (BHMF)

In this paper we produced a bio-based polyether-polyurethane foam PU1 through the prepolymer method. The prepolymer was obtained by the reaction of PEG 400 with L-Lysine ethyl ester diisocyanate (L-LDI). The freshly prepared prepolymer was extended with 2,5-bis(hydroxymethyl)furan (BHMF) to produce the final polyurethane. The renewable chemical BHMF was produced through the chemical reduction of HMF by sodium borohydride. HMF was produced by a previously reported procedure from fructose using choline chloride and ytterbium triflate. To evaluate the degradation rate of the foam PU1, we tested the chemical stability by soaking it in a 10% sodium hydroxide solution. The weight loss was only 12% after 30 days. After that, we proved that enzymatic hydrolysis after 30 days using cholesterol esterase was more favoured than hydrolysis with NaOH, with a weight loss of 24%, probably due to the hydrophobic character of the PU1 and a better adhesion of the enzyme on the surface with respect to water. BHMF was proved to be of crucial importance for the enzymatic degradation assay at 37 °C in phosphate buffer solution, because it represents the breaking point inside the polyurethane chain. Soil burial degradation test was monitored for three months to evaluate whether the joint activity of sunlight, climate changes and microorganisms, including bacteria and fungi, could further increase the biodegradation. The unexpected weight loss after soil burial degradation test was 45% after three months. This paper highlights the potential of using sustainable resources to produce new biodegradable materials.

Fungal Biodegradation of Polyurethanes

Polyurethanes (PURs) are versatile polymers used in a wide variety of fields, such as the medical, automotive, textile, thermal insulation, and coating industries as well as many everyday objects. Many PURs have applications that require a long service life, sometimes with exposure to aggressive conditions. They can undergo different types of physicochemical and biological degradation, but they are not compostable, and many of them constitute persistent waste in the environment. Although both bacteria and fungi can be involved in the degradation of PURs, fungi are often the main biodegradation agents. The chemical structure of PURs determines their degree of biodegradation. Fungal biodegradation of PURs is linked to the production of enzymes, mainly esterases and proteases, alongside laccases, peroxidases, and tyrosinases, which can modify the structure of polyurethane compounds by forming carbonyl groups. The experimental analysis of the biodegradation of PUR can be carried out by bringing the polymer into contact with a mold in pure culture or with a microbial consortium. Then, global measurements can be taken, such as weight loss, tensile tests, or the ability of microorganisms to grow in the presence of PUR as the sole carbon source. The analysis of the chemical structure of the polymer and its degradation products after fungal growth can confirm biodegradation and specify the mechanism. The main avenues of future research are directed towards the development of fully biodegradable PURs and, on the contrary, towards the development of PURs that are more resistant to degradation phenomena, in particular biodegradation, for applications where the material is in contact with living organisms.

The distinct plastisphere microbiome in the terrestrial-marine ecotone is a reservoir for putative degraders of petroleum-based polymers

Research into plastic-degrading bacteria and fungi is important for understanding how microorganisms can be used to address the problem of plastic pollution and for developing new approaches to sustainable waste management and bioplastic production. In the present study, we isolated 55 bacterial and 184 fungal strains degrading polycaprolactone (PCL) in plastic waste samples from Dafeng coastal salt marshes, Jiangsu, China. Of these, Jonesia and Streptomyces bacteria also showed potential to degrade other types of petroleum-based polymers. The metabarcoding results proved the existence of plastisphere as a distinct ecological niche regardless of the plastic types where 27 bacterial and 29 fungal amplicon sequence variants (ASVs) were found to be significantly (p < 0.05) enriched, including some belonging to Alternaria (Ascomycota, Fungi) and Pseudomonas (Gammaproteobacteria, Bacteria) that were also mined out by the method of cultivation. Further assembly analyses demonstrated the importance of deterministic processes especially the environmental filtering effect of carbon content and pH on bacteria as well as the carbon and cation content on fungi in shaping the plastisphere communities in this ecosystem. Thus, the unique microbiome of the plastisphere in the terrestrial-marine ecotone is enriched with microorganisms that are potentially capable of utilizing petroleum-based polymers, making it a valuable resource for screening plastic biodegraders.

Review on disposal, recycling and management of waste polyurethane foams: A way ahead

With the burning issue of air, land and water pollution, the premonition of looking forward towards a future devoid of any kind of oil and gas reserves has caused a paradigm shift towards recycling, recovery of any synthetic polymer and also to dispose them off environmentally. Among them are plastics such as polyethylene terephthalate and poly vinyl chloride. Polyurethane (PU) is also under the scanner to dispose of or recycle it environmentally and sustainably. PU is at present the sixth most utilized polymer all over the world with a production of nearly 18 million tonnes per annum, which roughly estimates a daily production of PU products of greater than a million of cubic metres. Its thermostable nature is one of the major reasons for its higher preference over other polymers. This review article discusses the current disposal and technologies available to recycle waste PU foams and also sheds some light on some additional work being done in the field to upgrade the existing technology. Interestingly, some methods mentioned here are probably undergoing scale-up trials runs by now. Currently, the most researched and studied ones are mechanical recycling and glycolysis. But microbial and enzymatic disposal methods can be turned into full-scale industrial recycling processes in the near future. Additionally, we can see an archetypal shift from traditional oil-based sources to the agrarian sources.

Biodegradation of polyester polyurethane by Cladosporium sp. P7: Evaluating its degradation capacity and metabolic pathways

Microorganisms capable of decomposing polyurethane (PU) and other plastics have the potential to be used in bio-recycling processes. In this study, 20 PU-degrading strains were isolated, including 11 bacteria and 9 fungi, using a synthesized poly(1,4-butylene adipate)-based PU (PBA-PU) as the screening substrate. Three PU substrates with increasing structure complexities were used for a thorough evaluation of microbial degradation capacity: Impranil® DLN-SD, PBA-PU film and PU foam waste. After 4 days, the best fungal PBA-PU degrader, Cladosporium sp. P7, could degrade 94.5% of Impranil® DLN-SD. After 28 days of cultivation, 32.42% and 43.91% of solid PBA-PU film was converted into soluble small molecules when used as the sole carbon source or in a medium with other co-carbon sources, respectively. Accordingly, the weight loss of PU foam waste after 15 days was 15.3% for the sole carbon condition and 83.83% for the co-carbon conditions. Furthermore, PBA-PU was used for metabolic pathway analysis because of its known composition and chemical structure. Six metabolites were identified during the degradation process of PBA-PU, including adipic acid (AA), 1,4-butanediol (BDO), and 4,4'-methylenedianiline (MDA), which can also be used as the sole carbon source to grow the fungal strain P7, resulting in the discovery of two MDA metabolites during the cultivation processes. Based on the presence of these eight metabolites, we hypothesized that PBA-PU is first depolymerized by the fungal strain P7 via ester and urethane bond hydrolysis, followed by intracellular metabolism and mineralization of the three monomers to CO2 and H2O.

Aquatic plastisphere: Interactions between plastics and biofilms

Because of the high production rates, low recycling rates, and poor waste management of plastics, an increasing amount of plastic is entering the aquatic environment, where it can provide new ecological niches for microbial communities and form a so-called plastisphere. Recent studies have focused on the one-way impact of plastic substrata or biofilm communities. However, our understanding of the two-way interactions between plastics and biofilms is still limited. This review first summarizes the formation process and the co-occurrence network analysis of the aquatic plastisphere to comprehensively illustrate the succession pattern of biofilm communities and the potential consistency between keystone taxa and specific environmental behavior of the plastisphere. Furthermore, this review sheds light on mutual interactions between plastics and biofilms. Plastic properties, environmental conditions, and colonization time affect biofilm development. Meanwhile, the biofilm communities, in turn, influence the environmental behaviors of plastics, including transport, contaminant accumulation, and especially the fragmentation and degradation of plastics. Based on a systematic literature review and cross-referencing from these disciplines, the current research focus, and future challenges in exploring aquatic plastisphere development and biofilm-plastic interactions are proposed.

Preliminary identification of soil fungi for the degradation of polyurethane film

Polyurethane (PU) is a versatile plastic that boasts high environmental resistance. The biodegradation of PU has become a hot topic of research aimed at finding ways to potentially solve PU pollutants. Identifying microorganisms capable of efficiently degrading PU plastics is pivotal for the development of a green recycling process for PU. This study aimed to isolate and characterize PU-degrading fungi from the soil of a waste transfer station in Luoyang, China. We isolated four different fungal strains from the soil. Among the isolates, the P2072 and P2073 strains were identified as Rhizopus oryzae (internal transcribed spacer identity, 99.66%) and Alternaria alternata (internal transcribed spacer identity, 99.81%), respectively, through microscopic, morphologic, as well as 18S rRNA sequencing. The degradation ability of strains P2072 and P2073 was analyzed through measurement of weight loss, and they exhibited a degradation rate of 2.7% and 3.3%, respectively, for the PU films after 2 months' growth in mineral salt medium (MSM) with PU films as the sole carbon source. In addition, the P2073 strain exhibited protease activity in the presence of PU. To our knowledge, R. oryzae has never been reported as a PU-degrading fungus. This study provides a new perspective on the biodegradation of PU.

Solving the plastic dilemma: the fungal and bacterial biodegradability of polyurethanes

Polyurethane (PU) is a plastic polymer which, due to its various desirable characteristics, has been applied extensively in domestic, industrial and medical fields for the past 50 years. Subsequently, an increasing amount of PU waste is generated annually. PU, like many other plastics, is highly resistant to degradation and is a substantial threat to our environment. Currently PU wastes are handled through conventional disposal techniques such as landfill, incineration and recycling. Due to the many drawbacks of these techniques, a 'greener' alternative is necessary, and biodegradation appears to be the most promising option. Biodegradation has the potential to completely mineralise plastic waste or recover the input materials and better enable recycling. There are hurdles to overcome however, primarily the efficiency of the process and the presence of waste plastics with inherently different chemical structures. This review will focus on polyurethanes and their biodegradation, outlining the difficulty of degrading different versions of the same material and strategies for achieving more efficient biodegradation.

Microbial engineering strategies for synthetic microplastics clean up: A review on recent approaches

Microplastics are the small fragments of the plastic molecules which find their applications in various routine products such as beauty products. Later, it was realized that it has several toxic effects on marine and terrestrial organisms. This review is an approach in understanding the microplastics, their origin, dispersal in the aquatic system, their biodegradation and factors affecting biodegradation. In addition, the paper discusses the major engineering approaches applied in microbial biotechnology. Specifically, it reviews microbial genetic engineering, such as PET-ase engineering, MHET-ase engineering, and immobilization approaches. Moreover, the major challenges associated with the plastic removal are presented by evaluating the recent reports available.

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

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

Adsorptive behavior of micro(nano)plastics through biochar: Co-existence, consequences, and challenges in contaminated ecosystems

The abundance of micro(nano)plastics in natural ecosystems is a crucial global challenge, as these small-sized plastic particles originate from land-based and marine-based activities and are widely present in marine, freshwater, and terrestrial ecosystems. Micro(nano)plastics can significantly be reduced through various methods, such as biological, chemical, and physical techniques. Biochar is a low-cost adsorbent and is considered an efficient material and its application is ecologically effective carbon-negative for remediation of organic and inorganic pollutants. Therefore, this review critically discusses the fate and transport of micro(nano)plastics and their interactions with different biochar in aqueous and column porous media. This review outlines the implications of biochar with the co-existence of micro(nano)plastics in efforts to understand their coupled effects on soil physicochemical properties, microbial communities, and plant growth, along with the removal of heavy metals and other toxic contaminants. In batch experiments, biochar synthesized from various biomasses such as corn straw, hardwood, pine and spruce bark, corncob, and Prosopis juliflora had shown high level of removal efficiency (>90 %) for microplastic adsorption under varying environmental conditions viz., pH, temperature, ionic strength, particle size, and dose due to chemical bonding and electrostatic attractions. Increased temperature of the aqueous solutions encouraged higher adsorption, while higher pH and dissolved organic matter and nutrients may show decreased adsorption capacities for micro(nano)plastics using biochar. Compared to other available physical, chemical, and biological methods, biochar-amended sand filters in column experiments have been very efficient in removing micro(nano)plastics. In saturated column porous media, various microplastics could be inhibited using biochar due to decreased electrostatic repulsion, steric hindrance, and competitive sorption due to humic acid, ionic strength, and cations. Finally, this review provides in-depth insights on further investigations and recommendations for overall micro(nano)plastics removal using biochar-based materials.

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

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

Myco-degradation of microplastics: an account of identified pathways and analytical methods for their determination

Microplastics (MPs) have sparked widespread concern due to their non-degradable and persistent nature in ecosystems. Long-term exposure to microplastics can cause chronic toxicity, including impaired reproduction and malnutrition, threatening biota and humans. Microplastics can also cause ingestion, choking, and entanglement in aquatic populations. Thus, it is crucial to establish remarkably effective approaches to diminish MPs from the environment. In this regard, using fungi for microplastic degradation is beneficial owing to its diverse nature and effective enzymatic system. Extracellular and intracellular enzymes in fungi degrade the plastic polymers into monomers and produce carbon dioxide and water under aerobic conditions whereas methane under anaerobic conditions. Further, fungi also secrete hydrophobins (surface proteins) which serve as a crucial aid in the bioremediation process by promoting substrate mobility and bioavailability. Therefore, the present review provides insight into the mechanism and general pathway of fungal-mediated microplastic degradation. Additionally, analytical techniques for the monitoring of MPs degradation along with the roadblocks and future perspectives have also been discussed. However, more research is required to fully perceive the underlying process of microplastic biodegradation in the environment using fungus, to establish an effective and sustainable practice for its management.

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

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

Microplastic pollution in fragile coastal ecosystems with special reference to the X-Press Pearl maritime disaster, southeast coast of India

Microplastics (MPs) are a global environmental concern and pose a serious threat to marine ecosystems. This study aimed to determine the abundance and distribution of MPs in beach sediments (12 beaches), marine biota (6 beaches) and the influence of microbes on MPs degradation in eco-sensitive Palk Bay and Gulf of Mannar coast. The mean MP abundance 65.4 ± 39.8 particles/m² in beach sediments; 0.19 ± 1.3 particles/individual fish and 0.22 ± 0.11 particles g^-1 wet weight in barnacles. Polyethylene fragments (33.4%) and fibres (48%) were the most abundant MPs identified in sediments and finfish, respectively. Histopathological examination of fish has revealed health consequences such as respiratory system damage, epithelial degradation and enterocyte vacuolization. In addition, eight bacterial and seventeen fungal strains were isolated from the beached MPs. The results also indicated weathering of MPs due to microbial interactions. Model simulations helped in tracking the fate and transboundary landfall of spilled MPs across the Indian Ocean coastline after the X-Press Pearl disaster. Due to regional circulations induced by the monsoonal wind fields, a potential dispersal of pellets has occurred along the coast of Sri Lanka, but no landfall and ecological damage are predicted along the coast of India.

Lessons From Insect Fungiculture: From Microbial Ecology to Plastics Degradation

Anthropogenic activities have extensively transformed the biosphere by extracting and disposing of resources, crossing boundaries of planetary threat while causing a global crisis of waste overload. Despite fundamental differences regarding structure and recalcitrance, lignocellulose and plastic polymers share physical-chemical properties to some extent, that include carbon skeletons with similar chemical bonds, hydrophobic properties, amorphous and crystalline regions. Microbial strategies for metabolizing recalcitrant polymers have been selected and optimized through evolution, thus understanding natural processes for lignocellulose modification could aid the challenge of dealing with the recalcitrant human-made polymers spread worldwide. We propose to look for inspiration in the charismatic fungal-growing insects to understand multipartite degradation of plant polymers. Independently evolved in diverse insect lineages, fungiculture embraces passive or active fungal cultivation for food, protection, and structural purposes. We consider there is much to learn from these symbioses, in special from the community-level degradation of recalcitrant biomass and defensive metabolites. Microbial plant-degrading systems at the core of insect fungicultures could be promising candidates for degrading synthetic plastics. Here, we first compare the degradation of lignocellulose and plastic polymers, with emphasis in the overlapping microbial players and enzymatic activities between these processes. Second, we review the literature on diverse insect fungiculture systems, focusing on features that, while supporting insects' ecology and evolution, could also be applied in biotechnological processes. Third, taking lessons from these microbial communities, we suggest multidisciplinary strategies to identify microbial degraders, degrading enzymes and pathways, as well as microbial interactions and interdependencies. Spanning from multiomics to spectroscopy, microscopy, stable isotopes probing, enrichment microcosmos, and synthetic communities, these strategies would allow for a systemic understanding of the fungiculture ecology, driving to application possibilities. Detailing how the metabolic landscape is entangled to achieve ecological success could inspire sustainable efforts for mitigating the current environmental crisis.

Biodegradation of plastics for sustainable environment

Plastics are a kind of utility product that has become part and parcel of one's life. Their continuous usage, accumulation, and contamination of soil and water pose a severe threat to the biotic and abiotic components of the environment. It not only increases the carbon footprints but also contributes to global warming. This calls for an urgent need to develop novel strategies for the efficient degradation of plastics. The microbial strains equipped with the potential of degrading plastic materials, which can further be converted into usable products, are blessings for the ecosystem. This review comprehensively summarizes the microbial technologies to degrade different plastic types, such as polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), and polyurethane (PU). The study also describes the utilization of degraded plastic material as feedstock for its conversion into high-value chemicals.

Feeding preference of insect larvae to waste electrical and electronic equipment plastics

Waste electrical and electronic equipment (WEEE) plastics not only pollute the environment, but are challenging to treat in an environmentally friendly manner. Biodegradation by insect larvae is potentially an eco-friendly method to treat WEEE plastics, but information about the feeding preference of insect larvae to WEEE plastics is lacking. In this study, a total of nine WEEE and pristine plastics were chosen to feed larvae of the following two insect species, i.e. Galleria mellonella and Tenebrio molitor. G. mellonella larvae significantly favor corresponding pristine plastics compared to two types of WEEE plastics, waste rigid polyurethane (RPU) and waste polystyrene (PS). One possible explanation is the increased chlorine or metals in the WEEE plastics measured using X-ray fluorescence spectrometer analysis. Scanning electron microscopy and Fourier transform infrared spectroscopy show that the destruction of physical structures and changes in surface functional groups were found in the two types of WEEE plastics in the larval frass, implying that the larvae partly biodegraded the plastics. Meanwhile, the powdered waste high impact polystyrene plastics (WHIPS) were ingested, but not the lumpy ones, indicating that the consumption by G. mellonella larvae is improved by the WHIPS physical modification. In addition, G. mellonella larvae presented the following decreasing preference for pristine plastics under individual-plastic-fed mode: RPU > phenol-formaldehyde resin > polyethylene (PE) > polypropylene > PS ≈ polyvinyl chloride; this is possibly due to differences in physical properties and chemical structures of the plastics; feeding preference of the larvae under multiple-plastics-fed mode is relatively consistent to that under individual-plastic-fed mode. Interestingly, the consumption by G. mellonella larvae of PE is higher than that of PS, while T. molitor larvae showed the opposite trend, implying that insect larvae have different plastics preference. The findings provide insights into biodegradation of WEEE plastics by insect larvae.

A review on marine plastisphere: biodiversity, formation, and role in degradation

The pollution of plastic waste has become an increasingly serious environmental crisis. Recently, plastic has been detected in various kinds of environments, even in human tissues, which is an increasing threat to the ecosystems and humans. In the ocean, the plastic waste is eventually fragmentized into microplastics (MPs) under the disruption of physical and chemical processes. MPs are colonized by microbial communities such as fungi, diatoms, and bacteria, which form biofilms on the surface of the plastic called “plastisphere”. In this review, we summarize the studies related to microorganisms in the plastisphere in recent years and describe the microbial species in the plastisphere, mainly including bacteria, fungi, and autotrophs. Secondly, we explore the interactions between MPs and the plastisphere. The depth of MPs in the ocean and the nutrients in the surrounding seawater can have a great impact on the community structure of microorganisms in the plastisphere. Finally, we discuss the types of MP-degrading bacteria in the ocean, and use the “seed bank” theory to speculate on the potential sources of MP-degrading microorganisms. Challenges and future research prospects are also discussed.

The metabolic potential of plastics as biotechnological carbon sources - Review and targets for the future

The plastic crisis requires drastic measures, especially for the plastics' end-of-life. Mixed plastic fractions are currently difficult to recycle, but microbial metabolism might open new pathways. With new technologies for degradation of plastics to oligo- and monomers, these carbon sources can be used in biotechnology for the upcycling of plastic waste to valuable products, such as bioplastics and biosurfactants. We briefly summarize well-known monomer degradation pathways and computed their theoretical yields for industrially interesting products. With this information in hand, we calculated replacement scenarios of existing fossil-based synthesis routes for the same products. Thereby, we highlight fossil-based products for which plastic monomers might be attractive alternative carbon sources. Notably, not the highest yield of product on substrate of the biochemical route, but rather the (in-)efficiency of the petrochemical routes (i.e., carbon, energy use) determines the potential of biochemical plastic upcycling. Our results might serve as a guide for future metabolic engineering efforts towards a sustainable plastic economy.

Green Recycling Process for Polyurethane Foams by a Chem-Biotech Approach

Polyurethanes (PUs) are highly resistant materials used for building insulation or automotive seats. The polyurethane end-of-life issue must be addressed by the development of efficient recycling techniques. Since conventional recycling processes are not suitable for thermosets, waste management of PU foam is particularly questioning. By coupling biological and chemical processes, this study aimed at developing a green recycling pathway for PU foam using enzymes for depolymerization. For instance, enzymatic degradation of a PU foam synthesized with polycaprolactone and toluene diisocyanate led to a weight loss of 25 % after 24 h of incubation. The corresponding degradation products were recovered and identified as 6-hydroxycaproic acid and a short acid-terminated diurethane. An organometallic-catalyzed synthesis of second-generation polymers from these building blocks was carried out. A polymer with a high average molar mass of 74000 (M_w ) was obtained by mixing 50 % of recycled building blocks and 50 % of neat 6-hydroxycaproic acid. A poly(ester urethane) was synthesized without the use of toxic and decried polyisocyanates. It is the first time that a study offers the vision of a recycling loop starting from PU wastes and finishing with a second-generation polymer in a full circular approach.

Microplastic contaminants in the aqueous environment, fate, toxicity consequences, and remediation strategies

Microplastic is a fragmented plastic part that emerges as a potential marine and terrestrial contaminant. The microplastic wastes in marine and soil environments cause severe problems in living systems. Microplastic wastes have been linked to various health problems, including reproductive harm and obesity, plus issues such as organ problems and developmental delays in children. Recycling plastic/microplastics from the environment is very low, so remediating these polymers after their utilization is of paramount concern. The microplastic causes severe toxic effects and contaminates the environment. Microplastic affects marine life, microorganism in soil, soil enzymes, plants system, and physicochemical properties. Ecotoxicology of the microplastic raised many questions about its use and development from the environment. Various physicochemical and microbial technologies have been developed for their remediation from the environment. The microplastic effects are linked with its concentration, size, and shape in contaminated environments. Microplastic is able to sorb the inorganic and organic contaminants and affect their fate into the contaminated sites. Microbial technology is considered safer for the remediation of the microplastics via its unique metabolic machinery. Bioplastic is regarded as safer and eco-friendly as compared to plastics. The review article explored an in-depth understanding of the microplastic, its fate, toxicity to the environment, and robust remediation strategies.

Starch-based isocyanate- and non-isocyanate polyurethane hybrids: A review on synthesis, performance and biodegradation

The challenges related to the persistence of plastics in natural ecosystems fostered strong interest in developing biodegradable bioplastics. Among natural biopolymers, starch gained both academic and industrial interest owing to its impressive physicochemical properties. The use of starch in production of polyurethane (PU) composites not only yields PUs with outstanding mechanical properties but also makes the final PU products biodegradable. The hydrophilic nature of starch limits its dispersion in hydrophobic PU polymers, although it is a significant benefit in creating starch-embedded non-isocyanate polyurethane (NIPU) composites. We present a comprehensive overview to highlight important strategies that are used to improve the compatibility of starch with various PU matrices. This review also gives an overview of the recent advances in the synthesis of starch-NIPU hybrids. Moreover, we aim to deliver critical insight into strategies that boost the biodegradation characteristics of PUs along with a discussion on various methods to assess their biodegradation.

From lignocellulose to plastics: Knowledge transfer on the degradation approaches by fungi

In this review, we argue that there is much to be learned by transferring knowledge from research on lignocellulose degradation to that on plastic. Plastic waste accumulates in the environment to hazardous levels, because it is inherently recalcitrant to biological degradation. Plants evolved lignocellulose to be resistant to degradation, but with time, fungi became capable of utilising it for their nutrition. Examples of how fungal strategies to degrade lignocellulose could be insightful for plastic degradation include how fungi overcome the hydrophobicity of lignin (e.g. production of hydrophobins) and crystallinity of cellulose (e.g. oxidative approaches). In parallel, knowledge of the methods for understanding lignocellulose degradation could be insightful such as advanced microscopy, genomic and post-genomic approaches (e.g. gene expression analysis). The known limitations of biological lignocellulose degradation, such as the necessity for physiochemical pretreatments for biofuel production, can be predictive of potential restrictions of biological plastic degradation. Taking lessons from lignocellulose degradation for plastic degradation is also important for biosafety as engineered plastic-degrading fungi could also have increased plant biomass degrading capabilities. Even though plastics are significantly different from lignocellulose because they lack hydrolysable C-C or C-O bonds and therefore have higher recalcitrance, there are apparent similarities, e.g. both types of compounds are mixtures of hydrophobic polymers with amorphous and crystalline regions, and both require hydrolases and oxidoreductases for their degradation. Thus, many lessons could be learned from fungal lignocellulose degradation.

Fungi and biochar applications in bioremediation of organic micropollutants from aquatic media

The conventional wastewater treatment system such as bacteria, is not able to remove recalcitrant micropollutants effectively. While, fungi have shown high capacity in degradation of recalcitrant compounds. Biochar, on the other hand, has gained attention in water and wastewater treatment as a low cost and sustainable adsorbent. This paper aims to review the recent applications of three major fungal divisions including Basidiomycota, Ascomycota, and Mucoromycotina, in organic micropollutants removal from wastewater. Moreover, it presents an insight into fungal bioreactors, fungal biofilm and immobilization system. Biochar adsorption capacities for organic micropollutants removal under different operating conditions are summarized. Finally, few recommendations for further research are established in the context of the combination of fungal biofilm with the technologies relying on the adsorption by porous carbonaceous materials.

Isolation of a soil bacterium for remediation of polyurethane and low-density polyethylene: a promising tool towards sustainable cleanup of the environment

A soil bacterium, designated strain AKS31, was isolated on the plastic polyurethane (PUR) and based on the molecular and biochemical analysis was tentatively assigned to the genus Pseudomonas. Preliminary studies suggested that strain AKS31 had the capability of biodegrading polyurethane (PUR) and low-density polyethylene (LDPE). This observation was confirmed by the analysis of the biodegradation products. The hydrolyzed products of PUR analyzed sequentially by High-Performance Liquid Chromatography (HPLC) and Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) showed the presence of diethylene glycol suggesting the presence of an esterase. A gene that could be involved in producing an esterase-like activity (PURase gene) was identified after the amplification and sequencing of a PCR product. Fourier Transformed Infrared (FTIR) spectrophotometric analysis of AKS31-treated LDPE film revealed the incorporation of hydroxyl groups suggesting the involvement of a hydroxylase in the degradation of LDPE. It is established that plastics form microplastics and microbeads in soils which negatively impact the health of living organisms and there have been concentrated research efforts to remediate this problem. Microcosm studies revealed that when strain AKS31 was bioaugmented with soil both the polymers were degraded during which time the heterotrophic plate counts, soil respiration and soil organic carbon content increased but this was not the case with the control nonbioaugmented microcosm. The results demonstrate that the strain AKS31 may have the potential in biodegradation of PUR and LPDE present as plastic microbeads and thereby improving soil health. Further studies in this direction are warranted.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-020-02592-9.

Polyurethane Recycling and Disposal: Methods and Prospects

Growing water and land pollution, the possibility of exhaustion of raw materials and resistance of plastics to physical and chemical factors results in increasing importance of synthetic polymers waste recycling, recovery and environmentally friendly ways of disposal. Polyurethanes (PU) are a family of versatile synthetic polymers with highly diverse applications. They are class of polymers derived from the condensation of polyisocyanates and polyalcohols. This paper reports the latest developments in the field of polyurethane disposal, recycling and recovery. Various methods tested and applied in recent years have proven that the processing of PU waste can be economically and ecologically beneficial. At the moment mechanical recycling and glycolysis are the most important ones. Polyurethanes' biological degradation is highly promising for both post-consumer and postproduction waste. It can also be applied in bioremediation of water and soil contaminated with polyurethanes. Another possibility for biological methods is the synthesis of PU materials sensitive to biological degradation. In conclusion, a high diversity of polyurethane waste types and derivation results in demand for a wide range of methods of processing. Furthermore, already existing ones appear to be enough to state that the elimination of not reprocessed polyurethane waste in the future is possible.

Microbial Degradation and Valorization of Plastic Wastes

A growing accumulation of plastic wastes has become a severe environmental and social issue. It is urgent to develop innovative approaches for the disposal of plastic wastes. In recent years, reports on biodegradation of synthetic plastics by microorganisms or enzymes have sprung up, and these offer a possibility to develop biological treatment technology for plastic wastes. In this review, we have comprehensively summarized the microorganisms and enzymes that are able to degrade a variety of generally used synthetic plastics, such as polyethylene (PE), polystyrene (PS), polypropylene (PP), polyvinyl chloride (PVC), polyurethane (PUR), and polyethylene terephthalate (PET). In addition, we have highlighted the microbial metabolic pathways for plastic depolymerization products and the current attempts toward utilization of such products as feedstocks for microbial production of chemicals with high value. Taken together, these findings will contribute to building a conception of bio-upcycling plastic wastes by connecting the biodegradation of plastic wastes to the biosynthesis of valuable chemicals in microorganisms. Last, but not least, we have discussed the challenges toward microbial degradation and valorization of plastic wastes.

Unraveling 1,4-Butanediol Metabolism in Pseudomonas putida KT2440

Plastics, in all forms, are a ubiquitous cornerstone of modern civilization. Although humanity undoubtedly benefits from the versatility and durability of plastics, they also cause a tremendous burden for the environment. Bio-upcycling is a promising approach to reduce this burden, especially for polymers that are currently not amenable to mechanical recycling. Wildtype P. putida KT2440 is able to grow on 1,4-butanediol as sole carbon source, but only very slowly. Adaptive laboratory evolution (ALE) led to the isolation of several strains with significantly enhanced growth rate and yield. Genome re-sequencing and proteomic analysis were applied to characterize the genomic and metabolic basis of efficient 1,4-butanediol metabolism. Initially, 1,4-butanediol is oxidized to 4-hydroxybutyrate, in which the highly expressed dehydrogenase enzymes encoded within the PP_2674-2680 ped gene cluster play an essential role. The resulting 4-hydroxybutyrate can be metabolized through three possible pathways: (i) oxidation to succinate, (ii) CoA activation and subsequent oxidation to succinyl-CoA, and (iii) beta oxidation to glycolyl-CoA and acetyl-CoA. The evolved strains were both mutated in a transcriptional regulator (PP_2046) of an operon encoding both beta-oxidation related genes and an alcohol dehydrogenase. When either the regulator or the alcohol dehydrogenase is deleted, no 1,4-butanediol uptake or growth could be detected. Using a reverse engineering approach, PP_2046 was replaced by a synthetic promotor (14g) to overexpress the downstream operon (PP_2047-2051), thereby enhancing growth on 1,4-butanediol. This work provides a deeper understanding of microbial 1,4-butanediol metabolism in P. putida, which is also expandable to other aliphatic alpha-omega diols. It enables the more efficient metabolism of these diols, thereby enabling biotechnological valorization of plastic monomers in a bio-upcycling approach.

Comparative study on the pyrolysis kinetics of polyurethane foam from waste refrigerators

Thermal treatment offers advantages of significant volume reduction and energy recovery for the polyurethane foam from waste refrigerators. In this work, the pyrolysis kinetics of polyurethane foam was investigated using the model-fitting, model-free and distributed activation energy model methods. The thermogravimetric analysis indicated that the polyurethane foam decomposition could be divided into three stages with temperatures of 38°C-400°C, 400°C-550°C and 550°C-1000°C. Peak temperatures for the major decomposition stage (<400°C) were determined as 324°C, 342°C and 344°C for heating rates of 5, 15 and 25 K min^-1, respectively. The activation energy (E_α) from the Friedman, Flynn-Wall-Ozawa and Tang methods increased with degree of conversion (α) in the range of 0.05 to 0.5. The coefficients from the Flynn-Wall-Ozawa method were larger and the resulted Eα values fell into the range of 163.980-328.190 kJ mol^-1 with an average of 206.099 kJ mol^-1. For the Coats-Redfern method, the diffusion models offered higher coefficients, but the E values were smaller than that from the Flynn-Wall-Ozawa method. The Eα values derived from the distributed activation energy model method were determined as 163.536-334.231 kJ mol^-1, with an average of 206.799 kJ mol^-1. The peak of activation energy distribution curve was located at 205.929 kJ mol^-1, consistent with the thermogravimetric results. The Flynn-Wall-Ozawa and distributed activation energy model methods were more reliable for describing the polyurethane foam pyrolysis process.

Degradation of Recalcitrant Polyurethane and Xenobiotic Additives by a Selected Landfill Microbial Community and Its Biodegradative Potential Revealed by Proximity Ligation-Based Metagenomic Analysis

Polyurethanes (PU) are the sixth most produced plastics with around 18-million tons in 2016, but since they are not recyclable, they are burned or landfilled, generating damage to human health and ecosystems. To elucidate the mechanisms that landfill microbial communities perform to attack recalcitrant PU plastics, we studied the degradative activity of a mixed microbial culture, selected from a municipal landfill by its capability to grow in a water PU dispersion (WPUD) as the only carbon source, as a model for the BP8 landfill microbial community. The WPUD contains a polyether-polyurethane-acrylate (PE-PU-A) copolymer and xenobiotic additives (N-methylpyrrolidone, isopropanol and glycol ethers). To identify the changes that the BP8 microbial community culture generates to the WPUD additives and copolymer, we performed chemical and physical analyses of the biodegradation process during 25 days of cultivation. These analyses included Nuclear magnetic resonance, Fourier transform infrared spectroscopy, Thermogravimetry, Differential scanning calorimetry, Gel permeation chromatography, and Gas chromatography coupled to mass spectrometry techniques. Moreover, for revealing the BP8 community structure and its genetically encoded potential biodegradative capability we also performed a proximity ligation-based metagenomic analysis. The additives present in the WPUD were consumed early whereas the copolymer was cleaved throughout the 25-days of incubation. The analysis of the biodegradation process and the identified biodegradation products showed that BP8 cleaves esters, C-C, and the recalcitrant aromatic urethanes and ether groups by hydrolytic and oxidative mechanisms, both in the soft and the hard segments of the copolymer. The proximity ligation-based metagenomic analysis allowed the reconstruction of five genomes, three of them from novel species. In the metagenome, genes encoding known enzymes, and putative enzymes and metabolic pathways accounting for the biodegradative activity of the BP8 community over the additives and PE-PU-A copolymer were identified. This is the first study revealing the genetically encoded potential biodegradative capability of a microbial community selected from a landfill, that thrives within a WPUD system and shows potential for bioremediation of polyurethane- and xenobiotic additives-contamitated sites.

Microbial Ecotoxicology of Marine Plastic Debris: A Review on Colonization and Biodegradation by the "Plastisphere"

Over the last decades, it has become clear that plastic pollution presents a global societal and environmental challenge given its increasing presence in the oceans. A growing literature has focused on the microbial life growing on the surfaces of these pollutants called the "plastisphere," but the general concepts of microbial ecotoxicology have only rarely been integrated. Microbial ecotoxicology deals with (i) the impact of pollutants on microbial communities and inversely (ii) how much microbes can influence their biodegradation. The goal of this review is to enlighten the growing literature of the last 15 years on microbial ecotoxicology related to plastic pollution in the oceans. First, we focus on the impact of plastic on marine microbial life and on the various functions it ensures in the ecosystems. In this part, we also discuss the driving factors influencing biofilm development on plastic surfaces and the potential role of plastic debris as vector for dispersal of harmful pathogen species. Second, we give a critical view of the extent to which marine microorganisms can participate in the decomposition of plastic in the oceans and of the relevance of current standard tests for plastic biodegradability at sea. We highlight some examples of metabolic pathways of polymer biodegradation. We conclude with several questions regarding gaps in current knowledge of plastic biodegradation by marine microorganisms and the identification of possible directions for future research.