Current Advances in Biodegradation of Polyolefins

Biodegradation of polypropylene by Bacillus cereus PP-5 isolated from waste landfill

Waste polypropylene (PP) plastic has caused serious environmental pollution, and biological methods provide a feasible strategy to deal with the environmental pollution and resource waste caused by waste plastics. In this study, we investigated the physicochemical and structural changes of PP plastic degraded by Bacillus cereus PP-5, which was isolated from a waste landfill. After 30-day incubation with PP-5, structural properties of PP powder were analyzed using high-temperature gel permeation chromatography, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and differential scanning calorimetry. We found that PP-5 colonized the plastic surface through biofilm, and the bio-deterioration with visible cracks was also observed from the PP surfaces, the carbonyl index of PP-5-treated PP powder was identified as 0.536. Meantime, the weight-average molecular weight and thermal stability of PP decreased, while melting enthalpy and average crystallinity increased after PP-5treatment. Moreover, oxidative cleavage of carbon-carbon bonds of PP was observed from the appearance of quaternary carbon and elevated CO groups of PP-5-treated PP plastics, suggesting microbial oxidation. Our findings elucidate a potential bio-oxidizing mechanism for microbial-driven PP degradation, and also highlight the application prospects in bio-recycling systems, particularly for managing plastic waste in landfills or marine environments.

Biocatalytic recycling of plastics: facts and fiction

Due to the lack of efficient end-of-life management, the mass production of plastics has resulted in serious environmental problems. Sustainable biological approaches using enzymes to degrade and recycle plastic waste are emerging as a complement to conventional methods to promote a circular economy of plastics. Only a fraction of the plastic waste generated is currently suitable for biocatalytic deconstruction and the development of economically and environmentally competitive processes is still pending. Inconsistent claims about new plastic-degrading enzymes reveal a need for robust and standardized analysis methods to ensure reproducible results and a realistic evaluation of their potential. This paper critically reviews enzymatic synthetic polymer degradation and its recycling challenges.

Polyethylene biodegradation: A multifaceted approach

The inert nature, durability, low cost, and wide applicability of plastics have made this material indispensable in our lives. This dependency has resulted in a growing number of plastic items, of which a substantial part is disposed in landfills or dumped in the environment, thereby affecting terrestrial and aquatic ecosystems. Among plastic materials, polyolefins are the most abundant and are impervious to biodegradation, owing to the presence of strong CC and CH bonds. Nevertheless, naturally occurring biodegradation of polyolefins, albeit limited, has been reported. This observation has sparked research on microbial polyolefin degradation. More efficient and targeted versions of this process could be developed also in the laboratory by designing synthetic microbial consortia with engineered enzymes. In this review, we discuss strategies for the development of such microbial consortia and identification of novel polyolefin-degrading microorganisms, as well as the engineering of polyethylene-oxidizing enzymes with greater catalytic efficacy. Finally, different techniques for the design of synthetic microbial consortia capable of successful polyolefin bioremediation will be outlined.

Marine microalgae - Mediated biodegradation of polystyrene microplastics: Insights from enzymatic and molecular docking studies

Biodegradation of microplastics (MPs) through microalgal strains would be of eco-friendly approach for significant pollution abatement. Polystyrene (PS) is a major contaminant in the marine environment; however studies on marine microalgal degradation of PS MPs have been very limited. In the present study, six marine microalgal strains viz. Picochlorum maculatum, Dunaliella salina, Amphora sp., Navicula sp., Synechocystis sp. and Limnospira indica were investigated for their ability to degrade PS MPs for the incubation period of 45 days. Results from weight reduction, ATR-FTIR, SEM, and molecular docking analysis confirmed that microalgae formed biofilms on PS MPs, causing structural changes, and laccase-driven enzymatic breakdown. A maximum weight loss of 23.2 ± 0.21% and a minimum of 11.3 ± 0.026% were caused by the colonized microalgae Synechocystis sp. and Amphora sp. respectively. The study indicated that a higher reduction rate was observed in the Synechocystis sp. Treated PS MPs with a rate of 0.0058 g/day and a lower half-life of 119.34 days. SEM analysis showed that microalgae caused pits, erosion, and damage to the PS film. ATR-FTIR confirmed the chemical modifications and proved biodegradation. Laccase enzyme activity was higher in Synechocystis sp., and molecular docking showed the laccase interaction with the derivatives of PS, elucidating the breakdown process. This study highlights the potential of microalgae for eco-friendly microplastic degradation and paves the way for future research on the by-products of this process. Exploring the ecological impact of by-products and optimizing scalable methods can further enhance the sustainability and practical applications of this promising solution.

Recent progresses and perspectives of polyethylene biodegradation by bacteria and fungi: A review

Plastics pollution has become a serious threat to the people and environment due to the mass production, unreasonable disposal and continuous pollution. Polyethylene (PE), one of the most utilized plastics all over the world, is considered as a highly recalcitrant environmental destruction problem on account of strong hydrophobicity and high molecular weight. Therefore, it is urgently necessary to seek economical and efficient treatment and disposal methods for PE. Considering microorganisms can use various carbon sources for anabolism, they are recognized to have great potential in the biodegradation of microplastics including PE. From this point of view, the present review concentrates on providing information regarding the current status of PE biodegradation microorganisms (bacteria and fungi), and the influencing factors such as PE characteristics, cellular surface hydrophobicity, physical treatments, chemicals addition, as well as environmental conditions for biodegradation are thoroughly discussed. Furthermore, the possible biodegradation mechanisms for PE involve the biofilm formation, biodeterioration, fragmentation, assimilation, and mineralization are elucidated in detail. Finally, the future research directions and application prospects of microbial degradation are prospected in this review. It is expected to provide reference and guidance for PE biodegradation and their potential applications in real contaminated sites.

The microplastic menace: a critical review of its impact on marine photoautotrophs and their environment

Seaweeds contribute to the energy input in marine communities and affect the chemical makeup, species composition, nutrient availability, pH, and seawater oxygen levels. However, the annual introduction of 28.5 million tons of plastic waste into oceans makes up 85% of marine litter, which is expected to grow fourfold in the next 25 years, causing a rise in concern for human health and the environment. Microplastics are small plastic particles of 1-5 mm that are either manufactured or formed due to the degradation of large plastic materials. This study analyzes the prevalence of microplastics in marine environments, their interaction with marine macro- and microalgae, environmental implications, genetic responses to microplastic exposure, and potential strategies for mitigating microplastic pollution. The leading causes identified were high plastic production rate (390 million tons annually), increased usage, inefficient waste management, meager recycling (9% is recycled), slow degradation (up to 1200 years), easy distribution via oceanic currents, and industrialization that has led to the accumulation of microplastics in the marine ecosystems. Therefore, it is recommended that the waste management system be strengthened, focusing on recycling, repurposing, reducing single-use plastics, and redirecting plastic waste away from water bodies. Developing reliable detection technologies, studying the long-term effects of microplastics in marine ecosystems, and collaborating with the public and private sectors may be encouraged. Further investigations on microplastic-seaweed interaction, the bioremediation potential of various species, and the involved molecular mechanisms may lead to new strategies for reducing microplastic loads in marine ecosystems.

A Simple Technique for Studying the Interaction of Polypropylene-Based Microplastics with Adherent Mammalian Cells Using a Holder

Microplastics pose a great challenge to human health and could prove to be the most dangerous environmental contaminant of the 21st century. The study presented here is an attempt at proposing a new methodology for studying the interaction of microplastics with adherent mammalian cells using aides. The disposable holders proposed here provide direct contact between microplastics (with a density lower than that of water) and cells in the course of culturing, which is necessary as we postulate the existence of an interaction. Using several microscopic methods (confocal fluorescence microscopy and scanning electron microscopy (SEM)), we have observed that this interaction causes a non-destructive penetration of the cell monolayer and adhesion of microplastics to the cell surface. The Caco-2 cells were used for the experiments. The said cells are the approximation of the digestive system, which, due to the presence of plastics in drinking water, is particularly vulnerable to direct interactions with these contaminants. Model microplastics were obtained by grinding pellets of chemically pure polypropylene. The imaging of cells in both space and on the surface was supplemented by an assay to determine the cell welfare in the studied microplastic-exposed models, which did not show the occurrence of apoptosis or necrosis after a 24 h exposure.

Design of Plastic Binding Lytic Polysaccharide Monooxygenases via Modular Engineering

The worldwide accumulation of plastic waste in the environment, along with its lifespan of hundreds of years, represents a serious threat to ecosystems. Enzymatic recycling of plastic waste offers a promising solution, but the high chemical inertness and hydrophobicity of plastics pose several challenges to enzymes. In nature, lytic polysaccharide monooxygenases (LPMOs) can act at the surface of recalcitrant biopolymers, taking advantage of their solvent-exposed active sites and appended carbohydrate-binding modules (CBMs). LPMOs can disrupt the densely packed chains of polysaccharides (e.g., cellulose) by the oxidation of C-H bonds. Given the similarities between these natural and artificial polymers, we aimed here at promoting plastic-binding properties to LPMOs, by swapping their CBM with three natural, surface-active accessory modules displaying different amphipathic properties. The polymer binding capacity of the resulting LPMO chimeras was assessed on a library of synthetic polymers, including polyester, polyamide, and polyolefin substrates. We demonstrated that the plastic binding properties of these engineered LPMOs are polymer-dependent and can be tuned by playing on the nature of the accessory module and reaction conditions. Remarkably, we gained full binding for some chimera LPMOs with striking results for polyhydroxyalkanoates (PHA). In the long term perspective of harnessing the unique copper chemistry of LPMOs to degrade plastics, we also provided the first evidence of LPMO-dependent modification of the PHA polymer, as supported by enzyme assays, gel permeation chromatography, and scanning electron microscopy. Altogether, our study provides the first roadmap for engineering plastic-binding ability in LPMOs, constituting a crucial first step on the evolutionary path toward efficient interfacial catalysis of plastic-active enzymes.

Metagenomic landscape of sediments of river Ganga reveals microbial diversity, potential plastic and xenobiotic degradation enzymes

The Ganga is the largest river in India, serves as a lifeline for agriculture, drinking water, and religious rites. However, it became highly polluted due to the influx of industrial wastes and untreated sewages, leading to the decline of aquatic biodiversity. This study investigated the microbial diversity and plastic-xenobiotic degrading enzymes of six sediment metagenomes of river Ganga at Prayagraj (RDG, TSG, SDG) and Devprayag (KRG, BNG, BRG). The water quality parameters, higher values of BOD (1.8-3.7 ppm), COD (23-29.2 ppm) and organic carbon (0.18-0.51%) were recorded at Prayagraj. Comparative analysis of microbial community structure between Prayagraj and Devprayag revealed significant differences between Bacteroidetes and Firmicutes, which emerging as the predominant bacterial phyla across six sediment samples. Notably, their prevalence was highest in the BRG samples. Furthermore, 25 OTUs at genus level were consistent across all six samples. Alpha diversity exhibited minimal variation among samples, while beta diversity indicated an inverse relationship between species richness and diversity. Co-occurrence network analysis established that genera from the same and different groups of phyla show positive co-relations with each other. Thirteen plastic degrading enzymes, including Laccase, Alkane-1 monooxygenase and Alkane monooxygenase, were identified from six sediment metagenomes of river Ganga, which can degrade non-biodegradable plastic viz. Polyethylene, Polystyrene and Low-density Polyethelene. Further, 18 xenobiotic degradation enzymes were identified for the degradation of Bisphenol, Xylene, Toluene, Polycyclic aromatic hydrocarbon, Styrene, Atrazene and Dioxin etc. This is the first report on the identification of non-biodegradable plastic degrading enzymes from sediment metagenomes of river Ganga, India. The findings of this study would help in pollution abatement and sustainable management of riverine ecosystem.

Elucidating polyethylene microplastic degradation mechanisms and metabolic pathways via iron-enhanced microbiota dynamics in marine sediments

The extensive use of plastics has given rise to microplastics, a novel environmental contaminant that has sparked considerable ecological and environmental concerns. Biodegradation offers a more environmentally friendly approach to eliminating microplastics, but their degradation by marine microbial communities has received little attention. In this study, we used iron-enhanced marine sediment to augment the natural bacterial community and facilitate the decomposition of polyethylene (PE) microplastics. The introduction of iron-enhanced sediment engendered an augmented bacterial biofilm formation on the surface of polyethylene (PE), thereby leading to a more pronounced degradation effect. This novel observation has been ascribed to the oxidative stress-induced generation of a variety of oxygenated functional groups, including hydroxyl (-OH), carbonyl (-CO), and ether (-C-O) moieties, within the microplastic substrate. The analysis of succession in the community structure of sediment bacteria during the degradation phase disclosed that Acinetobacter and Pseudomonas emerged as the principal bacterial players in PE degradation. These taxa were directly implicated in oxidative metabolic pathways facilitated by diverse oxidase enzymes under iron-facilitated conditions. The present study highlights bacterial community succession as a new pivotal factor influencing the complex biodegradation dynamics of polyethylene (PE) microplastics. This investigation also reveals, for the first time, a unique degradation pathway for PE microplastics orchestrated by the multifaceted marine sediment microbiota. These novel insights shed light on the unique functional capabilities and internal biochemical mechanisms employed by the marine sediment microbiota in effectively degrading polyethylene microplastics.

Designing biodegradable alternatives to commodity polymers

The development and widespread adoption of commodity polymers changed societal landscapes on a global scale. Without the everyday materials used in packaging, textiles, construction and medicine, our lives would be unrecognisable. Through decades of use, however, the environmental impact of waste plastics has become grimly apparent, leading to sustained pressure from environmentalists, consumers and scientists to deliver replacement materials. The need to reduce the environmental impact of commodity polymers is beyond question, yet the reality of replacing these ubiquitous materials with sustainable alternatives is complex. In this tutorial review, we will explore the concepts of sustainable design and biodegradability, as applied to the design of synthetic polymers intended for use at scale. We will provide an overview of the potential biodegradation pathways available to polymers in different environments, and highlight the importance of considering these pathways when designing new materials. We will identify gaps in our collective understanding of the production, use and fate of biodegradable polymers: from identifying appropriate feedstock materials, to considering changes needed to production and recycling practices, and to improving our understanding of the environmental fate of the materials we produce. We will discuss the current standard methods for the determination of biodegradability, where lengthy experimental timescales often frustrate the development of new materials, and highlight the need to develop better tools and models to assess the degradation rate of polymers in different environments.

Unique Raoultella species isolated from petroleum contaminated soil degrades polystyrene and polyethylene

Polyolefin plastics, such as polyethylene (PE) and polystyrene (PS), are the most widely used synthetic plastics in our daily life. However, the chemical structure of polyolefin plastics is composed of carbon-carbon (C-C) bonds, which is extremely stable and makes polyolefin plastics recalcitrant to degradation. The growing accumulation of plastic waste has caused serious environmental pollution and has become a global environmental concern. In this study, we isolated a unique Raoultella sp. DY2415 strain from petroleum-contaminated soil that can degrade PE and PS film. After 60 d of incubation with strain DY2415, the weight of the UV-irradiated PE (UVPE) film and PS film decreased by 8% and 2%, respectively. Apparent microbial colonization and holes on the surface of the films were observed by scanning electron microscopy (SEM). Furthermore, the Fourier transform infrared spectrometer (FTIR) results showed that new oxygen-containing functional groups such as -OH and -CO were introduced into the polyolefin molecular structure. Potential enzymes that may be involved in the biodegradation of polyolefin plastics were analyzed. These results demonstrate that Raoultella sp. DY2415 has the ability to degrade polyolefin plastics and provide a basis for further investigating the biodegradation mechanism.

An integrated metagenomic model to uncover the cooperation between microbes and magnetic biochar during microplastics degradation in paddy soil

The free radicals released from the advanced oxidation processes can enhance microplastics degradation, however, the existence of microbes acting synergistically in this process is still uncertain. In this study, magnetic biochar was used to initiate the advanced oxidation process in flooded soil. paddy soil was contaminated with polyethylene and polyvinyl chloride microplastics in a long-term incubation experiment, and subsequently subjected to bioremediation with biochar or magnetic biochar. After incubation, the total organic matter present in the samples containing polyvinyl chloride or polyethylene, and treated with magnetic biochar, significantly increased compared to the control. In the same samples there was an accumulation of "UVA humic" and "protein/phenol-like" substances. The integrated metagenomic investigation revealed that the relative abundance of some key genes involved in fatty acids degradation and in dehalogenation changed in different treatments. Results from genome-centric investigation suggest that a Nocardioides species can cooperate with magnetic biochar in the degradation of microplastics. In addition, a species assigned to the Rhizobium taxon was identified as a candidate in the dehalogenation and in the benzoate metabolism. Overall, our results suggest that cooperation between magnetic biochar and some microbial species involved in microplastic degradation is relevant in determining the fate of microplastics in soil.

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

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

Special Issue "Biodegradation and Environmental Microbiomes": Editorial

The Earth is unique, and we as human beings rely on its air, water, and land [...].

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

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

Construction of microbial consortia for microbial degradation of complex compounds

Increasingly complex synthetic environmental pollutants are prompting further research into bioremediation, which is one of the most economical and safest means of environmental restoration. From the current research, using microbial consortia to degrade complex compounds is more advantageous compared to using isolated bacteria, as the former is more adaptable and stable within the growth environment and can provide a suitable catalytic environment for each enzyme required by the biodegradation pathway. With the development of synthetic biology and gene-editing tools, artificial microbial consortia systems can be designed to be more efficient, stable, and robust, and they can be used to produce high-value-added products with their strong degradation ability. Furthermore, microbial consortia systems are shown to be promising in the degradation of complex compounds. In this review, the strategies for constructing stable and robust microbial consortia are discussed. The current advances in the degradation of complex compounds by microbial consortia are also classified and detailed, including plastics, petroleum, antibiotics, azo dyes, and some pollutants present in sewage. Thus, this paper aims to support some helps to those who focus on the degradation of complex compounds by microbial consortia.