Biodegradation of PET by the membrane-anchored PET esterase from the marine bacterium Rhodococcus pyridinivorans P23

Biodegradation of PET by Deep-Sea Pseudomonas chengduensis BC1815 through Utilization of Ethylene Glycol Monomer for Growth

An important environmental issue is the pollution caused by poly(ethylene terephthalate) (PET) and the emitted monomers terephthalic acid (TPA) and ethylene glycol (EG). The TPA biodegradation pathway has been well documented for the microbial biodegradation and assimilation of PET; however, the PET biodegradation process by marine microorganisms via the EG biodegradation pathway is less understood. Here, we demonstrate how the marine bacteria Pseudomonas chengduensis BC1815's membrane-anchored PET esterase (OF113_10420) breaks down PET. We also explain the characteristics of this enzyme and demonstrate that the strain assimilates PET via the EG biodegradation pathway. In addition to depolymerizing PET, PET esterase (OF113_10420) hydrolyzes BHET and MHET to generate EG more efficiently in alkaline circumstances. It has been discovered that P. chengduensis BC1815 cells exhibiting surface-displayed PET esterase (OF113_10420) have the potential to function as cell biocatalysts for the breakdown of PET. Additionally, we look into the microbial communities that have PET esterase linked to the EG biodegradation pathway, primarily those belonging to the phyla Proteobacteria and Actinobacteriota. Consequently, research on the microbial absorption and biodegradation of PET via the EG metabolism route increases our knowledge of the bioremediation of PET pollution in the marine environment and contributes to our understanding of the environmental destiny of PET pollutants in the marine environment.

Lack of functional polyester-biodegrading potential in marine versus terrestrial environments evidenced by an innovative airbrushing technique

Biodegradable plastics, primarily aliphatic polyesters, degrade to varying extents in different environments. However, the absence of easily implementable techniques for screening microbial biodegradation potential -coupled with the limitations of non-functional omics analyses- has restricted comparative studies across diverse polymer types and ecosystems. In this study, we optimized a novel airbrushing method that facilitates functional analyses by simplifying the preparation of polyester-coated plates for biodegradation screening. By repurposing an airbrush kit, polyester microparticles (MPs) could be evenly sprayed onto solid media, enabling rapid detection of extracellular depolymerizing activity via clearing zone halos. This technique was effective in screening both isolated microbial cultures and natural environmental samples, demonstrating its versatility. The method was successfully applied across multiple environments, ranking the biodegradability of six polyesters, from most to least biodegradable: poly[(R)-3-hydroxybutyrate] (PHB), polycaprolactone (PCL), poly(ethylene succinate) (PES), poly(butylene succinate) (PBS), poly(lactic acid) (PLA), and poly(butylene adipate-co-terephthalate) (PBAT). Most notably, it revealed a consistent 1,000-fold higher biodegradation potential in terrestrial compared to marine environments. This approach offers a valuable tool for isolating novel polyester-degrading microbes with significant biotechnological potential, paving the way for improved plastic waste management solutions.

Perspectives on the microorganisms with the potentials of PET-degradation

Polyethylene terephthalate (PET), a widely used synthetic polymer in daily life, has become a major source of post-consumer waste due to its complex molecular structure and resistance to natural degradation, which has posed a significant threat to the global ecological environment and human health. Current PET-processing methods include physical, chemical, and biological approaches, however each have their limitations. Given that numerous microbial strains exhibit a remarkable capacity to degrade plastic materials, microbial degradation of PET has emerged as a highly promising alternative. This approach not only offers the possibility of converting waste into valuable resources but also contributes to the advancement of a circular economy. Therefore in this review, it is mainly focused on the cutting-edge microbial technologies and the key role of specific microbial strains such as Ideonella sakaiensis 201-F6, which can efficiently degrade and assimilate PET. Particularly noteworthy are the catalytic enzymes related to the metabolism of PET, which have been emphasized as a sustainable and eco-friendly strategy for plastic recycling within the framework of a circular economy. Furthermore, the study also elucidates the innovative utilization of degraded plastic materials as feedstock for the production of high-value chemicals, highlighting a sustainable path forward in the management of plastic waste.

Producing multiple chemicals through biological upcycling of waste poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) waste is of low degradability in nature, and its mismanagement threatens numerous ecosystems. To combat the accumulation of waste PET in the biosphere, PET bio-upcycling, which integrates chemical pretreatment to produce PET-derived monomers with their microbial conversion into value-added products, has shown promise. The recently discovered Rhodococcus jostii RPET strain can metabolically degrade terephthalic acid (TPA) and ethylene glycol (EG) as sole carbon sources, and it has been developed into a microbial chassis for PET upcycling. However, the scarcity of synthetic biology tools, specifically designed for this non-model microbe, limits the development of a microbial cell factory for expanding the repertoire of bioproducts from postconsumer PET. Herein, we describe the development of potent genetic tools for RPET, including two inducible and titratable expression systems for tunable gene expression, along with serine integrase-based recombinational tools (SIRT) for genome editing. Using these tools, we systematically engineered the RPET strain to ultimately establish microbial supply chains for producing multiple chemicals, including lycopene, lipids, and succinate, from postconsumer PET waste bottles, achieving the highest titer of lycopene ever reported thus far in RPET [i.e., 22.6 mg/l of lycopene, ~10 000-fold higher than that of the wild-type (WT) strain]. This work highlights the great potential of plastic upcycling as a generalizable means of sustainable production of diverse chemicals.

Biochemical and molecular mechanisms of Rhodococcus rhodochrous IITR131 for polyethylene terephthalate degradation

AIMS

To isolate polyethylene terephthalate (PET)-degrading bacteria and elucidate the underlying mechanisms of PET biodegradation through biochemical and genome analysis.

METHODS AND RESULTS

Rhodococcus rhodochrous IITR131 was found to degrade PET. Strain IITR131 genome revealed metabolic versatility of the bacterium and had the ability to form biofilm on PET sheet, resulting in the cracks, abrasions, and degradation. IITR131 showed a reduction of 19.7%, exhibiting a half-life of 189.9 d of 0.1 mm PET film in 60 d and formed metabolites bis(2-hydroxyethyl) terephthalate (BHET), terephthalic acid (TPA), and benzoic acid (BA). The draft genome of 5.9 Mb of IITR131 revealed that this bacterium has plethora of genes such as terephthalate 1, 2 dioxygenase, carboxylesterase that together constituted a complete pathway for PET degradation. Moreover, strain IITR131 was found to have a variety of genes encoding for enzymes for the metabolism of several plastic polymers, xenobiotics including chloroalkanes, and polycyclic aromatic hydrocarbons.

CONCLUSIONS

Rhodococcus rhodochrous IITR131 demonstrated a significant potential in the biodegradation of PET. The comprehensive genomic and metabolic analyses further elucidated the molecular pathway involved in PET degradation, enhancing our understanding of the mechanisms underlying microbial PET biodegradation. These findings underscore the applicability of R. rhodochrous IITR131 in biotechnological approaches for mitigating plastic pollution.

The Emerging Threat of Micro- and Nanoplastics on the Maturation and Activity of Immune Cells

With the increasing use of plastics worldwide, the amount of plastic waste being discarded has also risen. This plastic waste undergoes physical and chemical processes, breaking down into smaller particles known as microplastics (MPs) or nanoplastics (NPs). Advances in technology have enhanced our ability to detect these smaller particles, and it has been confirmed that plastics can be found in marine organisms as well as within the human body. However, research on the effects of MPs or NPs on living organisms has only recently been started, and our understanding remains limited. Studies on the immunological impacts are still ongoing, revealing that MPs and NPs can differentially affect various immune cells based on the material, size, and shape of the plastic particles. In this review, we aim to provide a comprehensive understanding of the effects of MPs and NPs on the immune system. We will also explore the methods for plastic removal through physicochemical, microbial, or biological means.

Enhanced degradation of polyethylene terephthalate (PET) microplastics by an engineered Stenotrophomonas pavanii in the presence of biofilm

Polyethylene terephthalate (PET) microplastics pose significant environmental and human health risks due to their resistance to degradation and accumulation in ecosystems. In this study, we engineered Stenotrophomonas pavanii JWG-G1, a robust biofilm-forming bacterium, to overexpress the PET hydrolase (DuraPETase) for PET microplastics degradation at ambient temperature. Nine endogenous PET hydrolases were identified through genome sequencing of S. pavanii, and were successfully expressed in Escherichia coli BL21(DE3). Among them, hydrolase Est_B achieved 100% degradation of bis(2-hydroxyethyl) terephthalate (BHET) at an initial concentration of 0.23 mg/mL at 30 °C within 4 h, identifying it as a novel BHETase. However, the PET degradation performance of all endogenous PET hydrolases was inferior to that of DuraPETase. The engineered strain overexpressing DuraPETase demonstrated a significant enhancement in PET degradation, achieving a 38.04 μM total product release of high-crystallinity PET microplastics after 30 days at 30 °C. The degradation extent was greater than that of low biofilm-forming engineered strains, attributing to the aggregation of DuraPETase on the PET surface in the presence of biofilm. Additionally, this engineered strain also maintained PET degradation activity across various water environments and demonstrated effectiveness in degrading other polyester plastics. This is the first report demonstrating that an engineered strain of Stenotrophomonas species is capable of simultaneously secreting exogenous hydrolase and degrading polyester microplastics, representing a novel approach in the development of engineered bacteria with potential applications in bioreactor systems and environmental remediation.

Metagenomic analysis of soil from landfill site reveals a diverse microbial community involved in plastic degradation

In this study, we have investigated microbial communities structure and function using high throughput amplicon sequencing and whole metagenomic sequencing of DNA extracted from different depths of a plastic-laden landfill site. With diverse taxonomic groups inhabiting the plastic-rich soil, our study demonstrates the remarkable adaptability of microbes to use this new substrate as a carbon source. FTIR spectroscopic analysis of soil indicated degradation of plastic as perceived from the carbonyl index of 0.16, 0.72, and 0.44 at 0.6, 0.9 and 1.2 m depth, respectively. Similarly, water contact angles of 108.7 degree, 99.7 degree, 62.7 degree, and 77.8 degree of plastic pieces collected at 0.3, 0.6, 0.9, and 1.2 m depths respectively showed increased wettability and hydrophilicity of the plastic. Amplicon analysis of 16S and 18 S rRNA revealed a high abundance of several plastic-degrading bacterial groups, including Pseudomonas, Rhizobiales, Micrococcaceae, Chaetomium, Methylocaldum, Micromonosporaceae, Rhodothermaceae and fungi, including Trichoderma, Aspergillus, Candida at 0.9 m. The co-existence of specific microbial groups at different depths of landfill site indicates importance of bacterial and fungal interactions for plastic. Whole metagenome analysis of soil sample at 0.9 m depth revealed a high abundance of genes encoding enzymes that participate in the biodegradation of PVC, polyethylene, PET, and polyurethane. Curation of the pathways related to the degradation of these materials provided a blueprint for plastic biodegradation in this ecosystem. Altogether, our study has highlighted the importance of microbial cooperation for the biodegradation of pollutants. Our metagenome-based investigation supports the current perception that consortia of fungi-bacteria are preferable to axenic cultures for effective bioremediation of the environment.

Microplastics: The imperative influencer in blueprint of blue economy

The burgeoning issue of microplastic pollution in marine ecosystems has emerged as a significant concern, presently multifaceted difficulty to the sustainability and prosperity of the blue economy. This review examines the intricate link between microplastics (MPs) and the blue economy (BE), exploring how microplastics infiltrate marine environments, their persistence, and their impacts on economic activities reliant on healthy oceans in a global scenario. Diminished seafood quality and quantity, degraded coastal aesthetics affecting tourism revenues, and increased operational costs due to fouling and contamination are among the economic repercussions identified. Additionally, the review discusses the potential long-term consequences on human health and food security, emphasizing the urgency for proactive mitigation measures and policy interventions in the global scenario. The study highlights the interconnectedness of the blue economy and environmental health, prompting a comprehensive strategy to mitigate microplastic pollution. It calls for collaborative efforts among stakeholders, including policymakers, industries, academia, and civil society, to develop innovative strategies for combating microplastic pollution and promoting sustainable blue economic practices. In conclusion, the review stresses the pressing need for concerted action to address microplastic threats to the blue economy, recommending science-based policies, technological innovations, and public awareness campaigns to protect marine ecosystems and ensure the resilience and prosperity of ocean-dependent economic activities.

An efficient strategy to tailor PET hydrolase: Simple preparation with high yield and enhanced hydrolysis to micro-nano plastics

Polyethylene terephthalate (PET) nano/microplastics (PET-NMPs) are regarded as an emergent hazardous waste for the environment. Enzymatic treatment of PET-NMPs is one of the most promising methods. However, strategies for mining or engineering of PET hydrolases with better characteristics and the simple and cost-effective preparation of them are the bottlenecks currently. Herein, we proposed a gene fusion strategy to tailor PET hydrolase (ICCG) with ferritin (namely F-C) towards micro-nano PET degradation. The purified F-C was obtained by an easy scalable low-speed centrifugation with 80.8 % activity recovery and 82.9 % protein recovery compared to the crude protein extraction, with the final high yield of 2.17 g/L. Encouragingly, unlike only hydrolyzing amorphous PET (crystallinity lower than 10 %), the resulted F-C showed 84.53 mgTPA/h/mgEnzyme specific activity at 70 °C for 5 h towards micro-PET with relatively high crystallinity (20.54 %) at the optimized enzyme/PET ratio of 1:100 (Wt), without producing intermediates. The supreme activity of F-C was closely related to its enhanced affinity towards substrate, increased substrate's ester bond tensions and binding pocket volume. More interestingly, F-C exhibited promising stability not only in storage or high temperature, but also in simulated seawater (hypersaline environment), with the half-lives of 128.4 days at 30 °C. Thus, the all-in-one strategy will offer a green and alternative solution to assist the PET-NMPs waste treatments such as recycling in the high-temperature reactor or degradation in seawater.

Metagenome-derived SusD-homologs affiliated with Bacteroidota bind to synthetic polymers

Starch utilization system (Sus)D-homologs are well known for their carbohydrate-binding capabilities and are part of the sus operon in microorganisms affiliated with the phylum Bacteroidota. Until now, SusD-like proteins have been characterized regarding their affinity toward natural polymers. In this study, three metagenomic SusD homologs (designated SusD1, SusD38489, and SusD70111) were identified and tested with respect to binding to natural and non-natural polymers. SusD1 and SusD38489 are cellulose-binding modules, while SusD70111 preferentially binds chitin. Employing translational fusion proteins with superfolder GFP (sfGFP), pull-down assays, and surface plasmon resonance (SPR) has provided evidence for binding to polyethylene terephthalate (PET) and other synthetic polymers. Structural analysis suggested that a Trp triad might be involved in protein adsorption. Mutation of these residues to Ala resulted in an impaired adsorption to microcrystalline cellulose (MC), but not so to PET and other synthetic polymers. We believe that the characterized SusDs, alongside the methods and considerations presented in this work, will aid further research regarding bioremediation of plastics.

IMPORTANCE

SusD1 and SusD38489 can be considered for further applications regarding their putative adsorption toward fossil-fuel based polymers. This is the first time that SusD homologs from the polysaccharide utilization loci (PUL), largely described for the phylum Bacteroidota, are characterized as synthetic polymer-binding proteins.

Mining strategies for isolating plastic-degrading microorganisms

Plastic waste is a growing global pollutant. Plastic degradation by microorganisms has captured attention as an earth-friendly tactic. Although the mechanisms of plastic degradation by bacteria, fungi, and algae have been explored over the past decade, a large knowledge gap still exists regarding the identification, sorting, and cultivation of efficient plastic degraders, primarily because of their uncultivability. Advances in sequencing techniques and bioinformatics have enabled the identification of microbial degraders and related enzymes and genes involved in plastic biodegradation. In this review, we provide an outline of the situation of plastic degradation and summarize the methods for effective microbial identification using multidisciplinary techniques such as multiomics, meta-analysis, and spectroscopy. This review introduces new strategies for controlling plastic pollution in an environmentally friendly manner. Using this information, highly efficient and colonizing plastic degraders can be mined via targeted sorting and cultivation. In addition, based on the recognized rules and plastic degraders, we can perform an in-depth analysis of the associated degradation mechanism, metabolic features, and interactions.

Biodegradation of Typical Plastics: From Microbial Diversity to Metabolic Mechanisms

Plastic production has increased dramatically, leading to accumulated plastic waste in the ocean. Marine plastics can be broken down into microplastics (<5 mm) by sunlight, machinery, and pressure. The accumulation of microplastics in organisms and the release of plastic additives can adversely affect the health of marine organisms. Biodegradation is one way to address plastic pollution in an environmentally friendly manner. Marine microorganisms can be more adapted to fluctuating environmental conditions such as salinity, temperature, pH, and pressure compared with terrestrial microorganisms, providing new opportunities to address plastic pollution. Pseudomonadota (Proteobacteria), Bacteroidota (Bacteroidetes), Bacillota (Firmicutes), and Cyanobacteria were frequently found on plastic biofilms and may degrade plastics. Currently, diverse plastic-degrading bacteria are being isolated from marine environments such as offshore and deep oceanic waters, especially Pseudomonas spp. Bacillus spp. Alcanivoras spp. and Actinomycetes. Some marine fungi and algae have also been revealed as plastic degraders. In this review, we focused on the advances in plastic biodegradation by marine microorganisms and their enzymes (esterase, cutinase, laccase, etc.) involved in the process of biodegradation of polyethylene terephthalate (PET), polystyrene (PS), polyethylene (PE), polyvinyl chloride (PVC), and polypropylene (PP) and highlighted the need to study plastic biodegradation in the deep sea.