Biocatalytic oxidation of polyethylene by Agrocybe aegerita mycelium

Breaking Down Linear Low-Density Polyethylene (LLDPE) Using Fungal Mycelium (Part A): A Path Towards Sustainable Waste Management and Its Possible Economic Impacts

Linear low-density polyethylene (LLDPE) waste presents a major environmental concern due to its high and widespread use. This study explores the potential of fungal mycelium as a bioremediation solution for LLDPE degradation, by evaluating on mycelial growth efficiency, ligninolytic enzyme activity, weight loss, surface morphology changes, and economic feasibility. Among the tested fungal species, Schizophyllum commune WE032, Lentinus sajor-caju TBRC6266, and Trametes flavida AM011, S. commune demonstrated the most vigorous mycelial expansion (20.53 mm/day) and highest biomass accumulation (276.87 mg). Screening for ligninolytic enzymes revealed significant laccase (Lac) and manganese peroxidase (MnP) activity in all three species indicating their potential in polymer degradation. Weight loss analysis showed that S. commune achieved the greatest LLDPE degradation (1.182% after 30 days), highlighting its enzymatic and metabolic efficiency in breaking down synthetic polymers. Surface morphology studies supported these findings, revealing substantial erosion was observed in LLDPE sheets treated with S. commune and L. sajor-caju, confirming their effectiveness in polymer disruption. FTIR analysis indicated the formation of new functional groups and alterations in the carbon backbone, suggesting active depolymerization processes. Economic evaluation demonstrated that fungal biodegradation is a cost-effective and environmentally sustainable strategy, aligning with circular economy principles by enabling the generation of value-added products from plastic waste. Additionally, fungal-based waste treatment aligns with circular economy principles, generating value-added products while mitigating plastic pollution. These findings highlight fungal mycelium's potential for plastic waste management, advocating for further research on optimizing growth conditions, enhancing enzyme expression, and scaling industrial applications. Future research will focus on integrating fungal bioremediation with biomass residues from agricultural and forestry sectors, offering a comprehensive solution for waste management and environmental sustainability.

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

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

Discovery and adaptation of microbes that degrade oxidized low-density polyethylene films

There is a growing interest in developing a methodology for effectively cleaving carbon-carbon (C-C) bonds in polymer backbones through bioconversion processes that utilize microorganisms and their enzymes. This upsurge of interest is driven by the goal of achieving a circular economy. Polyolefin post-consumer plastics are a substantial source of carbon, but the recycling potential is severely limited. Upcycling routes are needed for converting polyolefin post-consumer plastics into value-added products while concurrently mitigating adverse environmental effects. These materials contain carbon-based chemicals that can, in principle, serve as the feedstock for microbial metabolism. Some microbes have been reported to grow on polyolefin plastics, but the rate of biodegradation is insufficient for industrial processes. In this study, low-density polyethylene (LDPE) films were subjected to two mild ozone-based oxidation treatments, which facilitated biodegradation. The degree of oxidation was determined by Fourier transform infrared spectroscopy via analysis of the carbonyl index (1,710/1,460 cm-1), which ranged from 0.3 to 2.0, and also via analysis of the carboxylic acid content. Following oxidation of the films, studies were conducted to investigate the ability of a panel of polyvinyl alcohol-degrading microbes to degrade the oxidized films. A defined minimal medium was used to cultivate and assess microbial growth on the oxidized films. Following 45 days of cultivation, the most effective strains were further cultivated up to three additional generations on the oxidized film substrates to improve their ability to degrade the oxidized LDPE films. After these enrichments, we identified a strain from the third generation of Pseudomonas sp. Rh926 that exhibited significant cell growth and reduced the oxidized LDPE film mass by 25% in 30 days, demonstrating an enhanced capacity for degrading the oxidized LDPE films.

ONE-SENTENCE SUMMARY

Discovery and adaptation techniques were used to enhance the metabolic capability of microorganisms for increased biodegradation of ozone-oxidized LDPE films as a step toward a future upcycling process.

Biodegradation of plastics by white-rot fungi: A review

Plastic pollution is one of the most environmental problems in the last two centuries, because of their excessive usage and their rapidly increasing production, which overcome the ability of natural degradation. Moreover, this problem become an escalating environmental issue caused by inadequate disposal, ineffective or nonexistent waste collection methods, and a lack of appropriate measures to deal with the problem, such as incineration and landfilling. Consequently, plastic wastes have become so ubiquitous and have accumulated in the environment impacting ecosystems and wildlife. The above, enhances the urgent need to explore alternative approaches that can effectively reduce waste without causing harsh environmental consequences. For example, white-rot fungi are a promising alternative to deal with the problem. These fungi produce ligninolytic enzymes able to break down the molecular structures of plastics, making them more bioavailable and allowing their degradation process, thereby mitigating waste accumulation. Over the years, several research studies have focused on the utilization of white-rot fungi to degrade plastics. This review presents a summary of plastic degradation biochemistry by white-rot fungi and the function of their ligninolytic enzymes. It also includes a collection of different research studies involving white-rot fungi to degrade plastic, their enzymes, the techniques used and the obtained results. Also, this highlights the significance of pre-treatments and the study of plastic blends with natural fibers or metallic ions, which have shown higher levels of degradation. Finally, it raises the limitations of the biotechnological processes and the prospects for future studies.

Enzymatic polyethylene biorecycling: Confronting challenges and shaping the future

Polyethylene (PE) is a widely used plastic known for its resistance to biodegradation, posing a significant environmental challenge. Recent advances have shed light on microorganisms and insects capable of breaking down PE and identified potential PE-degrading enzymes (PEases), hinting at the possibility of PE biorecycling. Research on enzymatic PE degradation is still in its early stages, especially compared to the progress made with polyethylene terephthalate (PET). While PET hydrolases have been extensively studied and engineered for improved performance, even the products of PEases remain mostly undefined. This Perspective analyzes the current state of enzymatic PE degradation research, highlighting obstacles in the search for bona fide PEases and suggesting areas for future exploration. A critical challenge impeding progress in this field stems from the inert nature of the C-C and C-H bonds of PE. Furthermore, breaking down PE into small molecules using only one monofunctional enzyme is theoretically impossible. Overcoming these obstacles requires identifying enzymatic pathways, which can be facilitated using emerging technologies like omics, structure-based design, and computer-assisted engineering of enzymes. Understanding the mechanisms underlying PE enzymatic biodegradation is crucial for research progress and for identifying potential solutions to the global plastic pollution crisis.

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

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