A theoretical systems-biology framework for the degradation of mixed plastics and conversion into fertilizer-grade compounds via engineered microbial consortia
A theoretical Plastic-to-Fertilizer (P2F) framework that proposes an engineered four-member microbial consortium capable of partially depolymerizing mixed plastic waste, including polyethylene terephthalate (PET), high-density polyethylene (HDPE), polystyrene (PS), and polypropylene (PP), and channeling selected plastic-derived carbon intermediates toward biosynthesis of agronomically beneficial compounds is presented.
Abstract
Plastic pollution is a global environmental challenge of increasing severity. Global plastic production reached approximately 413.8 million metric tonnes in 2023, yet global assessments, including those by Geyer et al., suggest that fewer than 10% of post-consumer plastics are effectively recycled. Here we present a theoretical Plastic-to-Fertilizer (P2F) framework that proposes an engineered four-member microbial consortium capable of partially depolymerizing mixed plastic waste, including polyethylene terephthalate (PET), high-density polyethylene (HDPE), polystyrene (PS), and polypropylene (PP), and channeling selected plastic-derived carbon intermediates toward biosynthesis of agronomically beneficial compounds, including organic acids, amino acids, and humic-like macromolecules (HLMs). The proposed consortium comprises an engineered Pseudomonas putida KT2440 chassis expressing heterologous PETase and MHETase [mono(2-hydroxyethyl) terephthalate hydrolase] for PET depolymerization and harboring a native styrene catabolic pathway for PS intermediates; Bacillus subtilis 168 providing CotA laccase-mediated polyolefin surface oxidation; Aspergillus niger serving as a biofilm scaffold and oxidative enzyme source; and a biocontained Azotobacter vinelandii strain with a conditionally active, speculative nitrogen-fixation module. A theoretical mathematical framework encompassing Langmuir-adsorption-based surface degradation kinetics, substrate-specific Haldane-Andrews growth models, and enzyme synergy quantification is presented alongside a corrected stoichiometric mass balance for the P2F metabolic funnel. Techno-economic projections are presented as illustrative scenarios only, given the current technology readiness level (TRL 1–2). Key biological constraints are explicitly acknowledged throughout: HDPE and PP are highly crystalline polymers requiring mandatory abiotic pre-treatment before enzymatic action is feasible; PS depolymerization to metabolisable intermediates requires abiotic pre-treatment as no biological route has been demonstrated for bulk PS; heterologous nitrogen fixation is technically challenging and is framed as a speculative high-risk long-term aspiration rather than a functional module; and all stoichiometric yields are theoretical upper bounds. This paper provides a conceptual foundation, a corrected mathematical framework, and a five-phase experimental roadmap intended to guide empirical validation.
Plastics are high-molecular-mass polymers made of synthetic or semi-synthetic organic compounds used in the production of water bottles, medical supplies and food packaging and more. Increased plastic production in recent years has resulted in an accumulation of plastic garbage in our environment, which is quite concerning. This review aims to synthesize knowledge on plastics and microbial plastic degradation, with particular focus on emerging and re-emerging challenges that hinder its large-scale application. The discharge of plastic additives, the buildup of microplastics in the marine environment, and their lack of degradability can all have a negative impact on aquatic life and human health. Synthetic polymers have been broken down using physicochemical techniques, such as photodegradation and thermal treatment, but reported efficiencies are often below 40% and can generate toxic byproducts such as aldehydes and microplastics.One environmentally beneficial solution to the plastic pollution problem is biodegradation. Several plastic- degrading bacteria, including Pseudomonas species, Bacillus species, Alcanivorax species, and Actinomycetes, have been isolated have also been found to degrade plastics while microbial plastic degradation has gained attention as an eco-friendly approach, several emerging and re-emerging challenges hinder its widespread application. These include the slow degradation rates, microbial adaptability to synthetic polymers, genetic and metabolic limitations, and the influence of environmental factors on microbial efficiency. Recent advancements in biotechnology, such as enzyme engineering, metagenomics, and synthetic biology, offer promising prospects for enhancing microbial plastic degradation. This review presents the current challenges, potential solutions, and future directions in microbial plastic degradation.
Agbiji, N.N., Eknog M.O, Akubuenyi F et al.· Biological and Environmental...· 0 citations
Plastic pollution has become the major global environmental problem due to the extensive accumulation and recalcitrance of synthetic polymers in terrestrial and aquatic environments. Traditional methods of plastic waste degradation, such as landfilling, incineration, and mechanical recycling, have various environmental limitations, like the production of more harmful toxic components, secondary pollutants, and inefficient waste handling. Therefore, current research is focused on more promising and environmentally sustainable alternatives for plastic waste management by microbial biodegradation. This review includes various bacterial and fungal enzymes such as PETase, MHETase, cutinase, laccase, and polyesterase associated with major stages of microbial plastic degradation, including biodeterioration, biofragmentation, bioassimilation, and mineralization. The degradation mechanism of synthetic polymers like polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyurethane (PU), polystyrene (PS), and polyvinyl chloride (PVC) are discussed along with the importance of analytical validation techniques such as FTIR, SEM, GC–MS, respirometry assays, and stable isotope probing for accurately confirming biodegradation. Additionally, the existing limitations of poor degrading efficiency, polymer recalcitrance, mixed plastic waste complexity, scaling challenges, and the gap between laboratory results and environmental application are comprehensively analyzed. Overall, the review provides a comprehensive overview of microbial and enzymatic plastic biodegradation and highlights recent advancements in metagenomics, enzyme engineering, synthetic biology, and multi‐omics approaches that helps in improving the efficiency and large‐scale industrial feasibility of microbial plastic degradation.
This study outlines existing metabolic engineering techniques for bio-upcycling PET into high-value compounds, as well as a number of engineering approaches intended to improve the performance of PET-degrading enzymes. One of the most popular aromatic polyesters in the world, polyethylene terephthalate (PET) has an annual demand of over 29 million metric tons in 2022 and is expected to rise by 40% by 2030. Due to the growing amount of PET waste and the existing insufficiency of recycling techniques, it has accumulated in terrestrial ecosystems, posing serious hazards to world health. These technologies seek to convert recovered PET into more valuable items in order to address energy issues as well as environmental sustainability. One potentially biosustainable technique for handling and recycling plastics is enzyme-mediated biocatalytic depolymerization. Protein engineering developments have been applied to modify and improve the many plastic-degrading enzymes that have been discovered from microbial sources. Additionally, microbial metabolic engineering makes it possible to create customized microbial chassis that can break down PET substrates and transform the resulting monomers into compounds that are useful for industry.
Abdul Rauf Bhatti, Rabiya Asim, Muddasar Jamal et al.· Practices in Science and Tec...· 0 citations
The production and utilization of petroleum‐based plastics cause severe environmental degradation and climate alteration. These conventional plastics release greenhouse gases and hazardous chemicals during production, and their resistance to degradation—persisting undamaged for over 60 years—fuels critical marine pollution. To mitigate these issues, research is shifting toward biobased plastics as sustainable, biocompatible, and biodegradable alternatives. Derived from renewable biomass or microbes, these materials include starches, cellulose, casein, and diverse polysaccharides sourced from red (
Rhodophyta
), green (
Chlorophyta
), and brown (
Phaeophyta
) algae. Aligning with the principles of a circular bioeconomy, this approach maximizes resource efficiency and minimizes waste. Furthermore, innovative materials like Bio‐PET, polybutylene succinate (PBS), polylactic acid (PLA), and polyhydroxyalkanoates (PHAs) are increasingly deployed to replace traditional plastics. Beyond offering excellent preservation against oxidation and microbial decomposition in food packaging, these bioplastics show immense promise in medicine, nutraceuticals, and pharmaceuticals. This review article evaluates the diverse natural sources of bioplastics, analyzes their mechanical, thermal, and physical properties, and highlights their most promising future applications.
Polyhydroxyalkanoate (PHA) production from plastic-derived substrates offers a promising route to mitigate plastic pollution while reducing dependence on conventional PHA feedstocks. Plastic waste represents an abundant carbon source for microbial fermentation, but efficient conversion remains limited by incomplete deconstruction, inhibitory intermediates, low carbon recovery, and challenges in process integration. Plastic-derived streams contain diverse compounds, including fatty acids, hydrocarbons, fatty alcohols, aldehydes, esters, and aromatic compounds generated during depolymerization. These intermediates can be metabolized by selected microorganisms, particularly Pseudomonas species with versatile fatty-acid and hydrocarbon pathways, as well as Cupriavidus necator and mixed microbial cultures. Unlike reviews that address plastic upcycling or PHA biosynthesis separately, this review focuses on the deconstruction-fermentation interface that governs plastic-to-PHA conversion. It consolidates current progress in plastic deconstruction, substrate conditioning, microbial metabolism, fermentation control, polymer recovery, and techno-economic and life-cycle considerations. By emphasizing substrate composition, biological compatibility, plastic‑carbon recovery, and final polymer quality, the review identifies priorities for scalable and environmentally sustainable PHA production from plastic-derived substrates.
Masoumeh Mohandessi, K. Bandara, N. A. Nosratabad et al.· Biotechnology Advances· 0 citations
Polyethylene (PE) remains environmentally persistent due to its inert backbone and high molecular weight, with biodegradation hindered by low efficiency and unclear community-level mechanisms. In this study, we reconstructed a synthetic consortium, Z123, comprising Nitratireductor sp. Z-1 and Gordonia spp. Z-2 and Z-3 isolated from a consistent enrichment system. Z123 achieved 9.98% weight loss and 50.88% molecular weight reduction within 30 days, outperforming most consortia degrading pristine low-density polyethylene (LDPE). Integrated genomic and proteomic analyses suggested functional differentiation among consortium members involving oxidative activation, chain scission, and downstream metabolism. Gas chromatography-mass spectrometry (GC-MS) analysis further detected putative LDPE-associated extracellular compounds consistent with oxidative polymer modification. Recombinant MCO1 and Lcp3 modified LDPE in vitro, and their combined application caused greater depolymerization than either enzyme at the corresponding half dose, suggesting complementary catalytic contributions. Collectively, these results indicate that functional differentiation and cooperative interactions contribute to enhanced LDPE degradation by Z123. This work provides mechanistic insights into consortium-based plastic biodegradation and supports the rational design of microbial platforms for plastic waste management.
Zhen Rong, Jun-Qing Chen, Yue-hong Wu et al.· Water Research· 0 citations