The ubiquity of plastic pollution represents one of the most pressing environmental challenges of the Anthropocene. Global plastic production has surged to exceed 400 million metric tons annually, a substantial portion of which enters and accumulates in natural ecosystems (Rangel-Buitrago and Galgani, 2026). Through processes of mechanical abrasion, photodegradation, and biological weathering, larger plastic debris undergoes fragmentation into microplastics (MPs), defined as synthetic polymer particles less than 5 mm in diameter (Matavos-Aramyan, 2024; Jolaosho et al., 2025). These micropollutants have permeated every corner of the planet’s hydrosphere, from pristine alpine lakes and deep-sea trenches to urban rivers and coastal estuaries (Tarigan et al., 2025). Their small size, combined with their persistent nature and high surface-area-to-volume ratio, renders them bioavailable to a vast range of aquatic organisms, facilitating trophic transfer and posing a significant threat to biodiversity, ecosystem function, and potentially human health through seafood consumption (Bulannga and Schmidt, 2024; Pal et al., 2025). The environmental persistence of conventional polymers, which may span centuries, underscores the urgency of developing effective remediation strategies (Beena Unni and Muringayil Joseph, 2024).

Microplastics originate from a complex mixture of primary sources, such as microbeads from personal care products and pre-production pellets, and secondary sources derived from the breakdown of larger items like packaging materials and fishing gear (Ashrafy et al., 2023; Nkin, 2025). Pathways into aquatic environments are multifaceted, including wastewater discharge, agricultural runoff, atmospheric deposition, and improper waste management (Rothman et al., 2023; Matavos-Aramyan, 2024). Once introduced, their ecological impacts are multifaceted. Physically, ingestion can lead to gut blockage, false satiation, and internal injury in aquatic fauna (Liu and Li, 2025). Chemically, MPs can act as vectors for toxic additives (e.g., plasticizers, flame retardants) and hydrophobic environmental contaminants (e.g., heavy metals, persistent organic pollutants), concentrating them and enhancing their bioavailability (Mbachu et al., 2020; Rashid et al., 2025. Furthermore, the plastisphere the unique microbial community colonizing MP surfaces can include potential pathogens and facilitate the transport of antibiotic resistance genes, adding a complex biological dimension to the threat (Wu et al., 2024).

Conventional methods for MP removal from water bodies, such as filtration and coagulation, are often energy-intensive, costly, and impractical for large-scale application in open environments. They primarily focus on sequestration rather than degradation, leading to a secondary waste problem (Puteri et al., 2025). In this context, bioremediation the use of biological organisms to detoxify or remove pollutants has emerged as a promising, eco-friendly, and potentially scalable alternative. Among biological agents, bacteria are at the forefront of MP bio-remediation research due to their ubiquitous distribution, metabolic versatility, and rapid reproduction rates (Kuppan et al., 2024). A growing body of evidence has identified diverse bacterial taxa, including genera such as Pseudomonas, Bacillus, Rhodococcus, and Ideonella, capable of adhering to plastic surfaces and utilizing them as a carbon and energy source through the secretion of specific extracellular enzymes like hydrolases and laccases (Yadav et al., 2025). This enzymatic activity can break down the long-chain polymers into smaller oligomers, monomers, and ultimately, carbon dioxide and water, offering a pathway for the complete mineralization of plastic waste.

Despite a surge in primary research articles over the past decade, the field of bacterial degradation of microplastics remains characterized by significant fragmentation and heterogeneity. Studies are often conducted in isolation, using disparate methodologies, different bacterial strains, and a wide array of polymer types, making cross-comparison and the drawing of general conclusions challenging (Przygoda-Kuś et al., 2025). Critical knowledge gaps persist regarding the specific enzymatic mechanisms and their genetic regulation, the kinetics of degradation under environmentally relevant conditions (as opposed to optimized lab settings), the efficacy of bacterial consortia versus individual isolates, and the potential ecotoxicological risks associated with degradation by-products (Parab et al., 2025). While several narrative reviews have summarized progress in this area, a comprehensive, methodologically rigorous, and transparent synthesis of the global evidence is lacking. A systematic review is therefore imperative to consolidate the scattered findings, critically appraise the quality of the evidence, quantify the overall efficacy where possible, and identify the most robust and promising pathways for future research and application.

This systematic review aims to provide a comprehensive and critical synthesis of the current state of knowledge on the bacterial degradation of microplastics in aquatic environments. Guided by the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, this review seeks to address the following specific research questions:

What is the taxonomic and functional diversity of bacteria identified as capable of degrading the most prevalent microplastic polymers (e.g., polyethylene, polypropylene, polystyrene, PET) in aquatic environments?

By systematically collating and evaluating the evidence, this review will delineate the current frontiers of knowledge, highlight critical research gaps, and provide an evidence-based foundation to guide future scientific inquiry, policy development, and biotechnological innovation in the fight against microplastic pollution.

Prior to the commencement of the literature search, a detailed review protocol was developed outlining the objectives, search strategy, inclusion/exclusion criteria, data extraction framework, and synthesis methods. The protocol was designed to minimize selection and publication bias and to ensure reproducibility. While registration in a prospective register such as PROSPERO was considered, the interdisciplinary scope of this review spanning environmental microbiology, biotechnology, and polymer science extended beyond the biomedical focus of such registries. Therefore, an internal protocol was maintained as the guiding document for all subsequent steps.

A systematic literature search was conducted in June 2025 across three major electronic databases: Scopus, Web of Science Core Collection, and PubMed. These databases were selected for their extensive coverage of peer-reviewed literature in environmental science, microbiology, biotechnology, and chemical engineering. The search strategy was constructed around four central conceptual themes: micro-plastics, bacteria, biodegradation, and aquatic environments. A comprehensive set of keywords and Boolean operators (AND, OR) was employed for each concept. The full, detailed search strategy as executed in each database is provided in Supplementary Table S1. For example, the search string used in Scopus was: (micro-plastic OR nano-plastic) AND (bacterial OR microbial) AND (degradation OR biodegradation OR mineral OR de-polymer) AND (aquatic OR marine OR freshwater OR river OR lake).

The search was restricted to peer-reviewed journal articles, systematic reviews, and meta-analyses published in English between 1 January 2000 and 30 June 2025. This date range captures the modern era of micro-plastic research and ensures the review reflects current advancements. Grey literature, preprints, and non-English publications were excluded to maintain consistency in peer-review standards and reproducibility of findings.

Study selection was guided by predefined eligibility criteria structured according to the PICOS (Population, Intervention, Comparator, Outcomes, Study design) framework, as detailed in Table 1. This framework ensured a focused and relevant selection of studies.

The study selection process followed a rigorous two-stage screening protocol to minimize bias, as illustrated in the PRISMA flow diagram (Figure 1). Initial searches across the databases yielded 639 records. After merging the records, 244 duplicates were identified and removed using a combination of automated tools in EndNote XX and manual verification. This resulted in 395 unique records proceeding to the title and abstract screening stage.

Two independent reviewers screened all 395 records against the eligibility criteria, with any discrepancies resolved through discussion and consensus. During this initial screening, 241 records were excluded as clearly irrelevant to the review’s objectives. The full texts of the remaining 154 articles were then retrieved and subjected to a detailed eligibility assessment by the same two reviewers. At this stage, 74 articles were excluded for specific reasons, including failure to meet the PICOS criteria, lack of original data, or unavailability of the full text. Through this stringent process, a total of 80 studies were identified as meeting all inclusion criteria and were therefore selected for data extraction and qualitative synthesis.

Data from the 80 included studies were systematically extracted using a standardized, pre-piloted form in Microsoft Excel. The extracted information encompassed essential bibliographic details (authors, publication year, journal), key study characteristics (including design, polymer type, bacterial agents, and incubation conditions), and methodological specifics such as the analytical techniques employed.

Additionally, the extraction captured the core research outcomes, including quantitative degradation metrics, identified enzymes or genes, metabolic pathways, and main conclusions, as well as important contextual factors like limitations reported by the authors. All compiled data are presented in Supplementary Table S2, providing a comprehensive overview and enabling effective cross-study comparison. Supplementary Table S2 summarizes key characteristics of the 80 studies included in the systematic review. For each study, information is provided on the polymer type investigated, the bacterial system used (species or consortium), the study design (e.g., laboratory experiment, mesocosm, or field study), the primary degradation metrics reported, and the main findings.

The quality and risk of bias of the included primary studies were evaluated using a customized critical appraisal checklist, adapted from established tools for laboratory-based environmental research. This process ensured a systematic and rigorous assessment of the methodological soundness of each study.

Each study was appraised against four key criteria. These were: the adequacy of material characterization for both the polymer and bacterial inoculum; the inclusion of appropriate sterile or abiotic controls; the sufficiency of biological and technical replication; and the analytical rigor demonstrated through the use of multiple, complementary methods to confirm degradation. For each criterion, studies were assigned a rating of low, high, or unclear risk of bias.

The results of this assessment are synthesized visually in Figure 2 and detailed in Supplementary Table S3. This evaluation directly informed the critical analysis within the review’s discussion (Section 8), serving to highlight the prevailing methodological strengths and limitations across the entire evidence base. Figure 2 elucidates the risk of bias assessment summary. The results of this assessment were used to inform the critical analysis of methodological strengths and limitations in Section 8. The below stacked bar chart summarizes the risk of bias across four domains for the 80 included studies. The y-axis shows the percentage of studies in each risk category. The green segments indicate Low Risk, yellow indicate Unclear Risk, and red indicate High Risk (Figure 2).

Due to substantial methodological heterogeneity across the included studies, a quantitative meta-analysis was deemed inappropriate. A critical analysis revealed profound variability across four key domains (Table 2), which collectively preclude the statistical pooling of results. These domains are: 1) the polymer substrate’s form, crystallinity, and pre-treatment; 2) the biological system, ranging from pure cultures to complex consortia; 3) the incubation conditions, including media, duration, and environmental parameters; and 4) the reported degradation metrics, which employ different analytical endpoints with varying sensitivity. This heterogeneity prevents direct cross-study comparison of quantitative efficacy data. Therefore, a qualitative thematic synthesis approach was employed to integrate complementary evidence, identify consistent trends, and draw comparative insights across these methodologically diverse studies.

The synthesis of findings was structured according to pre-defined thematic categories, which were directly derived from the research questions and encompassed the diversity and dynamics of plastisphere communities, the molecular and biochemical mechanisms underpinning degradation, the measured efficacy and kinetics of the process under varying conditions, and the persistent challenges in translating laboratory results to field applications.

Findings were tabulated where possible (e.g., Tables 3–9) to facilitate comparison. Subgroup exploration was conducted within homogeneous clusters (e.g., PET degradation by Ideonella sakaiensis) to identify trends, but formal statistical pooling was not performed due to inconsistent outcome reporting.

Analysis confirms that specific bacterial genera are consistently enriched on microplastics (MPs) across diverse aquatic habitats due to their metabolic versatility and adaptive traits (Scott et al., 2025). Notable primary colonizers include Pseudomonas spp., which dominate on polyethylene and polystyrene via robust biofilm formation and the secretion of nonspecific oxidoreductases (Zhang et al., 2022). Similarly, Bacillus spp., resilient through endospore formation, is frequently associated with polyethylene terephthalate and polypropylene through their secretion of hydrolytic enzymes (Gupta and Devi, 2020). Rhodococcus spp. also shows a strong affinity for polyolefins like polyethylene and polypropylene, leveraging hydrophobic cell walls and established alkane metabolic pathways for polymer oxidation (Yadav et al., 2025).

Beyond these well-known genera, specialized and emerging taxa highlight advanced degradative strategies. The landmark discovery of Ideonella sakaiensis 201-F6, which utilizes the specialized PETase and MHETase enzyme system, demonstrates highly efficient, polymer-specific hydrolysis (Yip et al., 2024). Furthermore, recurrent identification of genera such as Acinetobacter, Comamonas, and Streptomyces in plastisphere studies indicates their significant, though often less characterized, roles within complex microbial consortia dedicated to degradation (Bocci et al., 2024).

Colonization begins with pioneering bacteria (e.g., Pseudomonas, Bacillus) adhering to the conditioned “eco-corona” of the MP. They secrete extracellular polymeric substances (EPS), forming a biofilm matrix that concentrates enzymes and facilitates microbial cross-feeding. As degradation initiates, the microenvironment changes; driving microbial succession (Scheidweiler et al., 2019). Secondary colonizers, often specialists in utilizing intermediary breakdown products, establish themselves, leading to a more complex and functionally synergistic consortium crucial for complete mineralization (Battulga et al., 2024; Bocci et al., 2024).

Critically, the chemical composition of the polymer acts as a strong selective pressure, directly shaping the microbial community dynamics on its surface (Battulga et al., 2024). Non-hydrolyzable, hydrophobic polymers like polyethylene (PE) and polypropylene (PP) select for communities dominated by Rhodococcus and Pseudomonas, which possess oxidative enzymatic systems for the slow oxidation of C-C bonds (Porter et al., 2023). In contrast, the presence of hydrolysable ester bonds in polyethylene terephthalate (PET) enriches for a distinct community with bacteria like Ideonella sakaiensis, Bacillus, and Thermobifida species that secrete potent hydrolases, particularly when polymer crystallinity is reduced. Meanwhile, the aromatic backbone of polystyrene (PS) presents a unique challenge, often resulting in a lower-diversity community dominated by specific Pseudomonas and Cupriavidus species capable of aromatic ring cleavage via dioxygenases. This polymer-driven niche differentiation underscores that the plastisphere is not a single entity but a collection of polymer-specific habitats (Mulky et al., 2025). Consequently, successful bioremediation strategies must be “tailored,” matching specific bacterial consortia or enzymes to the predominant polymer pollutant. This relationship between polymer type, microbial community structure, and the resulting degradation pathway is illustrated in the accompanying tables (Tables 3, 4).

The systematic analysis of the included literature reveals that bacterial degradation of microplastics is primarily mediated by a limited yet versatile set of extracellular enzymes, which can be broadly categorized based on their catalytic mechanism and polymer target, and this class of enzymes is paramount for the degradation of polymers containing hydrolysable bonds, such as polyesters, where the discovery of PETase from Ideonella sakaiensis represents a landmark finding, as this enzyme specifically targets the aromatic ester bonds in polyethylene terephthalate (PET), yielding mono(2-hydroxyethyl) terephthalic acid (MHET) as a primary product (Khairul Anuar et al., 2022; Zhang, X. et al., 2024), and subsequently, MHETase further hydrolyzes MHET into the monomers terephthalic acid and ethylene glycol (Palit et al., 2025), while beyond this specialized system, more ubiquitous hydrolytic enzymes like cutinases (from Thermobifida and Bacillus spp.) and lipases have demonstrated significant efficacy against PET and other aliphatic polyesters by attacking their ester linkages (Maurya et al., 2020), with the effectiveness of hydrolases being highly dependent on polymer accessibility, as amorphous regions are degraded preferentially over crystalline ones.

For non-hydrolyzable polymers like polyethylene (PE) and polypropylene (PP), which possess inert C-C backbones, oxidative cleavage is the initial and rate-limiting step, where enzymes such as alkane hydroxylases (e.g., from Pseudomonas and Rhodococcus) introduce hydroxyl groups into the polymer chain, making it more susceptible to further oxidation (Kim et al., 2025), and monooxygenases and dioxygenases play a critical role, particularly in attacking the aromatic rings of polystyrene (PS), as demonstrated by the styrene degradation pathway involving styrene monooxygenase (SMO) and styrene oxide isomerase, which has been implicated in the breakdown of PS oligomers (Oelschlägel et al., 2018).

These multi-copper oxidases are noted for their broad substrate specificity and ability to act on a range of polymers, including PE, PS, and polyvinyl chloride (PVC), where laccases catalyze the one-electron oxidation of various substrates, often generating reactive radicals that can lead to polymer chain scission, and their activity is often enhanced in the presence of redox mediators, which can expand their target range (Liu X-h et al., 2025), and while more commonly associated with fungi, bacterial laccases (e.g., from Bacillus spp.) are increasingly being recognized for their role in the plastisphere, with Table 5 providing a systematic summary of these key enzymatic systems, their targets, and the resulting breakdown products.

The initial enzymatic attack generates intermediary compounds that are subsequently assimilated into central metabolic pathways, and our synthesis indicates that bacteria commonly achieve this by co-opting pre-existing catabolic routes originally evolved for natural hydrocarbons and aromatic compounds, as, for example, the degradation of polyethylene terephthalate (PET) yields the monomers terephthalic acid and ethylene glycol, which are then processed via dedicated bacterial pathways for terephthalic acid degradation and glycolytic metabolism, respectively, ultimately feeding into the tricarboxylic acid (TCA) cycle, and in the case of polyolefins like polyethylene (PE) and polypropylene (PP), oxidized products such as fatty alcohols and acids are typically channeled into the β-oxidation cycle to generate acetyl-CoA, while polystyrene (PS) degradation is more complex, with evidence pointing to ring cleavage products entering central metabolism through modified routes of styrene catabolism, and a critical finding is the importance of consortia-based metabolism and cross-feeding, where no single bacterium may possess the complete enzymatic suite for full mineralization (Salinas et al., 2024; Hakkarainen and Albertsson, 2026), meaning the breakdown products from one species serve as substrates for another, leading to synergistic degradation more efficient than any single isolate.

This degradative process is an active, regulated cellular response, as genomic and transcriptomic studies confirm that genes encoding key enzymes (e.g., petase, mhetase, alkane hydroxylase operons) are often located on mobile genetic elements, suggesting potential for horizontal gene transfer (Yang et al., 2023; Yip et al., 2024), and their expression is tightly regulated and induced by the presence of plastic polymers or their breakdown intermediates, with the molecular response to plastic exposure being an active, regulated process, and genomic and transcriptomic studies included in this review consistently show that the genes encoding the key degradative enzymes are often located on plasmids or genomic islands, suggesting a potential for horizontal gene transfer (Julius et al., 2025).

The expression of these genes is tightly regulated, as, for instance, the expression of petase and mhetase in I. sakaiensis is induced in the presence of PET or its intermediate MHET, and similarly, the genes for alkane hydroxylation in Pseudomonas spp. are often part of operons (e.g., the alk system) whose expression is upregulated when the bacterium encounters long-chain alkanes, a regulatory logic it apparently applies to polyethylene (Xiang et al., 2023), which confirms that bacterial degradation is not a passive process but an active metabolic response to the availability of plastic as a potential carbon source, and Figure 3 provides a conceptual summary of the key degradation pathways for the most common plastic polymers, integrating the enzymatic, metabolic, and genetic concepts discussed.

The included studies employ a suite of complementary analytical techniques to quantify biodegradation, as no single metric provides a complete assessment. Direct gravimetric analysis of weight loss remains a fundamental, widely reported measure, though it is often slow to manifest significant change, particularly for recalcitrant polymers like polyolefins. Consequently, more sensitive surface characterization methods are crucial for detecting early-stage degradation (Zhang Z. et al., 2024). Scanning Electron Microscopy (SEM) provides visual evidence of physical erosion, while Fourier-Transform Infrared Spectroscopy (FTIR) identifies key chemical changes, such as carbonyl formation on polyethylene or the reduction of ester bonds in PET (Azeez and Shenbagaraman, 2025).

The most definitive proof of complete biodegradation is the measurement of polymer carbon mineralization into CO₂ via respirometric assays, which serves as a gold-standard metric despite often revealing very low conversion rates on laboratory timescales (Guo et al., 2010). Complementing these approaches, Gel Permeation Chromatography (GPC) offers critical insight into the depolymerization process by detecting reductions in average molecular weight, a clear indicator of chain scission that can occur prior to measurable mass loss. Our synthesis confirms that the most compelling studies utilize this multi-method approach to build a robust, convergent body of evidence (Rydholm et al., 2006).

The efficacy of bacterial degradation is not an intrinsic property but is profoundly modulated by environmental conditions, with the synthesized evidence revealing several key determinants, where temperature exerts a dual effect, influencing both microbial metabolic rates and polymer physical properties, as, for instance, the activity of PET-degrading enzymes from Ideonella sakaiensis and Thermobifida spp. is significantly higher at mesophilic (25 °C–37 °C) and thermophilic (55 °C–70 °C) ranges, respectively, and higher temperatures also increase polymer chain mobility, particularly above the glass transition temperature (Tg), making the material more accessible to enzymatic attack (Akram et al., 2024).

Furthermore, enzyme activity is pH-dependent, with most reported bacterial hydrolases and oxidoreductases operating optimally in a neutral to slightly alkaline pH range (7.0–9.0), and significant deviations from this range can inhibit microbial growth and enzymatic efficiency, limiting degradation in highly acidic or alkaline environments (Błońska et al., 2015); additionally, nutrient availability has complex, context-dependent effects, where while essential for microbial growth, easily metabolizable co-substrates can lead to catabolite repression, causing bacteria to preferentially consume simple nutrients over the complex polymer, but conversely, in nutrient-poor oligotrophic environments (which mimic many aquatic systems), the plastic may serve as a crucial carbon source, potentially enhancing its biodegradation (Jeske and Gallert, 2021).

A central finding of this systematic review is the vast disparity in degradation efficacy and kinetics across different polymer-bacteria systems, a central finding of this systematic review is the vast disparity in degradation efficacy and kinetics across different polymer-bacteria systems, and this variability is quantitatively summarized and graphically compared in the accompanying Table 6 and Figure 4.

A primary strategic question in bioremediation is whether to introduce specialized degraders (bio-augmentation) or to enhance the activity of the indigenous microbial community (bio-stimulation). Evidence from mesocosm studies which bridge the gap between lab flasks and natural ecosystems provides critical, albeit mixed, insights.

The transition from successful mesocosm experiments to field-scale application is hindered by several critical, interconnected barriers, including ecological competition and predation, where in a natural environment, introduced or stimulated degraders must contend with a highly diverse and competitive microbial community, facing pressure from bacteriophages and protozoan grazing, which can rapidly decimate their populations, and where the presence of more easily degradable organic carbon can lead to catabolite repression, causing microbes to preferentially metabolize simple substrates over complex polymers (Kumar et al., 2022).

Scalability and cost present further monumental challenges, as laboratory processes are optimized in small, homogeneous volumes, and scaling these processes to treat vast, heterogeneous aquatic environments like oceans or lakes presents monumental engineering and economic challenges, making the production, stabilization, and uniform dispersal of effective bacterial consortia or nutrients across square kilometers currently impractical and prohibitively expensive (Crater and Lievense, 2018).

Finally, monitoring and verification are exceptionally difficult, as accurately measuring the efficacy of a bioremediation intervention in a dynamic open environment requires distinguishing the microplastic mass loss due to the specific intervention from background processes like fragmentation, sedimentation, and transport, which is a major methodological hurdle, highlighting the pressing need for the development of robust tracer techniques and standardized monitoring protocols to validate in-situ degradation (Vuković Domanovac, et al., 2025), with Table 7 summarizing these key challenges and the associated research gaps that need to be addressed.

The transition from controlled experiments to field-scale application is hindered by profound ecological and practical barriers. A major, often understated, challenge is the paradox of nutrient availability. In oligotrophic open waters, MPs may serve as a crucial carbon source, potentially enhancing biodegradation. However, in nutrient-rich coastal or estuarine environments, the presence of easily metabolizable organic matter can lead to catabolite repression, where microbes preferentially consume simple substrates over complex polymers, effectively halting targeted degradation efforts (Mishra et al., 2025). Withal, the ecological competence of introduced strains is frequently overestimated. Native microbial communities possess established interactions and defense mechanisms; introduced degraders must compete for space and resources while facing pressure from protozoan grazing and bacteriophage predation, which can rapidly, decimate their populations. This enliven that efficacy in a flask is a poor predictor of environmental persistence and impact.

Despite the challenges, a limited number of pioneering studies have attempted to demonstrate bioremediation in real-world contexts, providing valuable proof-of-concept insights.

The fundamental understanding of degradation mechanisms, as synthesized in Sections 4, 5, must directly inform the strategic design and selection of field applications. The choice between in-situ and ex-situ approaches, and between bioaugmentation and biostimulation, is not merely logistical but is dictated by the inherent biochemical and ecological constraints of the system.

The superior kinetics and specificity of hydrolytic enzymes like PETase for PET depolymerization argue strongly for their deployment in controlled, ex-situ bioreactor systems. Here, the optimal temperature, pH, and enzyme-to-substrate ratios required for high-efficiency breakdown (Section 5.2) can be maintained, turning waste into valuable monomers for a circular economy (Section 7.1). In contrast, the slow, oxidative breakdown of polyolefins (PE, PP) by enzymes like alkane hydroxylases, which often requires abiotic pre-weathering and yields minimal energy gain for microbes, renders large-scale in-situ bioremediation of these polymers ecologically and energetically implausible with current technology.

Furthermore, the microbial ecology of the plastisphere (Section 3) underscores why simple bioaugmentation with a single, high-performing strain is likely to fail. The degradation process relies on successional biofilm development and consortia-based metabolism, where primary degraders initiate breakdown and secondary specialists mineralize the intermediates through cross-feeding (Sections 3.2, 4.2). Introducing a single non-native strain ignores this requisite functional network and subjects it to intense competition and predation (Section 6.2). Therefore, biostimulation of native plastisphere communities tailored to the polymer type present emerges as a more ecologically sound strategy, as it leverages pre-adapted, complex consortia. Where bioaugmentation is considered, it should involve engineered, ecologically competent consortia designed with synthetic ecology principles to perform coordinated degradation, though their release is mired in the significant regulatory challenges associated with GMOs (Section 7.2.2). Consequently, the most viable near-term applications are those where biological mechanisms align with engineering and regulatory feasibility: enzymatic recycling in contained facilities for specific polymers like PET, and carefully managed biostimulation for targeted in-situ remediation where conditions and polymer types are favorable.

The current global plastic economy is predominantly linear (take-make-dispose), a model that is environmentally unsustainable. The concept of a circular economy aims to eliminate waste and keep materials in continuous cycles of use. Within this framework, bacterial degradation offers unique value propositions, primarily at the recycling and recovery stages.

The translation of promising bacterial degradation strategies from the laboratory to field-scale environmental applications faces a critical bottleneck: the existing regulatory landscape. Current international frameworks, such as the US Toxic Substances Control Act (TSCA) and the EU’s Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) regulations, are primarily designed to manage the risks of chemical substances. These systems are not well-adapted to assess the complex risks, benefits, and long-term ecological consequences of novel bioremediation agents, particularly for in-situ remediation of microplastics. Our analysis identifies three foundational gaps that must be addressed to enable safe and effective deployment.

The most immediate and technologically feasible application of the discoveries in this field is not the in-situ cleanup of environmental microplastics, but the development of ex-situ enzyme-based biorecycling processes. This approach leverages the specificity and efficiency of bacterial enzymes in controlled industrial settings.

The overall evidence base is characterized by high enthusiasm but variable methodological rigor, with the strength of the field lying in the consistent, independent identification of key bacterial taxa (e.g., Pseudomonas, Bacillus) across studies, the elucidation of specific enzymatic pathways (e.g., PETase/MHETase), and the clear demonstration of principle that biodegradation is possible; however, significant limitations temper the translation of these findings, including the fact that a vast majority of studies provide proof-of-principle under idealized laboratory conditions that are not representative of environmental realities, and many reported degradation rates, while statistically significant, are ecologically irrelevant on short timescales (e.g., <10% weight loss over several months) (Singh and Borthakur, 2018).

Further limitations arise from the lack of environmental context, as studies frequently use pure bacterial cultures and pristine, often commercially sourced polymer powders or films, neglecting the effects of environmental aging, biofilm succession, and the complex chemical cocktail of additives and adsorbed pollutants present in environmental microplastics (Heris, 2024; Deng et al., 2024). There is insufficient analytical rigor, because while many studies use SEM and FTIR, fewer employ the more definitive metrics of mineralization (e.g., respirometry to measure CO₂ evolution) or polymer integrity (e.g., GPC to confirm chain scission), leaving open the possibility that observed changes are surface modifications rather than substantive degradation (Grima et al., 2000; Keridou et al., 2020; Silva et al., 2023; Tarhan and Kestek, 2024).

Our analysis identified specific areas where the risk of bias is high and methodological heterogeneity impedes cross-study comparison and meta-analysis.

Beyond methodological issues, this review identifies several fundamental scientific gaps that represent the Frontier of research in this field.