The microplastics (MPs) are considered emerging contaminants due to their occurrence in different environmental compartments, including atmospheric, aquatic, and terrestrial. They are defined as plastic particles ranging in size from 1 μm to 5 mm and are found in various types, sizes, shapes, and primary and secondary polymeric compositions (Miri et al., 2022; Thakur et al., 2023).

Microplastics (MPs) are considered harmful to wildlife and humans due to their persistent properties and bioaccumulation. This is attributed to the addition of various substances during their manufacturing process, such as pigments, plasticizers, and flame retardants. Additionally, due to their chemical-physical characteristics, they exhibit high durability, requiring an extended period for degradation in the environment (Cai et al., 2023; Niu et al., 2023).

Therefore, the production of plastics in the industry has been going on since the 1950s, with annual production reaching around 2 million tons, so that in 2015 this production rose significantly to 380 million tons per year. As a result, looking back from 1950 to 2015, approximately more than 7,800 million tons of plastics were produced, resulting in approximately 6,300 million tons of waste. Over the past 70 years, global plastic production has increased from 1.5 million tons to approximately 359.0 million tons, with an estimated projection of reaching 500.0 million tons by 2025. This trend raises significant concerns within civil society, as MPs are primarily generated through the degradation of larger polymers, a process influenced by physical, chemical, or biological factors (Cverenkárová et al., 2021; Torena et al., 2021; Villalobos et al., 2022; Osman et al., 2023). As microplastics increasingly contaminate the environment, the food chain has also been significantly impacted. Plastic contamination has occurred in invertebrates such as polychaetes, 51 crustaceans, echinoderms, bivalves, and vertebrates, including fish, seabirds, and mammals. These particles have entered the food chain either directly or through trophic transfer. Indeed, one of the main concerns arising from microplastic contamination is its bioaccumulative effect in the digestive tract (Cverenkárová et al., 2021).

Microplastics (MPs) enter the environment through various pathways due to poor management and dumping practices. However, there are mechanisms that can be employed to control their presence in the environment, such as biological, thermal, and photocatalytic degradation. Biological degradation occurs through the use of different types of microorganisms, as some have the potential to be employed in bioremediation processes (Park and Kim, 2019).

These microorganisms are widely distributed in nature, with abundance among bacteria due to their rapid reproduction, diverse nutritional capabilities, strong adaptability, and significant potential for degrading MPs. They demonstrate high efficiency in degrading MPs such as Polyethylene terephthalate (PET), Polyethylene (PE), and Polypropylene (PP) in the natural environment (Yuan et al., 2020; Li et al., 2022). Although polymers have a relatively simple chemical structure, they are known for their high resistance to biodegradation, especially due to their hydrophobic structure, high molecular weight, and lack of a favorable functional group. Consequently, when present in the environment in combination with biotic and abiotic factors, they can undergo transformations leading to the formation of alcoholic or carbonyl groups. This process increases plastic hydrophilicity and provides anchors that facilitate the attachment of bacterial species (Villalobos et al., 2022; Pathak, 2023; Thakur et al., 2023).

Thus, exploring the capability of bacteria and the interaction between bacterial enzymes and microplastics is crucial for obtaining and identifying key microorganisms with potential for bioremediation through the biodegradation of synthetic polymers. Therefore, the present study aims to identify the main bacteria that demonstrate viability for the biodegradation of MPs in various environments, as well as the enzymes produced during the degradation process.

In this systematic search, initially, 954 studies were found. Of these, 58 were excluded due to duplication, 685 due to title, 69 due to abstract, and 74 did not meet eligibility criteria, resulting in a total of 68 eligible studies for systematic review. Figure 1 presents the flowchart demonstrating the main quantitative and qualitative data of the excluded and included articles.

According to the eligible studies, the first analysis was conducted to identify the pre-dominance of microorganisms with the potential for microplastic biodegradation. Table 1 presents the main genera and species of microorganisms and their action in the biodegradation of different types of microplastics and the main enzymes analysis related to the degradation of microplastics.

The literature describes different types of microplastics (MPs), and for this study, the biodegradation actions were investigated for the following types: Polyethylene (PE), Poly-propylene (PP), Polyvinyl chloride (PVC), Polyethylene terephthalate (PET), Polystyrene (PS), High-density polyethylene (HDPE), Low-density polyethylene (LDPE), Polycaprolactone (PCL), Polyhydroxybutyrate (PHB), Polylactic acid (PLA), Bisphenol (Dimethylphenol, BPA), Polyurethane (PU), Biodegradable plastic, Nylon, and Polyvinyl acetate (PVA).

Also for this study, biodegradation analysis actions were investigated: attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) as well as electron microscope (SEM), Fourier transform infrared spectroscopy (IRS-FTIR), and gas chromatography-mass spectrometry analyses of hydroform (GC-MS), high-performance liquid chromatography (HPLC), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetry and differential scanning calorimetry (TG-DSC), nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), universal tensile machine (UTM), atomic force microscope (AFM), immobilized metal ion affinity chromatography (IMAC), size exclusion chromatography (SEC), gel permeation chromatography (GPC), matrix assisted laser desorption/ionization time of flight (MALDI TOF), mobile amorphous fraction (MAF) and determination of dry weight.

A total of 34 different bacterial genera and 63 species were observed. The most frequently found genera were Bacillus (n = 20), Pseudomonas (n = 14), Stenotrophomonas (n = 4), Rhodococcus (n = 3), and their respective species. For the genus Bacillus, the following species were identified: Bacillus sp., B. cereus, B. vallismortis, B. siamensis, B. wiedmannii, B. subtilis, B. niacini, B. paralicheniformis, B. gottheilii, B. brevies, B. pumilus, B. sphericus, and B. amyloliquefaciens. For the genus Pseudomonas, the identified species included Pseudomonas sp., P. fluorescens, P. aeruginosa, P. aestusnigri, P. protegens, P. geniculata, and P. citronellolis. Stenotrophomonas genus included the species Stenotrophomonas sp., S. rhizophila, S. panacihumi, and S. pavanii. For the genus Rhodococcus, the identified species were Rhodococcus sp., R. ruber, and R. rhodochrous.

In the qualitative synthesis regarding the main enzymes found with biodegradation activities, hydrolases and alkane hydroxylase were described as more abundant, especially for the genera Bacillus, Pseudomonas, Rhodococcus, and Ideonella.

Regarding the bias risk from the JBI checklist, it was observed that the majority of responses to the critical appraisal questionnaire from the 68 studies consisted of > 80% “Yes” responses. This indicates that the eligible studies in this investigation had a low risk of bias, meaning they demonstrated high methodological quality.

The degradation of MPs in the environment is considered an integrated process, involving biological, physical, and chemical actions. Studies have shown that biodegradation has been the most frequent and represents a future perspective for reducing these pollutants in aquatic and terrestrial environments, known as bioremediation (Yuan et al., 2020).

Thus, this work aimed to conduct a literature review on the main bacteria and microbial enzymes involved in the degradation of MPs.

Approximately 80% of commercially marketed plastic materials are obtained from thermoplastic polymers, named for their ability to change from a solid to a viscous state when subjected to high temperatures. The main industrial polymers derived from these thermoplastics and marketed worldwide are Polyethylene, Polypropylene, Polyvinyl chloride, Polyethylene terephthalate, and Polystyrene (Kotova et al., 2021).

This review found that the degradation of MPs through microbial biodegradation can occur in various sediments, including wastewater, landfill deposits, sanitary landfills, sewage residues, soil, among others (Yuan et al., 2020). This occurs because MPs represent a favorable compartment for bacterial colonization and growth, mainly by providing carbon as an energy source (Rujnić-Sokele and Pilipović, 2017). Therefore, studying pure cultures of bacterial isolates is advantageous most of the time, as it enables a controlled analysis of the metabolic pathways of these respective MPs degrading organisms. In this study, the main species and bacterial enzymes (Table 1) involved in this process of MP degradation can be observed, although this data is still not sufficient to understand the entire degradation mechanism (Bacha et al., 2021).

Over the years, an increase in the number of bacterial species with the potential for MP degradation has been observed. The most reported genera are Bacillus, Pseudomonas, Stenotrophomonas, and Rhodococcus (Auta et al., 2018; Wei et al., 2018; Amobonye et al., 2021; Li et al., 2023; Thakur et al., 2023).

The action of these bacteria occurs mainly by forming pores and irregularities on the surfaces of MPs, making them rough with various grooves and fissures, as well as by gaining the ability to adhere, colonize, and damage the MPs (Du et al., 2021; Golmohammadi et al., 2023).

Auta et al. (2017, 2018), used isolates from the genera Rhodococcus sp. and Bacillus sp. and detected a weight reduction of PP by 6.4 and 4.0%, respectively, after a period of just over a month of incubation with the MPs. Additionally, the authors found that the species B. cereus and B. gottheilii showed degradative capacity for PE of 1.6 and 6.2%, for PET of 6.6 and 3.0%, and for PS of 7.4 and 5.8%, respectively. In this perspective, Shimpi et al. (2012) identified a biodegradative capacity of 10% for PS and PLA by the species P. aeruginosa.

The studies demonstrate that these microorganisms not only cause changes in the appearance of MPs but also enable conformational changes in their structures, especially in the functional groups, in addition to reducing the molecular weight and tensile properties, as seen in the work of Yuan et al. (2020) using Stenotrophomonas maltophilia.

Biodegradation of some plastic materials such as PVC and PET is challenging because PVC contains various additives in its composition, such as plasticizers, heat stabilizers, flame retardants, and/or biocides, resulting in a total weight of approximately 50–75% of the final material. PET, due to its high content of aromatic terephthalate elements, limits the mobility of the polymeric chains, making it highly resistant to degradation by bacteria (Kotova et al., 2021).

Thus, it can be observed that the respective studies addressed have shown a more significant effect on the degradation of modified plastics such as PS, PE, and PLA, which can be explained by these plastic materials presenting better biodegradability (Chandra and Singh, 2020; Yuan et al., 2020).

Initially, the biodegradation of MPs by bacteria occurs from the degradation of larger polymer structures to smaller particles, consequently, degradation into oligomers, dimers, and monomers, finally leading to mineralization through microbial biomass. Therefore, this decomposition is aided by a diversity of enzymes that produce intermediate products (Miri et al., 2022).

Such bacterial enzymes with the potential for biodegradation are demonstrated in the studies of Shahnawaz et al. (2019), Taniguchi et al. (2019), and Sol et al. (2020). These studies reinforce that extracellular enzymes are the most studied in the literature, such as esterases, lipases, lignin peroxidases, laccases, depolymerases, cutinases, and manganese peroxidases, as they increase the hydrophilicity of MPs, allowing the conversion of carboxylic and/or alcoholic groups and significantly improving bacterial attachment and the degradation of these compounds.

Thus, the biodegradation of microplastics by bacteria through enzymes is capable of digesting these particles into carbon sources, thus changing the structure, function, molecular weight, etc., making it less toxic to the environment. Therefore, the main products obtained after mineralization by biodegradation of microplastics by bacteria are CO₂ and H₂O molecules (Anand et al., 2023).

The biodegradation of MPs by bacteria has been significantly reported in several studies as a bioremediation factor for the elimination of these compounds in the environment, as plastic materials have been increasingly used extensively and indiscriminately, causing pollution in terrestrial and aquatic environments and even impacting the public and health due to its cumulative effect. Thus, promising biotechnological techniques such as biodegradation of MPs by bacteria, however, is a challenging approach, given its high cost, since the species of bacteria and their main enzymes involved in the degradation process is still considered a high-quality treatment. Therefore, studies have intensified so that this biotechnological tactic can be incorporated into practice in order to reduce its cost, be reproducible and apply it appropriately on a large scale. Therefore, even though it is a methodology with a future perspective, it is still necessary at present for there to be a worldwide economy of polymers so that it can be directed toward a green and sustainable environmental future.

The findings in this investigation highlighted that the genera Bacillus, Pseudomonas, Stenotrophomonas, and Rhodococcus, along with their corresponding species and enzymes—hydroxylases, lipases, proteases, esterases, hydrolases, and laccases—were the main ones reported in the scientific literature regarding the potential for MP biodegradation. This indicates that these microorganisms can act as functional agents in reducing MPs.

Therefore, studies like this emphasize the importance of conducting further research, especially considering the establishment of protocols with experiments under real environmental conditions. This is crucial so that, in the future, the interaction of bacteria with MPs holds practical and biotechnological value on a large scale, aiming to reduce the impacts caused by these compounds in the environment.

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found below: PubMed, Medline, and LILACS.

MS: Writing – original draft, Writing – review & editing. KS: Formal Analysis, Investigation, Methodology, Validation, Writing – original draft, Writing – review & editing. FM: Writing – original draft, Writing – review & editing. LA: Writing – original draft, Writing – review & editing. RS: Writing – original draft, Writing – review & editing. RB: Writing – original draft, Writing – review & editing. MO: Supervision, Writing – original draft, Writing – review & editing.