The process of plastic waste decomposition by microbes is closely linked to the chemical makeup of the polymers, environmental factors, and microbial behaviour. Microorganisms are essential in the process of decomposing plastic polymers into smaller pieces, which eventually results in the transformation of these pieces into innocuous chemicals such as carbon dioxide and water. The degradation of polymers is an intricate process that is affected by both inherent characteristics of the polymer and external environmental influences. The chemical composition of a polymer, which includes its arrangement, presence of different atoms, and other substances, greatly affects its vulnerability to degradation [59]. Polymers consisting only of carbon chains, particularly those containing double bonds, exhibit greater inertness in comparison to polymers including heteroatoms or additives [60]. Their high level of purity reduces their susceptibility to external influences, hence decelerating the process of deterioration.

The length and content of the carbon backbone are significant factors. Polypropylene, which has longer chains, often demonstrates resistance to degradation [61]. However, the inclusion of heteroatoms might potentially undermine this resistance. Moreover, the degradation rates are influenced by the polarity of the polymer, with nonpolar molecules exhibiting lower susceptibility to degradation. The degree of crystallinity of a polymer also impacts its degradation. Crystalline polymers have a higher resistance to degradation compared to amorphous compounds [62]. They require less water and oxygen to start decomposing. The molecular weight of polymers is a significant factor that affects their degradation rate. Polymers with larger molecular weights have smaller relative surface areas, resulting in slower degradation [63].

The degradability of a polymer is further influenced by the production method and the additives employed. Within landfills, the combination of UV radiation and heat can trigger breakdown by auto-oxidation, causing polymers to break down into microplastics [64, 65]. These microplastics are then further degraded by microbes, resulting in the production of carbon dioxide and water. Polymers such as polyethylene, polypropylene, and polystyrene mostly break down in the presence of oxygen and exposure to UV radiation [66]. This process results in the formation of different end products, which vary depending on the kind of polymer.

The process of anaerobic degradation that occurs in landfills leads to the generation of methane and water, which is facilitated by microbial enzymes that aid in the breakdown of polymers [67]. During the process of degradation, petrochemicals undergo changes such as increased brittleness, discoloration, and the formation of new functional groups. Microorganisms have a tendency to attack the shapeless parts of plastics, whereas the structured sections break down at a slower rate.

Bioremediation by Achromobacter sp.

Achromobacter (Alcaligenaceae family) is a bacterial genus belonging to the Burkholderiales order. The cells are straight rods motile by one to twenty percent of flagella. They are aerobic and may be found in fresh and saltwater and soil. Also recognized as a contaminant in laboratory cell cultures [68, 69]. In a study published in 2022, to expedite the biodegradation of thermo-oxidatively pretreated PVC and Low-Density Polyethylene (LDPE), researchers have successfully identified Achromobacter denitrificans from compost [70]. In bacterial flasks made of PVC and LDPE, the percentage of dry weight lost was 12.3% and 6.5%, respectively, and the amount of extracellular protein was 326.4 and 112.32 mg/L, respectively. PVC underwent treatment that caused its pH to rise to 5.12, and its thermal stability was enhanced by 29 °C. Fourier Transform Infrared Spectroscopy (FTIR) results show that chain breakage in the major backbone, synthesis of new groups, and oxidation of antioxidants have all altered the chemical composition of LDPE. The carbonyl groups formed as a byproduct of LDPE breakdown are responsible for the appearance of peaks between 1700 and 1850 cm−1. Scanning Electron Microscopy (SEM) verified surface changes in LDPE and PVC.

Another research found that a novel bacterial Achromobacter xylosoxidans influences the structure of High-Density Polyethylene (HDPE) [71]. By studying the coding sequences of the 16S ribosomal subunit, a hitherto undiscovered strain of A. xylosoxidans known as PE-1 was extracted from the soil and identified. Degradation of the HDPE chemical structure was seen in analyses of foil samples performed using SEM and Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR). As a consequence, HDPE foil was found to lose around 9% of its weight. On the basis of a comparison between the spectrum of the raw material before the bacterial treatment and the range from a database of spectra, it was anticipated that the microorganisms primarily depended on the HDPE for their carbon and energy needs.

Bioremediation by Aspergillus sp.

Fungi of the genus Aspergillus are often found living as saprophytes in the soil, where they consume dead plants and other organic matter, including seeds and grains. The individuals that belong to this genus can flourish in environments with high osmotic pressure. Because of the high oxygen tension, species of the genus Aspergillus may be found in almost all environments rich in oxygen. In these environments, they often take the form of moulds on the surface of the substrate [72,73,74]. An investigation was carried out on the biodegradation of black LDPE sheets by a fungus isolated from several Egyptian landfills [75]. For 16 weeks, minimum salt medium and LDPE sheets were heated to 30 °C and rotated at 120 rpm in a rotary shaker. The fungal strains A. fumigatus MF 276893 and A. carbonarius MH 856457.1 were found to be promising LDPE biodegradation agents. The sheet weight loss percentage was much higher in a mixed culture of the two strains compared to a single isolate. Physical and chemical treatments were also used to increase the degradation capacity. By 5.89% (chemical treatment), 17.76% (HNO3 treatment), and 39.1% (heat treatment), biodegradation was found to be accelerated. New functional groups associated with hydrocarbon biodegradation were validated by FTIR, demonstrating the essential involvement of manganese peroxidase in the process. In addition to surface changes in biodegraded LDPE (as determined by SEM), differences in FTIR spectra of mixed culture biomass before and after biodegradation proved that LDPE was depolymerized. It has been reported that these strains are capable of complete biodegradation of plasticizers such as tributyl acetylcitrate, 1,2-benzenedicarboxylic acid diisooctyl ester, diisssctyl phthalate, and bis(2-ethylhexyl) phthalate, using Gas Chromatography-Mass Spectrometry (GC–MS). Another research determined five fungal isolates, including Brown rot, White rot, A. flavus, and A. Niger fungi isolated from various landfills in Peshawar, Pakistan [29]. Weight loss percentage analysis after 30 days of incubation was used to determine the biodegradation potential of these isolates against LDPE polymers. white rot, brown rot, A. flavus, and A. niger fungus all demonstrated biodegradation percentages of 22.7%, 18.4%, 16.1%, and 22.9%, respectively.

Further research used Fusarium solani, A. versicolor, and A. flavus, all of which were retrieved from a municipal waste yard in Chennai, India, to study the biodegradation of LDPE [76]. The polymers were tested for degradation by exposure to microbial cultures for 60 days in the lab. FTIR spectra verified the biodegradation of LDPE, whereas Field Emission Scanning Electron Microscopy (FESEM) micrographs demonstrated that the fungi had colonized the polythene matrix as a result of their metabolic activities. Sturm test results suggest A. versicolor strain is a more promising LDPE-degrading option than the F. solani and A. flavus strains. Under controlled laboratory conditions, the biodegradation rate of LDPE sheets was measured after being inoculated with bacteria and fungi collected from various locations around the Dandora dumpsite [77]. Researchers incubated the LDPE sheets for 16 weeks at 37 °C for bacteria and 28 °C for fungus. A.s oryzae strain A5 showed the greatest fungal degradation activity, decreasing the average weight by 36.42 ± 5.53%. Findings suggest that Aspergillus, Bacillus, and Brevibacillus are promising candidates for biodegrading LDPE. Moreover, a group of researchers extracted fungal candidates from a nearby dumping site. Mushrooms were grown in a broth made of mineral salts and LDPE powder. In broth medium supplemented with LDPE, only two (RH06 and RH03) of the nine isolates showed the maximum growth response. The findings showed that after 45 days of culture, there was a 5.13% drop in the weight of LDPE film when using isolate RH03, and there was a 6.63% decrease when using isolate RH06. In addition to this, the tensile strength of the treated film was found to be reduced by 58% over the board and 40% in each isolate. The LDPE film's surface developed a groove and a roughness, as shown by an electron microscopy analysis. Moreover, DNA sequencing and Polymerase Chain Reaction data confirmed that strains RH06 is A. nomius and RH03 is Trichoderma viride, with a 96% and 97% degree of similarity, respectively. The ability of A. clavatus to degrade LDPE in an aqueous medium was observed for 90 days [78]. PE mass loss, CO2 evolution measured by the Strum test, FTIR, and SEM/Atomic Force Microscopy (AFM) morphological alterations all corroborated the deterioration. Researchers used enrichment culture and screening processes to identify two strains of Lysinibacillus sp. and Aspergillus sp. from waste soils in Tehran, which showed outstanding capacities to break down LDPE [79]. UV-irradiated and non-irradiated pure LDPE films without pro-oxidant additives underwent 126 days of biodegradation in soil with and without mixed cultures of selected microorganisms. As seen by carbon dioxide soil measurements taken after 126 days, biodegradation was moderate in the absence of microorganisms; UV-irradiated and non-UV-irradiated LDPE mineralization was only 8.6% and 7.6%, respectively. Biodegradation was much more effective when the targeted microorganisms were present, with biodegradation percentages for UV-irradiated and non-UV-irradiated films being 29.5% and 15.8%, respectively. When UV-irradiated LDPE was biodegraded in soil containing the designated microorganisms, the percentage decline in the carbonyl index was more pronounced. X-ray diffraction (XRD), FTIR, and SEM confirmed that the chosen microorganisms were able to alter and colonize both kinds of PE.

An A. flavus fungi PEDX3 was identified from the digestive tract of the wax moth, Galleria mellonella [41]. The results of a 28-day incubation period demonstrated that strain PEDX3 was capable of breaking down HDPE MPP (microplastic particles) into the MPP with reduced molecular weight. As measured by FTIR, the breakdown of PE was further confirmed by the presence of carbonyl and ether groups of MPP. Additionally, Reverse Transcription-Polymerase Chain Reaction (RT-PCR) was used to look for possible degradation enzymes. At the end of the degradation process, two genes, AFLA 053930 and AFLA 006190, encoding laccase-like multicopper oxidases, were found to have had their expression levels increase, indicating that they encode probable PE-degrading enzymes. In another investigation, A. flavus VRKPT2 and A. tubingensis VRKPT1 isolated from the PE trash deposited in marine coastal regions were tested under in vitro conditions to be efficient in HDPE breakdown [80]. The isolated fungus was identified based on internal transcribed space (ITS) homology sequence analysis. Even after 1 month of incubation, the biofilm development detected using an epifluorescent microscope revealed the vitality of fungal strains.

Bioremediation by Bacillus sp.

Bacillus species are rod-shaped, aerobic, sporulating bacteria abundant in nature. They may be either obligatory aerobes, which are oxygen-dependent, or facultative anaerobes and may thrive without oxygen [81]. A study was set out to determine how effective bacterial isolates were in degrading microplastics in the Vaigai River in Madurai, India [82]. After being properly processed, the isolates were included in the degradation of UV-treated PE and PP. Four bacterial isolates, including Bacillus sp. (BS-2), Bacillus paramycoides (BP), Bacillus cereus (BC), and Bacillus sp. (BS-1), passed the first screening and were evaluated for the 21-day degrading experiment. Bacterial isolates were stuffed into the microplastics, and a shake flask experiment was conducted using two different methods, each with a control. Degradation of the microplastics was demonstrated by a decrease in their weight, an increase in their fragmentation, and a shift in their surface area compared to control studies (microplastics without isolates). Although PP degradation was most significant with BP (78.99 ± 0.005%) and BC (63.08 ± 0.009%) when used separately, the greatest PP and PE degradation were achieved when BC and BP were used together (78.62 ± 2.16% and 72.50 ± 20.53%).

Activated sludge was studied as a potential biocatalyst for the degradation of microplastics in water [83]. It was initially tested for its ability to hydrolyze PET polymers pretreated at 100 °C for an hour. To assess degradation potential, the consortium undertook a typical CO2 evolution test at pH 7–7.5, 30 °C, 168 days reactor residence time, and 2.63 g/L PET concentration. After being incubated, the group was able to break down 17% of the PET. Surface erosion was responsible for the unaltered molecular weight. Biodegradation was also noticeably accelerated in the presence of abundant oxygen. Agromyces mediolanus PNP3 and B. cereus SEHD031MH were discovered to be two of the consortium's isolated bacterial strains. Even though growth was optimal for both strains when grown on PET medium alone, only B. cereus showed enzyme activity in a clear-zone assay. The bacterial degradation of polyhydroxybutyrate (PHB) was studied in a solid-media culture setting over a range of temperatures and salinities [53]. After 14 days of cultivation on PHB film, studies show that Bacillus sp. JY14 can destroy around 98% of PHB. This species was shown to be able to biodegrade P(3HB-co-3HV) and P(3HB-co-4HB).

In a study, sixty marine bacteria were tested for their capacity to digest LDPE [84]. When tested using polythene as the only carbon source for growth, only three were discovered to be effective. Positive isolates were identified by comparing their 16S rRNA gene sequences. The researcher determined that they belonged to the genus Kocuria, species M16; genus Bacillus, species M27; and genus Bacillus subtilis, species H1584. During a 30-day incubation period with H1584, M27, and M16 isolates, PE lost 1.7%, 1.5%, and 1% of its weight. Hydrophobicity on the cell surface was highest (32% in M16), then 15% in H1584, and finally 27% in M27. A triphenyltetrazolium chloride reduction assay was used to verify the vitality of the isolates grown on the PE surface. Calculations of the Keto Carbonyl Bond Index, Ester Carbonyl Bond Index, and Vinyl Bond Index from FTIR spectra showed increases consistent with PE biodegradation.

Bioremediation by Collectotrichum sp.

Colletotrichum (sexual stage: Glomerella) is a genus of endophytes or phytopathogens that are symbionts to plants. Some species in this genus may have a symbiotic relationship with their host plants [85]. Thirty fungi were tested for biodegradability of LDPE films in mineral salt medium agar [86]. Stagonosporopsis citrulli, Collectotrichum fructicola, Thyrostroma jaczewskii, and Diaporthe italiana grew much faster than Aspergillus niger when grown on LDPE film as the sole carbon source. For a further 90 days, they were grown in a broth made of mineral salts and LDPE film instead of any other carbon source. CO2 emissions ranged from 0.45 to 1.45 g/L for D. italiana, 0.36 to 1.22 g/L for T. jaczewskii, 0.33 to 1.26 g/L for C. fructicola, 0.37 to 1.27 g/L for S. citrulli, and 0.33 to 1.27 g/L for A. niger when they were cultured on LDPE film. Compared to the levels of lignin peroxidase and manganese peroxidase secreted by the same fungus, the quantity of laccase enzyme produced was reported to be much higher. It was further investigated how these fungi degrade LDPE sheets when cultured. Weight loss was recorded as 28.78, 45.12, 48.78, 46.34, and 43.90%; tensile strength as 3.34, 1.86, 0.43, 1.78, and 1.56 MPa for LDPE films cultured with A. niger, S. citrulli, C. fructicola, T. jaczewskii, and D. italiana, respectively. After incubation with various fungi, especially C. fructicola, FTIR measurement revealed an increased carbonyl index in LDPE films. The biodegradation of LDPE films was validated by SEM analysis, which revealed morphological changes on the film's surface, including cracks, scions, and holes. The Volatile Organic Compounds, 1,1-dimethoxy-decane, 1,3-dimethoxy-5-(1-methylethyl)-benzene, and 1,3-dimethoxy-benzene were found in these fungi. In terms of biodegradation of LDPE, C. fructicola shows promise as a resource and may be incorporated in fungal-based plastic degrading systems.

Bioremediation by Comamonas sp.

Gram-negative, rod-shaped spirilla (often called “rods”) are found in bacteria of the genus Comamonas. These microorganisms are chemoorganotrophic, meaning they feed off of organic matter rather than sugars, and they are aerobic [87]. The breakdown of dimethyl phthalate (DMP) by a Comamonas testosterone bacterial strain, DB-7, was investigated in a study [88]. The results indicate that DMP at varying doses was quickly destroyed, with over 99% degradation occurring within 14 h at 450 mg/L. The breakdown rate of DMP was found to be positively proportional to the inoculum volume of the bacteria, with the ideal degradation temperature being 30–35 °C and pH 9.0, respectively. According to HPLC (High-performance liquid chromatography) and LC/MS (Liquid Chromatography-Mass Spectrometry) studies of metabolic products, phthalic acid (PA) and mono-methyl phthalate (MMP) are the primary degrading intermediates formed by DB-7 during the breakdown of DMP.

Bioremediation by Enterobacter sp.

The genus Enterobacter includes rod-shaped, non spore-forming, gram-negative, facultatively anaerobic bacteria of the Enterobacteriaceae family. The type genus of the family Enterobacterales [89]. A group of researchers conducted research on the breakdown of LDPE by the recently discovered Enterobacter cloacae AKS7 [90]. A progressive rise in Extracellular Polymeric Substance (EPS) production by the organism (AKS7) was also identified, indicating the establishment of an effective biofilm on the LDPE surface. In addition, two AKS7 mutants with significantly reduced cell-surface hydrophobicity compared to their wild type were screened. The results of which contrasted to wild-type AKS7 cells, the mutants exhibited lower levels of LDPE breakdown. Further analysis showed that, in contrast to wild-type cells, AKS7 mutant cells lacked the ability to adhere to LDPE. The findings showed that AKS7's hydrophobic cell surface promotes the growth of microbial biofilm on LDPE, leading to more efficient breakdown of the plastic by the microbe. Given these results, the organism may be evaluated as a bio-remediating agent for the long-term degradation of polythene-based toxic waste.

Bioremediation by Halomonas sp.

Halomonas is a genus of salt-tolerant (halophilic) bacteria. They are rod-shaped gram-negative bacteria and develop in the presence of oxygen. However, it has been reported that some may grow without oxygen [91]. Four bacterial strains with the ability to biodegrade LDPE were identified by a research group [92]. The 16S rRNA gene sequencing technique indicated that bacterial isolates H-265, H-256, H-255, and H-237 were closely related to Alcanivorax sp., Exigobacterium sp., Halomonas sp., and Cobetia sp., respectively. Researchers used the Bushnell-Haas medium to incubate these bacterial strains separately for 90 days while providing them with LDPE sheets as a carbon source. Bacterial isolates were able to develop a viable biofilm on the surface of LDPE during the biodegradation experiment, reducing the films' thermal stability. After the incubation research, the bacterial isolate H-255 was shown to have caused a maximum LDPE film weight decrease of 1.72%. FESEM and AFM demonstrated that bacterial adhesion to the film altered its physical structure (surface erosion, roughness, and deterioration). When compared to a control LDPE film, the spectra obtained using ATR-FTIR demonstrated a shift in the peaks associated with C–H stretching and C=C bond stretching and the development of additional peaks associated with C–O stretching and –C=C– bond stretching. Furthermore, carbon remineralization and enzymatic activity validated the biodegradation of LDPE film. This research demonstrated that some marine bacteria actively biodegrade LDPE film, and that these bacteria have the potential to lessen marine plastic pollution.

Bioremediation by Klebsiella sp.

The gram-negative, encapsulated, non-motile, facultatively anaerobic, lactose-fermenting, rod-shaped bacterium Klebsiella pneumoniae is characterized by its unique characteristics. It occurs naturally in the soil, and around 30% of strains are capable of fixing nitrogen under anaerobic environments [93]. Klebsiella pneumoniae CH001, a clinical isolate, was screened for bioremediation of HDPE [94]. After 60 days of growth in nutritional broth at 30 °C and 120 rpm, results indicated that this strain could develop a substantial biofilm on HDPE surfaces. The Universal testing machine (UTM) results indicated a considerable drop in HDPE film's tensile strength (60%) and weight (18.4%). In addition, SEM research revealed surface fractures in the HDPE, while AFM findings demonstrated an increase in surface roughness during bacterial incubation. Taken together, findings suggest that K. pneumoniae CH001 is a promising option for the environmentally responsible breakdown of HDPE in natural settings.

Bioremediation by Penicillium Sp.

Penicillium is a genus of ascomycetous fungus that is an integral component of the mycobiome of several species. Certain species of the genus generate penicillin, an antibiotic chemical that kills or inhibits the development of certain types of bacteria. Other species are used in cheese production. According to the tenth edition of the Dictionary of the Fungi (2008), the broad genus has more than 300 species [95]. Because of its rapid colony development in the screening medium, the isolate Penicillium citrinum was chosen for biodegradation research. In a research, 16 plastic-degrading fungi were isolated from plastic-laden landfill soil in Bhopal, India [44]. Fungi capable of decomposing PE were screened for using a mineral salt agar medium spiked with 3% LDPE powder. Untreated LDPE fragments lost 38.82 ± 1.08% of their weight when exposed to P. citrunum; however, after being pretreated with nitric acid, biodegradation increased by 47.22 ± 2.04%. New functional groups ascribed to hydrocarbon biodegradation appeared in FTIR spectra, suggesting enzymatic participation in the process. Depolymerization of LDPE was validated by changes in the FTIR spectra and FE-SEM of LDPE samples (both untreated and pretreated) before and after biodegradation. Variations in the rates of thermal breakdown between biodegraded and control samples provide more evidence of biodegradation. The remarkable competence of P. citrinum in LDPE degrading without any pre-treatment has been reported for the first time in this work.

To effectively biodegrade polyvinyl alcohol (PVA) in vitro, researchers set out to discover and broadly screen endophytic fungi (from specified plants) [42]. Seventy-six endophytic fungi were cultured in total on a PVA screening agar medium. Using a combination of phenotypic traits, ITS ribosomal gene sequences, and phylogenetic analysis, 10 isolates were found to have a potential biodegrading effect and were subsequently identified. After 10 days of growth at 150 rpm and 28 °C, four strains showed maximal PVA-degradation in the liquid medium. Penicillium brevicompactum OVR-5 removed 81% of PVA, Talaromyces verrucosus PRL-2 removed 67%, Penicillium polonicum BJL-9 removed 52%, and Aspergillus tubingensis BJR-6 removed 41%. OVR-5 was found to be the most promising PVA biodegradation isolate, producing laccase, manganese peroxidase, and lipase enzymes at an ideal pH of 7.0 and an optimal temperature of 30 °C. This work hypothesized a possible PVA breakdown mechanism for OVR-5 in light of investigations of its metabolic intermediates, which GC–MS discovered. Both SEM and FTIR verified the biodegradation findings.

The antarctic filamentous fungus was studied for its ability to degrade polyurethane (PU), polystyrene (PS), and PE samples in a liquid solution [96]. Plastic samples were either inoculated with Antarctic fungus (Mortierella, Geomyces, Penicillium species), treated, left untreated, or artificially aged in a UV chamber for 500 h per ASTM G155. All samples were kept in an incubator for 90 days at 18 °C. The rate of weight loss was examined as a function of time to evaluate the physical–chemical and biological degradation of plastics. In the artificial ageing chamber, polymers suffered an oxidative breakdown, which sped up their biodegradation (seen as morphological and structural alterations). Penicillium sp., of the three fungal strains, showed the most significant breakdown at 28.3% in PU, 8.39% in PS, and 3.5% in LDPE.

In a study, the researcher used garbage bags to isolate fungi and their ability to degrade LDPE. In this case, ethanol-treated LDPE was used alongside untreated LDPE [43]. F1 isolation demonstrated the most degradation out of the three fungal isolates, and this isolate damaged the untreated sheet similarly. Areas of degradation were seen in the surface morphology of F1-treated LDPE as analyzed by SEM. FTIR testing revealed that F1 affected the polymer’s production of carbonyl and C=C groups. F1 fungus, when grown in the laboratory, was discovered to release the lipase enzyme. Molecular testing confirmed that isolate F1 was indeed P. simplicissimum strain Bar2. In another study, P. simplicissimum was discovered in a Shivamogga district landfill by a group of researchers [97]. Findings indicate that treated PE (38%) was more easily degraded by P. simplicissimum than autoclaved (16%) or surface-sterilized (7.7%) PE. P. simplicissimum was tested for enzymes that degrade PE. Laccase and manganese peroxidase were shown to be active enzymes. Based on these findings, P. simplicissimum was reported as a potential answer to the world’s PE crisis.

A group of investigators evaluated "Bionolle®" polyester-modified PET films biodegradation in comparison with unmodified PET films in terms of time to decompose [98]. The films' weight was recorded before and after being incubated with the filamentous fungus P. funiculosum or their extracellular hydrolytic enzymes released by "Bionolle®" for 84 days. FTIR and X-ray Photoelectron Spectroscopy (XPS) studies revealed significant chemical alterations in polymeric chains. In addition to hydrolytic enzymes, oxidative ones were likely involved in the degradation of films by fungi, as shown by the significant decrease in the number of aromatic rings formed from terephthalic acid. Additionally, "Bionolle®" did not accelerate modified film deterioration.

Bioremediation by Phanerochaete sp.

Phanerochaete is a crust fungus genus belonging to the Phanerochaetaceae family. It has historically been classified based on the fruit body's general shape and microscopic features, such as the spores, cystidia, and hyphal structure. According to molecular analyses, the genus is polyphyletic, with members scattered over the phlebioid clade of the Polyporales order [99, 100]. A study examined the biodegradability of starch-blended PVC films using controlled laboratory studies utilizing selected fungus isolates and in-situ burial in soil [101]. SEM revealed the surface anomalies such as colour change and mild disintegration in PVC films after 90 days. Isolation of fungal strains characterized by robust growth and adhesion to plastic sheets. Phanerochaete chrysosporium PV1 was chosen among the strains exhibiting the highest levels of activity and later confirmed to be this species by rDNA sequencing. FTIR and Nuclear Magnetic Resonance (NMR) studies revealed new peaks, suggesting substantial structural changes and transformation in the films. Gel permeation chromatography (GPC) backed this up by showing a considerable reduction in the molecular weight of polymer film from 80,275 to 78,866 Da (treated). The release of more carbon dioxide (7.85 g/l) than the control (2.32 g/l) in the respirometric technique provided further evidence of the biodegradation of starch-blended PVC films. Hence, suggesting P. chrysosporium PV1 is a fungal strain with excellent potential for bioremediation of plastic waste.

Bioremediation by Pseudomonas sp.

There are 191 different species of the genus Pseudomonas, which are all gram-negative gamma-proteobacteria in the family Pseudomonadaceae. Members of this genus exhibit a high degree of metabolic variability, allowing them to colonize a wide variety of habitats [102, 103]. It is suggested by research that the Pseudomonas sp. found in the digestive tracts of superworms might effectively biodegrade Polyphenylene sulphide (PPS) [49]. The biodegradation time of the bead form of plastic was drastically reduced due to its superior degradation efficiency compared to the standard film type of plastic. Therefore, this work employed plastic beads with a diameter of 300 m to assess the Pseudomonas sp. mediated PPS biodegradation over 10 days instead of film-type plastics. This technology not only compares and verifies the biodegradation performance of different polymers in 10 days, but it also quickly identifies the best bacteria for plastic biodegradation.

As reported, another research set out to examine the biodegradation capabilities of five bacterial strains against PVC, PS, PP, and PE films under aerobic conditions [51]. A generalised aerobic breakdown mechanism for plastics is shown in Fig. 2. B. flexus and P. citronellolis were chosen as suitable PVC film degraders after preliminary screening. Biodegradation of PVC films was tested using the two strains in 2-L flasks. Fragmentation of the film was found after 45 days of incubation, indicating PVC biodegradation. PVC incubated with P. citronellolis had a 10% decrease in average molecular weight, as determined by GPC, suggesting that PVC polymer chains were attacked. These findings led to the selection of the P. citronellolis strain for biodegradation experiments. As determined by chemical evaluation of the films after 30 days of incubation, the waste PVC polymers had biodegraded, resulting in a gravimetric weight loss of up to 19%. In conclusion, this study documents B. flexus and P. citronellolis ability to biodegrade PVC sheets. Both strains were shown to have a negligible effect on PVC polymer, suggesting that they work primarily against PVC additives.

Fig. 2

A generalised aerobic breakdown mechanism for plastics

A soil-dwelling bacteria capable of degrading polyester PU was isolated and characterized as strain MZA-85 [104]. It was determined that the bacterium was Pseudomonas aeruginosa by 16S rRNA gene sequencing. The strain MZA-85 altered the surface morphology of PU film, as shown in SEM. The FTIR spectrum exhibited an augmentation of the organic acid functional group and a concomitant diminution of the ester functional group. Results from GPC showed a rise in polydispe