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The flexibility and the low production costs offered by plastics have made them crucial to society. Unfortunately, due to their resistance to biological degradation, plastics remain in the environment for an extended period of time, posing a growing risk to life on earth. Synthetic treatments of plastic waste damage the environment and may cause damage to human health. Bacterial and fungal isolates have been reported to degrade plastic polymers in a logistic safe approach with the help of their microbial cell enzymes. Recently, the bacterial strain Ideonella sakaiensis (201-F6) was discovered to break down and assimilate polyethylene terephthalate (PET) plastic via metabolic processes at 30 °C to 37 °C. PETase and MHETase enzymes help the bacterium to accomplish such tremendous action at lower temperatures than previously discovered enzymes. In addition to functioning at low temperatures, the noble bacterium's enzymes have amazing qualities over pH and PET plastic degradation, including a shorter period of degradation. It has been proven that using the enzyme PETase, this bacterium hydrolyzes the ester linkages of PET plastic, resulting in production of terephthalic acid (TPA), nontoxic compound and mono-2-hydroxyethyl (MHET), along with further depolymerization of MHET to release ethylene glycogen (EG) and terephthalic acid (TPA) by the second enzyme MHETase. Enzymatic plastic degradation has been proposed as an environmentally friendly and long-term solution to plastic waste in the environment. As a result, this review focuses on the enzymes involved in hydrolyzing PET plastic polymers, as well as some of the other microorganisms involved in plastic degradation. [ABSTRACT FROM AUTHOR]

Plastic and microplastic pollution has caused a great deal of ecological problems because of its persistence and potential adverse effects on human health. The degradation of plastics through biological processes is of great significance for ecological health, therefore, the feasibility of plastic degradation by microorganisms has attracted a lot of attention. This study comprises a preliminary discussion on the biodegradation mechanism and the advantages and roles of different bacterial enzymes, such as PET hydrolase and PCL-cutinase, in the degradation of different polymers, such as PET and PCL, respectively. With a particular focus on their modes of action and potential enzymatic mechanisms, this review sums up studies on the biological degradation of plastics and microplastics related to mechanisms and influencing factors, along with their enzymes in enhancing the degradation of synthetic plastics in the process. In addition, biodegradation of plastic is also affected by plastic additives and plasticizers. Plasticizers and additives in the composition of plastics can cause harmful impacts. To further improve the degradation efficiency of polymers, various pretreatments to improve the efficiency of biodegradation, which can cause a significant reduction in toxic plastic pollution, were also preliminarily discussed here. The existing research and data show a large number of microorganisms involved in plastic biodegradation, though their specific mechanisms have not been thoroughly explored yet. Therefore, there is a significant potential for employing various bacterial strains for efficient degradation of plastics to improve human health and safety. [ABSTRACT FROM AUTHOR]

The widespread use of polyethylene terephthalate (PET) in various industries has led to a surge in microplastics (MPs) pollution, posing a significant threat to ecosystems and human health. To address this, we have developed a bacterial enzyme cascade reaction system (BECRS) that focuses on the efficient degradation of PET. This system harnesses the Escherichia coli (E. coli) surface to display CsgA protein, which forms curli fibers, along with the carbohydrate-binding module 3 (CBM3) and PETases, to enhance the adsorption and degradation of PET. The study demonstrated that the BECRS achieved a notable PET film degradation rate of 3437 ± 148 μg/(d*cm²), with a degradation efficiency of 21.40% for crystalline PET MPs, and the degradation products were all converted to TPA. The stability of the system was evidenced by retaining over 80% of its original activity after multiple uses and during one month of storage. Molecular dynamics simulations confirmed that the presence of CsgA did not interfere with the enzymatic activity of PETases. This BECRS represents a significant step forward in the biodegradation of PET, particularly microplastics, offering a practical and sustainable solution for environmental pollution control. [Display omitted] • Surface display of PETase on E. coli using the CsgA module-mediated display system. • Co-displaying CBM3 and PET hydrolase on the ECN surface with MHETase intracellularly. • Structural modeling analysis of the effect of CsgA on the catalytic mechanism. • The system exhibits robust repeatability and long-term storage stability. • BECRS effectively converts PET MPs to TPA without byproducts. [ABSTRACT FROM AUTHOR]

The microbial degradation of polyethylene (PE) and polypropylene (PP) resins in rivers and lakes has emerged as a crucial issue in the management of microplastics. This study revealed that as the flow rate decreased longitudinally, ammonia nitrogen (NH 4 +-N), heavy fraction of organic carbon (HFOC), and small-size microplastics (< 1 mm) gradually accumulated in the deep and downstream estuarine sediments. Based on their surface morphology and carbonyl index, these sediments were identified as the potential hot zone for PE/PP degradation. Within the identified hot zone, concentrations of PE/PP-degrading genes, enzymes, and bacteria were significantly elevated compared to other zones, exhibiting strong intercorrelations. Analysis of niche differences revealed that the accumulation of NH 4 +-N and HFOC in the hot zone facilitated the synergistic coexistence of key bacteria responsible for PE/PP degradation within biofilms. The findings of this study offer a novel insight and comprehensive understanding of the distribution characteristics and synergistic degradation potential of PE/PP in natural freshwater environments. [Display omitted] • Microplastic was enriched in freshwater estuarine sediments with reduced flow rate. • Deep and downstream sediment was the hot zone of PE/PP degradation in estuaries. • PE/PP-degrading genes and enzymes of plastic biofilms were higher in the hot zone. • PE/PP-degrading core bacteria and enzymes in biofilms were positively correlated. • NH 4 +-N and HFOC benefit the coexistence of synergistic-degrading bacteria of PE/PP. [ABSTRACT FROM AUTHOR]

Wastewater treatment plants (WWTPs) usually contain microplastics (MPs) due to daily influents of domestic and municipal wastewater. Thus, the WWTPs act as a point source of MPs distribution in the environment due to their incapability to remove MPs completely. In this study, MPs occurrence and distribution in anaerobic sludge from WWTPs in different regions (Kaifeng "KHP", Jinan "JSP", and Lanzhou "LGP") were studied. Followed by MPs identification by microscopy and Fourier transform infrared (FTIR) spectrum. The microbial communities associated with anaerobic sludge and MPs were also explored. The results showed that MPs concentrations were 16.5, 38.5, and 17.2 particles/g of total solids (TS) and transparent MPs accounted for 49.1%, 58.5%, and 48.3% in KHP, JSP, and LGP samples, respectively. Fibers represented the most common shape of MPs in KHP (49.1%), JSP (56.0%), and LGP (69.0%). The FTIR spectroscopy indicated the predominance of polyethylene polymer in 1–5 mm MPs. The Proteobacteria, Chloroflexi, Actinobacteria, Bacteroidetes, and Planctomycetes were the abundant phyla in all anaerobic sludge. The bacterial genera in KHP and LGP were similar, in which Caldilinea (>23%), Terrimonas (>10%), and Ferruginibacter (>7%) formed the core bacterial genera. While Rhodococcus (15.3%) and Rhodoplanes (10.9%) were dominating in JSP. The archaeal genera Methanosaeta (>69%) and Methanobrevibacter (>10%) were abundant in KHP and LGP sludge. While Methanomethylovorans accounted for 90% of JSP. Acetyltransferase and hydratase were the major bacterial enzymes, while reductase was the key archaeal enzyme in all anaerobic sludge. This study provided the baseline for MPs distribution, characterization, and MPs associated microbes in WWTPs. [Display omitted] • Microplastics varied from 16.5 to 38.5 items/g total solids in anaerobic sludge. • Transparent (48.3–58.5%) and fiber (49.1–69%) were the main MPs colors and shapes. • Larger MPs (1–5 mm) accounted for less (9.1–19%) in anaerobic sludge. • Caldilinea (23.6–38.7%) and Terrimonas (22.1%) are the dominant bacterial genera. • Methanosaeta and Methanomethylovorans were the dominant archaeal genus. [ABSTRACT FROM AUTHOR]

Polyhydroxyalkanoates (PHAs) are biopolymers synthesized by a wide range of bacteria, which serve as a promising candidate in replacing some conventional petrochemical-based plastics. PHA synthase (PhaC) is the key enzyme in the polymerization of PHA, and the crystal structures were successfully determined using the catalytic domain of PhaC from Cupriavidus necator (PhaCCn-CAT) and Chromobacterium sp. USM2 (PhaCCs-CAT). Here, we review the beneficial mutations discovered in PhaCs from a structural perspective. The structural comparison of the residues involved in beneficial mutation reveals that the residues are near to the catalytic triad, but not inside the catalytic pocket. For instance, Ala510 of PhaCCn is near catalytic His508 and may be involved in the open-close regulation, which presumably play an important role in substrate specificity and activity. In the class II PhaC1 from Pseudomonas sp. 61-3 (PhaC1Ps), Ser325 stabilizes the catalytic cysteine through hydrogen bonding. Another residue, Gln508 of PhaC1Ps is located in a conserved hydrophobic pocket which is next to the catalytic Asp and His. A class I, II-conserved Phe420 of PhaCCn is one of the residues involved in dimerization and its mutation to serine greatly reduced the lag phase. The current structural analysis shows that the Phe362 and Phe518 of PhaC from Aeromonas caviae (PhaCAc) are assisting the dimer formation and maintaining the integrity of the core beta-sheet, respectively. The structure-function relationship of PhaCs discussed in this review will serve as valuable reference for future protein engineering works to enhance the performance of PhaCs and to produce novel biopolymers. [ABSTRACT FROM AUTHOR]

• We isolated 11 novel strains of a polyamide 4 (PA4)-degrading bacterium from the sea. • A novel PA4-degrading enzyme was purified and its properties were characterized. • The enzyme hydrolyzes PA4 at amide bonds into gamma-aminobutyric acid oligomers. • The enzyme has substrate-binding, linker, and catalytic domains. Polyamide 4 (PA4) is a biobased plastic that has superior mechanical properties. PA4 shows good biodegradability in terrestrial and marine environments; however, the detailed interaction between PA4 and PA4-degrading enzymes from PA4-degrading microorganisms remains unclear. In this study, we isolated 11 novel strains of a PA4-degrading bacterium belonging to Pseudoalteromonas from a marine environment. Pseudoalteromonas sp. Y-5, which showed the highest PA4-degrading activity among the isolates, produced maximum PA4-degrading activity in culture supernatant after 4 days of incubation at 15 °C in Marine Broth 2216 containing 0.5 w/v% PA4 powder. We purified an enzyme that hydrolyzes PA4 at amide bonds into γ-aminobutyric acid oligomers (2–3 mers) from the culture supernatant. Based on a homology search using the amino acid sequence and predicted 3D structure of the enzyme, it was predicted to be composed of a substrate binding domain (SBD), linker domain, and catalytic domain (CD). The enzyme is a homodimer consisting of 75-kDa subunits, and the SBD is digested by autolysis in the absence of Ca2+. Interestingly, enzymatic properties, such as optimum temperature, pH, and NaCl concentration for high activity, differed between the full-size enzyme and autolyzed enzyme. In the predicted 3D structure of the enzyme, the structure of the CD overlapped with that of 6-aminohexanoate-dimer hydrolase, with a root mean square deviation of 1.084 Å. To our knowledge, this is the first report on the enzymatic and structural properties of a marine PA4-degrading enzyme. Our findings contribute to the understanding of the mechanisms of PA4 degradation in the marine environment. [ABSTRACT FROM AUTHOR]

This study focused on the biodegradation of LDPE films using a novel isolate of Bacillus obtained from soil samples collected from a 20-year-old plastic waste dump. The aim was to evaluate the biodegradability of LDPE films treated with this bacterial isolate. The results indicated a 43% weight loss of LDPE films within 120 days of treatment. The biodegradability of LDPE films was confirmed through various testing methods, including BATH, FDA, CO 2 evolution tests, and changes in total cell growth count, protein content, viability, pH of the medium, and release of microplastics. The bacterial enzymes, including laccases, lipases, and proteases, were also identified. SEM analysis revealed biofilm formation and surface changes in treated LDPE films, while EDAX analysis showed a reduction in carbon elements. AFM analysis demonstrated differences in roughness compared to the control. Furthermore, wettability increased and tensile strength decreased, confirming the biodegradation of the isolate. FTIR spectral analysis showed changes in skeletal vibrations, such as stretches and bends, in the linear structure of polyethylene. FTIR imaging and GC-MS analysis also confirmed the biodegradation of LDPE films by the novel isolate identified as Bacillus cereus strain NJD1. The study highlights the potentiality of the bacterial isolate for safe and effective microbial remediation of LDPE films. [Display omitted] • Bacillus cereus NJD1 isolate from plastic dump degrades Non-pre-treated LDPE films • Treated LDPE with the novel isolate showed 43% weight loss in 120 days • Validation experiments for biofilm formations and biodegradation summarized • SEM and AFM analysis reveals biofilm formation and surface changes • FTIR and GC-MS confirm LDPE biodegradation by Bacillus cereus [ABSTRACT FROM AUTHOR]

Environment plastic litter accumulation is a significant concern, needing urgent advancements in plastic waste management. Recent investigations into plastic biodegradation by bacteria and their enzymes are creating exciting unique opportunities for the development of biotechnological plastic waste treatment methods. This review summarizes information on bacterial and enzymatic biodegradation of plastic in a wide range of synthetic plastics such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyurethane (PUR), polytetrafluoroethylene (PTFE) and polyvinyl chloride (PVC). Plastic biodegradation is facilitated by Acinetobacter, Bacillus, Brevibacillus, Escherichia, Pseudomonas, Micrococcus, Streptomyces, and Rhodococcus bacteria, and enzymes such as proteases, esterases, lipases, and glycosidases. Molecular and analytical procedures used to analyze biodegradation processes are outlined, as are the obstacles in verifying plastic breakdown using these methods. Taken together, the findings of this study will contribute significantly to the construction of a library of high-efficiency bacterial isolates and consortiums and their enzymes for use in plastic biosynthesis. This information is useful to researchers investigating plastic bioremediation and a supplement to the scientific and grey literature already accessible. Finally, the review focuses on expanding the understanding of bacterial capacity to break-down plastic utilizing modern biotechnological methods, bio-nanotechnological-based materials, and their future role in resolving pollution problems. • Bacterial species exhibiting plastic bioremediation characteristics. • Recent advances in the use of highly effective bacterial consortiums as long-term remedies to plastic pollution. • Identifying and overcoming issues and obstacles in plastic bacterial bioremediation for potential new advances in pollution control is required for plastic bioremediation. • In the future, enzyme-based technologies, biotechnology, and bio-nanotechnology may increase plastic biodegradation. • Plastic degradation necessitates the development of systematic ways to enhance bacterial consortia enrichment processes. • Clear procedures for confirming biodegradation and selecting isolates are necessary. [ABSTRACT FROM AUTHOR]