Polyurethane biodegradation by Serratia sp. HY-72 isolated from the intestine of the Asian mantis Hierodula patellifera

Experimental and Computational Insights into Polyurethane Plastic Waste Conversion to Microbial Bioplastic

In this study, a seven-factor Hoke experimental design and the response surface methodology were used to optimize the fermentation conditions for the maximum polyhydroxyalkanoates (PHA) yield using polyurethane plastic waste (PUPW) as a source of carbon and energy for the microbial growth and biobased polyester production. The highest PHA yield (0.80 g/L ± 0.01) was obtained under a pH of 8; a temperature of 35 °C; a NaCl concentration of 5%; a PUPW concentration of 1%; an inoculum size of 15%, a monoculture of Pseudomonas rhizophila S211; and an incubation time of 6 days. The response values predicted by the Hoke design model at each combination of factor levels aligned with the experimental results, and the analysis of variance demonstrated the predictability and accuracy of the postulated model. In addition to the experimental evidences, P. rhizophila genome was explored to predict the PUPW-degrading enzymes and the associated protein secretion systems. Moreover, physicochemical properties, phylogenetic analysis, and 3D structure of S211 LipA2 polyurethanase were elucidated through an in-silico approach. Taken all together, integrated experimental tests and computational modeling suggest that P. rhizophila S211 has the necessary enzymatic machinery to effectively convert the non-biodegradable PUPW into PHA bioplastics.

A systematic review of methodologies and solutions for recycling polyurethane foams to safeguard the environment

Today, plastic plays a pervasive role in everyday life. Their improper disposal can create ongoing environmental challenges. Polyurethane (PU) is a polymer with elastomeric properties that exhibits significant adhesion and durability. PU has various colors and resistance to acid and alkali substances. The widespread use of PU has caused a significant presence of these compounds in landfills. Therefore, it can cause significant plastic pollution globally. This increased environmental concern has prompted researchers and innovators to explore sustainable methods for recycling PU foam. Therefore, the recycling of PU waste is recognized as an essential requirement due to its economic and environmental benefits. Although the latest reviews focused on physical, chemical, and biological methods of PU recycling, a comprehensive review of other PU recycling methods is needed. Therefore, the present study is a systematic review of recent initiatives and innovations in the field of recycling and modification of PU foam production methods to recognize and reduce environmental impacts. In the present study, major global databases such as Web of Science, PubMed, Scopus, Google Scholar, and Iranian databases (up to January 2024) were searched with relative keywords to identify studies published in authoritative journals. Data were collected from qualified articles on different PU recycling methods and innovative processes. From a total of 1088 articles found, finally, 46 studies met the objectives and inclusion criteria. Based on the results, today various methods are used to recycle PU compounds, but more attention has been paid to efficient methods such as energy production and high-consumption products such as rubber and adhesive from these compounds. In addition, it highlights some approaches, such as the production of absorbents from PU foams, which not only improve the current technology but also show promise in reducing the environmental impact of this ubiquitous material.

Discovery of a polyurethane-degrading enzyme from the gut bacterium of plastic-eating mealworms

Although numerous polyurethane (PU)-degrading enzymes were identified from a diverse array of microorganisms in soil or compost, it is intriguing to investigate whether novel PU-degrading enzymes can be discovered in other biological environments. This study reports the discovery of an enzyme (MTL) for PU plastic degradation from the bacterial strain Mixta tenebrionis BIT-26, isolated from the gut of plastic-eating mealworms. MTL shows significant degradation activity towards three commercial PU substrates, including Impranil®DLN-SD, thermoplastic films (PEGA-HDI), and thermoset foams (PEGA-TDI), by cleaving the ester bonds in the polyester polyol moieties. The structure, molecular docking, and site-directed mutagenesis analyses elucidate the substrate binding model. A combination of structure-based comparison and mutational studies reveals the underlying architecture of the enzyme's specificity. These findings provide a fresh perspective into understanding plastic metabolism in the gut of plastic-eating insects and a prospective path for developing a biodegradation technique for plastic waste disposal.

Harnessing insects mediated plastic biodegradation: Current insight and future directions

Plastic polymers pose a significant challenge due to their resistance to degradation, resulting in their persistent accumulation in the environment and exacerbating a critical environmental concern. Urgent innovation and novel management technologies are essential to tackle this issue. Plastic biodegradation, distinguished by its environmentally friendly and safe attributes, has garnered substantial attention as a viable solution. Insects are pivotal in this process, utilizing their gut microbes to facilitate plastic degradation. The enzymatic action within the digestive tracts of diverse insect hosts and their microbial symbionts contributes to the breakdown of these polymers. This comprehensive review delves into the current landscape and strategies aimed at combating plastic pollution, with a specific focus on the involvement of insects such as mealworms (Tenebrio molitor Linnaeus), superworms (Zophobas atratus Blanchard), greater wax moths (Galleria mellonella Linnaeus), and various other insect species in the degradation of plastics. This review explores the different insects involved in plastic degradation, the mechanisms by which insects degrade plastics and delineates the characteristics of resultant degradable products. Furthermore, it investigates the future potential for plastic degradation by insects and examines the prospective developmental pathways for degradable plastics. Ultimately, this review provides an array of solutions by using various insects to pervasive the issue of plastic pollution.

A Valuable Source of Promising Extremophiles in Microbial Plastic Degradation

Plastics have accumulated in open environments, such as oceans, rivers, and land, for centuries, but their effect has been of concern for only decades. Plastic pollution is a global challenge at the forefront of public awareness worldwide due to its negative effects on ecological systems, animals, human health, and national economies. Therefore, interest has increased regarding specific circular economies for the development of plastic production and the investigation of green technologies for plastic degradation after use on an appropriate timescale. Moreover, biodegradable plastics have been found to contain potential new hazards compared with conventional plastics due to the physicochemical properties of the polymers involved. Recently, plastic biodegradation was defined as microbial conversion using functional microorganisms and their enzymatic systems. This is a promising strategy for depolymerizing organic components into carbon dioxide, methane, water, new biomass, and other higher value bioproducts under both oxic and anoxic conditions. This study reviews microplastic pollution, the negative consequences of plastic use, and the current technologies used for plastic degradation and biodegradation mediated by microorganisms with their drawbacks; in particular, the important and questionable role of extremophilic multi-enzyme-producing bacteria in synergistic systems of plastic decomposition is discussed. This study emphasizes the key points for enhancing the plastic degradation process using extremophiles, such as cell hydrophobicity, amyloid protein, and other relevant factors. Bioprospecting for novel mechanisms with unknown information about the bioproducts produced during the plastic degradation process is also mentioned in this review with the significant goals of CO2 evolution and increasing H2/CH4 production in the future. Based on the potential factors that were analyzed, there may be new ideas for in vitro isolation techniques for unculturable/multiple-enzyme-producing bacteria and extremophiles from various polluted environments.

XTT assay for detection of bacterial metabolic activity in water-based polyester polyurethane

Cellular metabolic activity can be detected by tetrazolium-based colorimetric assays, which rely on dehydrogenase enzymes from living cells to reduce tetrazolium compounds into colored formazan products. Although these methods have been used in different fields of microbiology, their application to the detection of bacteria with plastic-degrading activity has not been well documented. Here, we report a microplate-adapted method for the detection of bacteria metabolically active on the commercial polyester polyurethane (PU) Impranil®DLN using the tetrazolium salt 2,3-bis [2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide (XTT). Bacterial cells that are active on PU reduce XTT to a water-soluble orange dye, which can be quantitatively measured using a microplate reader. We used the Pseudomonas putida KT2440 strain as a study model. Its metabolic activity on Impranil detected by our novel method was further verified by Fourier-transform infrared spectroscopy (FTIR) analyses. Measurements of the absorbance of reduced XTT at 470 nm in microplate wells were not affected by the colloidal properties of Impranil or cell density. In summary, we provide here an easy and high-throughput method for screening bacteria active on PU that can be adapted to other plastic substrates.

Biodegradation of Typical Plastics: From Microbial Diversity to Metabolic Mechanisms

Plastic production has increased dramatically, leading to accumulated plastic waste in the ocean. Marine plastics can be broken down into microplastics (<5 mm) by sunlight, machinery, and pressure. The accumulation of microplastics in organisms and the release of plastic additives can adversely affect the health of marine organisms. Biodegradation is one way to address plastic pollution in an environmentally friendly manner. Marine microorganisms can be more adapted to fluctuating environmental conditions such as salinity, temperature, pH, and pressure compared with terrestrial microorganisms, providing new opportunities to address plastic pollution. Pseudomonadota (Proteobacteria), Bacteroidota (Bacteroidetes), Bacillota (Firmicutes), and Cyanobacteria were frequently found on plastic biofilms and may degrade plastics. Currently, diverse plastic-degrading bacteria are being isolated from marine environments such as offshore and deep oceanic waters, especially Pseudomonas spp. Bacillus spp. Alcanivoras spp. and Actinomycetes. Some marine fungi and algae have also been revealed as plastic degraders. In this review, we focused on the advances in plastic biodegradation by marine microorganisms and their enzymes (esterase, cutinase, laccase, etc.) involved in the process of biodegradation of polyethylene terephthalate (PET), polystyrene (PS), polyethylene (PE), polyvinyl chloride (PVC), and polypropylene (PP) and highlighted the need to study plastic biodegradation in the deep sea.

Antimicrobial resistance and biotechnological potential of plastic-associated bacteria isolated from an urban estuary

Plastics have quickly become one of the major pollutants in aquatic environments worldwide and solving the plastic pollution crisis is considered a central goal of modern society. In this study, 10 different plastic samples, including high- and low-density polyethylene and polypropylene, were collected from a deeply polluted urban estuary in Brazil. By employing different isolation and analysis approaches to investigate plastic-associated bacteria, a predominance of potentially pathogenic bacteria such as Acinetobacter, Aeromonas, and Vibrio was observed throughout all plastic samples. Bacteria typically found in the aquatic environment harboured clinically relevant genes encoding resistance to carbapenems (blaKPC ) and colistin (such as mcr-3 and mcr-4), along with genetic determinants associated with potentially active gene mobilization. Whole genome sequencing and annotation of three plastic-associated Vibrio strains further demonstrated the carriage of mobile genetic elements and antimicrobial resistance and virulence genes. On the other hand, bacteria isolated from the same samples were also able to produce esterases, lipases, and bioemulsifiers, thus highlighting that the plastisphere could also be of special interest from a biotechnological perspective.

Biodegradation of polyurethanes by Serratia liquefaciens L135 and its polyurethanase: In silico and in vitro analyses

Polyurethanes (PUs) are found in many everyday products and their disposal leads to environmental accumulation. Therefore, there is an urgent need to develop ecologically sustainable techniques to biodegrade and recycle this recalcitrant polymer and replace traditional methods that form harmful by-products. Serratia liquefaciens L135 secretes a polyurethanase with lipase activity, and this study explores the biodegradation of PUs by this bacterium and its enzyme through in silico and in vitro analyses. PUs monomers and tetramers were constructed in silico and tested with modeled and validated structure of the polyurethanase from S. liquefaciens. The molecular docking showed that all PUs monomers presented favorable interactions with polyurethanase (values of binding energy between -84.75 and -121.71 kcal mol-1), including PU poly[4,4'-methylenebis (phenyl isocyanate)-alt-1,4-butanediol/di (propylene glycol)/polycaprolactone] (PCLMDI). Due to repulsive steric interactions, tetramers showed less favorable interactions (values between 24.26 and -45.50 kcal mol-1). In vitro analyses evaluated the biodegradation of PUs: Impranil® and PCLMDI; this latter showed high binding energy with this polyurethanase in silico. The biodegradation of Impranil® by S. liquefaciens and its partially purified polyurethanase was confirmed in agar by forming a transparent halo. Impranil® disks inoculated with S. liquefaciens and incubated at 30 °C for six days showed rupture of the PU structure, possibly due to the formation of cracks visualized by scanning electron microscopy (SEM). PCLMDI films were also biodegraded by S. liquefaciens after 60 days of incubation, with the formation of pores and cracks visualized by SEM. The biodegradation may have occurred due to the action of polyurethanase produced by this bacterium. This work provides essential information on the potential of S. liquefaciens to biodegrade PUs through in silico analyses combined with in vitro analyses.

Biodegradation Potential of Polyethylene Terephthalate by the Two Insect Gut Symbionts Xanthomonas sp. HY-74 and Bacillus sp. HY-75

Polyethylene terephthalate (PET) is a plastic material that is widely used in beverage bottles, food packaging, and other consumer products, which is highly resistant to biodegradation. In this study, we investigated the effects of two insect gut symbionts, Xanthomonas sp. HY-74 and Bacillus sp. HY-75, during PET biodegradation. Both strains degraded PET-containing agar plates, and the sole nutrition source assay showed that HY-74 had different degradation rates depending on the presence of specific carbon and nitrogen sources, whereas HY-75 exhibited comparable degradation across all tested conditions. The two strains biodegraded the PET film with 1.57 ± 0.21% and 1.42 ± 0.46% weight loss after 6 weeks, respectively. Changes in the morphology and structure of the PET films, such as erosion, scratching, and surface roughening, were determined using scanning electron microscopy (SEM). Further, the two strains biodegraded PET powder, broke it into its degradation products, and changed the surface functional groups. This is the first study to investigate the biodegradation of PET by Hymenoptera gut-derived microbes and offers promising insights into the potential applications of insect gut symbionts in PET waste management.

Endophytic, extremophilic and entomophilic fungi strains biodegrade anthracene showing potential for bioremediation

Anthropogenic activities have been increasing Polycyclic Aromatic Hydrocarbons (PAHs) release, promoting an urgent need for decontamination methods. Therefore, anthracene biodegradation by endophytic, extremophilic, and entomophilic fungi was studied. Moreover, a salting-out extraction methodology with the renewable solvent ethanol and the innocuous salt K₂HPO₄ was employed. Nine of the ten employed strains biodegraded anthracene in liquid medium (19-56% biodegradation) after 14 days at 30 °C, 130 rpm, and 100 mg L^-1. The most efficient strain Didymellaceae sp. LaBioMMi 155, an entomophilic strain, was employed for optimized biodegradation, aiming at a better understanding of how factors like pollutant initial concentration, pH, and temperature affected this process. Biodegradation reached 90 ± 11% at 22 °C, pH 9.0, and 50 mg L^-1. Futhermore, 8 different PAHs were biodegraded and metabolites were identified. Then, experiments with anthracene in soil ex situ were performed and bioaugmentation with Didymellaceae sp. LaBioMMi 155 presented better results than natural attenuation by the native microbiome and biostimulation by the addition of liquid nutrient medium into soil. Therefore, an expanded knowledge about PAHs biodegradation processes was achieved with emphasis to the action of Didymellaceae sp. LaBioMMi 155, which can be further employed for in situ biodegradation (after strain security test), or for enzyme identification and isolation aiming at oxygenases with optimal activity under alkaline conditions.