Biodegradation of Polystyrene by Dark ( Tenebrio obscurus) and Yellow ( Tenebrio molitor) Mealworms (Coleoptera: Tenebrionidae)

Microplastics act as vectors for antibiotic resistance genes in landfill leachate: The enhanced roles of the long-term aging process

Microplastics (MPs) are found to be ubiquitous and serve as vectors for other contaminants, and the inevitable aging process changes MP properties and fates. However, whether the MPs in aging process affects the fates of antibiotic resistance gene (ARGs) in aquatic environments is poorly understood. Herein, the physicochemical property alteration of MPs being aged in landfill leachate, an important reservoir of MPs and ARGs, was investigated, and microbial community evolution and ARGs occurrence of MP surface during the aging process were analyzed. Aging process remarkably altered surface properties, including increasing specific surface areas, causing the formation of oxygen-containing groups, and changing surface morphology, which further increased the probability of microbial colonization. The bacterial assemblage on MPs showed higher biofilm-forming and pathogenic potential compared to leachate. ARGs quantification results suggested that MPs exhibited selective enrichment for ARGs in a ratio of 5.7-10³ folds, and the aging process enhanced the enrichment potential. Further co-occurrence networks suggested that the existence of non-random, closer and more stable ARGs-bacterial taxa relations on MP surface affected the ARG transmission. The study of ARG partitioning on MPs indicated that extracellular DNA was a nonnegligible reservoir of ARGs attached on MP surface, and that biofilm bacterial community influenced ARGs partitioning pattern during the aging process. This study confirmed that the aging process could enhance the potential of MPs as vectors for ARGs, which would promote the holistic understanding of MP behavior and risk in natural environments.

Potential for and Distribution of Enzymatic Biodegradation of Polystyrene by Environmental Microorganisms

Polystyrene (PS) is one of the main polymer types of plastic wastes and is known to be resistant to biodegradation, resulting in PS waste persistence in the environment. Although previous studies have reported that some microorganisms can degrade PS, enzymes and mechanisms of microorganism PS biodegradation are still unknown. In this study, we summarized microbial species that have been identified to degrade PS. By screening the available genome information of microorganisms that have been reported to degrade PS for enzymes with functional potential to depolymerize PS, we predicted target PS-degrading enzymes. We found that cytochrome P4500s, alkane hydroxylases and monooxygenases ranked as the top potential enzyme classes that can degrade PS since they can break C-C bonds. Ring-hydroxylating dioxygenases may be able to break the side-chain of PS and oxidize the aromatic ring compounds generated from the decomposition of PS. These target enzymes were distributed in Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes, suggesting a broad potential for PS biodegradation in various earth environments and microbiomes. Our results provide insight into the enzymatic degradation of PS and suggestions for realizing the biodegradation of this recalcitrant plastic.

Plastics and the microbiome: impacts and solutions

Global plastic production has increased exponentially since manufacturing commenced in the 1950's, including polymer types infused with diverse additives and fillers. While the negative impacts of plastics are widely reported, particularly on marine vertebrates, impacts on microbial life remain poorly understood. Plastics impact microbiomes directly, exerting toxic effects, providing supplemental carbon sources and acting as rafts for microbial colonisation and dispersal. Indirect consequences include increased environmental shading, altered compositions of host communities and disruption of host organism or community health, hormone balances and immune responses. The isolation and application of plastic-degrading microbes are of substantial interest yet little evidence supports the microbial biodegradation of most high molecular weight synthetic polymers. Over 400 microbial species have been presumptively identified as capable of plastic degradation, but evidence for the degradation of highly prevalent polymers including polypropylene, nylon, polystyrene and polyvinyl chloride must be treated with caution; most studies fail to differentiate losses caused by the leaching or degradation of polymer monomers, additives or fillers. Even where polymer degradation is demonstrated, such as for polyethylene terephthalate, the ability of microorganisms to degrade more highly crystalline forms of the polymer used in commercial plastics appears limited. Microbiomes frequently work in conjunction with abiotic factors such as heat and light to impact the structural integrity of polymers and accessibility to enzymatic attack. Consequently, there remains much scope for extremophile microbiomes to be explored as a source of plastic-degrading enzymes and microorganisms. We propose a best-practice workflow for isolating and reporting plastic-degrading taxa from diverse environmental microbiomes, which should include multiple lines of evidence supporting changes in polymer structure, mass loss, and detection of presumed degradation products, along with confirmation of microbial strains and enzymes (and their associated genes) responsible for high molecular weight plastic polymer degradation. Such approaches are necessary for enzymatic degraders of high molecular weight plastic polymers to be differentiated from organisms only capable of degrading the more labile carbon within predominantly amorphous plastics, plastic monomers, additives or fillers.

Characterization of biodegradation of plastics in insect larvae

Biodegradation of plastics has been observed at rapid turnover rate by some insect larvae, especially those of Coleoptera, in particular Tenebrionidae. Tenebrio molitor larva is well studied and capable of biodegrading polystyrene (PS), polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC) in their digestive intestine in synergy with their gut microflora. This chapter includes the methods, protocols, and procedures used to characterize biodegradation of plastics in T. molitor larvae and their gut microbiomes with polystyrene as the model feedstock. The methods used can be expanded to enable investigation of other plastics and/or insects.

Critical evaluation of biodegradation studies on synthetic plastics through a systematic literature review

Increasing amounts of plastic waste in the environment and their fragmentation into smaller particles known as microplastics (particles, <5mm) have raised global concerns due to their persistency in the environment and their potential to act as vectors for harmful substances or pathogenic microorganisms. One possible solution to this problem is biodegradation of plastics by microorganisms. However, the scientific information on plastic-degrading microorganisms is scattered across different scientific publications. We conducted a systematic literature review (SLR) with predefined criteria using the online databases of Scopus and Web of Science to find papers on bacterial biodegradation of synthetic petroleum-based polymers. The aims of this SLR were to provide an updated list of all of the currently known bacteria claimed to biodegrade synthetic plastics, to determine and define the best methods to assess biodegradation, to critically evaluate the existing studies, and to propose directions for future research on polymer biodegradation in support of more rapid development of biodegradation technologies. Most of the bacteria identified here from the 145 reviewed papers belong to the phyla Proteobacteria, Firmicutes and Actinobacteria, and most were isolated from contaminated sites, such as landfill sites. Just under a half of the studies (44%) investigated the biodegradability of polyethylenes and derivates, particularly low-density polyethylenes. The methods used to monitor the biodegradation were mainly scanning electron microscopy and Fourier-transform infrared spectroscopy. We propose that: (1) future research should focus on biodegradation of microplastics arising from the most common pollutants (e.g. polyethylenes); (2) bacteria should be isolated from environments that are permanently contaminated with plastics; and (3) a combination of different observational methods should be used to confirm bacterial biodegradation of these plastics. Finally, when reporting, researchers need to follow standard protocols and include all essential information needed for repetition of the experiments by other research groups.

Use Them for What They Are Good at: Mealworms in Circular Food Systems

Future food systems must provide more food produced on less land with fewer greenhouse gas emissions if the goal is to keep planetary boundaries within safe zones. The valorisation of agricultural and industrial by-products by insects is an increasingly investigated strategy, because it can help to address resource scarcities and related environmental issues. Thus, insects for food and feed have gained increasing attention as a sustainable protein production strategy in circular food systems lately. In this article, we provide an overview on by-products, which have already been fed to T. molitor (mealworms), a common edible insect species. In addition, we investigate other by-products in Austria, which can be suitable substrates for T. molitor farming. We also provide an overview and discuss different perspectives on T. molitor and link it with the circular economy concept. We identify several future research fields, such as more comprehensive feeding trials with other by-products, feeding trials with mealworms over several generations, and the development of a standardized framework for insect rearing trials. In addition, we argue that due to their ability to convert organic by-products from agricultural and industrial processes into biomass in an efficient way, T. molitor can contribute towards resource-efficient and circular food and feed production. However, several hurdles, such as legal frameworks, need to be adapted, and further research is needed to fully reap the benefits of mealworm farming.

Biodegradation of expanded polystyrene and low-density polyethylene foams in larvae of Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae): Broad versus limited extent depolymerization and microbe-dependence versus independence

Yellow mealworms (Tenebrio molitor larvae) are capable of biodegrading polystyrene (PS) and low-density polyethylene (LDPE). This study tested biodegradation of one expanded PS (EPS) with a weight-average molecular weight (M_w) 256.4 kDa and two LDPE foams with respective M_w of 130.6 kDa (PE-1) and 288.7 kDa (PE-2) in T. monitor larvae obtained in Beijing, China. The larvae consumed EPS and both LDPEs over a 60 day. Fourier transform infrared spectroscopy and thermogravimetric analyses of frass confirmed the formation of new oxygen-containing functional groups, as well as a change in physical property and chemical modification, indicating that biodegradation of EPS and LDPE occurred. Gel permeation chromatography analysis confirmed broad depolymerization of EPS and PE-1 (i.e., a decrease in both M_w and a number-average molecular weight (M_n)) but revealed limited extent depolymerization of PE-2 (i.e., increase in M_n and decrease in M_w). For all materials, the size-average molecular weight (M_z) was decreased. Biodegradation and oxidation of EPS and LDPE were confirmed using FTIR and TGA analysis. Depression of gut microbes by the antibiotic gentamicin resulted in significant inhibition of EPS depolymerization but did not stop LDPE depolymerization, resulting in the increase in M_n and revealing that PS biodegradation was gut microbe-dependent but LDPE biodegradation was less dependent or independent of gut microbes. Gut microbial community analysis indicated that, as expected, under different dietary conditions, the intestinal flora significantly shifted to communities associated with biodegradation of EPS and LDPE. The results indicated the complexity and limitation of biodegradation of plastics in plastics-eating T. molitor larvae.

The impact of polystyrene consumption by edible insects Tenebrio molitor and Zophobas morio on their nutritional value, cytotoxicity, and oxidative stress parameters

The objective of this study was to determine of nutritional value, in vitro cytotoxicity, and oxidative stress parameters in cells of selected insect species (Tenebrio molitor and Zophobas morio) after 30 days of Styrofoam consumption. Furthermore, part of our research is also a consumer survey on the willingness to eat insects fed with Styrofoam (EPS 80). Mealworms fed with Styrofoam were determined to have higher protein (48.66 ± 0.92%) and ash content (4.81 ± 0.22%) with reduced fat (24.05 ± 0.55%) and carbohydrate content (2.95 ± 0.15%) than insects with a conventional diet (48.66 ± 0.92, 2.82 ± 0.12, 43.74 ± 0.77, and 4.78 ± 0.18, respectively) while in the case of superworms, no significant difference in nutrient composition was observed. Moreover, Styrofoam has no influence on the health status of gut cells in examined insects. Additionally, in studied concentrations of insects extracts standardized for protein replacement of the traditional insect diet with polystyrene foam did not increase the cytotoxic properties.

Biodegradation of Polyvinyl Chloride (PVC) in Tenebrio molitor (Coleoptera: Tenebrionidae) larvae

Tenebrio molitor larvae (Coleoptera: Tenebrionidae) are capable of depolymerizing and biodegrading polystyrene and polyethylene. We tested for biodegradation of Polyvinyl Chloride (PVC) in T. molitor larvae using rigid PVC microplastic powders (MPs) (70-150 μm) with weight-, number-, and size-average molecular weights (M_w, M_n and M_z) of 143,800, 82,200 and 244,900 Da, respectively, as sole diet at 25 °C. The ingestion rate was 36.62 ± 6.79 mg MPs 100 larvae^-1 d^-1 during a 16-day period. The egested frass contained about 34.6% of residual PVC polymer, and chlorinated organic carbons. Gel permeation chromatography (GPC) analysis indicated a decrease in the M_w, M_n and M_z by 33.4%, 32.8%, and 36.4%, respectively, demonstrating broad depolymerization. Biodegradation and oxidation of the PVC MPs was supported by the formation of OC and OC functional groups using frontier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance (¹H NMR), and by significant changes in the thermal characteristics using thermo-gravimetric analysis (TGA). Chloride released was counted as about 2.9% of the PVC ingested, indicating limited mineralization of the PVC MPs. T. molitor larvae survived with PVC as sole diet at up to 80% over 5 weeks but did not complete their life cycle with a low survival rate of 39% in three months. With PVC plus co-diet wheat bran (1:5, w/w), they completed growth and pupation as same as bran only in 91 days. Suppression of gut microbes with the antibiotic gentamicin severely inhibited PVC depolymerization, indicating that the PVC depolymerization/biodegradation was gut microbe-dependent. Significant population shifts and clustering in the gut microbiome and unique OTUs were observed after PVC MPs consumption. The results indicated that T. molitor larvae are capable of performing broad depolymerization/biodegradation but limited mineralization of PVC MPs.

Biodegradation and disintegration of expanded polystyrene by land snails Achatina fulica

Despite increasing evidence of widespread plastic pollution in soil, it remains largely unknown about the fate of plastic influenced by soil animals. In this study, ingestion and biodegradation capability of expanded polystyrene (PS) foam was investigated in a globally distributed soil invertebrate, Achatina fulica. After 4-week exposure, 18.5 ± 2.9 mg polystyrene was ingested per snail, and egested microplastics (1.343 ± 0.625 mm) in feces with significant mass loss of mean 30.7%. Gel permeation chromatography analysis indicated a significant increase in weight-average molecular weight (M_w) and number-average molecular weight (M_n) of feces-residual PS, indicating limited extent depolymerization. Fourier transform infrared spectroscopy and proton nuclear magnetic resonance confirmed the formation of functional groups of oxidized intermediates. Suppression of gut microbes with oxytetracycline did not affect the depolymerization, indicating the independence of gut microbes. High-throughput sequencing analysis revealed significant shifts in the gut microbiome after ingestion of PS, with an increase of family Enterobacteriaceae, Sphingobacteriaceae, and Aeromonadaceae, suggesting that gut microorganisms were associated with PS biodegradation. These findings suggest that plastic litter can be disintegrated into microplastics and partially biodegraded by A. fulica, which highlights the significance of soil animals for the fate of plastic and its biodegradation in soil environments.

Microbial and Enzymatic Degradation of Synthetic Plastics

Synthetic plastics are pivotal in our current lifestyle and therefore, its accumulation is a major concern for environment and human health. Petroleum-derived (petro-)polymers such as polyethylene (PE), polyethylene terephthalate (PET), polyurethane (PU), polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC) are extremely recalcitrant to natural biodegradation pathways. Some microorganisms with the ability to degrade petro-polymers under in vitro conditions have been isolated and characterized. In some cases, the enzymes expressed by these microbes have been cloned and sequenced. The rate of polymer biodegradation depends on several factors including chemical structures, molecular weights, and degrees of crystallinity. Polymers are large molecules having both regular crystals (crystalline region) and irregular groups (amorphous region), where the latter provides polymers with flexibility. Highly crystalline polymers like polyethylene (95%), are rigid with a low capacity to resist impacts. PET-based plastics possess a high degree of crystallinity (30-50%), which is one of the principal reasons for their low rate of microbial degradation, which is projected to take more than 50 years for complete degraded in the natural environment, and hundreds of years if discarded into the oceans, due to their lower temperature and oxygen availability. The enzymatic degradation occurs in two stages: adsorption of enzymes on the polymer surface, followed by hydro-peroxidation/hydrolysis of the bonds. The sources of plastic-degrading enzymes can be found in microorganisms from various environments as well as digestive intestine of some invertebrates. Microbial and enzymatic degradation of waste petro-plastics is a promising strategy for depolymerization of waste petro-plastics into polymer monomers for recycling, or to covert waste plastics into higher value bioproducts, such as biodegradable polymers via mineralization. The objective of this review is to outline the advances made in the microbial degradation of synthetic plastics and, overview the enzymes involved in biodegradation.

A Very Hungry Caterpillar: Polyethylene Metabolism and Lipid Homeostasis in Larvae of the Greater Wax Moth (Galleria mellonella)

Larvae of the greater wax moth (Galleria mellonella) possess the remarkable ability to consume and rapidly degrade low-density polyethylene. Previous studies have investigated the involvement of the animal's microbiome, but little is known about the host's actual role and if it benefits from biodegradation of this synthetic polymer. We used a combination of RNA sequencing and biochemical approaches to assess caterpillars fed honeycomb, fed polyethylene (PE), or starved for up to 72 h. Sequencing of gut transcripts revealed PE-fed larvae retain an expression profile consistent with normal intestinal function but also show distinct molecular signatures indicative of enhanced fatty acid metabolism (FAM). Further, quantification of total lipid content validated the impact of a PE diet on FAM; in contrast to lipid-depleted starved animals, PE-fed caterpillars maintain lipid reserves similar to honeycomb-fed larvae. Additionally, we found the activity of putative enzymes involved in lipid oxidation (e.g., alcohol dehydrogenase) are considerably higher in PE-fed larvae, indicating that on a functional level, these caterpillars are inducing pathways to effectively metabolize PE. Overall, we put forward a hypothesized model where the similarity in chemical structure between PE and its natural honeycomb diet has endowed larvae of G. mellonella with the extraordinary capability to derive energy from PE as an exclusive food source through pre-existing metabolic pathways.

Biodegradation of low-density polyethylene and polystyrene in superworms, larvae of Zophobas atratus (Coleoptera: Tenebrionidae): Broad and limited extent depolymerization

Larvae of Zophobas atratus (synonym as Z. morio, or Z. rugipes Kirsch, Coleoptera: Tenebrionidae) are capable of eating foams of expanded polystyrene (EPS) and low-density polyethylene (LDPE), similar to larvae of Tenebrio molitor. We evaluated biodegradation of EPS and LDPE in the larvae from Guangzhou, China (strain G) and Marion, Illinois, U.S. (strain M) at 25 °C. Within 33 days, strain G larvae ingested respective LDPE and PS foams as their sole diet with respective consumption rates of 58.7 ± 1.8 mg and 61.5 ± 1.6 mg 100 larvae^-1d^-1. Meanwhile, strain M required co-diet (bran or cabbage) with respective consumption rates of 57.1 ± 2.5 mg and 30.3 ± 7.7 mg 100 larvae^-1 d^-1. Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and thermal gravimetric analyses indicated oxidation and biodegradation of LDPE and EPS in the two strains. Gel permeation chromatography analysis revealed that strain G performed broad depolymerization of EPS, i.e., both weight-average molecular weight (M_w) and number-average molecular weight (M_n) of residual polymers decreased, while strain M performed limited extent depolymerization, i.e., M_w and M_n increased. However, both strains performed limited extent depolymerization of LDPE. After feeding antibiotic gentamicin, gut microbes were suppressed, and M_w and M_n of residual LDPE and EPS in frass were basically unchanged, implying a dependence on gut microbes for depolymerization/biodegradation. Our discoveries indicate that gut microbe-dependent LDPE and EPS biodegradation is present within Z. atratus in Tenebrionidae, but that the limited extent depolymerization pattern resulted in undigested polymers with high molecular weights in egested frass.

Evaluation of the Biodegradation Efficiency of Four Various Types of Plastics by Pseudomonas aeruginosa Isolated from the Gut Extract of Superworms

Plastic waste worldwide is becoming a serious pollution problem for the planet. Various physical and chemical methods have been tested in attempts to remove plastic dumps. However, these have usually resulted in secondary pollution issues. Recently, the biodegradation of plastic by fungal and bacterial strains has been spotlighted as a promising solution to remove plastic wastes without generating secondary pollution. We have previously reported that a Pseudomonas aeruginosa strain isolated from the gut of a superworm is capable of biodegrading polystyrene (PS) and polyphenylene sulfide (PPS). Herein, we demonstrate the extraordinary biodegradative power of P. aeruginosa in efficiently depolymerizing four different types of plastics: PS, PPS, polyethylene (PE) and polypropylene (PP). We further compared biodegradation rates for these four plastic types and found that PE was biodegraded fastest, whereas the biodegradation of PP was the slowest. Moreover, the growth rates of P. aeruginosa were not always proportional to biodegradation rates, suggesting that the rate of bacterial growth could be influenced by the composition and properties of intermediate molecules produced during plastic biodegradation, and these may supply useful cellular precursors and energy. In conclusion, an initial screening system to select the most suitable bacterial strain to biodegrade certain types of plastic is particularly important and may be necessary to solve plastic waste problems both presently and in the future.

Effects of polystyrene diet on Tenebrio molitor larval growth, development and survival: Dynamic Energy Budget (DEB) model analysis

The presence of polystyrene (PS) waste increases constantly. Styrofoam, the most popular form of PS, is one of the major plastic pollutants in the environment. An efficient and environmentally friendly method of PS recycling is still needed. The biodegradation of PS by insects has been presented by researchers as a promising alternative to chemical, mechanical and thermal methods. The main aim of this study was to assess the survival, growth, and development of yellow mealworms (the larvae of Tenebrio molitor) fed with PS to determine if the insects are able to use PS as a source of mass and energy. The Dynamic Energy Budget (DEB) model was used to analyze the effects of food type on the growth trajectory and metabolism of tested organisms. We investigated five possible modes of influence of PS diet on DEB model parameters including a decrease of food availability, an increase in somatic maintenance power, an increase in costs for structure, allocation of energy, and a decrease in somatic maintenance power. Our results show that changes in the development of larvae fed with PS are mainly caused by a decrease in reserves density and reaction of the organism to the insufficient food supply. The inability or difficulty in completing the life cycle of T. molitor larvae fed with PS raises doubts about the use of mealworms as an effective technology for utilizing polystyrene.

Fast and Facile Biodegradation of Polystyrene by the Gut Microbial Flora of Plesiophthalmus davidis Larvae

Polystyrene (PS), which accounts for a significant fraction of plastic wastes, is difficult to biodegrade due to its unique molecular structure. Therefore, biodegradation and chemical modification of PS are limited. In this study, we report PS biodegradation by the larvae of the darkling beetle Plesiophthalmus davidis (Coleoptera: Tenebrionidae). In 14 days, P. davidis ingested 34.27 ± 4.04 mg of Styrofoam (PS foam) per larva and survived by feeding only on Styrofoam. Fourier transform infrared spectroscopy confirmed that the ingested Styrofoam was oxidized. Gel permeation chromatography analysis indicated the decrease in average molecular weight of the residual PS in the frass compared with the feed Styrofoam. When the extracted gut flora was cultured for 20 days with PS films, biofilm and cavities were observed by scanning electron microscopy and atomic force microscopy. X-ray photoelectron spectroscopy (XPS) studies revealed that C-O bonding was introduced into the biodegraded PS film. Serratia sp. strain WSW (KCTC 82146), which was isolated from the gut flora, also formed a biofilm and cavities on the PS film in 20 days, but its degradation was less prominent than the gut flora. XPS confirmed that C-O and C=O bonds were introduced into the biodegraded PS film by Serratia sp. WSW. Microbial community analysis revealed that Serratia was in the gut flora in significant amounts and increased sixfold when the larvae were fed Styrofoam for 2 weeks. This suggests that P. davidis larvae and its gut bacteria could be used to chemically modify and rapidly degrade PS.IMPORTANCE PS is widely produced in the modern world, but it is robust against biodegradation. A few studies reported the biodegradation of PS, but most of them merely observed its weight loss; fewer were able to find its chemical modifications, which are rather direct evidence of biodegradation, by using limited organisms. Therefore, it is required to find an effective way to decompose PS using various kinds of organisms. Herein, we discovered a new PS-degrading insect species and bacterial strain, and we found that the genus that includes the PS-degrading bacterial strain occurs in significant amounts in the larval gut flora, and the proportion of this genus increased as the larvae were fed Styrofoam. Our research offers a wider selection of PS-degrading insects and the possibility of using a certain mixture of bacteria that resemble the gut flora of a PS-degrading insect to biodegrade PS, and thus could contribute to solving the global plastic crisis.

A polystyrene-degrading Acinetobacter bacterium isolated from the larvae of Tribolium castaneum

Polystyrene (PS) has been widely used in various fields, whereas this thermoplastic material is generally considered to be resistant to biodegradation. Tribolium castaneum (Coleoptera: Tenebrionidae), a common pest of stored agricultural products, is a powerful model organism for general insect research. In this study, the larvae of T. castaneum were observed chewing and eating extruded polystyrene foam (XPS). Investigation of the gut microbiome of plastic- and bran-fed T. castaneum larvae showed that Acinetobacter sp. was strongly associated with PS ingestion. Additionally, one bacterial strain capable of PS degradation, was successfully isolated from the gut of these larvae and identified as Acinetobacter sp. AnTc-1 by its 16S rDNA sequence. Gel penetration chromatography (GPC), ¹H nuclear magnetic resonance (¹H NMR) spectroscopy, thermo gravimetric analysis (TGA) and scanning electron microscope (SEM) were employed to characterize the PS degradation. After incubation with AnTc-1 for 60 days, the mass weight (12.14%) and molecular weight (13%/25%, weight-average molecular weight (Mw)/number-average molecular weight (Mn)) of PS powder were significantly reduced. The results indicated that the isolated strain of Acinetobacter sp. AnTc-1 has PS-degrading capacity. The isolated strain may play a role in the larval gut for biodegradation of PS and has potential to be applied for petroleum-based plastic degradation study and development of remediation approaches.

Biodegradation of Polystyrene by Pseudomonas sp. Isolated from the Gut of Superworms (Larvae of Zophobas atratus)

Recently, various attempts have been made to solve plastic waste problems, such as development of biodegradation without producing pollution. Polystyrene (PS) is the fifth most used plastic in many industries; therefore, degrading PS becomes a critical global issue. Here, we reported Pseudomonas aeruginosa strain DSM 50071, initially isolated from the gut of the superworms, Zophobas atratus, and the PS degradation by Pseudomonas sp. DSM 50071. We examined PS degradation using electronic microscopy and measured changes in atomic composition and contact angles with water droplets on the PS surface that represents a chemical change from hydrophobicity to hydrophilicity. We have further examined chemical structural changes using X-ray photoelectron spectroscopy, Fourier-transform-infrared spectroscopy, and nuclear magnetic resonance (NMR) to confirm the formation of carbonyl groups (C═O) in the oxidation pathway during PS biodegradation. In reverse transcription quantitative polymerase chain reaction analysis, the gene expression level of serine hydrolase (SH) in Pseudomonas sp. DSM 50071 was highly increased during PS degradation, and the enzyme-mediated biodegradation of PS was further confirmed by the SH inhibitor treatment test. Thus, the significance of these findings goes beyond the discovery of a novel function of Pseudomonas sp. DSM 50071 in the gut of superworms, highlighting a potential solution for PS biodegradation.

Non-Hydrolyzable Plastics - An Interdisciplinary Look at Plastic Bio-Oxidation

Enzymatic plastic conversion has emerged recently as a potential adjunct and alternative to conventional plastic waste management technology. Publicity over progress in the enzymatic degradation of polyesters largely neglects that the majority of commercial plastics, including polyethylene, polypropylene, polystyrene and polyvinyl chloride, are still not biodegradable. Details about the mechanisms used by enzymes and an understanding of macromolecular factors influencing these have proved to be vital in developing biodegradation methods for polyesters. To expand the application of enzymatic degradation to other more recalcitrant plastics, extensive knowledge gaps need to be addressed. By drawing on interdisciplinary knowledge, we suggest that physicochemical influences also have a crucial impact on reactions in less well-studied types of plastic, and these need to be investigated in detail.

Microbial Degradation and Valorization of Plastic Wastes

A growing accumulation of plastic wastes has become a severe environmental and social issue. It is urgent to develop innovative approaches for the disposal of plastic wastes. In recent years, reports on biodegradation of synthetic plastics by microorganisms or enzymes have sprung up, and these offer a possibility to develop biological treatment technology for plastic wastes. In this review, we have comprehensively summarized the microorganisms and enzymes that are able to degrade a variety of generally used synthetic plastics, such as polyethylene (PE), polystyrene (PS), polypropylene (PP), polyvinyl chloride (PVC), polyurethane (PUR), and polyethylene terephthalate (PET). In addition, we have highlighted the microbial metabolic pathways for plastic depolymerization products and the current attempts toward utilization of such products as feedstocks for microbial production of chemicals with high value. Taken together, these findings will contribute to building a conception of bio-upcycling plastic wastes by connecting the biodegradation of plastic wastes to the biosynthesis of valuable chemicals in microorganisms. Last, but not least, we have discussed the challenges toward microbial degradation and valorization of plastic wastes.

Biodegradation and mineralization of polystyrene by plastic-eating superworms Zophobas atratus

Polystyrene (PS) is one of the major plastic debris accumulated in environment. Previously, we reported that mealworm (Tenebrio molitor) was capable of degrading and mineralizing Styrofoam (PS foam). This finding arouses our curiosity to explore whether more other insect species have the same capability as mealworms. Here, an insect larva, superworm (Zophobas atratus), was newly proven to be capable of eating, degrading and mineralizing PS. Superworms could live with Styrofoam as sole diet as well as those fed with a normal diet (bran) over a 28-day period. The average consumption rate of Styrofoam for each superworm was estimated at 0.58 mg/d that was 4 times more than that of mealworm. Analyses of frass, using gel permeation chromatography (GPC), solid-state ¹³C cross-polarization/magic angle spinning nuclear magnetic resonance (CP/MAS NMR) spectroscopy, and thermogravimetric interfaced with Fourier transform infrared (TG-FTIR) spectroscopy, demonstrated that the depolymerization of long-chain PS molecules and the formation of low molecular-weight products occurred in the larval gut. A respirometry test showed that up to 36.7% of the ingested Styrofoam carbon was converted into CO₂ during a 16-day test period. The PS-degrading capability of superworm was inhibited by the antibiotic suppression of gut microbiota, indicating that gut microbiota contributed to PS degradation. This new finding extends the PS-degrading insects beyond the species within the Tenebrio genus and indicates that the gut microbiota of superworm would be a novel bioresource for pursuit of plastic-degrading enzymes.

Role of the intestinal microbiome in low-density polyethylene degradation by caterpillar larvae of the greater wax moth, Galleria mellonella

Recently, a few insects, including the caterpillar larva of the greater wax moth Galleria mellonella, have been identified as avid 'plastivores'. These caterpillars are able to ingest and metabolize polyethylene at unprecedented rates. While it appears that G. mellonella plays an important role in the biodegradation process, the contribution of its intestinal microbiome remains poorly understood and contested. In a series of experiments, we present strong evidence of an intricate relationship between an intact microbiome, low-density polyethylene (LDPE) biodegradation and the production of glycol as a metabolic by-product. First, we biochemically confirmed that G. mellonella larvae consume and metabolize LDPE, as individual caterpillars fed on polyethylene excreted glycol, but those excretions were reduced by antibiotic treatment. Further, while the gut bacterial communities remained relatively stable regardless of diet, we showed that during the early phases of feeding on LDPE (24-72 h), caterpillars exhibited increased microbial abundance relative to those starved or fed on their natural honeycomb diet. Finally, by isolating and growing gut bacteria with polyethylene as their exclusive carbon source for over 1 year, we identified microorganisms in the genus Acinetobacter that appeared to be involved in this biodegradation process. Taken collectively, our study indicates that during short-term exposure, the intestinal microbiome of G. mellonella is intricately associated with polyethylene biodegradation in vivo.

Impact of polyethylene on salivary glands proteome in Galleria melonella

Polyethylene pollutions are considered inert in nature and adversely affect the entire ecosystem. Larvae of greater wax moth (Galleria mellonella) have the ability to masticate and potentially biodegrade polyethylene films at elevated rates. The wax moth has been thought to metabolize PE independently of gut flora, however the role of the microbiome is poorly understood and degradation by the wax moth might be involved. To determine whether the salivary glands of the wax moth were potentially involved in the PE degradation, it was investigated how surface changes of polyethylene were affected by mastication and consumption. Formation of pitting and degradation intermediates including carbonyl groups, indicated that salivary glands could assist in polyethylene degradation. We investigated the biochemical effect of exposure by PE on the composition of the salivary gland proteome. The expression of salivary proteins was found to be affected by PE exposure. The proteins that were significantly affected by the exposure to PE revealed that the wax moth are undergoing general changes in energy levels, also enzymatic pathways associated to fatty acid beta oxidation during consumption to PE were induced.