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

Cockroach Blaptica dubia biodegrades polystyrene plastics: Insights for superior ability, microbiome and host genes

The report demonstrated that a member of cockroach family, Blaptica dubia (Blattodea: Blaberidae) biodegraded commercial polystyrene (PS) plastics with Mn of 20.3 kDa and Mw of 284.9 kDa. The cockroaches digested up to 46.6 % of ingested PS within 24 h. The biodegradation was confirmed by the 13C isotopic shift of the residual PS in feces versus pristine PS (Δ δ13C of 2.28 ‰), reduction of molecular weight and formation of oxidative functional groups in the residual PS. Further tests found that B.dubia cockroaches degraded all eight high purity PS microplastics with low to ultra-high molecular weights (MW) at 0.88, 1.20, 3.92, 9.55, 62.5, 90.9, 524.0, and 1040 kDa, respectively, with superior biodegradation ability. PS depolymerization/biodegradation pattern was MW-dependent. Ingestion of PS shifted gut microbial communities and elevated abundances of plastic-degrading bacterial genes. Genomic, transcriptomic and metabolite analyses indicated that both gut microbes and cockroach host contributed to digestive enzymatic degradation. PS plastic diet promoted a highly cooperative model of gut digestive system. Weighted gene co-expression network analysis revealed different PS degradation patterns with distinct MW profiles in B. dubia. These results have provided strong evidences of plastic-degrading ability of cockroaches or Blaberidae family and new understanding of insect and their microbe mediated biodegradation of plastics.

New insights on the degradation of polystyrene and polypropylene by larvae of the superworm Zophobas atratus and gut bacterial consortium enrichments obtained under different culture conditions

This study aims to deepen knowledge of the biodegradation of plastics, focusing on polypropylene (PP) fabric from surgical masks and polystyrene (PS) by larvae of Zophobas atratus as well as of specialized bacterial consortia from their gut, which were obtained in different enrichment conditions (aerobic, anaerobic, presence or absence of combined nitrogen). Plastics ingested by larvae obtained in Spain did not show any signs of oxidation but only limited depolymerization, preferably from the lowest molecular weight chains. Gut microbiota composition changed as an effect of plastic feeding. Such differences were more evident in bacterial enrichment cultures, where the polymer type influenced the composition more than by culture conditions, with an increase in the presence of nitrogen-fixers in anaerobic conditions. PS and PP degradation by different enrichment cultures was confirmed under aerobic and anaerobic conditions by respirometry tests, with anaerobic conditions favouring a more active plastic degradation. In addition, exposure to selected bacterial consortia in aerobiosis induced limited surface oxidation of PS. This possibly indicates that different biochemical routes are being utilized in the anaerobic gut and in aerobic conditions to degrade the polymer.

Isolation of marine polyethylene (PE)-degrading bacteria and its potential degradation mechanisms

Microbial degradation of polyethylene (PE) offers a promising solution to plastic pollution in the marine environment, but research in this field is limited. In this study, we isolated a novel marine strain of Pseudalkalibacillus sp. MQ-1 that can degrade PE. Scanning electron microscopy and water contact angle results showed that MQ-1 could adhere to PE films and render them hydrophilic. Analyses using X-ray diffraction, fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy showed a decrease in relative crystallinity, the appearance of new functional groups and an increase in the oxygen-to‑carbon ratio of the PE films, making them more susceptible to degradation. The results of gel permeation chromatography and liquid chromatography-mass spectrometry indicated the depolymerization of the long PE chains, with the detection of an intermediate, decanediol. Furthermore, genome sequencing was employed to investigate the underlying mechanisms of PE degradation. The results of genome sequencing analysis identified the genes associated with PE degradation, including cytochrome P450, alcohol dehydrogenase, and aldehyde dehydrogenase involved in the oxidative reaction, monooxygenase related to ester bond formation, and esterase associated with ester bond cleavage. In addition, enzymes involved in fatty acid metabolism and intracellular transport have been identified, collectively providing insights into the metabolic pathway of PE degradation.

Interactions of alumina and polystyrene nanoparticles with the innate immune system of Galleria mellonella

Nowadays, particularly metallic, and polymeric nanoparticles (NPs) are widely produced and used in many fields. Due to the increase in both their usage and diversity, their release and accumulation in the environment are also accelerating. Therefore, their interactions with cells, especially immune cells, and their health risks are not fully understood. The impacts of metallic alumina (Al) NPs and polystyrene (PS) NPs obtained after the polymerization of carcinogenic styrene on living organisms have not yet been elucidated. Galleria mellonella larvae can biodegrade plastics. While biodegradation and solving the waste problem have attracted much attention, the interactions of this distinctive property of G. mellonella larvae in the immune system and ecosystem are not yet completely understood. Al and PS NPs were applied to G. mellonella separately. Al NPs were purchased and PS NPs were prepared from PS by single-emulsion technique and characterized. Then LC50 values of these NPs on G. mellonella were determined. The interactions of these NPs with encapsulation, melanization, and phenoloxidase activity, which express innate immune responses in G. mellonella larvae, were revealed. NP exposure resulted in suppression of the immune response, probably because it affects the functions of hemocytes such as enzymatic activation, hemocyte division, and populations. In this context, our data suggest that Al and PS NPs induce toxic impacts and negatively alter the physiological status of G. mellonella. It is also shown that G. mellonella has the potential to be an impactful alternative model for biosafety and nanotoxicology studies.

Consumption and Digestion of Plastics by Greater Hive Moth Larvae

The accumulation and unsustainable management of plastic waste generate environmental pollution that affects ecosystems, wildlife, and human health. We studied the possibility of using the consumption and digestion of oxo-biodegradable, compostable plastics and polypropylene from face masks by the fifth-instar larvae of G. mellonella as a strategy for the sustainable management of plastic waste. We used Fourier transform infrared spectrophotometry (FTIR) to determine the percentage of consumption and presence of microplastics in the digestive tract and excreta for 10 treatments evaluated for 135 h. The effects of plastics on the continuity of the life cycle of the greater hive moth were also determined. We established that the larvae fragmented and consumed 35.2 ± 23% of the plastics evaluated, with significant differences between treatments. Larvae were able to consume more of the intermediate layers of masks (86.31%) than the other plastics. However, none of the plastics were digested. Instead, microplastics accumulated in the excreta, resulting in nutritional deficits that affected the continuity of the life cycle, including the induction of the early formation of pupae after 24 h and a reduction in the number of eggs laid by the females.

Soil-dwelling grub larvae of Protaetia brevitarsis biodegrade polystyrene: Responses of gut microbiome and host metabolism

Plastic pollution poses a significant threat to terrestrial ecosystems, yet the potential for soil fauna to contribute to plastic biodegradation remains largely unexplored. In this study, we reveal that soil-dwelling grubs, Protaetia brevitarsis larvae, can effectively biodegrade polystyrene (PS) plastics. Over a period of 4 weeks, these grubs achieved a remarkable 61.5 % reduction in PS foam mass. This biodegradation was confirmed by the depolymerization of ingested PS, formation of oxidative functional groups, noticeable chemical modifications, and an increase of δ13C of residual PS in frass. Additionally, antibiotic treatment to suppress gut microbes led to variations in the biodegradation process. PS ingestion induced a significant shift in the gut microbiome, promoting the growth of degradation-related bacteria such as Promicromonosporaceae, Bacillaceae, and Paenibacillaceae. Furthermore, the digestion of plastic triggered extensive metabolomic reprogramming of grubs' intestines, enhancing redox capabilities and facilitating PS biodegradation. These results indicate that responsive adaptation of both the gut microbiome and the host's intestinal metabolism contributes to PS degradation. Collectively, these findings demonstrate P. brevitarsis larvae's capability to alleviate soil plastic pollution, and highlight the potential of researching soil fauna further for sustainable plastic waste management solutions.

Molecular-Weight-Dependent Degradation of Plastics: Deciphering Host-Microbiome Synergy Biodegradation of High-Purity Polypropylene Microplastics by Mealworms

The biodegradation of polypropylene (PP), a highly persistent nonhydrolyzable polymer, by Tenebrio molitor has been confirmed using commercial PP microplastics (MPs) (Mn 26.59 and Mw 187.12 kDa). This confirmation was based on the reduction of the PP mass, change in molecular weight (MW), and a positive Δδ13C in the residual PP. A MW-dependent biodegradation mechanism was investigated using five high-purity PP MPs, classified into low (0.83 and 6.20 kDa), medium (50.40 and 108.0 kDa), and high (575.0 kDa) MW categories to access the impact of MW on the depolymerization pattern and associated gene expression of gut bacteria and the larval host. The larvae can depolymerize/biodegrade PP polymers with high MW although the consumption rate and weight losses increased, and survival rates declined with increasing PP MW. This pattern is similar to observations with polystyrene (PS) and polyethylene (PE), i.e., both Mn and Mw decreased after being fed low MW PP, while Mn and/or Mw increased after high MW PP was fed. The gut microbiota exhibited specific bacteria associations, such as Kluyvera sp. and Pediococcus sp. for high MW PP degradation, Acinetobacter sp. for medium MW PP, and Bacillus sp. alongside three other bacteria for low MW PP metabolism. In the host transcriptome, digestive enzymes and plastic degradation-related bacterial enzymes were up-regulated after feeding on PP depending on different MWs. The T. molitor host exhibited both defensive function and degradation capability during the biodegradation of plastics, with high MW PP showing a relatively negative impact on the larvae.

Biodegradation of polyethylene terephthalate by Tenebrio molitor: Insights for polymer chain size, gut metabolome and host genes

Polyethylene terephthalate (PET or polyester) is a commonly used plastic and also contributes to the majority of plastic wastes. Mealworms (Tenebrio molitor larvae) are capable of biodegrading major plastic polymers but their degrading ability for PET has not been characterized based on polymer chain size molecular size, gut microbiome, metabolome and transcriptome. We verified biodegradation of commercial PET by T. molitor larvae in a previous report. Here, we reported that biodegradation of commercial PET (Mw 29.43 kDa) was further confirmed by using the δ13C signature as an indication of bioreaction, which was increased from - 27.50‰ to - 26.05‰. Under antibiotic suppression of gut microbes, the PET was still depolymerized, indicating that the host digestive enzymes could degrade PET independently. Biodegradation of high purity PET with low, medium, and high molecular weights (MW), i.e., Mw values of 1.10, 27.10, and 63.50 kDa with crystallinity 53.66%, 33.43%, and 4.25%, respectively, showed a mass reduction of > 95%, 86%, and 74% via broad depolymerization. Microbiome analyses indicated that PET diets shifted gut microbiota to three distinct structures, depending on the low, medium, and high MW. Metagenome sequencing, transcriptomic, and metabolic analyses indicated symbiotic biodegradation of PET by the host and gut microbiota. After PET was fed, the host's genes encoding degradation enzymes were upregulated, including genes encoding oxidizing, hydrolyzing, and non-specific CYP450 enzymes. Gut bacterial genes for biodegrading intermediates and nitrogen fixation also upregulated. The multiple-functional metabolic pathways for PET biodegradation ensured rapid biodegradation resulting in a half-life of PET less than 4 h with less negative impact by PET MW and crystallinity.

Flying toward a plastic-free world: Can Drosophila serve as a model organism to develop new strategies of plastic waste management?

The last century was dominated by the widespread use of plastics, both in terms of invention and increased usage. The environmental challenge we currently face is not just about reducing plastic usage but finding new ways to manage plastic waste. Recycling is growing but remains a small part of the solution. There is increasing focus on studying organisms and processes that can break down plastics, offering a modern approach to addressing the environmental crisis. Here, we provide an overview of the organisms associated with plastics biodegradation, and we explore the potential of harnessing and integrating their genetic and biochemical features into a single organism, such as Drosophila melanogaster. The remarkable genetic engineering and microbiota manipulation tools available for this organism suggest that multiple features could be amalgamated and modeled in the fruit fly. We outline feasible genetic engineering and gut microbiome engraftment strategies to develop a new class of plastic-degrading organisms and discuss of both the potential benefits and the limitations of developing such engineered Drosophila melanogaster strains.

Is the gut microbiome of insects a potential source to meet UN sustainable development goals to eliminate plastic pollution?

As insects such as cockroaches can endure high radiation, flourish in unsanitary circumstances, thrive on germ-infested feed, and can even digest the organic polymer cellulose, the gut microbiota of these species likely produces enzymes contributing to their ability to digest a variety of materials. The use of cockroaches as a bio-resource to eliminate plastic is discussed. We explore whether species such as cockroaches are a potential bio-resource to eliminate plastic pollution and contribute to the sustainable development goals adopted by the United Nations as well as the global community to reduce and/or eliminate plastic pollution.

A Comparative Study of Effects of Biodegradable and Non-biodegradable Microplastics on the Growth and Development of Black Soldier Fly Larvae (Hermetia illucens)

Purpose

This study aimed to investigate the digestion process of biodegradable and non-biodegradable microplastics (MPs) within black soldier fly larvae (BSFL) and assess their impact on larval growth and development. The goal was to understand the fate of MPs within BSFL, considering their potential for waste conversion polluted with MPs.

Methods

BSFL were exposed to two types of MPs, and their growth, development, potential accumulation and excretion of MPs were monitored.

Results

The findings revealed that the MPs accumulated solely in the larval gut and had no adverse effects on the growth and development of BSFL. Larvae efficiently excreted MPs before reaching the pupation stage.

Conclusion

This research emphasizes the potential of BSFL as a bioconversion agent for organic waste, even in the presence of MPs. The effective excretion of MPs by BSFL before pupation suggests their ability to mitigate potential harm caused by MP accumulation. The fact that BSFL may excrete MPs before pupation would contribute to their safe use as animal feedstock. A careful evaluation of the effects of using BSFL reared on contaminated substrates especially containing visually non-detectable residuals like nanoplastics, chemicals or toxic metals and further examination of the broader implications for waste management and sustainable livestock farming remains important.

Graphical Abstract

Experimental design outlining the workflow for the analyses used to investigate the effect of two types of microplastics, polyamide (PA), and polylactic acid (PLA), on growth and development of black soldier fly larvae.

Plastics shape the black soldier fly larvae gut microbiome and select for biodegrading functions

BACKGROUND

In the last few years, considerable attention has been focused on the plastic-degrading capability of insects and their gut microbiota in order to develop novel, effective, and green strategies for plastic waste management. Although many analyses based on 16S rRNA gene sequencing are available, an in-depth analysis of the insect gut microbiome to identify genes with plastic-degrading potential is still lacking.

RESULTS

In the present work, we aim to fill this gap using Black Soldier Fly (BSF) as insect model. BSF larvae have proven capability to efficiently bioconvert a wide variety of organic wastes but, surprisingly, have never been considered for plastic degradation. BSF larvae were reared on two widely used plastic polymers and shotgun metagenomics was exploited to evaluate if and how plastic-containing diets affect composition and functions of the gut microbial community. The high-definition picture of the BSF gut microbiome gave access for the first time to the genomes of culturable and unculturable microorganisms in the gut of insects reared on plastics and revealed that (i) plastics significantly shaped bacterial composition at species and strain level, and (ii) functions that trigger the degradation of the polymer chains, i.e., DyP-type peroxidases, multicopper oxidases, and alkane monooxygenases, were highly enriched in the metagenomes upon exposure to plastics, consistently with the evidences obtained by scanning electron microscopy and 1H nuclear magnetic resonance analyses on plastics.

CONCLUSIONS

In addition to highlighting that the astonishing plasticity of the microbiota composition of BSF larvae is associated with functional shifts in the insect microbiome, the present work sets the stage for exploiting BSF larvae as "bioincubators" to isolate microbial strains and enzymes for the development of innovative plastic biodegradation strategies. However, most importantly, the larvae constitute a source of enzymes to be evolved and valorized by pioneering synthetic biology approaches. Video Abstract.

Responses of gut microbiomes to commercial polyester polymer biodegradation in Tenebrio molitor Larvae

Polyethylene terephthalate (PET) is a mass-produced fossil-based plastic polymer that contributes to catastrophic levels of plastic pollution. Here we demonstrated that Tenebrio molitor (mealworms) was capable of rapidly biodegrading two commercial PET resins (microplastics) with respective weight-average molecular weight (M_w) of 39.33 and 29.43 kDa and crystallinity of 22.8 ± 3.06% and 18 ± 2.25%, resulting in an average mass reduction of 71.03% and 73.28% after passage of their digestive tract, and respective decrease by 9.22% and 11.36% in M_w of residual PET polymer in egested frass. Sequencing of 16 S rRNA gene amplicons of gut microbial communities showed that dominant bacterial genera were enriched and associated with PET degradation. Also, PICRUSt prediction exhibited that oxidases (monooxygenases and dioxygenases), hydrolases (cutinase, carboxylesterase and chitinase), and PET metabolic enzymes, and chemotaxis related functions were up-regulated in the PET-fed larvae. Additionally, metabolite analyses revealed that PET uptake caused alterations of stress response and plastic degradation related pathways, and lipid metabolism pathways in the T. molitor larvae could be reprogrammed when the larvae fed on PET. This study provides new insights into gut microbial community adaptation to PET diet under nutritional stress (especially nitrogen deficiency) and its contribution to PET degradation.

Gut microbiome of mealworms (Tenebrio molitor Larvae) show similar responses to polystyrene and corn straw diets

BACKGROUND

Some insects can degrade both natural and synthetic plastic polymers, their host and gut microbes play crucial roles in this process. However, there is still a scientific gap in understanding how the insect adapted to the polystyrene (PS) diet from natural feed. In this study, we analyzed diet consumption, gut microbiota responses, and metabolic pathways of Tenebrio molitor larvae exposed to PS and corn straw (CS).

RESULTS

T. molitor larvae were incubated under controlled conditions (25 ± 1 °C, 75 ± 5% humidity) for 30 days by using PS foam with weight-, number-, and size-average molecular weight (Mw, Mn, and Mz) of 120.0, 73.2, and 150.7 kDa as a diet, respectively. The larvae exhibited lower PS consumption (32.5%) than CS (52.0%), and these diets had no adverse effects on their survival. The gut microbiota structures, metabolic pathways, and enzymatic profiles of PS- and CS-fed larvae showed similar responses. The gut microbiota of larvae analysis indicated Serratia sp., Staphylococcus sp., and Rhodococcus sp. were associated with both PS and CS diets. Metatranscriptomic analysis revealed that xenobiotics, aromatic compounds, and fatty acid degradation pathways were enriched in PS- and CS-fed groups; laccase-like multicopper oxidases, cytochrome P450, monooxygenase, superoxidase, and dehydrogenase were involved in lignin and PS degradation. Furthermore, the upregulated gene lac640 in both PS- and CS-fed groups was overexpressed in E. coli and exhibited PS and lignin degradation ability.

CONCLUSIONS

The high similarity of gut microbiomes adapted to biodegradation of PS and CS indicated the plastics-degrading ability of the T. molitor larvae originated through an ancient mechanism that degrades the natural lignocellulose. Video Abstract.

Exposure to polylactic acid induces oxidative stress and reduces the ceramide levels in larvae of greater wax moth (Galleria mellonella)

Plastic biodegradation by insects has made significant progress, opening up new avenues for the treatment of plastic waste. Wax moth larvae, for example, have attracted the attention of the scientific community because they are known to chew, ingest, and biodegrade natural polymer bee waxes. Despite this, we know very little about how these insects perform on manufactured plastics or how manufactured plastics affect insect metabolism. As a result, we studied the metabolism of greater wax moths (Galleria mellonella) fed on molasses-supplemented polylactic acid plastic (PLA) blocks. An analysis of the central carbon metabolism (CCM) metabolites was performed using liquid chromatography triple quadrupole mass spectrometry (LC-QQQ-MS), while an analysis of untargeted metabolites and lipids was conducted using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS). In total, 169 targeted CCM metabolites, 222 untargeted polar metabolites, and 196 untargeted nonpolar lipids were identified within the insect samples. In contrast, compared to control larvae, PLA-fed larvae displayed significantly different levels of 97 CCM metabolites, 75 polar metabolites, and 57 lipids. Purine and pyrimidine metabolisms were affected by PLA feeding, as well as amino acid metabolism, carbohydrates, cofactors, vitamins, and related metabolisms. Additionally, PLA exposure disrupted insect energy metabolism and oxidative stress, among other metabolic disturbances. The larvae fed PLA have lower levels of several lipids, suggesting a reduction in lipid reserves, and ceramide levels are likely to have changed due to apoptosis and inflammation. The study indicates that G. mellonella larvae could ingest PLA but this process causes some metabolic stress for the host. Future studies of the molecular pathways of this biodegradation process might help to provide strategies for stress reduction that would speed up insect digestion of plastic.

Why have we not yet solved the challenge of plastic degradation by biological means?

The invention of fossil fuel-derived plastics changed and reshaped society for the better; however, their mass production has created an unprecedented accumulation of waste and an environmental crisis. Scientists are searching for better ways to reduce plastic waste than the current methods of mechanical recycling and incineration, which are only partial solutions. Biological means of breaking down plastics have been investigated as alternatives, with studies mostly focusing on using microorganisms to biologically degrade sturdy plastics like polyethylene (PE). Unfortunately, after a few decades of research, biodegradation by microorganisms has not provided the hoped-for results. Recent studies suggest that insects could provide a new avenue for investigation into biotechnological tools, with the discovery of enzymes that can oxidize untreated PE. But how can insects provide a solution that could potentially make a difference? And how can biotechnology revolutionize the plastic industry to stop ongoing/increasing contamination?

The virtual microbiome: A computational framework to evaluate microbiome analyses

Microbiomes have been the focus of a substantial research effort in the last decades. The composition of microbial populations is normally determined by comparing DNA sequences sampled from those populations with the sequences stored in genomic databases. Therefore, the amount of information available in databanks should be expected to constrain the accuracy of microbiome analyses. Albeit normally ignored in microbiome studies, this constraint could severely compromise the reliability of microbiome data. To test this hypothesis, we generated virtual bacterial populations that exhibit the ecological structure of real-world microbiomes. Confronting the analyses of virtual microbiomes with their original composition revealed critical issues in the current approach to characterizing microbiomes, issues that were empirically confirmed by analyzing the microbiome of Galleria mellonella larvae. To reduce the uncertainty of microbiome data, the effort in the field must be channeled towards significantly increasing the amount of available genomic information and optimizing the use of this information.

Co-diet supplementation of low density polyethylene and honeybee wax did not influence the core gut bacteria and associated enzymes of Galleria mellonella larvae (Lepidoptera: Pyralidae)

The current plastic pollution throughout the world is a rising concern that demands the optimization of biodegradation processes. One avenue for this is to identify plastic-degrading bacteria and associated enzymes from the gut bacteria of insect models such as Tenebrio molitor, Plodia interpunctella or Galleria mellonella that have the ability to ingest and rapidly degrade polyethylene. Therefore, this study takes part in understanding the role of the gut bacteria by investigating G. mellonella as a biological model feeding with a diet based on honeybee wax mixed or not with low-density polyethylene. Gut microbiome was analyzed by high throughput 16S rRNA sequencing, and Enterococcaceae and Oxalobacteraceae were found to be the major bacterial families. Compared to the control, the supplementation of low-density polyethylene did not cause significant modification of the bacterial microbiota at community and taxa levels, suggesting bacterial microbiome resilience. The bacterial proteome analysis of gut contents was encouraging for the identification of plastic degrading enzymes such as the phenylacetaldehyde dehydrogenase which participate in styrene degradation. This study allowed a better characterization of the gut bacteria of G. mellonella and provided a basis for the further study of biodegradation of polyethylene based on the bacterial microbiota from insect guts.

Influence of Polymer Size on Polystyrene Biodegradation in Mealworms (Tenebrio molitor): Responses of Depolymerization Pattern, Gut Microbiome, and Metabolome to Polymers with Low to Ultrahigh Molecular Weight

Biodegradation of polystyrene (PS) in mealworms (Tenebrio molitor lavae) has been identified with commercial PS foams. However, there is currently limited understanding of the influence of molecular weight (MW) on insect-mediated plastic biodegradation and the corresponding responses of mealworms. In this study, we provided the results of PS biodegradation, gut microbiome, and metabolome by feeding mealworms with high-purity PS microplastics with a wide variety of MW. Over 24 days, mealworms (50 individuals) fed with 0.20 g of PS showed decreasing removal of 74.1 ± 1.7, 64.1 ± 1.6, 64.4 ± 4.0, 73.5 ± 0.9, 60.6 ± 2.6, and 39.7 ± 4.3% for PS polymers with respective weight-average molecular weights (M_w) of 6.70, 29.17, 88.63, 192.9, 612.2, and 1346 kDa. The mealworms degraded most PS polymers via broad depolymerization but ultrahigh-MW PS via limited-extent depolymerization. The gut microbiome was strongly associated with biodegradation, but that with low- and medium-MW PS was significantly distinct from that with ultrahigh-MW PS. Metabolomic analysis indicated that PS biodegradation reprogrammed the metabolome and caused intestinal dysbiosis depending on MW. Our findings demonstrate that mealworms alter their gut microbiome and intestinal metabolic pathways in response to in vivo biodegradation of PS polymers of various MWs.

Environmental risk, toxicity, and biodegradation of polyethylene: a review

Polyethylene is the second-most-commonly-used commercial polymer. It is used in various industries, including agricultural mulches, composite materials, and packaging. Since polyethylene is not biodegradable, it can persist for a long time in water and soil, strangling otherwise fruitful land. The ecological and toxicological consequences and the fate of polyethylene have only recently been revealed. As a result, the primary goal of this review is to shed light on the reported toxicity of polyethylene to the environment and living creatures and highlight recent research on its degradation process through bibliometric analysis. To do that, we searched Web of Science database literature up to August 2021 and performed the bibliometric analysis using VOSviewer. We found that relative research interest showed a positive trend, particularly in the last 5 years. China and the Chinese Academy of Sciences had the highest published papers. Methods for polyethylene biodegradation by invertebrates, bacteria, and fungi were also reported indicating the need for future research to investigate and develop new biodegradation technologies.

Wax worm saliva and the enzymes therein are the key to polyethylene degradation by Galleria mellonella

Plastic degradation by biological systems with re-utilization of the by-products could be a future solution to the global threat of plastic waste accumulation. Here, we report that the saliva of Galleria mellonella larvae (wax worms) is capable of oxidizing and depolymerizing polyethylene (PE), one of the most produced and sturdy polyolefin-derived plastics. This effect is achieved after a few hours’ exposure at room temperature under physiological conditions (neutral pH). The wax worm saliva can overcome the bottleneck step in PE biodegradation, namely the initial oxidation step. Within the saliva, we identify two enzymes, belonging to the phenol oxidase family, that can reproduce the same effect. To the best of our knowledge, these enzymes are the first animal enzymes with this capability, opening the way to potential solutions for plastic waste management through bio-recycling/up-cycling.

The crucial first step in the biodegradation of polyethylene plastic is oxidation of the polymer. This has traditionally required abiotic pre-treatment, but now Bertocchini and colleagues report two wax worm enzymes capable of catalyzing this oxidation and subsequent degradation at room temperature.

Diet and ontogeny drastically alter the larval microbiome of the invertebrate model Galleria mellonella

Larvae of the greater wax moth (Galleria mellonella) are an emerging animal model to study the innate immune response and biodegradation of plastic polymers. Both of these complex biological processes are likely impacted by the plasticity of host-microbe interactions, which remains understudied in lepidopterans. Consequently we carried out 16S rRNA sequencing to explore the effect diet (natural, artificial) has on the bacterial assemblages of G. mellonella in different tissues (gut, fat bodies, silk glands) throughout development (eggs, six instar stages, adults). The microbiome was rich in diversity, with Proteobacteria and Firmicutes being the most represented phyla. Contrary to other lepidopterans, G. mellonella appears to possess a resident microbiome dominated by Ralstonia. As larvae progress through development, the bacterial assemblages become increasingly shaped by the caterpillar's diet. In particular, a number of bacteria genera widely associated with the G. mellonella microbiome (e.g., Enterococcus and Enterbacter) were significantly enriched on an artificial diet. Overall these results indicate that the G. mellonella microbiome is not as simplistic and homogenous as previously described. Rather, its bacterial communities are drastically affected by both diet and ontogeny, which should be taken into consideration in future studies planning to use G. mellonella as model species.

The Bacterial and Fungal Gut Microbiota of the Greater Wax Moth, Galleria mellonella L. Consuming Polyethylene and Polystyrene

Plastic production has been increasing exponentially in the last 60 years, but plastic disposal is out of control, resulting in the pollution of all ecosystems on Earth. Finding alternative environmentally sustainable choices, such as biodegradation by insects and their associated gut microbiota, is crucial, however we have only begun to characterize these ecosystems. Some bacteria and one fungus have been previously identified in the gut of Greater Wax Moth larvae (Galleria mellonella L., Lepidoptera, Pyralidae) located mainly in the Northern hemisphere. The aim of this study was to describe changes in the gut microbiota associated with the consumption of polyethylene and polystyrene by the Greater Wax Moth in Argentina, considering both bacteria and fungi. Larvae were fed polyethylene, polystyrene and beeswax as control for 7 days. Next generation sequencing revealed changes in the bacterial gut microbiome of the wax moth larvae at the phyla and genus levels, with an increase in two Pseudomonas strains. The fungal communities showed no differences in composition between diets, only changing in relative abundance. This is the first report of both bacterial and fungal communities associated with a plastivore insect. The results are promising and call for more studies concerning a potential multi-kingdom synergy in the plastic biodegradation process.

Hydrocarbon-based plastics: Progress and perspectives on consumption and biodegradation by insect larvae

The obvious contrast between the remarkable durability and the high consumption of plastic products leads to the deposition of at least 100 million tons of plastics per year in nature. Since 2010, several studies have shown the potential of insect larvae to biodegrade different types of plastics, at higher rates than those reported for microorganisms. This review discusses a compilation of studies about the consumption and biodegradation of hydrocarbon-based plastics, particularly PE, PS, PP and PVC, by lepidopteran and coleopteran larvae. Insects of the Coleoptera order seem to have a better adaptation for PS biodegradation, while those of the Lepidoptera order can better biodegrade PE. Tenebrio molitor biomineralize PE and PS into CO₂, and PVC into HCl; while Tenebrio obscurus and Zophobas atratus converts PE and PS into CO₂, respectively. Plastic biodegradation by T. molitor has been shown to be dependent on microbiota, exception for PE. Similar PS and PE biodegradation profile has been shown for T. obscurus. PS, PP and PE biodegradation by Z. atratus is also reported to be microbial-dependent. For Galleria mellonella, microbial role on PE biodegradation is still controversial, but the PS metabolism was proved to be microbiota-independent. Advances in this field has stimulated new studies with other insect species, which need to be better explored. Uncovering and understanding the chemical processes behind the innate plastic biodegradation by insect larvae will open the perspective to new eco-friendly innovative biotechnological solutions for the challenge of plastic waste.

Fat on plastic: Metabolic consequences of an LDPE diet in the fat body of the greater wax moth larvae (Galleria mellonella)

The caterpillar larvae of the greater wax moth (Galleria mellonella) are avid plastivores, as when provided a diet of low-density polyethylene (LDPE) they actively feed on it. Recent work has highlighted the importance of their microbiome in the putative biodegradation of this plastic polymer, though the impact of plastic metabolism on the insect host is less clear. In the present study, we undertook an integrative approach spanning all levels of biological organization to explore the effects of a plastic diet on the metabolic physiology of this animal model of plastic biodegradation. We demonstrate that an LDPE diet is not sufficient to maintain optimal larval growth and survival. In addition, we confirm that plastic fed waxworms retain their fat body lipid stores in a manner proportional to their individual polyethylene consumption suggesting a direct effect of LDPE biodegradation. At the functional level, the oxidative capacity of the fat body of LDPE-fed larvae is maintained reflecting unaltered metabolic function of the tissue. Finally, metabolomic analyses confirmed fat body lipid stores maintenance in LDPE-fed worms, but uncovered various other nutritional deficiencies. Overall, this work unveils novel insights in the complex interplay between LDPE biodegradation and the metabolic physiology of this model plastivore.

Complete digestion/biodegradation of polystyrene microplastics by greater wax moth (Galleria mellonella) larvae: Direct in vivo evidence, gut microbiota independence, and potential metabolic pathways

Biodegradation of plastic polymers by plastic-eating insects such as the greater wax moth (Galleria mellonella) might be promising for reducing plastic pollution, but direct in vivo evidence along with the related metabolic pathways and role of gut microbiota require further investigation. In this study, we investigated the in vivo degradation process, underlying potential metabolic pathways, and involvement of the gut microbiota in polystyrene (PS) biodegradation via enforcing injection of G. mellonella larvae (Tianjin, China) with PS microbeads (0.5 mg/larva; M_n: 540 and M_w: 550) and general-purpose PS powders (2.5 mg/larva; M_n: 95,600 and M_w: 217,000). The results indicated that the PS microplastics were depolymerized and completely digested independent of gut microbiota in G. mellonella although the metabolism could be enhanced by gut microbiota. Based on comparative metabolomic and liquid chromatography analyses, we proposed two potential metabolic pathways of PS in the intestine of G. mellonella larvae: the styrene oxide-phenylacetaldehyde and 4-methylphenol-4-hydroxybenzaldehyde-4-hydroxybenzoate pathways. These results suggest that the enzymes of G. mellonella are responsible for the efficient biodegradation of PS. Further study is needed to identify these enzymes and investigate the underlying catalytic mechanisms.

Worming the Circular Economy for Biowaste and Plastics: Hermetia illucens, Tenebrio molitor, and Zophobas morio

The negative impact of the modern-day lifestyle on the environment was aggravated during the COVID-19 pandemic through the increased use of single-use plastics from food take-aways to medical supplies. Similarly, the closure of food outlets and disrupted supply chains have also resulted in significant food wastage. As the pandemic rages on, the aggravation of increased waste becomes an increasingly urgent problem that threatens the biodiversity, ecosystems, and human health worldwide through pollution. While there are existing methods to deal with organic and plastic waste, many of the solutions cause additional problems. Increasingly proposed as a natural solution to man-made problems, there are insect solutions for dealing with the artificial and organic waste products and moving towards a circular economy, making the use of natural insect solutions commercially sustainable. This review discusses the findings on how some of these insects, particularly Hermetia illucens, Tenebrio molitor, and Zophobas morio, can play an increasingly important role in food and plastics, with a focus on the latter.

Plastic biodegradation: Do Galleria mellonella Larvae Bioassimilate Polyethylene? A Spectral Histology Approach Using Isotopic Labeling and Infrared Microspectroscopy

Environmental pollution by the nearly nonbiodegradable polyethylene (PE) plastics is of major concern; thus, organisms capable of biodegrading PE are required. The larvae of the Greater Wax Moth, Galleria mellonella (Gm), were identified as a potential candidate to digest PE. In this study, we tested whether PE was metabolized by Gm larvae and could be found in their tissues. We examined the implication of the larval gut microbiota by using conventional and axenic reared insects. First, our study showed that neither beeswax nor LDPE alone favor the growth of young larvae. We then used Fourier transform infrared microspectroscopy (μFTIR) to detect deuterium in larvae fed with isotopically labeled food. Deuterated molecules were found in tissues of larvae fed with deuterium labeled oil for 24 and 72 h, proving that μFTIR can detect metabolization of 1 to 2 mg of deuterated food. Then, Gm larvae were fed with deuterated PE (821 kDa). No bioassimilation was detected in the tissues of larvae that had ingested 1 to 5 mg of deuterated PE in 72 h or in 19 days, but micrometer sized PE particles were found in the larval digestive tract cavities. We evidenced weak biodegradation of 641 kDa PE films in contact for 24 h with the dissected gut of conventional larvae and in the PED4 particles from excreted larval frass. Our study confirms that Gm larvae can biodegrade HDPE but cannot necessarily metabolize it.

Long-term effect of plastic feeding on growth and transcriptomic response of mealworms (Tenebrio molitor L.)

Plastic waste has been considered a serious global environmental problem for decades. Despite the high recalcitrance of synthetic plastics, the biodegradation of polyethylene (PE), polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC) by some insect larvae has been reported; however, the mechanism of degradation remains largely unknown. We investigated the effects of plastics on the growth of mealworms (larvae of Tenebrio molitor) and their role in PS and PE degradation. Mealworms were capable of ingesting high-impact polystyrene (HIPS), expanded polystyrene (EPS) and low-density polyethylene (LDPE) but not linear low-density polyethylene (LLDPE) or polypropylene (PP). Plastic consumption was negatively dependent on plastic crystallinity. Transcriptome analysis and KEGG mapping revealed that mealworms act as downstream decomposers in plastic depolymerization and that fatty acid degradation pathways may play important roles in the digestion of plastic degradation intermediates produced by gut bacteria. In addition, PS and PE degradation was achieved via the diffusion of extracellular depolymerases, which probably acted on the distal backbone and produce shorter linear chains that containing ≤16 C atoms instead of branched chains. Additionally, the intermediates of PS degradation are expected to be further decomposed by mealworms as xenobiotics. This study provided a preliminary understanding of plastic degradation mechanism by mealworms.

Enterococcus innesii sp. nov., isolated from the wax moth Galleria mellonella

Four bacterial strains were isolated from two different colony sources of the wax moth Galleria mellonella. They were characterized by a polyphasic approach including 16S rRNA gene sequence analysis, core-genome analysis, average nucleotide identity (ANI) analysis, digital DNA-DNA hybridization (dDDH), determination of G+C content, screening of antibiotic resistance genes, and various phenotypic analyses. Initial analysis of 16S rRNA gene sequence identities indicated that strain GAL7^T was potentially very closely related to Enterococcus casseliflavus and Enterococcus gallinarum, having 99.5-99.9 % sequence similarity. However, further analysis of whole genome sequences revealed a genome size of 3.69 Mb, DNA G+C content of 42.35 mol%, and low dDDH and ANI values between the genomes of strain GAL7^T and closest phylogenetic relative E. casseliflavus NBRC 100478^T of 59.0 and 94.5 %, respectively, indicating identification of a putative new Enterococcus species. In addition, all novel strains encoded the atypical vancomycin-resistance gene vanC-4. Results of phylogenomic, physiological and phenotypic characterization confirmed that strain GAL7^T represented a novel species within the genus Enterococcus, for which the name Enterococcus innesii sp. nov. is proposed. The type strain is GAL7^T (=DSM 112306^T=NCTC 14608^T).

Diseases and Pests of Honey Bees (Apis Mellifera)

Infectious and parasitic diseases plague honey bees similarly to that of other food animal species. A complete understanding of each is necessary for a honey bee veterinarian to establish a strong veterinarian-client-patient relationship and make sound treatment recommendations. Control and management of these diseases is paramount to success of the colony and apiary operation. The following is not meant to be an end-all of information on each of the common honey bee diseases but more so a review and photo-documentation of each. A deeper understanding can be established through various other sources previously published and referenced in this document.

A toxicological perspective of plastic biodegradation by insect larvae

Larvae of some insect species (Coleoptera and Lepidoptera) can consume and biodegrade synthetic polymers, including polyethylene, polystyrene, polyvinyl chloride, and polypropylene. Multiple chemical (polymer mass loss and shift of the molecular weight, alterations in chemical functionality, formation of biodegraded intermediates, CO₂ production), physical (surface hydrophobicity, thermal analysis), and biological approaches (antibiotic treatment, gut dysbiosis, isolation of plastic microbial degraders) have provided evidence for polymer biodegradation in the larva digestive tract. However, the extent and rate of biodegradation largely depend on the physicochemical structure of the polymer as well as the presence of additives. Additionally, toxicology associated with plastic biodegradation has not been investigated. This knowledge gap is critical to understand the gut symbiont-host interaction in the biodegradation process, its viability in the long term, the effects of plastic additives and their metabolites, and the phenotypic traits linked to a plastic-rich diet might be transferred in successive generations. Likewise, plastic-eating larvae represent a unique case study for elucidating the mechanisms of toxic action by micro- and nanoplastics because of the high concentration of plastics these organisms may be intentionally exposed to. This perspective review graphically summarizes the current knowledge on plastic biodegradation by insect larvae and describes the physiological processes (digestive and immune systems) that may be disrupted by micro- and nanoplastics. It also provides an outlook to advance current knowledge on the toxicity assessment of plastic-rich diets and the environmental risks of plastic-containing by-products (e.g., insect manure used as fertilizer).