Enhanced Bioavailability and Microbial Biodegradation of Polystyrene in an Enrichment Derived from the Gut Microbiome of Tenebrio molitor (Mealworm Larvae)

Microplastics Biofragmentation and Degradation Kinetics in the Plastivore Insect Tenebrio molitor

The insect Tenebrio molitor possesses an exceptional capacity for ultrafast plastic biodegradation within 1 day of gut retention, but the kinetics remains unknown. Herein, we investigated the biofragmentation and degradation kinetics of different microplastics (MPs), i.e., polyethylene (PE), poly(vinyl chloride) (PVC), and poly(lactic acid) (PLA), in T. molitor larvae. The intestinal reactions contributing to the in vivo MPs biodegradation were concurrently examined by utilizing aggregated-induced emission (AIE) probes. Our findings revealed that the intestinal biofragmentation rates essentially followed the order of PLA > PE > PVC. Notably, all MPs displayed retention effects in the intestine, with PVC requiring the longest duration for complete removal/digestion. The dynamic rate constant of degradable MPs (0.2108 h-1 for PLA) was significantly higher than that of persistent MPs (0.0675 and 0.0501 h-1 for PE and PVC, respectively) during the digestive gut retention. Surprisingly,T. molitor larvae instinctively modulated their internal digestive environment in response to in vivo biodegradation of various MP polymers. Esterase activity and intestinal acidification both significantly increased following MPs ingestion. The highest esterase and acidification levels were observed in the PLA-fed and PVC-fed larvae, respectively. High digestive esterase activity and relatively low acidification levels inT. molitor larvae may, to some extent, contribute to more efficient MPs removal within the plastic-degrading insect. This work provided important understanding of MPs biofragmentation and intestinal responses to in vivo MPs biodegradation in plastic-degrading insects.

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.

Metabolic activity of gut microbial enrichment cultures from different marine species and their transformation abilities to plastic additives

The role of the gut microbiota in host physiology has been previously elucidated for some marine organisms, but little information is available on their metabolic activity involved in transformation of environmental pollutants. This study assessed the metabolic profiles of the gut microbial cultures from grouper (Epinephelus coioides), green mussel (Perna viridis) and giant tiger prawn (Penaeus monodon) and investigated their transformation mechanisms to typical plastic additives. Community-level physiological profiling analysis confirmed the utilization profiles of the microbial cultures including carbon sources of carbohydrates, amines, carboxylic acids, phenolic compounds, polymers and amino acids, and the plastic additives of organophosphate flame retardants, tetrabromobisphenol A derivates and bisphenols. Using in vitro incubation, triphenyl phosphate (TPHP) was found to be rapidly metabolized into diphenyl phosphate by the gut microbiota as a representative ester-containing plastic additive, whereas the transformation of BPA (a representative phenol) was relatively slower. Interestingly, all three kinds of microbial cultures efficiently transformed the hepatic metabolite of BPA (BPA-G) back to BPA, thereby increasing its bioavailability in the body. The specific enzyme analysis confirmed the ability of the gut microbiota to perform the metabolic reactions. The results of 16S rRNA sequencing and network analysis revealed that the genera Escherichia-Shigella, Citrobacter, and Anaerospora were functional microbes, and their collaboration with fermentative microbes played pivotal roles in the transformation of the plastic additives. The structure-specific transformations by the gut microbiota and their distinct bioavailability deserve more attention in the future.

Corrigendum: Plastic biodegradation by in vitro environmental microorganisms and in vivo gut microorganisms of insects

[This corrects the article DOI: 10.3389/fmicb.2022.1001750.].

Response of petroleum-contaminated soil to chemical oxidation combined with biostimulation

In this study, a microcosm experiment was conducted to investigate the effects of Na2S2O8 preoxidation combined with biostimulation on petroleum-contaminated soil remediation. The response of microbial community during this process was explored using BIOLOG ECO microplate carbon utilization method and 16 s rDNA high-throughput sequencing. The results showed that use of 10 mg/g Na2S2O8 removed 19.8 % of the petroleum hydrocarbons, reduced soil biotoxicity and did not affect soil microbial activity compared to other concentrations. Therefore, sodium persulfate of ca. 10 mg/g was used to oxidize petroleum in soil before the biostimulation experiment with organic and inorganic fertilizers. Our finding showed that the content of total petroleum hydrocarbons (TPHs) in soil was reduced by 43.3 % in inorganic fertilizer treatment after 60 days. The results of BIOLOG ECO microplate carbon utilization analysis and 16 S rDNA high-throughput sequencing further confirmed that biostimulation quickly restored the microbial activities in oxidant treated soil. The main marker bacteria in chemical oxidation combined with biostimulation remediation were Arthrobacter and Paenarthrobacter, and their relative abundances were both significantly negatively correlated with the content of petroleum hydrocarbons in soil.

Integrating genomics, molecular docking, and protein expression to explore new perspectives on polystyrene biodegradation

Faced with the escalating challenge of global plastic pollution, this study specifically addresses the research gap in the biodegradation of polystyrene (PS). A PS-degrading bacterial strain was isolated from the gut of Tenebrio molitor, and genomics, molecular docking, and proteomics were employed to thoroughly investigate the biodegradation mechanisms of Pseudomonas putida H-01 against PS. Using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (ATR-FTIR), and contact angle analysis, significant morphological and structural changes in the PS films under the influence of the H-01 strain were observed. The study revealed several potential degradation genes and ten enzymes that were specifically upregulated in the PS degradation environment. Additionally, a novel protein with laccase-like activity, LacQ1, was purified from this strain for the first time, and its crucial role in the PS degradation process was confirmed. Through molecular docking and molecular dynamics (MD) simulations, the interactions between the enzymes and PS were detailed, elucidating the binding and catalytic mechanisms of the degradative enzymes with the substrate. These findings have deepened our understanding of PS degradation.

Generation and Fate of Nanoplastics in the Intestine of Plastic-Degrading Insect (Tenebrio molitor Larvae) during Polystyrene Microplastic Biodegradation

The insect Tenebrio molitor exhibits ultrafast efficiency in biodegrading polystyrene (PS). However, the generation and fate of nanoplastics (NPs) in the intestine during plastic biodegradation remain unknown. In this study, we investigated the biodegradation of PS microplastics (MPs) mediated by T. molitor larvae over a 4-week period and confirmed biodegradation by analyzing Δδ13C in the PS before and after biotreatment (-28.37‰ versus -24.88‰) as an effective tool. The ·OH radicals, primarily contributed by gut microbiota, and H2O2, primarily produced by the host, both increased after MP digestion. The size distribution of residual MP particles in excrements fluctuated within the micrometer ranges. PS NPs were detected in the intestine but not in the excrements. At the end of Weeks 1, 2, 3, and 4, the concentrations of PS NPs in gut tissues were 3.778, 2.505, 2.087, and 2.853 ng/lava, respectively, while PS NPs in glands were quantified at 0.636, 0.284, and 0.113 ng/lava and eventually fell below the detection limit. The PS NPs in glands remained below the detection limit at the end of Weeks 5 and 6. This indicates that initially, NPs generated in the gut entered glands, then declined gradually and eventually disappeared or possibly biodegraded after Week 4, associated with the elevated plastic-degrading capacities of T. molitor larvae. Our findings unveil rapid synergistic MP biodegradation by the larval host and gut microbiota, as well as the fate of generated NPs, providing new insights into the risks and fate associated with NPs during invertebrate-mediated plastic biodegradation.

Bottlenecks in biobased approaches to plastic degradation

Plastic waste is an environmental challenge, but also presents a biotechnological opportunity as a unique carbon substrate. With modern biotechnological tools, it is possible to enable both recycling and upcycling. To realize a plastics bioeconomy, significant intrinsic barriers must be overcome using a combination of enzyme, strain, and process engineering. This article highlights advances, challenges, and opportunities for a variety of common plastics.

Insects to the rescue? Insights into applications, mechanisms, and prospects of insect-driven remediation of organic contaminants

Traditional and emerging contaminants pose significant human and environmental health risks. Conventional physical, chemical, and bioremediation techniques have been extensively studied for contaminant remediation. However, entomo- or insect-driven remediation has received limited research and public attention. Entomo-remediation refers to the use of insects, their associated gut microbiota, and enzymes to remove or mitigate organic contaminants. This novel approach shows potential as an eco-friendly method for mitigating contaminated media. However, a comprehensive review of the status, applications, and challenges of entomo-remediation is lacking. This paper addresses this research gap by examining and discussing the evidence on entomo-remediation of various legacy and emerging organic contaminants. The results demonstrate the successful application of entomo-remediation to remove legacy organic contaminants such as persistent organic pollutants. Moreover, entomo-remediation shows promise in removing various groups of emerging contaminants, including microplastics, persistent and emerging organic micropollutants (e.g., antibiotics, pesticides), and nanomaterials. Entomo-remediation involves several insect-mediated processes, including bio-uptake, biotransfer, bioaccumulation, and biotransformation of contaminants. The mechanisms underlying the biotransformation of contaminants are complex and rely on the insect gut microbiota and associated enzymes. Notably, while insects facilitate the remediation of contaminants, they may also be exposed to the ecotoxicological effects of these substances, which is often overlooked in research. As an emerging field of research, entomo-remediation has several knowledge gaps. Therefore, this review proposes ten key research questions to guide future perspectives and advance the field. These questions address areas such as process optimization, assessment of ecotoxicological effects on insects, and evaluation of potential human exposure and health risks.

The role of insect gut microbiota in host fitness, detoxification and nutrient supplementation

Insects are incredibly diverse, ubiquitous and have successfully flourished out of the dynamic and often unpredictable nature of evolutionary processes. The resident microbiome has accompanied the physical and biological adaptations that enable their continued survival and proliferation in a wide array of environments. The host insect and microbiome's bidirectional relationship exhibits their capability to influence each other's physiology, behavior and characteristics. Insects are reported to rely directly on the microbial community to break down complex food, adapt to nutrient-deficit environments, protect themselves from natural adversaries and control the expression of social behavior. High-throughput metagenomic approaches have enhanced the potential for determining the abundance, composition, diversity and functional activities of microbial fauna associated with insect hosts, enabling in-depth investigation into insect-microbe interactions. We undertook a review of some of the major advances in the field of metagenomics, focusing on insect-microbe interaction, diversity and composition of resident microbiota, the functional capability of endosymbionts and discussions on different symbiotic relationships. The review aims to be a valuable resource on insect gut symbiotic microbiota by providing a comprehensive understanding of how insect gut symbionts systematically perform a range of functions, viz., insecticide degradation, nutritional support and immune fitness. A thorough understanding of manipulating specific gut symbionts may aid in developing advanced insect-associated research to attain health and design strategies for pest management.

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.

Sustainable degradation of synthetic plastics: A solution to rising environmental concerns

Plastics have a significant role in various sectors of the global economy since they are widely utilized in agriculture, architecture, and construction, as well as health and consumer goods. They play a crucial role in several industries as they are utilized in the production of diverse things such as defense materials, sanitary wares, tiles, plastic bottles, artificial leather, and various other household goods. Plastics are utilized in the packaging of food items, medications, detergents, and cosmetics. The overconsumption of plastics presents a significant peril to both the ecosystem and human existence on Earth. The accumulation of plastics on land and in the sea has sparked interest in finding ways to breakdown these polymers. It is necessary to employ suitable biodegradable techniques to decrease the accumulation of plastics in the environment. To address the environmental issues related to plastics, it is crucial to have a comprehensive understanding of the interaction between microorganisms and polymers. A wide range of creatures, particularly microbes, have developed techniques to survive and break down plastics. This review specifically examines the categorization of plastics based on their thermal and biodegradable properties, as well as the many types of degradation and biodegradation. It also discusses the various types of degradable plastics, the characterization of biodegradation, and the factors that influence the process of biodegradation. The plastic breakdown and bioremediation capabilities of these microbes make them ideal for green chemistry applications aimed at removing hazardous polymers from the ecosystem.

Differences in ingestion and biodegradation of the melamine formaldehyde plastic by yellow mealworms Tenebrio molitor and superworms Zophobas atratus, and the prediction of functional gut microbes

Plastics biodegradation by insect larvae is considered as a new strategy for plastic wastes treatment. To uncover the biodegradation of a more complex chemical polymer of melamine formaldehyde (MF) by insect larvae, two worm species of yellow mealworm Tenebrio molitor and superworm Zophobas atratus were fed on MF foam as sole diet for 45 days with sole bran diet as control. Although the MF foam consumption by yellow mealworms of 0.38 mg/d/g-larvae was almost 40% higher than that by superworms of 0.28 mg/d/g-larvae, a similar decrease of survival rates in both species were obtained at about 58%, indicating the adverse effects on their growth. Depolymerization and biodegradation of MF foam occurred in both larval guts, but was more extensive in yellow mealworms. MF foam sole diet influenced gut bacterial and fungal microbiomes of both larvae species, which were assessed by Illumina MiSeq on day 45. Compared to the bran-fed group, both gut bacterial and fungal communities significantly changed in MF-fed groups, but differed in the two larvae species. The results demonstrated a strong association between the distinctive gut microbiome and MF foam degradation, such as unclassified Enterobacteriaceae, Hyphopichia and Issatchenkia. However, sole MF foam diet negatively influenced worms, like lower survival rates and gut abnormalities. In summary, MF foam could be degraded by both yellow mealworms and superworms, albeit with adverse effects. Gut microbes were strongly associated to MF foam degradation, especially the gut fungi.

Insect-based agri-food waste valorization: Agricultural applications and roles of insect gut microbiota

Meeting the demands of the growing population requires increased food and feed production, leading to higher levels of agri-food waste. As this type of waste seriously threatens public health and the environment, novel approaches to waste management should be developed. Insects have been proposed as efficient agents for biorefining waste, producing biomass that can be used for commercial products. However, challenges in achieving optimal outcomes and maximizing beneficial results remain. Microbial symbionts associated with insects are known to have a critical role in the development, fitness, and versatility of insects, and as such, they can be utilized as targets for the optimization of agri-food waste insect-based biorefinery systems. This review discusses insect-based biorefineries, focusing on the agricultural applications of edible insects, mainly as animal feed and organic fertilizers. We also describe the interplay between agri-food waste-utilizing insects and associated microbiota and the microbial contribution in enhancing insect growth, development, and involvement in organic waste bioconversion processes. The potential contribution of insect gut microbiota in eliminating pathogens, toxins, and pollutants and microbe-mediated approaches for enhancing insect growth and the bioconversion of organic waste are also discussed. The present review outlines the benefits of using insects in agri-food and organic waste biorefinery systems, describes the roles of insect-associated microbial symbionts in waste bioconversion processes, and highlights the potential of such biorefinery systems in addressing the current agri-food waste-related challenges.

Recent trends in insect gut immunity

The gut is a crucial organ in insect defense against various pathogens and harmful substances in their environment and diet. Distinct insect gut compartments possess unique functionalities contributing to their physiological processes, including immunity. The insect gut's cellular composition is vital for cellular and humoral immunity. The peritrophic membrane, mucus layer, lumen, microvilli, and various gut cells provide essential support for activating and regulating immune defense mechanisms. These components also secrete molecules and enzymes that are imperative in physiological activities. Additionally, the gut microbiota initiates various signaling pathways and produces vitamins and minerals that help maintain gut homeostasis. Distinct immune signaling pathways are activated within the gut when insects ingest pathogens or hazardous materials. The pathway induced depends on the infection or pathogen type; include immune deficiency (imd), Toll, JAK/STAT, Duox-ROS, and JNK/FOXO regulatory pathways. These pathways produce different antimicrobial peptides (AMPs) and maintain gut homeostasis. Furthermore, various signaling mechanisms within gut cells regulate insect gut recovery following infection. Although some questions regarding insect gut immunity in different species require additional study, this review provides insights into the insect gut's structure and composition, commensal microorganism roles in Drosophila melanogaster and Tenebrio molitor life cycles, different signaling pathways involved in gut immune systems, and the insect gut post-infection recovery through various signaling mechanisms.

Diversity and community composition of strictly anaerobic and culturable bacteria from the feces of Styrofoam-fed Tenebrio molitor larvae: a culturomics-based study

Introduction

In recent years, researchers have been exploring the plastic-degrading abilities of bacteria residing in the guts of Styrofoam-eating Tenebrio molitor larvae. However, none of the reported strains have displayed highly efficient plastic degradation capabilities, and it's noteworthy that none of the existing studies have focused on strictly anaerobic microbes.

Methods

In this study, we exclusively fed Styrofoam to T. molitor larvae and examined how this dietary change influence the gut's bacterial community composition, as observed through fecal bacteria using bacterial 16S rRNA gene amplicon sequencing and the small-scale culturomics method with 20 types of anaerobic media under four different conditions.

Results

The results revealed a significant shift in the dominant phylogroup from Lactococcus (37.8%) to Escherichia-Shigella (54.7%) when comparing the feces of larvae fed with bran and Styrofoam, as analyzing through the bacterial 16S rRNA gene amplicon sequencing. For small-scale culturomics method, a total of 226 strains of anaerobic bacteria were isolated and purified using the rolling-tube/strictly anaerobic technique. Among them, 226 strains were classified into 3 phyla, 7 classes, 9 orders, 17 families, 29 genera, 42 known species and 34 potential novel species.

Discussion

Interestingly, 24 genera in total, identified through the culturomics method, were not found in the results obtained from amplicon sequencing. Here, we present a collection of culturable anaerobic bacteria from the feces of T. molitor larvae, which might be a promising avenue for investigating the biodegradability of plastics by combining specific strains, either randomly or intentionally, while considering the abundance ratio of the microbial community composition.

Advances in enzymatic and organismal technologies for the recycling and upcycling of petroleum-derived plastic waste

Biological catalysts are emerging with the capability to depolymerize a wide variety of plastics. Improving and discovering these catalysts has leveraged a range of tools, including microbial ecology studies, high-throughput selections, and computationally guided mutational studies. In this review, we discuss the prospects for biological solutions to plastic recycling and upcycling with a focus on major advances in polyethylene terephthalate depolymerization, expanding the range of polymers with known biological catalysts, and the utilization of derived products. We highlight several recent improvements in enzymes and reaction properties, the discovery of a wide variety of novel plastic-depolymerizing biocatalysts, and how depolymerization products can be utilized in recycling and upcycling.

Unveiling Fragmentation of Plastic Particles during Biodegradation of Polystyrene and Polyethylene Foams in Mealworms: Highly Sensitive Detection and Digestive Modeling Prediction

It remains unknown whether plastic-biodegrading macroinvertebrates generate microplastics (MPs) and nanoplastics (NPs) during the biodegradation of plastics. In this study, we utilized highly sensitive particle analyzers and pyrolyzer-gas chromatography mass spectrometry (Py-GCMS) to investigate the possibility of generating MPs and NPs in frass during the biodegradation of polystyrene (PS) and low-density polyethylene (LDPE) foams by mealworms (Tenebrio molitor larvae). We also developed a digestive biofragmentation model to predict and unveil the fragmentation process of ingested plastics. The mealworms removed 77.3% of ingested PS and 71.1% of ingested PE over a 6-week test period. Biodegradation of both polymers was verified by the increase in the δ13C signature of residual plastics, changes in molecular weights, and the formation of new oxidative functional groups. MPs accumulated in the frass due to biofragmentation, with residual PS and PE exhibiting the maximum percentage by number at 2.75 and 7.27 μm, respectively. Nevertheless, NPs were not detected using a laser light scattering sizer with a detection limit of 10 nm and Py-GCMS analysis. The digestive biofragmentation model predicted that the ingested PS and PE were progressively size-reduced and rapidly biodegraded, indicating the shorter half-life the smaller plastic particles have. This study allayed concerns regarding the accumulation of NPs by plastic-degrading mealworms and provided critical insights into the factors controlling MP and NP generation during macroinvertebrate-mediated plastic biodegradation.

Polystyrene microplastics biodegradation by gut bacterial Enterobacter hormaechei from mealworms under anaerobic conditions: Anaerobic oxidation and depolymerization

Synthetic plastic is used throughout daily life and industry, threatening organisms with microplastic pollution. Polystyrene is a major plastic polymer and also widely found sources of plastic wastes and microplastics. Here, we report that Enterobacter hormaechei LG3 (CP118279.1), a facultative anaerobic bacterial strain isolated from the gut of Tenebrio molitor larvae (mealworms) can oxidize and depolymerize polystyrene under anaerobic conditions. LG3 performed biodegradation while forming a biofilm on the plastic surface. PS biodegradation was characterized by analyses of surface oxidation, change in morphology and molecular weights, and production of biodegraded derivative. The biodegradation performance by LG3 was compared with PS biodegradation by Bacillus amyloliquefaciens SCGB1 under both anaerobic and aerobic conditions. In addition, through nanopore sequencing technology, we identified degradative enzymes, including thiol peroxidase (tpx), alkyl hydroperoxide reductase C (ahpC) and bacterioferritin comigratory protein (bcp). Along with the upregulation of degradative enzymes for biodegradation, changes in lipid A and biofilm-associated proteins were also observed after the cells were incubated with polystyrene microplastics. Our results provide evidence for anaerobic biodegradation by polystyrene-degrading bacteria and show alterations in gene expression patterns after polystyrene microplastics treatment in the opportunistic pathogen Enterobacter hormaechei.

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.

Biodegradation of polystyrene by intestinal symbiotic bacteria isolated from mealworms, the larvae of Tenebrio molitor

Objectives

Polystyrene is a plastic that leads to environmental pollution. In particular, expanded polystyrene is very light and takes up much space, causing additional environmental problems. The aim of this study was to isolate new symbiotic bacteria which degraded polystyrene from mealworms.

Methods

The population of polystyrene degrading bacteria was increased by enrichment culture of intestinal bacteria from mealworms with polystyrene as a sole carbon source. The degradation activity of isolated bacteria was evaluated by morphological change of micro-polystyrene particles and the surface change of polystyrene films.

Results

Eight isolated species (Acinetobacter septicus, Agrobacterium tumefaciens, Klebsiella grimontii, Pseudomonas multiresinivorans, Pseudomonas nitroreducens, Pseudomonas plecoglossicida, Serratia marcescens, and Yokenella regensburgei) were identified that degrade polystyrene.

Conclusion

Bacterial identification shows that a broad spectrum of bacteria decomposing polystyrene coexists in the intestinal tract of mealworms.

Physicochemical and Structural Evidence that Bacillus cereus Isolated from the Gut of Waxworms (Galleria mellonella Larvae) Biodegrades Polypropylene Efficiently In Vitro

Biodegradation of plastic waste using microorganisms has been proposed as one of the solutions to the increasing worldwide plastic waste. Polypropylene (PP) is the second most used plastic used in various industries, and it has been widely used in the production of personal protective equipment such as masks due to the COVID-19 pandemic. Therefore, biodegradation of PP becomes very important. Here, we present results on the physicochemical and structural studies of PP biodegradation by Bacillus cereus isolated from the gut of the waxworms, Galleria mellonella larvae. We also studied the biodegradability of PP by the gut microbiota compared with Bacillus cereus. We analyzed the microbial degradation of the PP surface using scanning electron microscopy and energy - dispersive X-ray spectroscopy and confirmed that the physical and chemical changes were caused by Bacillus cereus and the gut microbiota. The chemical structural changes were further investigated using X-ray photoelectron microscopy and Fourier - transform - infrared spectroscopy, and it was confirmed that the oxidation of the PP surface proceeded with the formation of carbonyl groups (C=O), ester groups (C-O), and hydroxyl groups (-OH) by Bacillus cereus. Additionally, the gut microbiota composed of diverse microbial species showed equal oxidation of PP compared to Bacillus cereus. More importantly, high temperature gel permeation chromatography (HT-GPC) analysis showed that Bacillus cereus exhibited quantitatively a higher biodegradability of PP compared to the gut microbiota. Our results suggest that Bacillus cereus possesses a complete set of enzymes required to initiate the oxidation of the carbon chain of PP and will be used to discover new enzymes and genes that are involved in degrading PP.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10924-023-02878-y.

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.

Biodegradation of vulcanized rubber by a gut bacterium from plastic-eating mealworms

The disposal of vulcanized rubber waste is difficult due to the presence of three-dimensional crosslinking network structure. Here, we report that a bacterium Acinetobacter sp. BIT-H3, isolated from the gut of plastic-eating mealworm, can grow on and degrade vulcanized poly(cis-1,4-isoprene) rubber (vPR). Scanning electronic microscopy (SEM) shows that strain BIT-H3 can penetrate into the vPR and produce craters and cracks. The tensile strength and the crosslink density of vPR decreased by 53.2% and 29.3% after ten weeks' incubation, respectively. The results of Horikx analysis, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and X-ray absorption near-edge structure (XANES) spectroscopy reveal that strain BIT-H3 can break down both sulfide bridges and double bonds of polymeric backbone within vPR. Sulfate and oligo(cis-1,4 isoprene) with terminal aldehyde and keto groups were identified as metabolic products released during vPR degradation. Through genomic and transcriptional analyses, five enzymes of dszA, dszC1, dszC2, Laccase2147, and Peroxidase1232 were found to be responsible for vPR degradation. Based on the chemical structure characterizations and molecular analyses, a vPR biodegradation pathway was proposed for strain BIT-H3. These findings pave a way for exploiting vulcanized rubber-degrading microorganisms from insect gut and contribute to establish a biodegradation method for vulcanized rubber waste disposal.

Recent Advances in Degradation of Polymer Plastics by Insects Inhabiting Microorganisms

Plastic pollution endangers all natural ecosystems and living creatures on earth. Excessive reliance on plastic products and excessive production of plastic packaging are extremely dangerous for humans because plastic waste has polluted almost the entire world, whether it is in the sea or on the land. This review introduces the examination of pollution brought by non-degradable plastics, the classification and application of degradable materials, and the current situation and strategy to address plastic pollution and plastic degradation by insects, which mainly include Galleria mellonella, Zophobas atratus, Tenebrio molitor, and other insects. The efficiency of plastic degradation by insects, biodegradation mechanism of plastic waste, and the structure and composition of degradable products are reviewed. The development direction of degradable plastics in the future and plastic degradation by insects are prospected. This review provides effective ways to solve plastic pollution.

Microplastics occurrence, detection and removal with emphasis on insect larvae gut microbiota

Microplastics have been identified in all living forms including human beings, the present need is to restrain its spread and devise measures to remediate microplastics from polluted ecosystems. In this regard, the present review emphasizes on the occurrence, sources detection and toxic effects of microplastics in various ecosystems. The removal of microplastics is prevalent by various physico-chemical and biological methods, although the removal efficiency by biological methods is low. It has been noted that the degradation of plastics by insect gut larvae is a well-known aspect, however, the underlying mechanism has not been completely identified. Studies conducted have shown the magnificent contribution of gut microbiota, which have been isolated and exploited for microplastic remediation. This review also focuses on this avenue, as it highlights the contribution of insect gut microbiota in microplastic degradation along with challenges faced and future prospects in this area.

Plastic biodegradation by in vitro environmental microorganisms and in vivo gut microorganisms of insects

Traditional plastics, such as polyethylene (PE), polystyrene (PS), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyurethane (PUR), and other plastic polymers, are difficult to degrade and are gradually accumulated in the environment to cause a serious environmental problem, which is urgently needed to develop novel treatments or control technology. The biodegradation of plastics has gained great attention due to the advantages of green and safe characteristics. Microorganisms play a vital role in the biodegradation of plastics, including environmental microbes (in vitro) and gut microbes of insects (in vivo). Microbial degradation in environmental conditions in vitro is extremely slow for major plastics at degradation rates on the basis of a month or even a year time, but recent discoveries show that the fast biodegradation of specific plastics, such as PS, PE, and PUR, in some invertebrates, especially insects, could be enhanced at rates on basis of hours; the biodegradation in insects is likely to be gut microbial-dependent or synergetic bioreactions in animal digestive systems. This review comprehensively summarizes the latest 7-year (2016-2022) publications on plastic biodegradation by insects and microorganisms, elucidates the mechanism of plastic degradation in insects and environmental microbes, and highlights the cutting-edge perspectives for the potential applications of plastic biodegradation.

Unveiling the potential of Lichtheimia ramosa AJP11 for myco-transformation of polystyrene sulfonate and its driving molecular mechanism

Plastic pollution is a major environmental concern due to its deleterious effects on various ecosystems. The limitations and shortcomings of waste management strategies has led to the over-accumulation of plastic waste, mainly comprised of single-use plastics, such as polystyrene (PS). Considering the advantages of biotransformation over the other plastic disposal methods, it has become a major focus of the modern research. Biotransformation of plastics involves its microbial hydrolysis into short chain oligomers and monomers that are eventually assimilated as carbon source by the microbes leading to the release of CO₂. As fungi are known to possess multifarious and highly regulated enzyme system capable of utilizing diverse nutrient sources, the present study explored the potential of Lichtheimia ramosa AJP11 towards myco-transformation of polystyrene sulfonate (PSS), a structural analogue of polystyrene (PS). During the 30-day incubation period of L. ramosa AJP11 in minimal salt medium (MSM)+1% PSS, the fungus showed 41.6% increment in its fresh weight biomass, indicating the utilization of PSS as sole carbon source. Further analysis revealed the generation of various reaction intermediates such as alkanes and fatty acids, crucial for the continuum of fungal metabolic pathways. Moreover, detection of PS oligomers such as cyclohexane and 2,4-DTBP confirmed the myco-transformation of PSS. The extracellular fungal protein profile showed considerable overexpression of a 14.4 kDa protein, characterized to be a hydrophobic surface binding (Hsb) protein, which is hypothesized to adsorb onto the PSS to facilitate its transformation. Further, in silico analysis of Hsb protein indicated it to be an amphiphilic α-helical protein with ability to bind styrene sulfonate unit via both hydrogen and hydrophobic interactions, with a binding energy of -5.02 kcal mol^-1. These findings open new avenues for over expression of Hsb under controlled reactor conditions to accelerate the PS waste disposal.

Gut microbiota contributes to lignocellulose deconstruction and nitrogen fixation of the larva of Apriona swainsoni

Apriona swainsoni is a vital forest pest prevalent in China. The larvae of A. swainsoni live solely in the branches of trees and rely entirely on the xylem for nutrition. However, there is still a lack of in-depth research on the gut microbiota's use of almost nitrogen-free wood components to provide bio-organic macromolecular components needed for their growth. Thus, in this study, the metagenome, metaproteome, and metabolome of the A. swainsoni larvae in four gut segments (foregut; midgut; anterior hindgut; posterior hindgut) were analyzed by the multi-omics combined technology, to explore the metabolic utilization mechanism of the corresponding gut microbiota of A. swainsoni. Firstly, we found that the metagenome of different gut segments was not significantly different in general, but there were different combinations of dominant bacteria and genes in different gut segments, and the metaproteome and metabolome of four gut segments were significantly different in general. Secondly, the multi-omics results showed that there were significant gradient differences in the contents of cellulose and hemicellulose in different segments of A. swainsoni, and the expression of corresponding metabolic proteins was the highest in the midgut, suggesting the metabolic characteristics of these lignocellulose components in A. swainsoni gut segments. Finally, we found that the C/N ratio of woody food was significantly lower than that of frass, and metagenomic results showed that nitrogen fixation genes mainly existed in the foregut and two hindgut segments. The expression of the key nitrogen fixing gene nifH occurred in two hindgut parts, indicating the feature of nitrogen fixation of A. swainsoni. In conclusion, our results provide direct evidence that the larvae of A. swainsoni can adapt to the relatively harsh niche conditions through the highly organized gut microbiome in four gut segments, and may play a major role in their growth.

Biodegradation of polyethylene by Meyerozyma guilliermondii and Serratia marcescens isolated from the gut of waxworms (larvae of Plodia interpunctella)

The widespread use of polyethylene (PE) causes a large amount of indigestible plastic waste. Waxworms (the larvae of Plodia interpunctella) can eat PE, but the degradation principle of PE under the action of intestinal microorganisms is still unclear, especially the insufficient research on key degradable PE strains. In this study, we fed waxworms with PE. Two strains with high PE degradation efficiency were isolated and purified, and the effects of single and microbial consortia on PE degradation were evaluated by water contact angle (WCA), FTIR, GC-MS, SEM and RT-qPCR. The results showed that Meyerozyma guilliermondii ZJC1 (MgZJC1) and Serratia marcescens ZJC2 (SmZJC2) could degrade PE. However, the degradation efficiency of the microbial consortium was higher, and the weight loss rate of PE was 15.87 %. In addition, the PE degradation products of MgZJC1 were C₉H₁₀O, C₂₀H₁₅NO, C₂₈H₄₄O₃ and C₁₆H₃₂O₂, and the PE degradation products of SmZJC2 were C₁₆H₁₈O, C₁₄H₁₈N₂O₇ and C₃₁H₄₈O₆. The PE degradation products of the microbial consortium were C₁₁H₂₄, C₁₉H₁₀O, C₁₅H₃₂, C₁₄H₃₀, C₁₆H₃₄, C₂₅H₅₂ and C₂₇H₅₆. RT-qPCR results showed that SmZJC2 promoted PE degradation by upregulating the expression of multiple genes, such as multicopper oxidase genes (PiSm-CueO). MgZJC1 responded to carbon deficiency by upregulating the expression of multiple genes, such as key enzyme genes in the tricarboxylic acid (TCA) cycle. This study can be used to develop an efficient microbial consortium for PE degradation and provide a basis for the reuse of PE waste. It can also provide a research basis for the joint degradation of PE by microbial consortia composed of bacteria and fungi.

Biodegradation of Graphene Oxide by Insects (Tenebrio molitor Larvae): Role of the Gut Microbiome and Enzymes

Biodegradation of graphene materials is critical for understanding their environmental process and fate. Thus, biodegradation and mineralization of graphene oxide (GO) by an insect (yellow mealworms, Tenebrio molitor larvae) were investigated. Twenty mealworms could eat up a piece of GO film (1.5 × 1.5 cm) in 15 days. The ingested GO film underwent degradation, and the residual GO sheets were observed in the frass. Raman imaging confirmed that the residual GO (I_D/I_G, 1.16) was more defective than the pristine GO film (I_D/I_G, 0.95). ¹⁴C analysis showed that GO sheets were partially mineralized into CO₂ (0.26%) and assimilated into biomass compositions (e.g., lipid and protein) (0.36%). Gut microbes and extracellular enzymes in yellow mealworms played crucial roles in GO degradation, and the predominant gut microbes for GO biodegradation were identified as Enterobacteriaceae bacteria (e.g., Escherichia-Shigella sp.). Two biodegradation products belonging to hydroxylated or carboxylated aromatic compounds were formed with the assistance of electrons and hydroxyl radicals in mealworm guts. These findings are useful for better understanding the environmental and biological fate of graphene materials.

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.

The gut microbiota, a key to understanding the health implications of micro(nano)plastics and their biodegradation

The effects of plastic debris on the environment and plant, animal, and human health are a global challenge, with micro(nano)plastics (MNPs) being the main focus. MNPs are found so often in the food chain that they are provoking an increase in human intake. They have been detected in most categories of consumed foods, drinking water, and even human feces. Therefore, oral ingestion becomes the main source of exposure to MNPs, and the gastrointestinal tract, primarily the gut, constantly interacts with these small particles. The consequences of human exposure to MNPs remain unclear. However, current in vivo studies and in vitro gastrointestinal tract models have shown that MNPs of several types and sizes impact gut intestinal bacteria, affecting gut homeostasis. The typical microbiome signature of MNP ingestion is often associated with dysbiosis and loss of resilience, leads to frequent pathogen outbreaks, and local and systemic metabolic disorders. Moreover, the small micro- and nano-plastic particles found in animal tissues with accumulated evidence of microbial degradation of plastics/MNPs by bacteria and insect gut microbiota raise the issue of whether human gut bacteria make key contributions to the bio-transformation of ingested MNPs. Here, we discuss these issues and unveil the complex interplay between MNPs and the human gut microbiome. Therefore, the elucidation of the biological consequences of this interaction on both host and microbiota is undoubtedly challenging. It is expected that microbial biotechnology and microbiome research could help decipher the extent to which gut microorganisms diversify and MNP-determinant species, mechanisms, and enzymatic systems, as well as become important to understand our response to MNP exposure and provide background information to inspire future holistic studies.

Effects of Polystyrene Diet on the Growth and Development of Tenebrio molitor

In recent years, the role of Tenebrio molitor in degrading polystyrene foam through its gut microbes has become the focus of research. However, little literature has reported the effect of feeding on polystyrene foam on the growth and development of Tenebrio molitor. In this study, we investigated the impacts of different polystyrene by evaluating the vital signs of Tenebrio molitor fed in the intestines and excrement fluids using RNA-Seq t.echnology and then verifying the transcriptome sequencing findings using qRT-PCR technology. The average weight of Tenebrio molitor larvae in the wheat bran group increased significantly. Tenebrio molitor larvae in the PS group, on the other hand, didn't grow as much and had a much lower average weight than those in the wheat bran group. Compared to the bran group, the excrement of Tenebrio molitor fed only on polystyrene foam was flaky and coarse, increased nitrogen and phosphorus atomic concentration ratios by about 50%, decreased potassium atomic concentration ratios by 63%, with the enterocytes and circular muscle of Tenebrio molitor falling as well. Kyoto Encyclopedia of Genes and Genomes enrichment indicated that the differential genes were mainly related to metabolic pathways. There was an agreement between qRT-PCR and RNA-Seq analyses for the growth and development genes chitinase, heat shock protein 70, and cytochrome P450. Only feeding polystyrene foam shall lead to the growth and development retardation of Tenebrio molitor.

Biodegradation of polyether-polyurethane foam in yellow mealworms (Tenebrio molitor) and effects on the gut microbiome

Polyurethane (PU) is one of the mass-produced recalcitrant plastics with a high environmental resistance but extremely low biodegradability. Therefore, improperly disposed PU waste adds significantly to plastic pollution, which must be addressed immediately. In recent years, there has been an increasing number of reports on plastic biodegradation in insect larvae, especially those that can feed on polyethylene and polystyrene. This study revealed that yellow mealworm (Tenebrio molitor) larvae can chew and ingest polyether-PU foams efficiently, resulting in a significant mass loss of nearly 67% after 35 days at a similar survival rate compared to when fed on bran. However, polyether-PU fragments were found in the frass of T. molitor, indicating that polyether-PU biodegradation and bioconversion in intestinal tracts were not complete. The scission of ether and urethane bonds in the polyether-PU can be evidenced by comparing polymer fragments recovered from frass with the pristine ones using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Gel permeation chromatography suggested the release of low-molecular-weight oligomers as a result of the biodegradation, which also resulted in poor thermal stability of the polyether-PU foam as determined by thermogravimetric analysis. High-throughput sequencing of the gut microbiome revealed significant changes in the microbial community populations due to the polyether-PU diet, for example, an increase in the families Enterobacteriaceae and Streptococcaceae, suggesting that these microorganisms may contribute to the polyether-PU biodegradation.

Comparison on the effectiveness of Fourier transform infrared (FT-IR) and attenuated total reflection Fourier transform infrared (ATR-FT-IR) in characterizing plastics biodegradation by insect larvae

The discovery that insect larvae can feed on foam plastics provided new exploration ideas and potential for plastic wastes biodegradation. In previous studies, both attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FT-IR) and conventional FT-IR have been used but no comparison has been done to evaluate the difference of effectiveness for the characterization of oxidization and biodegradation of plastics by insect larvae. To address this, foam plastics of polystyrene, polyurethane and polyethylene, as well as the frass of plastics-fed superworms Zophobas atratus were characterized using both FT-IR and ATR-FT-IR, and the differences were compared. For FT-IR, spectra were found to vary due to the difference in shape and thickness of the samples, as well as the moisture absorption of KBr. For ATR-FT-IR, although tests could be performed directly without pretreatment, the reflection with short wavelength could not deeply penetrate into the frass samples. Since the composition of plastics-fed larval frass is more complex than the original plastics, the spectra of FT-IR and ATR-FT-IR were observed significantly different. Therefore, the ATR-FT-IR was more effective in monitoring functional groups of original plastics, and be recommended to employ in combination with FT-IR for a more comprehensive characterization of plastics-fed larval frass in future studies.

Microbial enzymes will offer limited solutions to the global plastic pollution crisis

Global economies depend on the use of fossil-fuel-based polymers with 360-400 million metric tons of synthetic polymers being produced per year. Unfortunately, an estimated 60% of the global production is disposed into the environment. Within this framework, microbiologists have tried to identify plastic-active enzymes over the past decade. Until now, this research has largely failed to deliver functional biocatalysts acting on the commodity polymers such as polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), ether-based polyurethane (PUR), polyamide (PA), polystyrene (PS) and synthetic rubber (SR). However, few enzymes are known to act on low-density and low-crystalline (amorphous) polyethylene terephthalate (PET) and ester-based PUR. These above-mentioned polymers represent >95% of all synthetic plastics produced. Therefore, the main challenge microbiologists are currently facing is in finding polymer-active enzymes targeting the majority of fossil-fuel-based plastics. However, identifying plastic-active enzymes either to implement them in biotechnological processes or to understand their potential role in nature is an emerging research field. The application of these enzymes is still in its infancy. Here, we summarize the current knowledge on microbial plastic-active enzymes, their global distribution and potential impact on plastic degradation in industrial processes and nature. We further outline major challenges in finding novel plastic-active enzymes, optimizing known ones by synthetic approaches and problems arising through falsely annotated and unfiltered use of database entries. Finally, we highlight potential biotechnological applications and possible re- and upcycling concepts using microorganisms.

Different plastics ingestion preferences and efficiencies of superworm (Zophobas atratus Fab.) and yellow mealworm (Tenebrio molitor Linn.) associated with distinct gut microbiome changes

Larvae of superworms (Zophobas atratus Fab.) and yellow mealworms (Tenebrio molitor Linn.) can survive on sole plastic diets. However, no side-by-side comparison of plastics degradation by both species is available yet. Here, superworms and yellow mealworms were fed with polystyrene (PS) or polyurethane (PU) foam plastics as sole diets for 35 days with bran as control. Superworms survived 100% on all diets but decreased weights were observed after 20 days with sole plastic diets. In contrast, yellow mealworms survived 84.67% or 62.67% with PS or PU diet, respectively, both plastics diet groups showed increased weights. Cumulative consumption of plastics by superworms were 49.24 mg-PS/larva and 26.23 mg-PU/larva, which were 18 and 11 folds of that of yellow mealworms, respectively. When converted into mg/g-larvae, superworms had a higher PS consumption rate but both species had similar PU consumption rates. Similar changes of the plastic chemical functional groups in frass indicated occurrences of oxidation and biodegradation of plastics in the guts of both species. Changes of gut microbial communities were found associated with plastics feedstocks and larvae species. The increased relative abundances of unclassified Enterobacteriaceae, Klebsiella, Enterococcus, Dysgonomonas and Sphingobacterium were strongly associated with PS diet in superworms, while Hafnia was strongly associated with PS diet in yellow mealworms. Enterococcus and Mangrovibacter were dominant in PU-fed superworm guts, while unclassified Enterobacteriaceae and Hafnia were strongly associated with PU feeding in yellow mealworms. The results demonstrated that different plastics ingestion preferences and efficiencies of both species were associated with distinct dominant microbiomes although similar changes of chemical groups in plastics were observed.

Effect of Probiotics on Host-Microbiota in Bacterial Infections

Diseases caused by bacteria cause millions of deaths every year. In addition, the problem of resistance to antibiotics is so serious that it threatens the achievements of modern medicine. This is a very important global problem as some bacteria can also develop persistence. Indeed, the persistence of pathogenic bacteria has evolved as a potent survival strategy to overcome host organisms’ defense mechanisms. Additionally, chronic or persistent infections may be caused by persisters which could facilitate antibiotic resistance. Probiotics are considered good bacteria. It has been described that the modulation of gut microbiota by probiotics could have a great potential to counteract the deleterious impact and/or regulate gut microbiota after bacterial infection. Probiotics might provide health benefits through the inhibition of pathogen growth or the replacement of pathogenic bacteria. Bearing in mind that current strategies to avoid bacterial persistence and prevent antibiotic resistance are not effective, other strategies need to be assessed. We have carried out a comprehensive review, which included the reported literature between 2016 and 2021, highlighting the clinical trials that reported the probiotics’ potential to regulate gut microbiota after bacterial infection and focusing in particular on the context of antibiotic resistance and persister cells.

Oxidative degradation of pre-oxidated polystyrene plastics by dye decolorizing peroxidases from Thermomonospora curvata and Nostocaceae

Biodegradation of PS has attracted lots of public attentions due to its environmental friendliness. However, no specific PS degrading enzyme has been identified yet. Dye decolorizing peroxidases (DyPs) are heme-containing peroxidases named for the ability to degrade a variety of organic dyes. Herein, the abilities of two DyPs from Thermomonospora curvata (TcDyP) and Nostocaceae (AnaPX) to degrade PS were evaluated. Preoxidation methods by ultraviolet (UV) irradiation and chemical oxidants were developed to initially activate C-C bonds in the PS skeleton. DyPs degradation caused obvious etching and enhanced hydrophilicity of UV-PS films, and also generated new CO and C-OH groups. The cleavage of activated C-C bonds by DyPs was experimentally proven by analyzing the degradation products of UV-PS and model substrates. Furthermore, better pre-oxidation was obtained by using chemical oxidants KMnO₄/H₂SO₄ and ^mCPBA to oxidize PS materials in dissolved state. And AnaPX exhibited stronger degradation effects on KMnO₄/H₂SO₄-PS and ^mCPBA-PS by causing greater changes in functional groups CO, C-O, -OH groups and substituted benzenes and higher molecular weight reductions of 19.7% and 31.0%, respectively. To our knowledge, this is the first report on the identification of PS-degrading enzymes that provides experimental evidence.

Cellular lipids and protein alteration during biodegradation of expanded polystyrene by mealworm larvae under different feeding conditions

The present study reports the biodegradation of polystyrene (PS) by mealworm (Tenebrio molitor) following different feeding regimes. Changes in lipids and protein were studied to evaluate possible differences in the growth and metabolic pathways of the insects depending on the diets. Thermo-gravimetric analysis of the excretions (frass) revealed a decrease in the molecular mass of the PS polymers. The insects' biomass contained less protein when PS was part of the diet, suggesting that the insects undergo a certain level of stress compared to control diets. The frass also contained lower amount of nitrogen content compared to that from insects fed a control diet. NH₄⁺ and other cations involved in biochemical processes were also measured in insects' frass, including potassium, sodium, magnesium, and calcium, combined with a small pH change. The decrease in the mineral content of the frass was attributed to increased cellular activity in PS-fed insects. A higher amount of ceramides and cardiolipins, biomarkers of apoptosis, were also found in association with PS consumption. It was concluded that the insects could metabolize PS, but this caused an increase in its stress levels.

Polystyrene shaping effect on the enriched bacterial community from the plastic-eating Alphitobius diaperinus (Insecta: Coleoptera)

Plastic pollution has become a serious issue of global concern, and biodegradation of plastic wastes is representing one attractive environment-friendly alternative to traditional disposal paths. It is known that insects are involved in the plastic polymer degradation process, with reported evidence of tenebrionid beetle larvae capable to degrade polystyrene (PS), one of the most used plastics worldwide. Recently, a ribosomal RNA based survey on the insect gut microbiota of the lesser mealworm Alphitobius diaperinus has revealed differentially abundant microbial taxa between PS-fed larvae and control group. Following these findings, an enrichment bacterial culture was set up in liquid carbon-free basal medium with PS film as sole carbon source using PS-fed larvae of A. diaperinus as inoculum. After two-months the culture was analysed both by molecular and culture-based methods. Isolated bacteria which had become prevalent under the selective enrichment conditions resulted ascribable to three taxonomic groups: Klebsiella, Pseudomonas, and Stenothrophomonas. The predominance of these groups in PS-fed larvae was confirmed by using bacterial 16S rRNA gene amplicon sequencing, and it was consistent with the results of previous reports. Isolated bacteria were able to attach to PS surfaces and SEM observations showed the presence of thin fibrillar structures connecting the bacterial cells to the abiotic surface.

Biodegradation of polyethylene and polystyrene: From microbial deterioration to enzyme discovery

The global production of plastics has continuously been soaring over the last decades due to their extensive use in our daily life and in industries. Although synthetic plastics offer great advantages from packaging to construction and electronics, their low biodegradability induce serious plastic pollution that damage the environment, human health and make irreversible changes in the ecological cycle. In particular, plastics containing only carbon-carbon (C-C) backbone are less susceptible to degradation due to the lack of hydrolysable groups. The representative polyethylene (PE) and polystyrene (PS) account for about 40% of the total plastic production. Various chemical and biological processes with great potential have been developed for plastic recycle and reuse, but biodegradation seems to be the most attractive and eco-friendly method to combat this growing environmental problem. In this review, we first summarize the current advances in PE and PS biodegradation, including isolation of microbes and potential degrading enzymes from different sources. Next, the state-of-the-art techniques used for evaluating and monitoring PE and PS degradation, the scientific toolboxes for enzyme discovery as well as the challenges and strategies for plastic biodegradation are intensively discussed. In return, it inspires a further technological exploration in expanding the diversity of species and enzymes, disclosing the essential pathways and developing new approaches to utilize plastic waste as feedstock for recycling and upcycling.

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.

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.

Biodegradation of Polystyrene by Three Bacterial Strains Isolated from the Gut of Superworms (Zophobas atratus larvae)

AIMS

To isolate polystyrene degrading bacteria from the gut of superworms and investigate their ability to degrade polystyrene (PS).

METHODS AND RESULTS

Three PS degrading bacteria identified as Pseudomonas sp. EDB1, Bacillus sp. EDA4, and Brevibacterium sp. EDX were successfully isolated from the gut of superworms (Zophobas atratus Larvae) that ingest PS. Incubating PS with each strain for 30-day led to the formation of biofilm on the PS film. Scanning Electron Microscopy (SEM) revealed considerable damage (in terms of pits formation) on the surface of the PS films. FTIR analysis suggested the incorporation of carbonyl group into the carbon backbone of PS. Decreasing of WCA of microbial treated PS film confirmed a chemical change from hydrophobicity to hydrophilicity on the PS surface. Based on these results, we conclude that all isolates had the ability to degrade PS.

CONCLUSIONS

Brevibacterium sp. EDX (GenBank MZ32399) was isolated as the most efficient PS-degrading strain based on the most changing in both PS surface morphology (SEM and WCA analyses) and chemical modification (FTIR analysis) in its PS degradation process.

SIGNIFICANCE AND IMPACT OF THE STUDY

This was the first study to describe the PS degradation by Brevibacterium sp. EDX, and thus provided for its development in plastic remediation process.