Recent Advances in Degradation of Polymer Plastics by Insects Inhabiting Microorganisms

The effects of diverse microplastics on adzuki bean (Vigna angularis) growth and physiologic properties

Globally, microplastic pollution of soil ecosystems poses a major risk. The early studies found that the impact of microplastics on different plants could vary depending on the type of microplastic, the mass concentration or the plant species. This study investigated the effect of 3 mass concentrations (0.1%, 1%, and 2.5%) and 3 types of microplastics (PE MPs, PLA MPs, and PVC MPs) on adzuki bean biomass, root traits, Chlorophyll content and antioxidant enzymes. According to our findings, all microplastics had an impact on biomass, but PLA MPs had the strongest inhibitory effect. The high mass concentration of microplastics had a significant influence on chlorophyll content. Adzuki beans exhibited varying degrees of damage upon exposure to microplastics, but they were able to withstand the oxidative stress brought on by PE MPs by increasing the activity of antioxidant enzymes (SOD and POD). Comparing the adverse effects of PE MPs on adzuki beans to those of PLA MPs and PVC MPs, principal component analysis and membership function value analysis revealed that the former had fewer impacts. Disparities in the observed effects may be attributed to variations in the properties of microplastics. Subsequent investigations into the mechanisms underlying microplastic toxicity need a more comprehensive exploration.

Fabricating High Strength Bio-Based Dynamic Networks from Epoxidized Soybean Oil and Poly(Butylene Adipate-co-Terephthalate)

Amid the rapid development of modern society, the widespread use of plastic products has led to significant environmental issues, including the accumulation of non-degradable waste and extensive consumption of non-renewable resources. Developing healable, recyclable, bio-based materials from abundant renewable resources using diverse dynamic interactions attracts increasing global attention. However, achieving a good balance between the self-healing capacity and mechanical performance, such as strength and toughness, remains challenging. In our study, we address this challenge by developing a new type of dynamic network from epoxidized soybean oil (ESO) and poly(butylene adipate-co-terephthalate) (PBAT) with good strength and toughness. For the synthetic strategy, a thiol-epoxy click reaction was conducted to functionalize ESO with thiol and hydroxyl groups. Subsequently, a curing reaction with isocyanates generated dynamic thiourethane and urethane bonds with different bonding energies in the dynamic networks to reach a trade-off between dynamic features and mechanical properties; amongst these, the thiourethane bonds with a lower bonding energy provide good dynamic features, while the urethane bonds with a higher bonding energy ensure good mechanical properties. The incorporation of flexible PBAT segments to form the rational multi-phase structure with crystalline domains further enhanced the products. A typical sample, OTSO100-PBAT100, exhibited a tensile strength of 33.2 MPa and an elongation at break of 1238%, demonstrating good healing capacity and desirable mechanical performance. This study provides a promising solution to contemporary environmental and energy challenges by developing materials that combine mechanical and repair properties. It addresses the specific gap of achieving a trade-off between tensile strength and elongation at break in bio-based self-healing materials, promising a wide range of applications.

Current paradigms and future challenges in harnessing gut bacterial symbionts of insects for biodegradation of plastic wastes

The ubiquitous incorporation of plastics into daily life, coupled with inefficient recycling practices, has resulted in the accumulation of millions of metric tons of plastic waste, that poses a serious threat to the Earth's sustainability. Plastic pollution, a global problem, disrupts the ecological balance and endangers various life forms. Efforts to combat plastic pollution are underway, with a promising avenue being biological degradation facilitated by certain insects and their symbiotic gut microorganisms, particularly bacteria. This review consolidates existing knowledge on plastic degradation by insects and their influence on gut microbiota. Additionally, it delves into the potential mechanisms employed by insects in symbiosis with gut bacteria, exploring the bioconversion of waste plastics into value-added biodegradable polymers through mineralization. These insights hold significant promise for the bio-upcycling of plastic waste, opening new horizons for future biomanufacturing of high-value chemicals from plastic-derived compounds. Finally, we weigh the pros and cons of future research endeavors related to the bioprospection of plastic-degrading bacteria from underexplored insect species. We also underscore the importance of bioengineering depolymerases with novel characteristics, aiming for their application in the remediation and valorization of waste plastics.

Nature's Plastic Predators: A Comprehensive and Bibliometric Review of Plastivore Insects

Unprecedented plastic production has resulted in over six billion tons of harmful waste. Certain insect taxa emerge as potential agents of plastic biodegradation. Through a comprehensive manual and bibliometric literature analysis, this review analyses and consolidates the growing literature related to insect-mediated plastic breakdown. Over 23 insect species, representing Coleoptera, Lepidoptera, and 4 other orders, have been identified for their capacity to consume plastic polymers. Natural and synthetic polymers exhibit high-level similarities in molecular structure and properties. Thus, in conjunction with comparative genomics studies, we link plastic-degrading enzymatic capabilities observed in certain insects to the exaptation of endogenous enzymes originally evolved for digesting lignin, cellulose, beeswax, keratin and chitin from their native dietary substrates. Further clarification is necessary to distinguish mineralisation from physicochemical fragmentation and to differentiate microbiome-mediated degradation from direct enzymatic reactions by insects. A bibliometric analysis of the exponentially growing body of literature showed that leading research is emerging from China and the USA. Analogies between natural and synthetic polymer's degradation pathways will inform engineering robust enzymes for practical plastic bioremediation applications. By aggregating, analysing, and interpreting published insights, this review consolidates our mechanistic understanding of insects as a potential natural solution to the escalating plastic waste crisis.

Improved reference quality genome sequence of the plastic-degrading greater wax moth, Galleria mellonella

Galleria mellonella is a pest of honeybees in many countries because its larvae feed on beeswax. However, G. mellonella larvae can also eat various plastics, including polyethylene, polystyrene, and polypropylene, and therefore, the species is garnering increasing interest as a tool for plastic biodegradation research. This paper presents an improved genome (99.3% completed lepidoptera_odb10 BUSCO; genome mode) for G. mellonella. This 472 Mb genome is in 221 contigs with an N50 of 6.4 Mb and contains 13,604 protein-coding genes. Genes that code for known and putative polyethylene-degrading enzymes and their similarity to proteins found in other Lepidoptera are highlighted. An analysis of secretory proteins more likely to be involved in the plastic catabolic process has also been carried out.

Biodegradation of Polystyrene by Plastic-Eating Tenebrionidae Larvae

Polystyrene (PS) is an extremely stable polymer with a relatively high molecular weight and a strong hydrophobic character that makes it highly resistant to biodegradation. In this study, PS was subjected to biodegradation tests by Tenebrio Molitor (T. Molitor) and Zophobas Morio (Z. Morio) larvae. Specifically, six different experimental diets were compared: (i) T. Molitor fed with bran; (ii) T. Molitor fed only PS; (iii) T. Molitor fed only PS treated with H2O2; (iv) Z. Morio fed with bran; (v) Z. Morio fed only PS; and (vi) Z. Morio fed only PS treated with H2O2. Therefore, the mass change of the larvae and the survival rate were measured periodically, while the frass collected after 15 and 30 days was analyzed by different analyses, such as spectroscopy (FTIR), spectrometry (molecular weight and polydispersity), thermal analysis (TGA) and microscopy (scanning electron microscopy observations). The obtained results suggest that in the case of T. Molitor larvae, larvae feeding on bran showed the highest survival rate of ~94% at 30 days, while in the case of the Z. Morio larvae, the highest survival rate was exhibited by larvae eating PS-H2O2. Although not strongly pronounced, the Mw and Mn of PS in the frass of both T. Molitor and Z. Morio larvae decreased over 30 days, suggesting PS biodegradation. Finally, the morphological analysis shows that PS samples isolated from the frass of T. Molitor and Z. Morio larvae showed completely different, rough and irregularly carved surface structures, in comparison to PS before biodegradation.

Enhanced biodegradation of microplastic and phthalic acid ester plasticizer: The role of gut microorganisms in black soldier fly larvae

Hermetia illucens larvae are recognized for their ability to mitigate or eliminate contaminants by biodegradation. However, the biodegradation characteristics of microplastics and phthalic acid esters plasticizers, as well as the role of larval gut microorganisms, have remained largely unrevealed. Here, the degradation kinetics of plasticizers, and biodegradation characteristics of microplastics were examined. The role of larval gut microorganisms was investigated. For larval development, microplastics slowed larval growth significantly (P < 0.01), but the effect of plasticizer was not significant. The degradation kinetics of plasticizers were enhanced, resulting in an 8.11 to 20.41-fold decrease in degradation half-life and a 3.34 to 3.82-fold increase in final degradation efficiencies, compared to degradation without larval participation. The depolymerization and biodeterioration of microplastics were conspicuously evident, primarily through a weight loss of 17.63 %-25.52 %, variation of chemical composition and structure, bio-oxidation and bioerosion of microplastic surface. The synergistic effect driven by larval gut microorganisms, each with various functions, facilitated the biodegradation. Specifically, Ignatzschineria, Paenalcaligenes, Moheibacter, Morganella, Dysgonomonas, Stenotrophomonas, Bacteroides, Sphingobacterium, etc., appeared to be the key contributors, owing to their xenobiotic biodegradation and metabolism functions. These findings offered a new perspective on the potential for microplastics and plasticizers biodegradation, assisted by larval gut microbiota.

Progress in polystyrene biodegradation by insect gut microbiota

Polystyrene (PS) is frequently used in the plastics industry. However, its structural stability and difficulty to break down lead to an abundance of plastic waste in the environment, resulting in micro-nano plastics (MNPs). As MNPs are severe hazards to both human and environmental health, it is crucial to develop innovative treatment technologies to degrade plastic waste. The biodegradation of plastics by insect gut microorganisms has gained attention as it is environmentally friendly, efficient, and safe. However, our knowledge of the biodegradation of PS is still limited. This review summarizes recent research advances on PS biodegradation by gut microorganisms/enzymes from insect larvae of different species, and schematic pathways of the degradation process are discussed in depth. Additionally, the prospect of using modern biotechnology, such as genetic engineering and systems biology, to identify novel PS-degrading microbes/functional genes/enzymes and to realize new strategies for PS biodegradation is highlighted. Challenges and limitations faced by the application of genetically engineered microorganisms (GEMs) and multiomics technologies in the field of plastic pollution bioremediation are also discussed. This review encourages the further exploration of the biodegradation of PS by insect gut microbes/enzymes, offering a cutting-edge perspective to identify PS biodegradation pathways and create effective biodegradation strategies.

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.

Synthesis and Properties of Polystyrene Composite Material with Hazelnut Shells

In this study we evaluated the potential use of hazelnut shell powder in the production of a composite material. Polystyrene was used as a polymer matrix. This work presents the results of modifying hazelnut powder particles to create a polystyrene shell on their surfaces. Modification of the filler increased its contact angle wetted with water from θ=60.16±1.03° to θ=87.02±1.10°. Composite materials containing from 10 to 50 wt.% of modified hazelnut shell powder were prepared and studied. As a result of the experiments, it was found that the composites have optimal physical, mechanical, and operational properties at the following ratio: polystyrene 60-80 wt.%, modified hazelnut shell powder 20-40 wt.%. If the introduction of polystyrene was more than 90 wt.%, the flexural strength and Vickers hardness were quite low at the load of 200 g, and accordingly, the durability of such materials was not satisfactory. These samples are characterized by small percentages of hazelnut shells; therefore, the resulting material will be of pale, unsaturated color. The upper limit of the working temperature range for the composite lies between 265.0-376.0 °C, depending on the percentage of the hazelnut shell powder filling.

Study on the Biodegradation Process of D-Mannose Glycopolymers in Liquid Media and Soil

Polymers derived from natural raw materials have become of great interest due to their increased biodegradable features and possible biocompatibility. Our group has successfully synthesized and characterized polymers derived from D-mannose oligomer (M), 2-hydroxy propyl acrylate (HPA), and methacrylate (HPMA) in different weight ratios. Their biodegradation was studied in liquid media with pure Proteus mirabilis inoculum for the samples with the most sugar residue, and the results show that the methacrylate derivative M_HPMA1 lost about 50% of its weight during incubation. SEM/EDX techniques were employed to display the modifications of the samples during the biodegradation process. The glycopolymers were buried in garden soil, and the experiment proved that more than 40% of the weight of the M_HPA1 sample was lost during biodegradation, while the other samples encountered an average of about 32% weight loss. The biodegradation profile was fitted against linear and polynomial mathematical models, which enabled an estimate of about a year for the total degradation of the D-mannose glycopolymers sample in soil.