The biodegradative effect of Tenebrio molitor Linnaeus larvae on vulcanized SBR and tire crumb

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.

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.

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.

A 30-Year Review on Nanocomposites: Comprehensive Bibliometric Insights into Microstructural, Electrical, and Mechanical Properties Assisted by Artificial Intelligence

From 1990 to 2024, this study presents a groundbreaking bibliometric and sentiment analysis of nanocomposite literature, distinguishing itself from existing reviews through its unique computational methodology. Developed by our research group, this novel approach systematically investigates the evolution of nanocomposites, focusing on microstructural characterization, electrical properties, and mechanical behaviors. By deploying advanced Boolean search strategies within the Scopus database, we achieve a meticulous extraction and in-depth exploration of thematic content, a methodological advancement in the field. Our analysis uniquely identifies critical trends and insights concerning nanocomposite microstructure, electrical attributes, and mechanical performance. The paper goes beyond traditional textual analytics and bibliometric evaluation, offering new interpretations of data and highlighting significant collaborative efforts and influential studies within the nanocomposite domain. Our findings uncover the evolution of research language, thematic shifts, and global contributions, providing a distinct and comprehensive view of the dynamic evolution of nanocomposite research. A critical component of this study is the "State-of-the-Art and Gaps Extracted from Results and Discussions" section, which delves into the latest advancements in nanocomposite research. This section details various nanocomposite types and their properties and introduces novel interpretations of their applications, especially in nanocomposite films. By tracing historical progress and identifying emerging trends, this analysis emphasizes the significance of collaboration and influential studies in molding the field. Moreover, the "Literature Review Guided by Artificial Intelligence" section showcases an innovative AI-guided approach to nanocomposite research, a first in this domain. Focusing on articles from 2023, selected based on citation frequency, this method offers a new perspective on the interplay between nanocomposites and their electrical properties. It highlights the composition, structure, and functionality of various systems, integrating recent findings for a comprehensive overview of current knowledge. The sentiment analysis, with an average score of 0.638771, reflects a positive trend in academic discourse and an increasing recognition of the potential of nanocomposites. Our bibliometric analysis, another methodological novelty, maps the intellectual domain, emphasizing pivotal research themes and the influence of crosslinking time on nanocomposite attributes. While acknowledging its limitations, this study exemplifies the indispensable role of our innovative computational tools in synthesizing and understanding the extensive body of nanocomposite literature. This work not only elucidates prevailing trends but also contributes a unique perspective and novel insights, enhancing our understanding of the nanocomposite research field.

Role of organisms and their enzymes in the biodegradation of microplastics and nanoplastics: A review

Microplastic (MP) and Nanoplastic (NP) contamination have become a critical ecological concern due to their persistent presence in every aspect of the ecosystem and their potentially harmful effects. The current approaches to eradicate these wastes by burning up and dumping adversely impact the environment, while recycling has its own challenges. As a result, applying degradation techniques to eliminate these recalcitrant polymers has been a focus of scientific investigation in the recent past. Biological, photocatalytic, electrocatalytic, and, recently, nanotechnologies have been studied to degrade these polymers. Nevertheless, it is hard to degrade MPs and NPs in the environment, and these degradation techniques are comparatively inefficient and require further development. The recent research focuses on the potential use of microbes to degrade MPs and NPs as a sustainable solution. Therefore, considering the recent advancements in this important research field, this review highlights the utilization of organisms and enzymes for the biodegradation of the MPs and NPs with their probable degradation mechanisms. This review provides insight into various microbial entities and their enzymes for the biodegradation of MPs. In addition, owing to the lack of research on the biodegradation of NPs, the perspective of applying these processes to NPs degradation has also been looked at. Finally, a critical evaluation of the recent development and perspective for future research to improve the effective removal of MPs and NPs in the environment through biodegradation is also discussed.

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.

Nitrogen Fixation and Diazotrophic Community in Plastic-Eating Mealworms Tenebrio molitor L

Mealworms, the larvae of a coleopteran insect Tenebrio molitor L., are capable of eating, living on, and degrading non-hydrolyzable vinyl plastics as sole diet. However, vinyl plastics are carbon-rich but nitrogen-deficient. It remains puzzling how plastic-eating mealworms overcome the nutritional obstacle of nitrogen limitation. Here, we provide the evidence for nitrogen fixation activity within plastic-eating mealworms. Acetylene reduction assays illustrate that the nitrogen-fixing activity ranges from 12.3 ± 0.7 to 32.9 ± 9.3 nmol ethylene·h^-1·gut^-1 and the corresponding fixed nitrogen equivalents of protein are estimated as 8.6 to 23.0 µg per day per mealworm. Nature nitrogen isotopic analyses of plastic-eating mealworms provide further evidence for the assimilation of fixed nitrogen as a new nitrogen source. Eliminating the gut microbial microbiota with antibiotics impairs the mealworm's ability to fix nitrogen from the atmosphere, indicating the contribution of gut microbiota to nitrogen fixation. By using the traditional culture-dependent technique, PCR and RT-PCR of nifH gene, nitrogen-fixing bacteria diversity within the gut was detected, and the genus Klebsiella was demonstrated to be an important nitrogen-fixing symbiont. These findings first build the relationship between plastic degradation (carbon metabolism) and nitrogen fixation (nitrogen metabolism) within mealworms. Combined with previously reported plastic-degrading capability and nitrogen-fixing activity, mealworms may be potential candidates for up-recycling of plastic waste to produce protein sources.

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.

Tenebrio molitor Larvae-Based Magnetic Polyurea Employed as Crude Oil Spill Removal Tool

Renewable resources constitute an extremely rich and varied set of molecules and polymers produced by natural biological activities. Within the applications of these polymers, a very important application is the use of these materials as a sorber for oils or oil spills. The advantage of these nanocomposites is the fact that they integrate different component materials and their properties into a single component material. They have several applications, ranging from environmental remediation to the development of advanced medical applications. This work proposed using magnetic polyurea composites based on an animal substrate from Tenebrio molitor larvae to perform oil spill clean-up operations under a magnetic field in the presence of 1% and 3% of magnetite to be tested as magnetic crude oil sorber. The obtained materials were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA), Scanning Differential Calorimetry (DSC), and Low-Field Nuclear Magnetic Resonance (LF-NMR 1H). The sorber material is simple to prepare and inexpensive. The use of magnetite as a magnetic charge allowed for the efficient removal of oil from water with about 28 g of oil per gram of sorber. These results are very promising and encouraging for future environmental recovery studies involving magnetite and sustainable polymers.

Biodegradation of Different Types of Plastics by Tenebrio molitor Insect

Looking for new, sustainable ways to utilize plastics is still a very pertinent topic considering the amount of plastics produced in the world. One of the newest and intriguing possibility is the use of insects in biodegradation of plastics, which can be named entomoremediation. The aim of this work was to demonstrate the ability of the insect Tenebrio molitor to biodegrade different, real plastic waste. The types of plastic waste used were: remains of thermal building insulation polystyrene foam (PS), two types of polyurethane (kitchen sponge as PU1 and commercial thermal insulation foam as PU2), and polyethylene foam (PE), which has been used as packaging material. After 58 days, the efficiency of mass reduction for all of the investigated plastics was 46.5%, 41.0%, 53.2%, and 69.7% for PS, PU1, PU2, and PE, respectively (with a dose of 0.0052 g of each plastic per 1 mealworm larvae). Both larvae and imago were active plastic eaters. However, in order to shorten the duration of the experiment and increase the specific consumption rate, the two forms of the insect should not be combined together in one container.

Tenebrio molitor in the circular economy: a novel approach for plastic valorisation and PHA biological recovery

The increase in the world population leads to rising demand and consumption of plastic raw materials; only a small percentage of plastics is recovered and recycled, increasing the quantity of waste released into the environment and losing its economic value. The plastics represent a great opportunity in the circular perspective of their reuse and recycling. Research is moving, on the one hand, to implement sustainable systems for plastic waste management and on the other to find new non-fossil-based plastics such as polyhydroxyalkanoates (PHAs). In this review, we focus our attention on Tenebrio molitor (TM) as a valuable solution for plastic biodegradation and biological recovery of new biopolymers (e.g. PHA) from plastic-producing microorganisms, exploiting its highly diversified gut microbiota. TM's use for plastic pollution management is controversial. However, TM microbiota is recognised as a source of plastic-degrading microorganisms. TM-based plastic degradation is improved by co-feeding with food loss and waste as a dietary energy source, thus valorising these low-value substrates in a circular economy perspective. TM as a bioreactor is a valid alternative to traditional PHA recovery systems with the advantage of obtaining, in addition to highly pure PHA, protein biomass and rearing waste from which to produce fertilisers, chitin/chitosan, biochar and biodiesel. Finally, we describe the critical aspects of these TM-based approaches, mainly related to TM mass production, eventual food safety problems, possible release of microplastics and lack of dedicated legislation.

Biodegradation of polypropylene by yellow mealworms (Tenebrio molitor) and superworms (Zophobas atratus) via gut-microbe-dependent depolymerization

Polypropylene (PP), a fossil-based polyolefin plastics widely used worldwide, is non-hydrolyzable and resistant to biodegradation as a major source of plastic pollutants in environment. This study focused on feasibility of PP biodegradation in the larvae of two species of darkling beetles (Coleoptera: Tenebrionidae) i.e., yellow mealworms (Tenebrio molitor) and superworms (Zophobas atratus) using PP foam with number-, weight-, and size-average molecular weights (M_n, M_w, and M_z) of 109.8, 356.2, and 765.0 kDa, respectively. The tests were conducted in duplicates with respective larvae (300 T. molitor and 200 Z. atratus each incubator) at 25 °C and 65% humidity for over a 35-day period. The larvae of T. molitor and Z. atratus fed with PP foam as sole diet consumed PP at 1.0 ± 0.4 and 3.1 ± 0.4 mg 100 larvae^-1 days^-1, respectively; when fed the PP foam plus wheat bran, the consumption rates were enhanced by 68.11% and 39.70%, respectively. Gel permeation chromatography analyses of the frass of T. molitor and Z. atratus larvae fed PP only indicated that M_w was decreased by 20.4 ± 0.8% and 9.0 ± 0.4%; M_n was increased by 12.1 ± 0.4% and 61.5 ± 2.5%; M_z was decreased by 33.8 ± 1.5% and 32.0 ± 1.1%, indicating limited extent depolymerization. Oxidation and biodegradation of PP was confirmed through analysis of the residual PP in frass. Depression of gut microbes with the antibiotic gentamicin inhibited PP depolymerization in both T. molitor and Z. atratus larvae. High throughput 16S rRNA sequencing revealed that Citrobacter sp. and Enterobacter sp. were associated with PP diets in the gut microbiome of Z. atratus larvae while Kluyvera was predominant in the T. molitor larvae. The results indicated that PP can be biodegraded in both T. molitor and Z. atratus larvae via gut microbe-dependent depolymerization with diversified microbiomes.

Head and Neck Cancer Treatments from Chemotherapy to Magnetic Systems: Perspectives and Challenges

BACKGROUND

Cancer is one of the diseases causing society's fears as a stigma of death and pain. Head and Neck Squamous Cell Carcinoma (HNSCC) is a group of malignant neoplasms of different locations in this region of the human body. It is one of the leading causes of morbidity and mortality in Brazil, because these malignant neoplasias, in most cases, are diagnosed in late phases. Surgical excision, chemotherapy and radiotherapy encompass the forefront of antineoplastic therapy; however, the numerous side effects associated with these therapeutic modalities are well known. Some treatments present enough potential to help or replace conventional treatments, such as Magnetic Hyperthermia and Photodynamic Therapy. Such approaches require the development of new materials at the nanoscale, able to carry out the loading of their active components while presenting characteristics of biocompatibility mandatory for biomedical applications.

OBJECTIVE

This work aims to make a bibliographical review of HNSCC treatments. Recent techniques proven effective in other types of cancer were highlighted and raised discussion and reflections on current methods and possibilities of enhancing the treatment of HNSCC.

METHOD

The study was based on a bibliometric research between the years 2008 and 2019 using the following keywords: Cancer, Head and Neck Cancer, Chemotherapy, Radiotherapy, Photodynamic Therapy, and Hyperthermia.

RESULTS

A total of 5.151.725 articles were found, 3.712.670 about cancer, 175.470 on Head and Neck Cancer, 398.736 on Radiotherapy, 760.497 on Chemotherapy, 53.830 on Hyperthermia, and 50.522 on Photodynamic Therapy.

CONCLUSION

The analysis shows that there is still much room for expanding research, especially for alternative therapies since most of the studies still focus on conventional treatments and on the quest to overcome their side effects. The scientific community needs to keep looking for more effective therapies generating fewer side effects for the patient. Currently, the so-called alternative therapies are being used in combination with the conventional ones, but the association of these new therapies shows great potential, in other types of cancer, to improve the treatment efficacy.

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

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

Healable, Recyclable, and Mechanically Tough Polyurethane Elastomers with Exceptional Damage Tolerance

There is a huge requirement of elastomers for use in tires, seals, and shock absorbers every year worldwide. In view of a sustainable society, the next generation of elastomers is expected to combine outstanding healing, recycling, and damage-tolerant capacities with high strength, elasticity, and toughness. However, it remains challenging to fabricate such elastomers because the mechanisms for the properties mentioned above are mutually exclusive. Herein, the fabrication of healable, recyclable, and mechanically tough polyurethane (PU) elastomers with outstanding damage tolerance by coordination of multiblock polymers of poly(dimethylsiloxane) (PDMS)/polycaprolactone (PCL) containing hydrogen and coordination bonding motifs with Zn²⁺ ions is reported. The organization of bipyridine groups coordinated with Zn²⁺ ions, carbamate groups cross-linked with hydrogen bonds, and crystallized PCL segments generates phase-separated dynamic hierarchical domains. Serving as rigid nanofillers capable of deformation and disintegration under an external force, the dynamic hierarchical domains can strengthen the elastomers and significantly enhance their toughness and fracture energy. As a result, the elastomers exhibit a tensile strength of ≈52.4 MPa, a toughness of ≈363.8 MJ m^-3 , and an exceptional fracture energy of ≈192.9 kJ m^-2 . Furthermore, the elastomers can be conveniently healed and recycled to regain their original mechanical properties and integrity under heating.

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

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

Bacterial and enzymatic degradation of poly(cis-1,4-isoprene) rubber: Novel biotechnological applications

Poly(cis-1,4-isoprene) rubber is a highly demanded elastomeric material mainly used for the manufacturing of tires. The end-cycle of rubber-made products is creating serious environmental concern and, therefore, different recycling processes have been proposed. However, the current physical-chemical processes include the use of hazardous chemical solvents, large amounts of energy, and possibly generations of unhealthy micro-plastics. Under this scenario, eco-friendly alternatives are needed and biotechnological rubber treatments are demonstrating huge potential. The cleavage mechanisms and the biochemical pathways for the uptake of poly(cis-1,4-isoprene) rubber have been extensively reported. Likewise, novel bacterial strains able to degrade the polymer have been studied and the involved structural and functional enzymes have been analyzed. Considering the fundamentals, biotechnological approaches have been proposed considering process optimization, cost-effective methods and larger-scale experiments in the search for practical and realistic applications. In this work, the latest research in the rubber biodegradation field is shown and discussed, aiming to analyze the combination of detoxification, devulcanization and polymer-cleavage mechanisms to achieve better degradation yields. The modified superficial structure of rubber materials after biological treatments might be an interesting way to reuse old rubber for re-vulcanization or to find new materials.

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

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

Biodegradation of Vulcanized SBR: A Comparison between Bacillus subtilis, Pseudomonas aeruginosa and Streptomyces sp

Rubber residues present harmful impacts on health and environment, besides wasting valuable and huge amounts of rubber. Biological recycling technique is focused here to minimize this problem. A comparison of the biodegradation effect caused by Bacillus subtilis, Pseudomonas aeruginosa, and Streptomyces sp., separately, on vulcanized SBR-rubber during 4 weeks is reported. The surface and molecular analyses were studied by FTIR-ATR, TGA, DSC, TC and SEM/EDS, in addition to the contact angle and crosslinking tests. B. subtilis, P. aeruginosa, and Streptomyces sp. evoked after 4 weeks a loss in v-SBR crosslinks by 17.15, 10.68 and 43.39% and also in the contact angle with water by 14.10, 12.86 and 15.71%, respectively., if compared to Control samples. FTIR findings indicate that the polymeric chain has been partially consumed causing C-C bonds scission indicating the biodegradation and bio-devulcanization phenomena. The bacterial strains caused a carbon loss by 9.15, 5.97 and 4.55% after one week and 16.09, 16.79 and 18.13% after four weeks for B. subtilis, P. aeruginosa, and Streptomyces sp. mediums, respectively. DSC and EDS results are also promising and highlighting Streptomyces sp. strain as the most effective biodegradative one as an alternative and natural mean of degrading vulcanized rubber residues.