Rapid biodegradation of polyphenylene sulfide plastic beads by Pseudomonas sp

Distribution of microplastics and phthalic acid esters during dry anaerobic digestion of food waste and potential microbial degradation analysis

Food waste (FW) and its biogas residue were considered as sources of terrestrial microplastics (MPs) and phthalic acid esters (PAEs) contamination. However, there was a lack of research and understanding of the MPs and PAEs pollution problem in FW dry anaerobic digestion process (DADP). The MPs and PAEs in three stages of the DADP with the largest monomer disposal scale in China were identified. At the biogas residue extrusion stage, MPs abundance and PAEs concentration reached the highest values, which were 3.63 ± 0.45 × 103 N·kg-1 and 3.62 ± 0.72 mg·kg-1, respectively. Furthermore, there was a significant positive correlation between MPs and PAEs throughout the process (p < 0.05). Although bacteria and fungi with plastic degradation potential were present in all stages, the contamination problem of MPs and PAEs cannot be completely solved through DADP. This study provides a scientific basis for preventing and controlling the pollution of MPs and PAEs.

Eco-friendly approaches for mitigating plastic pollution: advancements and implications for a greener future

Plastic pollution has become a global problem since the extensive use of plastic in industries such as packaging, electronics, manufacturing and construction, healthcare, transportation, and others. This has resulted in an environmental burden that is continually growing, which has inspired many scientists as well as environmentalists to come up with creative solutions to deal with this problem. Numerous studies have been reviewed to determine practical, affordable, and environmentally friendly solutions to regulate plastic waste by leveraging microbes' innate abilities to naturally decompose polymers. Enzymatic breakdown of plastics has been proposed to serve this goal since the discovery of enzymes from microbial sources that truly interact with plastic in its naturalistic environment and because it is a much faster and more effective method than others. The scope of diverse microbes and associated enzymes in polymer breakdown is highlighted in the current review. The use of co-cultures or microbial consortium-based techniques for the improved breakdown of plastic products and the generation of high-value end products that may be utilized as prototypes of bioenergy sources is highlighted. The review also offers a thorough overview of the developments in the microbiological and enzymatic biological degradation of plastics, as well as several elements that impact this process for the survival of our planet.

Biodegradation of polyurethanes by Staphylococcus warneri and by microbial co-culture

With the increasing production and use of polyurethanes (PUs), it is necessary to develop sustainable techniques for the remediation of plastic pollution. The use of microorganisms capable of biodegrading PUs may be an environmentally desirable solution for controlling these plastic contaminants. To contribute to the discovery of alternatives for the mitigation of plastics in the environment, this study aimed to explore the potential of StaphylococcuswarneriUFV_01.21, isolated from the gut of Galleria mellonellalarvae, for biodegradation of PU in pure culture and microbial co-culture with Serratia liquefaciensL135. S. warneri grew using Impranil® PU as the sole carbon source in pure culture and co-culture. With six days of incubation, the biodegradation of Impranil® in Luria Bertani broth was 96, 88 and 76%, while in minimal medium, it was 58, 54 and 42% for S. warneri, S. liquefaciens, and co-culture, respectively. In addition, S. warneri in pure culture or co-culture was able to biodegrade, adhere and form biofilms on the surfaces of Impranil® disks and poly[4,4'-methylenebis (phenyl isocyanate)-alt-1,4-butanediol/di(propylene glycol)/polycaprolactone] (PCLMDI) films. Scanning electron microscopy also revealed biodegradation by detecting the formation of cracks, furrows, pores, and roughness on the surfaces of inoculated PU, both with pure culture and microbial co-culture. This study is the first to demonstrate the potential of S. warneriin PU biodegradation.

Biodegradation of polyethylene (PE), polypropylene (PP), and polystyrene (PS) microplastics by floc-forming bacteria, Bacillus cereus strain SHBF2, isolated from a commercial aquafarm

The ubiquitous proximity of the commonly used microplastic (MP) particles particularly polyethylene (PE), polypropylene (PP), and polystyrene (PS) poses a serious threat to the environment and human health globally. Biological treatment as an environment-friendly approach to counter MP pollution has recent interest when the bio-agent has beneficial functions in their ecosystem. This study aimed to utilize beneficial floc-forming bacteria Bacillus cereus SHBF2 isolated from an aquaculture farm in reducing the MP particles (PE, PP, and PS) from their environment. The bacteria were inoculated for 60 days in a medium containing MP particle as a sole carbon source. On different days of incubation (DOI), the bacterial growth analysis was monitored and the MP particles were harvested to examine their weight loss, surface changes, and alterations in chemical properties. After 60 DOI, the highest weight loss was recorded for PE, 6.87 ± 0.92%, which was further evaluated to daily reduction rate (k), 0.00118 day-1, and half-life (t1/2), 605.08 ± 138.52 days. The OD value (1.74 ± 0.008 Abs.) indicated the higher efficiency of bacteria for PP utilization, and so for the colony formation per define volume (1.04 × 1011 CFU/mL). Biofilm formation, erosions, cracks, and fragments were evident during the observation of the tested MPs using the scanning electron microscope (SEM). The formation of carbonyl and alcohol group due to the oxidation and hydrolysis by SHBF2 strain were confirmed using the Fourier transform infrared spectroscopic (FTIR) analysis. Additionally, the alterations of pH and CO2 evolution from each of the MP type ensures the bacterial activity and mineralization of the MP particles. The findings of this study have confirmed and indicated a higher degree of biodegradation for all of the selected MP particles. B. cereus SHBF2, the floc-forming bacteria used in aquaculture, has demonstrated a great potential for use as an efficient MP-degrading bacterium in the biofloc farming system in the near future to guarantee a sustainable green aquaculture production.

Biodegradation of Nitrile Gloves as Sole Carbon Source of Pseudomonas aeruginosa in Liquid Culture

Nitrile gloves have become a significant environmental pollutant after the COVID-19 pandemic due to their single-use design. This study examines the capability of P. aeruginosa to use nitrile gloves as its sole carbon energy source. Biodegradation was determined by P. aeruginosa adapting to increasing nitrile glove concentrations at 1%, 3%, and 5% (w/v). The growth kinetics of P. aeruginosa were evaluated, as well as the polymer weight loss. Topographic changes on the glove surfaces were examined using SEM, and FT-IR was used to evaluate the biodegradation products of the nitrile gloves. Following the establishment of a biofilm on the glove surface, the nitrile toxicity was minimized via biodegradation. The result of the average weight loss of nitrile gloves was 2.25%. FT-IR analysis revealed the presence of aldehydes and aliphatic amines associated with biodegradation. SEM showed P. aeruginosa immersed in the EPS matrix, causing the formation of cracks, scales, protrusions, and the presence of semi-spherical particles. We conclude that P. aeruginosa has the capability to use nitrile gloves as its sole carbon source, even up to 5%, through biofilm formation, demonstrating the potential of P. aeruginosa for the degradation of nitrile gloves.

An investigation of the environmental implications of bioplastics: Recent advancements on the development of environmentally friendly bioplastics solutions

The production and utilization of plastics may prove beneficial, but the environmental impact suggests the opposite. The single-use plastics (SUP) and conventional plastics are harmful to the environment and need prompt disposal. Bioplastics are increasingly being considered as a viable alternative to conventional plastics due to their potential to alleviate environmental concerns such as greenhouse gas emissions and pollution. However, the previous reviews revealed a lack of consistency in the methodologies used in the Life Cycle Assessments (LCAs), making it difficult to compare the results across studies. The current study provides a systematic review of LCAs that assess the environmental impact of bioplastics. The different mechanical characteristics of bio plastics, like tensile strength, Young's modulus, flexural modulus, and elongation at break are reviewed which suggest that bio plastics are comparatively much better than synthetic plastics. Bioplastics have more efficient mechanical properties compared to synthetic plastics which signifies that bioplastics are more sustainable and reliable than synthetic plastics. The key challenges in bioplastic adoption and production include competition with food production for feedstock, high production costs, uncertainty in end-of-life management, limited biodegradability, lack of standardization, and technical performance limitations. Addressing these challenges requires collaboration among stakeholders to drive innovation, reduce costs, improve end-of-life management, and promote awareness and education. Overall, the study suggests that while bioplastics have the potential to reduce environmental impact, further research is needed to better understand their life cycle and optimize their end-of-life (EoL) management and production to maximize their environmental benefits.

Organic composts as A vehicle for the entry of microplastics into the environment: A comprehensive review

Plastic pollution is a widespread issue that poses a threat to agroecosystems. Recent data on microplastic (MP) pollution from compost and its application to soil have highlighted the potential impact of micropollutants that may be transferred from compost. Thus, we aim with this review to elucidate the distribution-occurrence, characterization, fate/transport, and potential risk of MPs from organic compost to gain comprehensive knowledge and mitigate the adverse impacts of compost application. The concentration of MPs in compost was up to thousands of items/kg. Among micropollutants, fibers, fragments, and films are the most common, with small MPs having a higher potential to absorb other pollutants and cause harm to organisms. Various synthetic polymers, including polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), polyvinyl chloride (PVC), polyester (PES), and acrylic polymers (AP), have been widely used of plastic items. MPs are emerging pollutants that can have diverse effects on soil ecosystems, as they can transfer potential pollutants from MPs to compost and then to the soil. Following the microbial degradation scheme, the transfer chain from plastics to compost to soil can be broken down into main stages, i.e., colonization - (bio)fragmentation - assimilation - and mineralization. Microorganisms and adding biochar play an essential role during composting, which can be an effective solution to enhance MP degradation. Findings have shown that stimulating free radical generation could promote the biodegradation efficacy of MPs and possibly remove their occurrence in compost, thereby reducing their contribution to ecosystem pollution. Furthermore, future recommendations were discussed to reduce ecosystem risks and health challenges.

Salinity significantly reduces plastic-degrading bacteria from rivers to oceans

Microplastics (MPs) are found in rivers and offshore areas. However, there is a lack of detailed research on the changes of surface microbial species attached to MPs when MPs enter the sea. Moreover, no study has been conducted on changes to plastic-degrading bacteria during this process. In this study, using rivers and offshore in Macau, China as examples, bacterial diversity and bacterial species composition attached to surface water and MPs at four river sampling stations and four offshore sampling stations around Macau were studied. Plastic-degrading bacteria, plastic-related metabolic processes, and plastic-related enzymes were analyzed. The results showed that MPs-attached bacteria in rivers and offshore were different with the planktonic bacteria (PB). The proportion of major families on the surface of MPs continued to increase from rivers to estuaries. MPs could significantly enrich plastic-degrading bacteria both in rivers and offshore. The proportion of plastic-related metabolic pathways on the surface bacteria of MPs in rivers was higher than that in offshore waters. Bacteria on the surface of MPs in rivers may induce higher plastic degradation than offshore. Salinity significantly alters the distribution of plastic-degrading bacteria. MPs may degrade more slowly in the oceans, posing a long-term threat to marine life and human health.

Biodegradation of polyvinyl chloride by Citrobacter koseri isolated from superworms (Zophobas atratus larvae)

Polyvinyl chloride (PVC) is one of the widely used plastic products worldwide, and its accumulation in the natural environment has become a major global issue with regard to the environment and biotic health. There is accordingly strong demand for the development of solutions and methods for environmental remediation. Degrading plastic waste using microorganisms is an effective and eco-friendly method. However, evidence of bacteria that afford efficient biodegradation of unplasticized, pure PVC film has yet to be reported. Therefore, the biodegradation of PVC becomes very important. Here, we present results on the physicochemical and structural studies of PVC by Citrobacter koseri (C. koseri) isolated from the gut of the superworm, Zophobas atratus (Z. atratus) larvae. We also studied the biodegradability of PVC by the gut microbiota compared with C. koseri. We analyzed the microbial degradation of the PVC surface using field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) and confirmed that the physical and chemical changes were caused by C. koseri and the gut microbiota. The chemical structural changes were further investigated using X-ray photoelectron spectroscopy (XPS) and Fourier-transform-infrared (FTIR) spectroscopy, and it was confirmed that the oxidation of the PVC surface proceeded with the formation of carbonyl groups (C = O), and hydroxyl groups (-OH) by C. koseri. Additionally, the gut microbiota composed of diverse microbial species showed equal oxidation of PVC compared to C. koseri. Further, we evaluated the capabilities of single bacterial isolate and gut microbiota for pure PVC film biodegradation. Our results verified that C. koseri and the culturable microbiota from the gut of superworms present similar potential to utilize pure PVC film as a carbon source. These findings provide a potential solution for the biodegradation of unplasticized PVC.

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.

Isolation of a polyethylene-degrading bacterium, Acinetobacter guillouiae, using a novel screening method based on a redox indicator

Plastic, a polymer synthesized from petrochemicals, is used worldwide. However, natural degradation of plastic is difficult, causing environmental pollution, with microplastics posing a serious threat to human health. In this study, we aimed to use a new screening method based on the oxidation-reduction indicator, 2,6-dichlorophenolindophenol, to isolate a polyethylene-degrading bacterium, Acinetobacter guillouiae, from insect larvae. Plastic-degrading strains are identified by the color change in the redox indicator from blue to colorless as plastic metabolism occurs. Polyethylene biodegradation by A. guillouiae was verified through weight loss, surface erosion, physiological evidence, and chemical changes on the plastic surface. In addition, we analyzed the characteristics of hydrocarbon metabolism in polyethylene-degrading bacteria. Results suggested that alkane hydroxylation and alcohol dehydrogenation were key steps in polyethylene degradation. This novel screening method will pave the way for high-throughput screening of polyethylene-degrading microorganisms and extending its application to other types of plastics may potentially address plastic pollution.

Potential effects of micro- and nanoplastics on phyllosphere microorganisms and their evolutionary and ecological responses

Plastic pollution is among the most urgent environmental and social challenges of the 21st century, and their influxes in the environment have altered critical growth drivers in all biomes, attracting global concerns. In particular, the consequences of microplastics on plants and their associated soil microorganisms have gained a large audience. On the contrary, how microplastics and nanoplastics (M/NPs) may influence the plant-associated microorganisms in the phyllosphere (i.e., the aboveground portion of plants) is nearly unknown. We, therefore, summarize evidence that may potentially connect M/NPs, plants, and phyllosphere microorganisms based on studies on other analogous contaminants such as heavy metals, pesticides, and nanoparticles. We show seven pathways that may link M/NPs into the phyllosphere environment, and provide a conceptual framework explaining the direct and indirect (soil legacy) effects of M/NPs on phyllosphere microbial communities. We also discuss the adaptive evolutionary and ecological responses, such as acquiring novel resistance genes via horizontal gene transfer and microbial degradation of plastics of the phyllosphere microbial communities, to M/NPs-induced threats. Finally, we highlight the global consequences (e.g., disruption of ecosystem biogeochemical cycling and impaired host-pathogen defense chemistry that can lead to reduced agricultural productivity) of altered plant-microbiome interactions in the phyllosphere in the context of a predicted surge of plastic production and conclude with pending questions for future research priorities. In conclusion, M/NPs are very likely to produce significant effects on phyllosphere microorganisms and mediate their evolutionary and ecological responses.

Development of plastic-degrading microbial consortia by induced selection in microcosms

The increase in the production of highly recalcitrant plastic materials, and their accumulation in ecosystems, generates the need to investigate new sustainable strategies to reduce this type of pollution. Based on recent works, the use of microbial consortia could contribute to improving plastic biodegradation performance. This work deals with the selection and characterization of plastic-degrading microbial consortia using a sequential and induced enrichment technique from artificially contaminated microcosms. The microcosm consisted of a soil sample in which LLDPE (linear low-density polyethylene) was buried. Consortia were obtained from the initial sample by sequential enrichment in a culture medium with LLDPE-type plastic material (in film or powder format) as the sole carbon source. Enrichment cultures were incubated for 105 days with monthly transfer to fresh medium. The abundance and diversity of total bacteria and fungi were monitored. Like LLDPE, lignin is a very complex polymer, so its biodegradation is closely linked to that of some recalcitrant plastics. For this reason, counting of ligninolytic microorganisms from the different enrichments was also performed. Additionally, the consortium members were isolated, molecularly identified and enzymatically characterized. The results revealed a loss of microbial diversity at each culture transfer at the end of the induced selection process. The consortium selected from selective enrichment in cultures with LLDPE in powder form was more effective compared to the consortium selected in cultures with LLDPE in film form, resulting in a reduction of microplastic weight between 2.5 and 5.5%. Some members of the consortia showed a wide range of enzymatic activities related to the degradation of recalcitrant plastic polymers, with Pseudomonas aeruginosa REBP5 or Pseudomonas alloputida REBP7 strains standing out. The strains identified as Castellaniella denitrificans REBF6 and Debaryomyces hansenii RELF8 were also considered relevant members of the consortia although they showed more discrete enzymatic profiles. Other consortium members could collaborate in the prior degradation of additives accompanying the LLDPE polymer, facilitating the subsequent access of other real degraders of the plastic structure. Although preliminary, the microbial consortia selected in this work contribute to the current knowledge of the degradation of recalcitrant plastics of anthropogenic origin accumulated in natural environments.

Anaerobic-anoxic-oxic biological treatment of high-strength, highly recalcitrant polyphenylene sulfide wastewater

This paper outlines an integrated anaerobic-anoxic-oxic (A2O) treatment scheme for high-strength, highly recalcitrant wastewater from the production of polyphenylene sulfide (PPS) resins and their composite chemicals. An integrated anaerobic granular sludge blanket (GSB) and anoxic-oxic (AO) reactor indicated that the A2O removed chemical oxygen demand (COD) of up to 7,043 mg/L with no adverse impact from high total dissolved solids (25,000 mg/L) on the GSB COD removal and effluent suspended solids. At a Total Kjeldahl Nitrogen (TKN) nitrification load of 0.11 g TKN/L.d and 400 mg NH₃/L, almost 99 % of the NH₃ was degraded with effluent NH₃ < 5 mg/L, meeting the limit of 35 mg/L. High S^2- levels of up to 1470 mg/L can be transformed through aerobic microbial degradation to meet a limit of 1.0 mg/L. With proper microbial acclimation and process designs, the integrated A2O scheme offers a resilient and robust treatment for high-strength recalcitrant PPS wastewater.

Can wood-feeding termites solve the environmental bottleneck caused by plastics? A critical state-of-the-art review

The abundance of synthetic polymers has become an ever-increasing environmental threat in the world. The excessive utilization of plastics leads to the accumulation of such recalcitrant pollutants in the environment. For example, during the COVID-19 pandemic, unprecedented demand for personal protective equipment (PPE) kits, face masks, and gloves made up of single-use items has resulted in the massive generation of plastic biomedical waste. As secondary pollutants, microplastic particles (<5 mm) are derived from pellet loss and degradation of macroplastics. Therefore, urgent intervention is required for the management of these hazardous materials. Physicochemical approaches have been employed to degrade synthetic polymers, but these approaches have limited efficiency and cause the release of hazardous metabolites or by-products into the environment. Therefore, bioremediation is a proper option as it is both cost-efficient and environmentally friendly. On the other hand, plants evolved lignocellulose to be resistant to destruction, whereas insects, such as wood-feeding termites, possess diverse microorganisms in their guts, which confer physiological and ecological benefits to their host. Plastic and lignocellulose polymers share a number of physical and chemical properties, despite their structural and recalcitrance differences. Among these similarities are a hydrophobic nature, a carbon skeleton, and amorphous/crystalline regions. Compared with herbivorous mammals, lignocellulose digestion in termites is accomplished at ordinary temperatures. This unique characteristic has been of great interest for the development of a plastic biodegradation approach by termites and their gut symbionts. Therefore, transferring knowledge from research on lignocellulosic degradation by termites and their gut symbionts to that on synthetic polymers has become a new research hotspot and technological development direction to solve the environmental bottleneck caused by synthetic plastic polymers.

Does bacterial community succession within the polyethylene mulching film plastisphere drive biodegradation?

Agricultural fields are severely contaminated with polyethylene mulching film (PMF) and this plastic in the natural environment can be colonized by biofilm-forming microorganisms that differ from those in the surrounding environment. In this study, we investigated the succession of the soil microbial communities in the PMF plastisphere using an artificial micro-ecosystem as well as exploring the degradation of PMF by plastisphere communities. The results indicated a significant and gradual decrease in the alpha diversity of the bacterial communities in the plastisphere and surrounding liquid. The community compositions in the plastisphere and surrounding liquid differed significantly from that in agricultural soil. Phyla and genera with the capacity to degrade polyethylene and hydrocarbon were enriched in the plastisphere, and some of these microorganisms were core members of the plastisphere community. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis detected increases in metabolism pathways for PMF plastisphere Xenobiotics Biodegradation and Metabolism, thereby suggesting the possibility of polyethylene degradation in the plastisphere. Observations by scanning electron microscopy (SEM) and confocal laser scanning microscopy demonstrated the formation of biofilms on the incubated PMF. SEM, atomic force microscopy, Fourier transform infrared spectroscopy and water contact angle detected significant changes in the surface microstructure, chemical composition and hydrophobicity change of the films, thereby suggesting that the plastisphere community degraded PMF during incubation. In conclusion, this study provides insights into the changes in agricultural soil microorganisms in the PMF plastisphere and the degradation of PMF.

Biodeterioration of Microplastics: A Promising Step towards Plastics Waste Management

Polyethylene and Polyester materials are resistant to degradation and a significant source of microplastics pollution, which is an emerging concern. In the present study, the potential of a dumped site bacterial community was evaluated. After primary screening, it was observed that 68.5% were linear low-density polyethylene, 33.3% were high-density, and 12.9% were Polyester degraders. Five strains were chosen for secondary screening, in which they were monitored by FTIR, SEM and weight loss degradation trials. Major results were observed for Alcaligenes faecalis (MK517568) and Bacillus cereus (MK517567), as they showed the highest degradation activity. Alcaligenes faecalis (MK517568) degrades LLDPE by 3.5%, HDPE by 5.8% and Polyester by 17.3%. Bacillus cereus (MK517567) is better tolerated at 30 °C and degrades Polyester by 29%. Changes in infrared spectra indicated degradation pathways of different strains depending on the types of plastics targeted. Through SEM analysis, groves, piths and holes were observed on the surface. These findings suggest that soil bacteria develop an effective mechanism for degradation of microplastics and beads that enables them to utilize plastics as a source of energy without the need for pre-treatments, which highlights the importance of these soil bacteria for the future of effective plastic waste management in a soil environment.

Ranking of potential hazards from microplastics polymers in the marine environment

Microplastics (MPs) have been detected globally in the marine environment. MP polymers of various kinds have different toxicity potentials when decomposed into monomers. Also, the toxicity of MPs is influenced by the particle size distribution of MPs. Based on these parameters, a semi-quantitative risk assessment model has been developed in this study to rank MP polymers of potential health concern emerging from marine exposure pathways. A screening strategy was used to categorize three probability factors and two impact factors and calculate the final risk scores. Four different scenarios were assessed to investigate the influence of risk factors on the model output. The screening strategy prioritised PUR, PVC, PAN, ABS, PMMA, SAN, TPU, UP, PET, PS, and HDPE as the top-ranking polymers of concern (descending order). The sensitivity analysis revealed parameters that influenced the final risk score were hazard score based on monomer classification (RF5 coefficient +0.60)> particle size distribution of MPs (RF4 +0.54)> annual global waste generation (RF1 +0.52)> status of degradation in the marine environment (RF3 +0.32)> mean density of polymers (RF2 +0.16). The outcome of this study can inform the scientific community and the policymakers for better management of MPs where regulation and guidelines need to be considered.

Plastic-containing food waste conversion to biomethane, syngas, and biochar via anaerobic digestion and gasification: Focusing on reactor performance, microbial community analysis, and energy balance assessment

To manage the mixture of food waste and plastic waste, a hybrid biological and thermal system was investigated for converting plastic-containing food waste (PCFW) into renewable energy, focusing on performance evaluation, microbial community analysis, and energy balance assessment. The results showed that anaerobic digestion (AD) of food waste, polyethylene (PE)-containing food waste, polystyrene (PS)-containing food waste, and polypropylene (PP)-containing food waste generated a methane yield of 520.8, 395.6, 504.2, and 479.8 mL CH₄/gVS, respectively. CO₂ gasification of all the plastic-containing digestate produced more syngas than pure digestate gasification. Syngas from PS-digestate reached the maximum yield of 20.78 mol/kg. During the digestate-derived-biochar-amended AD of PCFW, the methane yields in the biochars-amended digesters were 6-30% higher than those of the control digesters. Bioinformatic analysis of microbial communities confirmed the significant difference between control and biochar-amended digesters in terms of bacterial and methanogenic compositions. The enhanced methane yields in biochars-amended digesters could be partially ascribed to the selective enrichment of genus Methanosarcina, leading to an improved equilibrium between hydrogenotrophic and acetoclastic methanogenesis pathways. Moreover, energy balance assessment demonstrated that the hybrid biological and thermal conversion system can be a promising technical option for the treatment of PCFW and recovery of renewable biofuels (i.e., biogas and syngas) and bioresource (i.e., biochar) on an industrial scale.

Synergistic poly(lactic acid) photoreforming and H2 generation over ternary NixCo1-xP/reduced graphene oxide/g-C3N4 composite

Effective utilization of photoexcited electrons and holes is always a challenge in photocatalytic reactions. Herein, we reported ternary Ni_xCo_1-xP/reduced graphene oxide/g-C₃N₄ (Ni_xCo_1-xP/rGO/CN) composite as a photocatalyst for synergistic poly(lactic acid) photoreforming and H₂ generation in alkaline aqueous solution. The rate of H₂ production over the optimal 15Ni_0·1Co_0·9P/rGO/CN reached 576.7 μmol h^-1 g^-1, which is 3.6 times as high as binary 15Ni_0·1Co_0·9P/CN composite. The apparent quantum efficiency of the optimal 15Ni_0·1Co_0·9P/rGO/CN was 1.7% at λ = 420 nm monochromatic light. Mott-Schottky analysis suggested that the photogenerated electrons transfer along the pathway of CN→rGO→Ni_0·1Co_0·9P, where rGO and Ni_0·1Co_0·9P functioned as the medium for electron transporting and reaction site for H₂ generation, respectively. Meanwhile, poly(lactic acid) was photoreformed into formate and acetate by the photogenerated holes and hydroxyl radical. This work demonstrates that ternary Ni_xCo_1-xP/rGO/CN composite can be applied as a cheap and promising photocatalyst for synergistic plastic photoreforming and H₂ generation.

Potential Use of Microbial Enzymes for the Conversion of Plastic Waste Into Value-Added Products: A Viable Solution

The widespread use of commercial polymers composed of a mixture of polylactic acid and polyethene terephthalate (PLA-PET) in bottles and other packaging materials has caused a massive environmental crisis. The valorization of these contaminants via cost-effective technologies is urgently needed to achieve a circular economy. The enzymatic hydrolysis of PLA-PET contaminants plays a vital role in environmentally friendly strategies for plastic waste recycling and degradation. In this review, the potential roles of microbial enzymes for solving this critical problem are highlighted. Various enzymes involved in PLA-PET recycling and bioconversion, such as PETase and MHETase produced by Ideonella sakaiensis; esterases produced by Bacillus and Nocardia; lipases produced by Thermomyces lanuginosus, Candida antarctica, Triticum aestivum, and Burkholderia spp.; and leaf-branch compost cutinases are critically discussed. Strategies for the utilization of PLA-PET's carbon content as C1 building blocks were investigated for the production of new plastic monomers and different value-added products, such as cyclic acetals, 1,3-propanediol, and vanillin. The bioconversion of PET-PLA degradation monomers to polyhydroxyalkanoate biopolymers by Pseudomonas and Halomonas strains was addressed in detail. Different solutions to the production of biodegradable plastics from food waste, agricultural residues, and polyhydroxybutyrate (PHB)-accumulating bacteria were discussed. Fuel oil production via PLA-PET thermal pyrolysis and possible hybrid integration techniques for the incorporation of thermostable plastic degradation enzymes for the conversion into fuel oil is explained in detail.

Rugose small colony variant and its hyper-biofilm in Pseudomonas aeruginosa: Adaption, evolution, and biotechnological potential

One of the hallmarks of the environmental bacterium Pseudomonas aeruginosa is its excellent ecological flexibility, which can thrive in diverse ecological niches. In different ecosystems, P. aeruginosa may use different strategies to survive, such as forming biofilms in crude oil environment, converting to mucoid phenotype in the cystic fibrosis (CF) lung, or becoming persisters when treated with antibiotics. Rugose small colony variants (RSCVs) are the adaptive mutants of P. aeruginosa, which can be frequently isolated from chronic infections. During the past years, there has been a renewed interest in using P. aeruginosa as a model organism to investigate the RSCVs formation, persistence and pathogenesis, as RSCVs represent a hyper-biofilm formation, high adaptability, high-tolerance sub-population in biofilms. This review will briefly summarize recent advances regarding the phenotypic, genetic and host interaction associated with RSCVs, with an emphasis on P. aeruginosa. Meanwhile, some non-pathogenic bacteria such as Pseudomonas fluorescence, Pseudomonas putida and Bacillus subtilis will be also included. Remarkable emphasis is given on intrinsic functions of such hyper-biofilm formation characteristic as well as its potential applications in several biocatalytic transformations including wastewater treatment, microbial fermentation, and plastic degradation. Hopefully, this review will attract the interest of researchers in various fields and shape future research focused not only on evolutionary biology but also on biotechnological applications related to RSCVs.

Effects of plastics on reactor performance and microbial communities during acidogenic fermentation of food waste for production of volatile fatty acids

The aim of this work was to study the effects of plastics (high-density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), and polyethylene terephthalate (PET)) on reactor performance and microbial communities during acidogenic fermentation of food waste for the production of volatile fatty acids (VFA). The addition of HDPE and PS increased total VFA yields by 28% and 47%, respectively, whereas the addition of PP and PET decreased total VFA yields by 6% and 2%, respectively. The highest enhancing performance of PS could be ascribed to its highly porous structure that could provide immobilization effects for microbial growth. Degradation of various plastics was confirmed by FESEM results, but the degrees were limited (i.e., 3.9-8.7%). Bacterial analysis showed that the addition of various plastics altered the community diversity. Phylum Thermotogae and genus Defluviitoga dominated all the reactors. Potential HDPE- and PS-degrading microbes could belong to genus Clostridium_sensu_stricto_8, while Tepidanaerobacter_syntrophicus could be PET-degrading microbes.

Plastic wastes biodegradation: Mechanisms, challenges and future prospects

The growing accumulation of plastic wastes is one of the main environmental challenges currently faced by modern societies. These wastes are considered a serious global problem because of their effects on all forms of life. There is thus an urgent need to demonstrate effective eco-environmental techniques to overcome the hazardous environmental impacts of traditional disposal paths. However, our current knowledge on the prevailing mechanisms and the efficacy of synthetic plastics' biodegradation still appears limited. Under this scope, our review aims to comprehensively highlight the role of microbes, with special emphasis on algae, on the entire plastic biodegradation process focusing on the depolarization of various synthetic plastic types. Moreover, our review emphasizes on the ability of insects' gut microbial consortium to degrade synthetic plastic wastes. In this view, we discuss the schematic pathway of the biodegradation process of six types of synthetic plastics. These findings may contribute to establishing bio-upcycling processes of plastic wastes towards biosynthesis of valuable metabolic products. Finally, we discuss the challenges and opportunities for microbial valorization of degraded plastic wastes.

The Superworm, Zophobas morio (Coleoptera:Tenebrionidae): A 'Sleeping Giant' in Nutrient Sources

The aim of this review is to compile up-to-date information on the superworm, Zophobas morio (F.), regarding its biology and ecology, but also its further potential for use as a nutrient source for food and feed. We illustrate certain basic characteristics of the morphology and bio-ecology of this species, which is marginally considered as a 'pest' in durable amylaceous commodities. More recent data show that Z. morio can be a valuable nutrient and antimicrobial source that could be utilized further in insect-based feed and food production. The inclusion of this species in aquafeed has provided promising results in a wide range of feeding trials, both in terms of fish development and health. Additional data illustrate its potential for use in poultry, indicating that this species provides comparable results with those of other insect species that are used in feed. Moreover, Z. morio can be a viable waste management agent. This review aims to summarize the available data and underline data gaps for future research, toward the potential of the utilization of Z. morio for human food and animal feed. Based on the data presented, Z. morio appears to be a well-promising insect-based protein source, which potential still remains to be unfold.

Global challenges in microplastics: From fundamental understanding to advanced degradations toward sustainable strategies

Currently, the global production and usage of plastics have increased rapidly with the expansion of synthetic polymers. Since plastics' degradation processes are prolonged and thus microplastics (MPs) potentially persist for very long periods in the environment. To date, there is a need for knowledge on the relevance of different potential entry pathways and the number of MPs entering the environment via different routes. Despite the vast quantity of studies that have been undertaken, many unanswered issues remain about the environmental impacts of MPs. The real impacts on a population subjected to many MPs of different structure, dimensions, and shapes over a lifetime are still hard to elucidate. Significantly, MPs can accumulate toxic substances, such as persistent organic pollutants, on their material surface. Hence, it represents a potential concentrated source of environmental pollution or acts as a vector of toxic pollutants in the food chain's interconnection with some severe health implications. Herein, we mainly discussed the global challenges in MPs, including the current production and use status of plastics and their impact on the environment. Additionally, finding the degradation of tiny fragment plastics (MPs level) is essential to remove plastics altogether. Some of the approaches to methods, including biodegradation, physical degradation, physicochemical degradation, have been successfully reviewed. More importantly, the sustainable concepts of using microorganisms and photocatalysis for MPs' degradation have been successfully proposed and demonstrated.

Greater Biofilm Formation and Increased Biodegradation of Polyethylene Film by a Microbial Consortium of Arthrobacter sp. and Streptomyces sp

The widespread use of polyethylene (PE) mulch films has led to a significant accumulation of plastic waste in agricultural soils. The biodegradation of plastic waste by microorganisms promises to provide a cost-effective and environmentally-friendly alternative for mitigating soil plastic pollution. A large number of microorganisms capable of degrading PE have been reported, but degradation may be further enhanced by the cooperative activity of multiple microbial species. Here, two novel strains of Arthrobacter sp. and Streptomyces sp. were isolated from agricultural soils and shown to grow with PE film as a sole carbon source. Arthrobacter sp. mainly grew in the suspension phase of the culture, and Streptomyces sp. formed substantial biofilms on the surface of the PE film, indicating that these strains were of different metabolic types and occupied different microenvironments with contrasting nutritional access. Individual strains were able to degrade the PE film to some extent in a 90-day inoculation experiment, as indicated by decreased hydrophobicity, increased carbonyl index and CO₂ evolution, and the formation of biofilms on the film surface. However, a consortium of both strains had a much greater effect on these degradation properties. Together, these results provide new insights into the mechanisms of PE biodegradation by a microbial consortium composed of different types of microbes with possible metabolic complementarities.

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

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

A Review of Bioresorbable Implantable Medical Devices: Materials, Fabrication, and Implementation

Implantable medical devices (IMDs) are designed to sense specific parameters or stimulate organs and have been actively used for treatment and diagnosis of various diseases. IMDs are used for long-term disease screening or treatments and cannot be considered for short-term applications since patients need to go through a surgery for retrieval of the IMD. Advances in bioresorbable materials has led to the development of transient IMDs that can be resorbed by bodily fluids and disappear after a certain period. These devices are designed to be implanted in the adjacent of the targeted tissue for predetermined times with the aim of measurement of pressure, strain, or temperature, while the bioelectronic devices stimulate certain tissues. They enable opportunities for monitoring and treatment of acute diseases. To realize such transient and miniaturized devices, researchers utilize a variety of materials, novel fabrication methods, and device design strategies. This review discusses potential bioresorbable materials for each component in an IMD followed by programmable degradation and safety standards. Then, common fabrication methods for bioresorbable materials are introduced, along with challenges. The final section provides representative examples of bioresorbable IMDs for various applications with an emphasis on materials, device functionality, and fabrication methods.