Distribution of poly(?-hydroxybutyrate) and poly(?-caprolactone)aerobic degrading microorganisms in different environments

Biodegradation of poly-3-hydroxybutyrate after soil inoculation with microbial consortium: Soil microbiome and plant responses to the changed environment

Biodegradable plastics play a vital role in addressing global plastics disposal challenges. Poly-3-hydroxybutyrate (P3HB) is a biodegradable bacterial intracellular storage polymer with substantial usage potential in agriculture. Poly-3-hydroxybutyrate and its degradation products are non-toxic; however, previous studies suggest that P3HB biodegradation negatively affects plant growth because the microorganisms compete with plants for nutrients. One possible solution to this issue could be inoculating soil with a consortium of plant growth-promoting and N-fixing microorganisms. To test this hypothesis, we conducted a pot experiment using lettuce (Lactuca sativa L. var. capitata L.) grown in soil amended with two doses (1 % and 5 % w/w) of P3HB and microbial inoculant (MI). We tested five experimental variations: P3HB 1 %, P3HB 1 % + MI, P3HB 5 %, P3HB 5 % + MI, and MI, to assess the impact of added microorganisms on plant growth and P3HB biodegradation. The efficient P3HB degradation, which was directly dependent on the amount of bioplastics added, was coupled with the preferential utilization of P3HB as a carbon (C) source. Due to the increased demand for nutrients in P3HB-amended soil by microbial degraders, respiration and enzyme activities were enhanced. This indicated an increased mineralisation of C as well as nitrogen (N), sulphur (S), and phosphorus (P). Microbial inoculation introduced specific bacterial taxa that further improved degradation efficiency and nutrient turnover (N, S, and P) in P3HB-amended soil. Notably, soil acidification related to P3HB was not the primary factor affecting plant growth inhibition. However, despite plant growth-promoting rhizobacteria and N2-fixing microorganisms originating from MI, plant biomass yield remained limited, suggesting that these microorganisms were not entirely successful in mitigating the growth inhibition caused by P3HB.

Deciphering heterogeneous enzymatic surface reactions on xylan using surface plasmon resonance spectroscopy

Xylans' unique properties make it attractive for a variety of industries, including paper, food, and biochemical production. While for some applications the preservation of its natural structure is crucial, for others the degradation into monosaccharides is essential. For the complete breakdown, the use of several enzymes is required, due to its structural complexity. In fact, the specificity of enzymatically-catalyzed reactions is guided by the surface, limiting or regulating accessibility and serving structurally encoded input guiding the actions of the enzymes. Here, we investigate enzymes at surfaces rich in xylan using surface plasmon resonance spectroscopy. The influence of diffusion and changes in substrate morphology is studied via enzyme surface kinetics simulations, yielding reaction rates and constants. We propose kinetic models, which can be applied to the degradation of multilayer biopolymer films. The most advanced model was verified by its successful application to the degradation of a thin film of polyhydroxybutyrate treated with a polyhydroxybutyrate-depolymerase. The herein derived models can be employed to quantify the degradation kinetics of various enzymes on biopolymers in heterogeneous environments, often prevalent in industrial processes. The identification of key factors influencing reaction rates such as inhibition will contribute to the quantification of intricate dynamics in complex systems.

Biodegradation of PHB/PBAT films and isolation of novel PBAT biodegraders from soil microbiomes

Polyhydroxyalkanoates (PHAs) are important candidates for replacing petroleum-based plastics. This transition is urgent for the development of a biobased economy and to protect human health and natural ecosystems. PHAs are biobased and biodegradable polyesters that when blended with other polymers, such as poly(butylene adipate-co-terephthalate) (PBAT), acquire remarkable improvements in their properties, which allow them to comply with the requirements of packaging applications. However, the biodegradation of such blends should be tested to evaluate the impact of those polymers in the environment. For instance, PBAT is a compostable aliphatic-aromatic copolyester, and its biodegradation in natural environments, such as soil, is poorly studied. In this work, we evaluated the biodegradation of a bilayer film composed of PHB and PBAT, by a soil microbiome. The bilayer film reached 47 ± 1 % mineralization in 180 days and PHB was no longer detected after this period. The increased crystallinity of the PBAT residue was a clear sign of biodegradation, indicating that the amorphous regions were preferentially biodegraded. Seven microorganisms were isolated, from which 4 were closely related to microorganisms already known as PHB degraders, but the other 3 species, closely related to Streptomyces coelicoflavus, Clonostachys rosea and Aspergillus insuetus, were found for the first time as PHB degraders. Most remarkably, two fungi closely related to Purpureocillium lilacinum and Aspergillus pseudodeflectus (99.83 % and 100 % identity by ITS sequencing) were isolated and identified as PBAT degraders. This is very interesting due to the rarity of isolating PBAT-degrading microorganisms. These results show that the bilayer film can be biodegraded in soil, at mesophilic temperatures, showing its potential to replace synthetic plastics in food packaging.

Review of nomenclature and methods of analysis of polyethylene terephthalic acid hydrolyzing enzymes activity

Enzymatic degradation of polyethylene terephthalic acid (PET) has been gaining increasing importance. This has resulted in a significant increase in the search for newer enzymes and the development of more efficient enzyme-based systems. Due to the lack of a standard screening process, screening new enzymes has relied on other assays to determine the presence of esterase activity. This, in turn, has led to various nomenclatures and methods used to describe them and measure their activity. Since all PET-hydrolyzing enzymes are α/β hydrolases, they catalyze a serine nucleophilic attack and cleave an ester bond. They are lipases, esterases, cutinases and hydrolases. This has been used interchangeably, leading to difficulties while comparing results and evaluating progress. This review discusses the varied enzyme nomenclature being adapted, the different assays and analysis methods reported, and the strategies used to increase PET-hydrolyzing enzyme efficiency. A section on the various ways to quantify PET hydrolysis is also covered.

Advancing sustainable agriculture: Evaluation of Poly (lactic acid) (PLA) based mulch films and identification of biodegrading microorganisms among soil microbiota

Non-biodegradable polyolefin based plastic mulch residues in agricultural fields after the end of a crop cycle have raised several concerns as an environmental pollutant in recent years. This study explores the potential of Poly (lactic acid) (PLA) and Poly (butylene adipate-co-terephthalate) (PBAT) based compostable films reactively blended with compatibilizers and chain extenders as a promising solution to environmental challenges associated with traditional plastic mulch films. Epoxidized soybean oil (ESO) and Epoxy-functionalized styrene acrylic copolymer (ESA) have been used as reactive compatibilizers and chain extenders respectively. In-depth analysis of the mechanical, thermal, and barrier properties of the developed films, revealed that the PLA/PBAT blend films at 75:25 weight ratio in the presence of 5 phr ESO and 0.5 phr ESA exhibit improved performance characteristics for application as mulch films. Furthermore, the films were subjected to 360-h UV exposure to gauge their stability under prolonged exposure, specifically investigating changes in the carbonyl index. Additionally, a rigorous real-time field trial of the mulch films spanning eight months with various crops was carried out to understand their performance in practical agricultural settings. The study also involved the identification of microorganisms responsible for the degradation of the developed mulch films employing 16S rRNA sequencing.

Effects of poly(3-hydroxybutyrate) [P(3HB)] coating on the bacterial communities of artificial structures

The expanding urbanization of coastal areas has led to increased ocean sprawl, which has had both physical and chemical adverse effects on marine and coastal ecosystems. To maintain the health and functionality of these ecosystems, it is imperative to develop effective solutions. One such solution involves the use of biodegradable polymers as bioactive coatings to enhance the bioreceptivity of marine and coastal infrastructures. Our study aimed to explore two main objectives: (1) investigate PHA-degrading bacteria on polymer-coated surfaces and in surrounding seawater, and (2) comparing biofilm colonization between surfaces with and without the polymer coating. We applied poly(3-hydroxybutyrate) [P(3HB)) coatings on concrete surfaces at concentrations of 1% and 6% w/v, with varying numbers of coating cycles (1, 3, and 6). Our findings revealed that the addition of P(3HB) indeed promoted accelerated biofilm growth on the coated surfaces, resulting in an occupied area approximately 50% to 100% larger than that observed in the negative control. This indicates a remarkable enhancement, with the biofilm expanding at a rate roughly 1.5 to 2 times faster than the untreated surfaces. We observed noteworthy distinctions in biofilm growth patterns based on varying concentration and number of coating cycles. Interestingly, treatments with low concentration and high coating cycles exhibited comparable biofilm enhancements to those with high concentrations and low coating cycles. Further investigation into the bacterial communities responsible for the degradation of P(3HB) coatings identified mostly common and widespread strains but found no relation between the concentration and coating cycles. Nevertheless, this microbial degradation process was found to be highly efficient, manifesting noticeable effects within a single month. While these initial findings are promising, it's essential to conduct tests under natural conditions to validate the applicability of this approach. Nonetheless, our study represents a novel and bio-based ecological engineering strategy for enhancing the bioreceptivity of marine and coastal structures.

Metagenomic investigations into the microbial consortia, degradation pathways, and enzyme systems involved in the biodegradation of plastics in a tropical lentic pond sediment

The exploitation of exciting features of plastics for diverse applications has resulted in significant plastic waste generation, which negatively impacts environmental compartments, metabolic processes, and the well-being of aquatic ecosystems biota. A shotgun metagenomic approach was deployed to investigate the microbial consortia, degradation pathways, and enzyme systems involved in the degradation of plastics in a tropical lentic pond sediment (APS). Functional annotation of the APS proteome (ORFs) using the PlasticDB database revealed annotation of 1015 proteins of enzymes such as depolymerase, esterase, lipase, hydrolase, nitrobenzylesterase, chitinase, carboxylesterase, polyesterase, oxidoreductase, polyamidase, PETase, MHETase, laccase, alkane monooxygenase, among others involved in the depolymerization of the plastic polymers. It also revealed that polyethylene glycol (PEG), polyhydroxyalkanoates (PHA), polyhydroxybutyrate (PHB), polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polyethylene terephthalate (PET), and nylon have the highest number of annotated enzymes. Further annotation using the KEGG GhostKOALA revealed that except for terephthalate, all the other degradation products of the plastic polymers depolymerization such as glyoxylate, adipate, succinate, 1,4-butanediol, ethylene glycol, lactate, and acetaldehyde were further metabolized to intermediates of the tricarboxylic acid cycle. Taxonomic characterization of the annotated proteins using the AAI Profiler and BLASTP revealed that Pseudomonadota members dominate most plastic types, followed by Actinomycetota and Acidobacteriota. The study reveals novel plastic degraders from diverse phyla hitherto not reported to be involved in plastic degradation. This suggests that plastic pollution in aquatic environments is prevalent with well-adapted degrading communities and could be the silver lining in mitigating the impacts of plastic pollution in aquatic environments.

Recycling and Degradation of Polyamides

As one of the five major engineering plastics, polyamide brings many benefits to humans in the fields of transportation, clothing, entertainment, health, and more. However, as the production of polyamide increases year by year, the pollution problems it causes are becoming increasingly severe. This article reviews the current recycling and treatment processes of polyamide, such as chemical, mechanical, and energy recovery, and degradation methods such as thermal oxidation, photooxidation, enzyme degradation, etc. Starting from the synthesis mechanism of polyamide, it discusses the advantages and disadvantages of different treatment methods of polyamide to obtain more environmentally friendly and economical treatment schemes. Finding enzymes that can degrade high-molecular-weight polyamides, exploring the recovery of polyamides under mild conditions, synthesizing environmentally degradable polyamides through copolymerization or molecular design, and finally preparing degradable bio-based polyamides may be the destination of polyamide.

Application of MicroResp™ for quick and easy detection of plastic degradation by marine bacterial isolates

Microplastic debris in the marine environment is a global problem. Biodegradable polymers are being developed as alternatives to petroleum-based plastics, and quick and easy methods for screening for bacterial strains that can degrade such polymers are needed. As a screening method, the clear zone method has been widely used but has technical difficulties such as plate preparation and interpretation of results. In this study, we adapted the MicroResp™ system to easily detect biodegradation activity of marine bacteria in a 3-day assay. Among the 6 bacterial strains tested, 3, 2 and 1 strain degraded poly (butylene succinate-co-adipate) (PBSA), poly (ε-caprolactone) (PCL) and poly (3-hydroxybutyrate-co-3-hydroxyhexanoate), respectively. Only one strain that showed degradation activity of PBSA and PCL in the MicroResp™ system was also positive in the clear zone assay on the respective emulsion plates. Our results show that the adapted MicroResp™ system can screen for bacterial strains that degrade plastic.

Influence of microbial biomass content on biodegradation and mechanical properties of poly(3-hydroxybutyrate) composites

Biodegradation rates and mechanical properties of poly(3-hydroxybutyrate) (PHB) composites with green algae and cyanobacteria were investigated for the first time. To the authors knowledge, the addition of microbial biomass led to the biggest observed effect on biodegradation so far. The composites with microbial biomass showed an acceleration of the biodegradation rate and a higher cumulative biodegradation within 132 days compared to PHB or the biomass alone. In order to determine the causes for the faster biodegradation, the molecular weight, the crystallinity, the water uptake, the microbial biomass composition and scanning electron microscope images were assessed. The molecular weight of the PHB in the composites was lower than that of pure PHB while the crystallinity and microbial biomass composition were the same for all samples. A direct correlation of water uptake and crystallinity with biodegradation rate could not be observed. While the degradation of molecular weight of PHB during sample preparation contributed to the improvement of biodegradation, the main reason was attributed to biostimulation by the added biomass. The resulting enhancement of the biodegradation rate appears to be unique in the field of polymer biodegradation. The tensile strength was lowered, elongation at break remained constant and Young's modulus was increased compared to pure PHB.

Insights into Genomic Features and Potential Biotechnological Applications of Bacillus halotolerans Strain HGR5

Algeria is one of the wealthiest countries in terms of hydrothermal sources, with more than two hundred hot springs. However, diverse and little-described microbial communities colonize these habitats, making them an intriguing research subject. This work reports the isolation of bacteria from two hot springs water samples in northeastern Algeria, evaluating their enzymatic activities and effect on plant pathogens. Out of the obtained 72 bacterial isolates and based on the 16S rRNA gene sequence analysis, the strain HGR5 belonging to Bacillus halotolerans had the most interesting activity profile. Interestingly, HGR5 was substantially active against Fusarium graminearum, Phytophthora infestans, and Alternaria alternata. Furthermore, this strain presented a high ability to degrade casein, Tween 80, starch, chitin, cellulose, and xylan. The genome sequence of HGR5 allowed taxonomic validation and screening of specific genetic traits, determining its antagonistic and enzymatic activities. Genome mining revealed that strain HGR5 encloses several secondary metabolite biosynthetic gene clusters (SM-BGCs) involved in metabolite production with antimicrobial properties. Thus, antimicrobial metabolites included bacillaene, fengycin, laterocidine, bacilysin, subtilosin, bacillibactin, surfactin, myxovirescin, dumulmycin, and elansolid A1. HGR5 strain genome was also mined for CAZymes associated with antifungal activity. Finally, the HGR5 strain exhibited the capacity to degrade polycaprolactone (PCL), a model substrate for polyester biodegradation. Overall, these results suggest that this strain may be a promising novel biocontrol agent with interesting plastic-degradation capability, opening the possibilities of its use in various biotechnological applications.

Tailoring the Nucleation and Crystallization Rate of Polyhydroxybutyrate by Copolymerization

In the polyester family, the biopolymer with the greatest industrial potential could be poly(3-hydroxybutyrate) (PHB), which can be produced nowadays biologically or chemically. The scarce commercial use of PHB derives from its poor mechanical properties, which can be improved by incorporating a flexible aliphatic polyester with good mechanical performance, such as poly(ε-caprolactone) (PCL), while retaining its biodegradability. This work studies the structural, thermal, and morphological properties of block and random copolymers of PHB and PCL. The presence of a comonomer influences the thermal parameters following nonisothermal crystallization and the kinetics of isothermal crystallization. Specifically, the copolymers exhibit lower melting and crystallization temperatures and present lower overall crystallization kinetics than neat homopolymers. The nucleation rates of the PHB components are greatly enhanced in the copolymers, reducing spherulitic sizes and promoting transparency with respect to neat PHB. However, their spherulitic growth rates are depressed so much that superstructural growth becomes the dominating factor that reduces the overall crystallization kinetics of the PHB component in the copolymers. The block and random copolymers analyzed here also display important differences in the structure, morphology, and crystallization that were examined in detail. Our results show that copolymerization can tailor the thermal properties, morphology (spherulitic size), and crystallization kinetics of PHB, potentially improving the processing, optical, and mechanical properties of PHB.

Spectrophotometric-Based Assay to Quantify Relative Enzyme-Mediated Degradation of Commercially Available Bioplastics

We present a spectrophotometric-based assay to identify enzymes that degrade commercially available bioplastics. Bioplastics comprise aliphatic polyesters with hydrolysis-susceptible ester bonds and are proposed as a replacement for petroleum-based plastics that accumulate in the environment. Unfortunately, many bioplastics can also persist in environments including seawater and waste centers. Our assay involves an overnight incubation of candidate enzyme(s) with plastic, followed by A610 spectrophotometry using 96-well plates to quantify both a reduction in residual plastic and the liberation of degradation by-products. We use the assay to show that Proteinase K and PLA depolymerase, two enzymes that were previously shown to degrade pure polylactic acid plastic, promote a 20-30% breakdown of commercial bioplastic during overnight incubation. We validate our assay and confirm the degradation potential of these enzymes with commercial bioplastic using established mass-loss and scanning electron microscopy methods. We show how the assay can be used to optimize parameters (temperature, co-factors, etc.) to enhance the enzyme-mediated degradation of bioplastics. The assay endpoint products can be coupled with nuclear magnetic resonance (NMR) or other analytical methods to infer the mode of enzymatic activity. Overall, the screening capacity of the spectrophotometric-based assay was demonstrated to be an accurate method to identify bioplastic-degrading enzymes.

Coir fiber as thermal insulator and its performance as reinforcing material in biocomposite production

Coir is a lignocellulosic natural fiber derived from the coconut's husk, an abundantly found fruit or nut worldwide. This fiber has some unique characteristics, such as its resistance to seawater, microbial attack, high impact, etc. But its low thermal conductivity or high thermal insulating property makes it suitable for being used as insulators in civil engineering sites. On the other hand, the sustainability of a material depends heavily on its environmental impact of the material. For making sustainable materials like biocomposite, there are no options other than using polymers derived from natural renewable sources. Polylactic acid(PLA) is an example of those types of material. And these materials are often being reinforced by fibers like coir for various reasons including improving mechanical properties, reducing the cost of the material, and improving the material's sustainability. Many coir-reinforced sustainable biopolymer composites have already been produced in many pieces of research, which will be discussed in this paper, along with the chemical and physical structure of coir fiber. In addition, this paper will try to focus on the insulating properties of coir and coir-reinforced composites while will also compare some properties of the composites with some commonly used materials based on different parameters to show the suitability of using the coir fiber in heat-insulating applications and to produce sustainable biocomposite materials.

High density polyethylene (HDPE) biodegradation by the fungus Cladosporium halotolerans

Polyethylene (PE) is high molecular weight synthetic polymer, very hydrofobic and hardly biodegradable. To increase polyethylene bio-degradability it is very important to find microorganisms that improve the PE hydrophilic level and/or reduce the length of its polymeric chain by oxidation. In this study, we isolated Cladosporium halotolerans, a fungal species, from the gastric system of Galleria mellonella larvae. Here, we show that C. halotolerans grows in the presence of PE polymer, it is able to interact with plastic material through its hyphae and secretes enzymes involved in PE degradation.

Biodegradation of Biodegradable Polymers in Mesophilic Aerobic Environments

Finding alternatives to diminish plastic pollution has become one of the main challenges of modern life. A few alternatives have gained potential for a shift toward a more circular and sustainable relationship with plastics. Biodegradable polymers derived from bio- and fossil-based sources have emerged as one feasible alternative to overcome inconveniences associated with the use and disposal of non-biodegradable polymers. The biodegradation process depends on the environment's factors, microorganisms and associated enzymes, and the polymer properties, resulting in a plethora of parameters that create a complex process whereby biodegradation times and rates can vary immensely. This review aims to provide a background and a comprehensive, systematic, and critical overview of this complex process with a special focus on the mesophilic range. Activity toward depolymerization by extracellular enzymes, biofilm effect on the dynamic of the degradation process, CO2 evolution evaluating the extent of biodegradation, and metabolic pathways are discussed. Remarks and perspectives for potential future research are provided with a focus on the current knowledge gaps if the goal is to minimize the persistence of plastics across environments. Innovative approaches such as the addition of specific compounds to trigger depolymerization under particular conditions, biostimulation, bioaugmentation, and the addition of natural and/or modified enzymes are state-of-the-art methods that need faster development. Furthermore, methods must be connected to standards and techniques that fully track the biodegradation process. More transdisciplinary research within areas of polymer chemistry/processing and microbiology/biochemistry is needed.

Isolation of a Nocardiopsis chromatogenes strain that degrades PLA (polylactic acid) in pig waste-based compost

A new Nocardiopsis species that degrades polylactic acid (PLA) was isolated from pig dung-based compost from a municipal composting facility in Japan. To obtain strains capable of efficient PLA degradation, the effect of non-enzymatic degradation of PLA was minimized by maintaining the temperature at or below 37 °C. Screening 15 animal waste-based compost samples, consisting of pig dung, cow dung, horse dung, or chicken droppings, revealed that compost derived from pig dung was most efficient for degradation of PLA films. Hence, pig waste-based compost was used to isolate PLA-degrading microorganisms by screening for PLA-degrading microorganisms in compost using an agar plate-based method in which an emulsifier was omitted to avoid selecting strains that assimilated the emulsifier instead of PLA in the medium. Repeated enrichment obtained six strains. The one that exhibited stable PLA degradation on agar plates was subjected to genomic analysis and identified as Nocardiopsis chromatogenes, an actinomycete.

Lessons From Insect Fungiculture: From Microbial Ecology to Plastics Degradation

Anthropogenic activities have extensively transformed the biosphere by extracting and disposing of resources, crossing boundaries of planetary threat while causing a global crisis of waste overload. Despite fundamental differences regarding structure and recalcitrance, lignocellulose and plastic polymers share physical-chemical properties to some extent, that include carbon skeletons with similar chemical bonds, hydrophobic properties, amorphous and crystalline regions. Microbial strategies for metabolizing recalcitrant polymers have been selected and optimized through evolution, thus understanding natural processes for lignocellulose modification could aid the challenge of dealing with the recalcitrant human-made polymers spread worldwide. We propose to look for inspiration in the charismatic fungal-growing insects to understand multipartite degradation of plant polymers. Independently evolved in diverse insect lineages, fungiculture embraces passive or active fungal cultivation for food, protection, and structural purposes. We consider there is much to learn from these symbioses, in special from the community-level degradation of recalcitrant biomass and defensive metabolites. Microbial plant-degrading systems at the core of insect fungicultures could be promising candidates for degrading synthetic plastics. Here, we first compare the degradation of lignocellulose and plastic polymers, with emphasis in the overlapping microbial players and enzymatic activities between these processes. Second, we review the literature on diverse insect fungiculture systems, focusing on features that, while supporting insects' ecology and evolution, could also be applied in biotechnological processes. Third, taking lessons from these microbial communities, we suggest multidisciplinary strategies to identify microbial degraders, degrading enzymes and pathways, as well as microbial interactions and interdependencies. Spanning from multiomics to spectroscopy, microscopy, stable isotopes probing, enrichment microcosmos, and synthetic communities, these strategies would allow for a systemic understanding of the fungiculture ecology, driving to application possibilities. Detailing how the metabolic landscape is entangled to achieve ecological success could inspire sustainable efforts for mitigating the current environmental crisis.

Biodegradation of PBSA Films by Elite Aspergillus Isolates and Farmland Soil

Plastic films are widely used in current agricultural practices; however, most mulch films used are discarded and buried in the land after harvest, having adverse environmental impacts. To solve this environmental problem, the demand for biodegradable mulch has been increasing in recent years. Polybutylene succinate-co-adipate (PBSA) is a biodegradable polymer with good ductility and can be used for packaging and mulching. In this study, we isolated two elite fungal strains for PBSA degradation from farmlands, i.e., Aspergillus fumigatus L30 and Aspergillus terreus HC, and the latter showed better degradation ability than the former. It is noteworthy that biodegradation of PBSA by A. terreus is reported for the first time, which revealed unique characteristics. In the soil burial test, even the soil with relatively poor degradation ability could be improved by the addition of elite fungal mycelia. In substrate specificity analyses of soil samples, PBSA could induce the synthesis of lipolytic enzymes of indigenous microbes to degrade substrates with medium and long carbon chains in soil. Furthermore, PBSA residues or fungal mycelia supplementation in soils had no adverse effect on the seed germination rate, seedling growth, or mature plant weight of the test green leafy vegetable. Taken together, the results of this study not only advance our understanding of the biodegradation of PBSA films by filamentous fungi but also provide insight into improving the efficiency of biodegradation in soil environments.

Biodegradation of polymers in managing plastic waste - A review

The modern economy that is fast-moving and convenience centric has led to excessive consumption of plastic. This has unwittingly led to egregious accumulation of plastic waste polluting the environment. Unfortunately, present means of plastic waste management have all been proven as less than adequate; namely recycling, landfill and incineration. Recent focus on plastic waste management has seen the confluence of the developments in biodegradable polymers and microbial engineering strategy for more expedient decomposition of plastic waste at composting facilities. This review paper is an assimilation of current developments in the areas of biodegradable polymer as well as microbial strategy towards management of polymer waste. Advents in biodegradable polymers have been promising, especially with aliphatic polyesters and starch in blends or co-polymers of these. Microbial strategies have been pursued for the identification of microbial strains and understanding of their enzymatic degradation process on polymers. New insights in these two areas have been focused in improving the rate of degradation of plastic waste at composting facilities. Recent alignment of testing and certification standards is outlined to give intimate insights into the mechanisms and factors influencing biodegradation. Despite recent milestones, economic viability of composting plastic waste in mainstream waste facilities is still a distance away. As it remains that a polymer that is biodegradable is functionally inferior to conventional polymers. Rather, it requires a shift in consumer behaviour to accept less durable biodegradable plastic products, this will then lower the threshold for biodegradable polymers to become a commercial reality.

Recent Advances in Biological Recycling of Polyethylene Terephthalate (PET) Plastic Wastes

Polyethylene terephthalate (PET) is one of the most commonly used polyester plastics worldwide but is extremely difficult to be hydrolyzed in a natural environment. PET plastic is an inexpensive, lightweight, and durable material, which can readily be molded into an assortment of products that are used in a broad range of applications. Most PET is used for single-use packaging materials, such as disposable consumer items and packaging. Although PET plastics are a valuable resource in many aspects, the proliferation of plastic products in the last several decades have resulted in a negative environmental footprint. The long-term risk of released PET waste in the environment poses a serious threat to ecosystems, food safety, and even human health in modern society. Recycling is one of the most important actions currently available to reduce these impacts. Current clean-up strategies have attempted to alleviate the adverse impacts of PET pollution but are unable to compete with the increasing quantities of PET waste exposed to the environment. In this review paper, current PET recycling methods to improve life cycle and waste management are discussed, which can be further implemented to reduce plastics pollution and its impacts on health and environment. Compared with conventional mechanical and chemical recycling processes, the biotechnological recycling of PET involves enzymatic degradation of the waste PET and the followed bioconversion of degraded PET monomers into value-added chemicals. This approach creates a circular PET economy by recycling waste PET or upcycling it into more valuable products with minimal environmental footprint.

New approaches for the characterization of plastic-associated microbial communities and the discovery of plastic-degrading microorganisms and enzymes

Plastics in the environment represent new substrates for microbial colonization, and recent methodological advances allow for in-depth characterization of plastic-associated microbial communities (PAMCs). Over the past several decades, discovery of plastic degrading enzymes (PDEs) and plastic degrading microorganisms (PDMs) has been driven by efforts to understand microbially-mediated plastic degradation in the environment and to discover biocatalysts for plastic processing. In this review, we discuss the evolution of methodology in plastic microbiology and highlight major advancements in the field stemming from computational microbiology. Initial research relied largely on culture-based approaches like clear-zone assays to screen for PDMs and microscopy to characterize PAMCs. New computational tools and sequencing technologies are accelerating discoveries in the field through culture-independent and multi-omic approaches, rapidly generating targets for protein engineering and improving the potential for plastic-waste management.

Biodegradation of poly (vinyl alcohol) by an orychophragmus rhizosphere-associated fungus Penicillium brevicompactum OVR-5, and its proposed PVA biodegradation pathway

In recent years, the utilisation of endophytes has emerged as a promising biological treatment technology for the degradation of plastic wastes such as biodegradation of synthetic plastics. This study, therefore, aimed to explore and extensively screen endophytic fungi (from selected plants) for efficient in vitro polyvinyl alcohol (PVA) biodegradation. In total, 76 endophytic fungi were isolated and cultivated on a PVA screening agar medium. Among these fungi, 10 isolates showed potential and were subsequently identified based on phenotypical characteristics, ITS ribosomal gene sequences, and phylogenetic analyses. Four strains exhibited a maximum level of PVA-degradation in the liquid medium when cultivated for 10 days at 28 °C and 150 rpm. These strains showed varied PVA removal rates of 81% (Penicillium brevicompactum OVR-5), 67% (Talaromyces verruculosus PRL-2), 52% (P. polonicum BJL-9), and 41% (Aspergillus tubingensis BJR-6) respectively. The most promising PVA biodegradation isolate 'OVR-5', with an optimal pH at 7.0 and optimal temperature at 30 °C, produced lipase, manganese peroxidase, and laccase enzymes. Based on analyses of its metabolic intermediates, as identified with GC-MS, we proposed the potential PVA degradation pathway of OVR-5. Biodegradation results were confirmed through scanning electron microscopy and Fourier transform infrared spectroscopy. This study provides the first report on an endophytic P. brevicompactum strain (associated with Orychophragmus violaceus) that has a great ability for PVA degradation providing more insight on potential fungus-based applications in plastic waste degradation.

Microbial degradation of polyhydroxybutyrate with embedded polyhexamethylene guanidine derivatives

The aim of this study was to isolate biofilm-forming bacteria that are capable of degrading polyhydroxybutyrate (PHB) with polyhexamethylene guanidine (PHMG) derivatives. The three types of derivatives incorporated in PHB and their concentration affected the biodegradability of the tested films in both water and compost. The PHMG derivative granular polyethylene wax at the highest concentration significantly inhibited BOD in both environments. At the same time, in water, PHB with PHMG stearate at 1% concentration was also found to inhibit biodegradation but to a lesser extent than PHMG polyethylene wax granulate. Analyzing the values of biofilm abundance and their hydrolytic activity in water, low concentrations of PHMG derivatives (0.2 and 0.6%) slightly inhibited biofilm abundance on the surface of the tested composites. Only granular polyethylene wax PHMG (at 1% concentration) significantly reduced biofilm formation and hydrolase activity in the compost to the greatest extent. Bacteria from biofilm were isolated and identified. Based on the 16S rRNA gene sequence, the strains belong to Bacillus toyonensis HW1 and Variovorax boronicumulans HK3. Introduction of the tested isolates to the environment can enhance composites degradation. However, this requires further research.

Inspired by nature: Microbial production, degradation and valorization of biodegradable bioplastics for life-cycle-engineered products

The global environmental pollution by micro- and macro-plastics reveals the consequences of an extensive use of recalcitrant plastic products together with inappropriate waste management practices that fail to sufficiently recycle the broad types of conventional plastic waste. Biobased and biodegradable plastics are experiencing an uprising as their properties offer alternative waste management solutions for a more circular material economy. However, although the production of such bioplastics has advanced on scale, the end-of-life (EOL) (bio)technologies to promote circularity are lacking behind. While composting and biogas plants are the only managed EOL options today, advanced biotechnological recycling technologies for biodegradable bioplastics are still in an embryonic stage. Thus, developing efficient biotechnologies capable of transforming bioplastic waste into high-value chemical building blocks or into the constituents of the original polymer offers promising routes towards life-cycle-engineered products. This review aims at providing a comprehensive state-of-the-art overview of microbial-based processes involved in the complete lifecycle of bioplastics. The current trends in the bioplastic market, the beginning and EOL scenarios of bioplastics, and a critical discussion on the key factors and mechanisms governing microbial degradation are systematically presented. Also, a critical evaluation of terminology and international standards to quantify polymer biodegradability is provided together with the latest biotechnological recycling strategies, including the use of different pre-treatments for (bio)plastic waste. Finally, the challenges and future perspectives for the development of life-cycle-engineered biobased and biodegradable plastic products are discussed.

The phylogenetic and global distribution of bacterial polyhydroxyalkanoate bioplastic-degrading genes

Polyhydroxyalkanoates (PHAs) are a family of microbially made polyesters commercialized as biodegradable plastics. PHA production rates are predicted to increase as concerns around environmental plastic contamination and limited fossil fuel resources have increased the importance of biodegradable and bio-based plastic alternatives. Microbially produced PHA depolymerases are the key enzymes mediating PHA biodegradation, but only a few PHA depolymerases have been well-characterized and screens employing metagenomic sequence data are lacking. Here, we used 3078 metagenomes to analyse the distribution of PHA depolymerases in microbial communities from diverse aquatic, terrestrial and waste management systems. We significantly expand the recognized diversity of this protein family by screening 1914 Gb of sequence data and identifying 13 869 putative PHA depolymerases in 1295 metagenomes. Our results indicate that PHA depolymerases are unevenly distributed across environments. We predicted the highest frequency of PHA depolymerases in wastewater systems and the lowest in marine and thermal springs. In tandem, we screened 5290 metagenome-assembled genomes to describe the phylogenetic distribution of PHA depolymerases, which is substantially broader compared with current cultured representatives. The Proteobacteria and Bacteroidota are key lineages encoding PHA depolymerases, but PHA depolymerases were predicted from members of the Bdellovibrionota, Methylomirabilota, Actinobacteriota, Firmicutes, Spirochaetota, Desulfobacterota, Myxococcota and Planctomycetota.

Plastics and the microbiome: impacts and solutions

Global plastic production has increased exponentially since manufacturing commenced in the 1950's, including polymer types infused with diverse additives and fillers. While the negative impacts of plastics are widely reported, particularly on marine vertebrates, impacts on microbial life remain poorly understood. Plastics impact microbiomes directly, exerting toxic effects, providing supplemental carbon sources and acting as rafts for microbial colonisation and dispersal. Indirect consequences include increased environmental shading, altered compositions of host communities and disruption of host organism or community health, hormone balances and immune responses. The isolation and application of plastic-degrading microbes are of substantial interest yet little evidence supports the microbial biodegradation of most high molecular weight synthetic polymers. Over 400 microbial species have been presumptively identified as capable of plastic degradation, but evidence for the degradation of highly prevalent polymers including polypropylene, nylon, polystyrene and polyvinyl chloride must be treated with caution; most studies fail to differentiate losses caused by the leaching or degradation of polymer monomers, additives or fillers. Even where polymer degradation is demonstrated, such as for polyethylene terephthalate, the ability of microorganisms to degrade more highly crystalline forms of the polymer used in commercial plastics appears limited. Microbiomes frequently work in conjunction with abiotic factors such as heat and light to impact the structural integrity of polymers and accessibility to enzymatic attack. Consequently, there remains much scope for extremophile microbiomes to be explored as a source of plastic-degrading enzymes and microorganisms. We propose a best-practice workflow for isolating and reporting plastic-degrading taxa from diverse environmental microbiomes, which should include multiple lines of evidence supporting changes in polymer structure, mass loss, and detection of presumed degradation products, along with confirmation of microbial strains and enzymes (and their associated genes) responsible for high molecular weight plastic polymer degradation. Such approaches are necessary for enzymatic degraders of high molecular weight plastic polymers to be differentiated from organisms only capable of degrading the more labile carbon within predominantly amorphous plastics, plastic monomers, additives or fillers.

Norwegian Soils and Waters Contain Mesophilic, Plastic-Degrading Bacteria

Plastic pollution has become one of the most critical environmental issues, as rapidly increasing production, compounded by persistence of plastic wastes in the environment, are outpacing efforts to keep ecosystems plastic-free. A switch to plastics more amenable to microbial attack is one of several possible responses. Against this background, the current study describes the isolation, enumeration and polyphasic characterization of plastic-degrading bacteria present in Norwegian terrestrial and aquatic habits. It shows that these bacteria are present in relatively high numbers, and that plastic-degrading capabilities are found in several taxa, most especially Streptomyces. Some isolates wereable to degrade several plastics. Notably, a Rhodococcus sp. and a Streptomyces sp. degraded, respectively, four and six of the eight plastics investigated and a number of other polymers relevant for plastic blends. The paper also has a methodological aspect, presenting various approaches for assaying plastic-degrading properties and a PCR/sequencing-based approach for the identification of potential polyethylene terephthalate-degrading genes. A candidate gene was detected in several Streptomyces isolates. The study shows that Norwegian environments are a rich source of bacteria with the ability to degrade bioplastics possibly representing a natural remediation capacity, as well as a potential source of useful enzymes.

Biochemical characterization and molecular docking analysis of novel esterases from Sphingobium chungbukense DJ77

We identified three novel microbial esterase (Est1, Est2, and Est3) from Sphingobium chungbukense DJ77. Multiple sequence alignment showed the Est1 and Est3 have distinct motifs, such as tetrapeptide motif HGGG, a pentapeptide sequence motif GXSXG, and catalytic triad residues Ser-Asp-His, indicating that the identified enzymes belong to family IV esterases. Interestingly, Est1 exhibited strong activity toward classical esterase substrates, p-nitrophenyl ester of short-chain fatty acids and long-chain. However, Est3 did not exhibit any activity despite having high sequence similarity and sharing the identical catalytic active residues with Est1. Est3 only showed hydrolytic degradation activity to polycaprolactone (PCL). MOE-docking prediction also provided the parameters consisting of binding energy, molecular docking score, and molecular distance between substrate and catalytic nucleophilic residue, serine. The engineered mutEst3 has hydrolytic activity for a variety of esters ranging from p-nitrophenyl esters to PCL. In the present study, we demonstrated that MOE-docking simulation provides a valuable insight for facilitating biocatalytic performance.

Review on the Biological Degradation of Polymers in Various Environments

Biodegradable plastics can make an important contribution to the struggle against increasing environmental pollution through plastics. However, biodegradability is a material property that is influenced by many factors. This review provides an overview of the main environmental conditions in which biodegradation takes place and then presents the degradability of numerous polymers. Polylactide (PLA), which is already available on an industrial scale, and the polyhydroxyalkanoates polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV), which are among the few plastics that have been proven to degrade in seawater, will be discussed in detail, followed by a summary of the degradability of further petroleum-, cellulose-, starch-, protein- and CO₂-based biopolymers and some naturally occurring polymers.

Conversion of Waste Plastic to Oils for Tribological Applications

Plastics are widely used owing to their light weight, easy production, and low cost. Even though plastics find application in different fields of industries and households, they do not degrade easily. If plastics are not disposed of appropriately, it has been shown that they cause widespread environmental pollution, which poses risks to human health. Recycling waste plastics has been an alternative to mitigating plastic pollution, which usually requires high labour costs and produces contaminated water during processing. If plastic recycling will contribute to the development of tribological products like lubricating oils, it is a safer alternative to disposing of plastics in the environment. In order to understand the tribological use of plastics by recycling, the present study reviews different techniques that can be employed to transform waste plastics into petroleum-based oils. The viscosity, density, and friction of pyrolyzed waste plastic oils are investigated and compared with commercial lubricants to assess their potential lubrication applications. The segregation processes, catalytic isomerization dewaxing, and Fischer–Tropsch method to recycle waste plastics are also reviewed to provide an insight into the methods to transform pyrolyzed waste plastic into lubricants.

Beyond oil degradation: enzymatic potential of Alcanivorax to degrade natural and synthetic polyesters

Pristine marine environments are highly oligotrophic ecosystems populated by well‐established specialized microbial communities. Nevertheless, during oil spills, low‐abundant hydrocarbonoclastic bacteria bloom and rapidly prevail over the marine microbiota. The genus Alcanivorax is one of the most abundant and well‐studied organisms for oil degradation. While highly successful under polluted conditions due to its specialized oil‐degrading metabolism, it is unknown how they persist in these environments during pristine conditions. Here, we show that part of the Alcanivorax genus, as well as oils, has an enormous potential for biodegrading aliphatic polyesters thanks to a unique and abundantly secreted alpha/beta hydrolase. The heterologous overexpression of this esterase proved a remarkable ability to hydrolyse both natural and synthetic polyesters. Our findings contribute to (i) better understand the ecology of Alcanivorax in its natural environment, where natural polyesters such as polyhydroxyalkanoates (PHA) are produced by a large fraction of the community and, hence, an accessible source of carbon and energy used by the organism in order to persist, (ii) highlight the potential of Alcanivorax to clear marine environments from polyester materials of anthropogenic origin as well as oils, and (iii) the discovery of a new versatile esterase with a high biotechnological potential.

Agar plate-based screening methods for the identification of polyester hydrolysis by Pseudomonas species

Hydrolases acting on polyesters like cutin, polycaprolactone or polyethylene terephthalate (PET) are of interest for several biotechnological applications like waste treatment, biocatalysis and sustainable polymer modifications. Recent studies suggest that a large variety of such enzymes are still to be identified and explored in a variety of microorganisms, including bacteria of the genus Pseudomonas. For activity-based screening, methods have been established using agar plates which contain nanoparticles of polycaprolactone or PET prepared by solvent precipitation and evaporation. In this protocol article, we describe a straightforward agar plate-based method using emulsifiable artificial polyesters as substrates, namely Impranil® DLN and liquid polycaprolactone diol (PLD). Thereby, the currently quite narrow set of screening substrates is expanded. We also suggest optional pre-screening with short-chain and middle-chain-length triglycerides as substrates to identify enzymes with lipolytic activity to be further tested for polyesterase activity. We applied these assays to experimentally demonstrate polyesterase activity in bacteria from the P. pertucinogena lineage originating from contaminated soils and diverse marine habitats.

Actinobacteria as Promising Candidate for Polylactic Acid Type Bioplastic Degradation

Polylactic acid (PLA) is one of the most commercially available and exploited bioplastics worldwide. It is an important renewable polymer for the replacement of petroleum-based plastic materials. They are both biodegradable and bio-based plastic. Microbial degrading activity is a desirable method for environmental safety and economic value for bioplastic waste managements. Members of the phylum actinobacteria are found to play an important role in PLA degradation. Most of the PLA degrading actinobacteria belong to the family Pseudonocardiaceae. Other taxa include members of the family Micromonosporaceae, Streptomycetaceae, Streptosporangiaceae, and Thermomonosporaceae. This mini-review aims to provide an overview on PLA degrading actinobacteria including their diversity and taxonomy, isolation and screening procedures and PLA degrading enzyme production from 1997 to 2019. Consideration is also given to where to sampling and how we might use these beneficial actinobacteria for PLA waste management.

In silico Screening and Heterologous Expression of a Polyethylene Terephthalate Hydrolase (PETase)-Like Enzyme (SM14est) With Polycaprolactone (PCL)-Degrading Activity, From the Marine Sponge-Derived Strain Streptomyces sp. SM14

Plastics, such as the polyethylene terephthalate (PET), are widely used for various industrial applications, due to their physicochemical properties which are particularly useful in the packaging industry. However, due to improper plastic waste management and difficulties in recycling, post-consumer plastic waste has become a pressing issue for both the environment and for human health. Hence, novel technologies and methods of processing plastic waste are required to address these issues. Enzymatic-assisted hydrolysis of synthetic polymers has been proposed as a potentially more efficient and environment-friendly alternative to the currently employed methods. Recently, a number of PET hydrolases have been described, and in particular a PETase derived from Ideonella sakaiensis 201-F6 (IsPETase), which appears to be the most efficient and substrate-specific bacterial PET hydrolase enzyme discovered to date. In order to further investigate this class of PETase-like enzymes, we employed an in silico-based screening approach on the biotechnologically relevant genus Streptomyces, including terrestrial and marine isolates; in a search for potential PETase homologs. From a total of 52 genomes analyzed, we were able to identify three potential PETase-like enzymes, all of which were derived from marine-sponge associated Streptomyces isolates. A candidate PETase-like gene (SM14est) was identified in Streptomyces sp. SM14. Further in silico characterization of the SM14est protein sequence and its predicted three-dimensional structure were performed and compared to the well-characterized IsPETase. Both the serine hydrolase motif Gly-x1-Ser-x2-Gly and the catalytic triad Ser, Asp, His are conserved in both sequences. Molecular docking experiments indicated that the SM14est enzyme possessed the capacity to bind plastics as substrates. Finally, polyesterase activity was confirmed using a polycaprolactone (PCL) plate clearing assay which is a model substrate for the degradation of plastics; following heterologous expression of SM14est in Escherichia coli, with secretion being facilitated by the native Streptomyces signal peptide. These findings provide further insights into this important class of PETase-like enzymes.

Biodegradation of Polymeric Mulch Films in Agricultural Soils: Concepts, Knowledge Gaps, and Future Research Directions

The agricultural use of conventional, polyethylene-based mulch films leads to the accumulation of remnant film pieces in agricultural soils with negative impacts for soil productivity and ecology. A viable strategy to overcome this accumulation is to replace conventional with biodegradable mulch films composed of polymers designed to be degraded by soil microorganisms. However, understanding polymer biodegradation in soils remains a significant challenge due to its dependence on polymer properties, soil characteristics, and prevailing environmental conditions. This perspective aims to advance our understanding of the three fundamental steps underlying biodegradation of mulch films in agricultural soils: colonization of the polymer film surfaces by soil microorganisms, depolymerization of the polymer films by extracellular microbial hydrolases, and subsequent microbial assimilation and utilization of the hydrolysis products for energy production and biomass formation. The perspective synthesizes the current conceptual understanding of these steps and highlights existing knowledge gaps. The discussion addresses future research and analytical advancements required to overcome the knowledge gaps and to identify the key polymer properties and soil characteristics governing mulch film biodegradation in agricultural soils.

Actinobacteria as Promising Candidate for Polylactic Acid Type Bioplastic Degradation

Polylactic acid (PLA) is one of the most commercially available and exploited bioplastics worldwide. It is an important renewable polymer for the replacement of petroleum-based plastic materials. They are both biodegradable and bio-based plastic. Microbial degrading activity is a desirable method for environmental safety and economic value for bioplastic waste managements. Members of the phylum actinobacteria are found to play an important role in PLA degradation. Most of the PLA degrading actinobacteria belong to the family Pseudonocardiaceae. Other taxa include members of the family Micromonosporaceae, Streptomycetaceae, Streptosporangiaceae, and Thermomonosporaceae. This mini-review aims to provide an overview on PLA degrading actinobacteria including their diversity and taxonomy, isolation and screening procedures and PLA degrading enzyme production from 1997 to 2019. Consideration is also given to where to sampling and how we might use these beneficial actinobacteria for PLA waste management.

Sphingobium aromaticivastans sp. nov., a novel aniline- and benzene-degrading, and antimicrobial compound producing bacterium

A strictly aerobic, orange-pigmented strain was isolated and designated as UCM-25^T. This strain is capable of degrading aniline and benzene, while is also producing antimicrobial compounds which inhibit the growth of some common pathogenic microbes. A near full-length 16S rRNA gene sequence revealed similarity to Sphingobium chlorophenolicum NBRC 16172^T (98.6%). The level of DNA-DNA hybridization between the new isolate and the related species suggests UCM-25^T to be a new species belonging to the genus Sphingobium. The bacterial cells contained phosphatidylglycerol, phosphatidylethanolamine, sphingoglycolipid, phosphatidylcholine, phosphatidylmonomethylethanolamine, phosphatidyldimethylethanolamine, three unidentified polar lipids, and an unidentified aminophospholipid. Ubiquinone Q-10 was the major quinone and spermidine was the major polyamine. The G+C content in the DNA of strain UCM-25^T was 62.9 mol%. Cells contained summed feature 8 (C_18:1ω7c and/or C_18:1ω6c), summed feature 3 (C_16:1ω7c and/or C_16:1ω6c), C_16:0, and C_14:0 2-OH as major fatty acids. Based on the comparison of phenotypic, genotypic, and chemotaxonomic characteristics, strain UCM-25^T represents a new member of the genus Sphingobium, for which the name S. aromaticivastans sp. nov. is proposed. The type strain is UCM-25^T (=KACC 19288^T =DSM 105181^T).

Plastic waste as a global challenge: are biodegradable plastics the answer to the plastic waste problem?

The strength, flexibility and light weight of traditional oil-derived plastics make them ideal materials for a large number of applications, including packaging, medical devices, building, transportation, etc. However, the majority of produced plastics are single-use plastics, which, coupled with a throw-away culture, leads to the accumulation of plastic waste and pollution, as well as the loss of a valuable resource. In this review we discuss the advances and possibilities in the biotransformation and biodegradation of oil-based plastics. We review bio-based and biodegradable polymers and highlight the importance of end-of-life management of biodegradables. Finally, we discuss the role of a circular economy in reducing plastic waste pollution.

Biodegradable Plastic Blends Create New Possibilities for End-of-Life Management of Plastics but They Are Not a Panacea for Plastic Pollution

Plastic waste pollution is a global environmental problem which could be addressed by biodegradable plastics. The latter are blended together to achieve commercially functional properties, but the environmental fate of these blends is unknown. We have tested neat polymers, polylactic acid (PLA), polyhydroxybutyrate, polyhydroxyoctanoate, poly(butylene succinate), thermoplastic starch, polycaprolactone (PCL), and blends thereof for biodegradation across seven managed and unmanaged environments. PLA is one of the world's best-selling biodegradable plastics, but it is not home compostable. We show here that PLA when blended with PCL becomes home compostable. We also demonstrate that the majority of the tested bioplastics and their blends degrade by thermophilic anaerobic digestion with high biogas output, but degradation times are 3-6 times longer than the retention times in commercial plants. While some polymers and their blends showed good biodegradation in soil and water, the majority of polymers and their blends tested in this study failed to achieve ISO and ASTM biodegradation standards, and some failed to show any biodegradation. Thus, biodegradable plastic blends need careful postconsumer management, and further design to allow more rapid biodegradation in multiple environments is needed as their release into the environment can cause plastic pollution.

Selection and evaluation of microorganisms for biodegradation of agricultural plastic film

Three Bacillus amyloliquefaciens isolates (HK1, GSDM02, and GSDM15) were tested for effectiveness in biodegradation of plastic films. Isolates were screened by plate on carbon-free medium and by using the clear-zone formation test. Their biodegradation ability was analyzed based on: film weight reduction, pH change of the fluid medium, a soil microbial biomass carbon test, scanning electron microscopy (SEM), and Fourier transform infrared spectrometry (FTIR). Polyvinyl alcohol (PVA) clear-zone and film weight reduction results revealed that the strain with a bigger clear-zone had a better biodegradation effect, that PVA can be evenly distributed in the medium, and that PVA can be a substitution for polyethylene in screening the biodegradation of strains. SEM and FTIR revealed that HK1 can tear the film apart and make surface chemical changes within 30 days. HK1 exhibited a better biodegradation effect in all tests, indicating its potential for helping solve the plastic pollution problems.