Microbial degradation of aliphatic and aliphatic-aromatic co-polyesters

Marine copepod culture as a potential source of bioplastic-degrading microbiome: The case of poly(butylene succinate-co-adipate)

The poly(butylene succinate-co-adipate) (PBSA) is emerging as environmentally sustainable polyester for applications in marine environment. In this work the capacity of microbiome associated with marine plankton culture to degrade PBSA, was tested. A taxonomic and functional characterization of the microbiome associated with the copepod Acartia tonsa, reared in controlled conditions, was analysed by 16S rDNA metabarcoding, in newly-formed adult stages and after 7 d of incubation. A predictive functional metagenomic profile was inferred for hydrolytic activities involved in bioplastic degradation with a particular focus on PBSA. The copepod-microbiome was also characterized in newly-formed carcasses of A. tonsa, and after 7 and 33 d of incubation in the plankton culture medium. Copepod-microbiome showed hydrolytic activities at all developmental stages of the alive copepods and their carcasses, however, the evenness of the hydrolytic bacterial community significantly increased with the time of incubation in carcasses. Microbial genera, never described in association with copepods: Devosia, Kordia, Lentibacter, Methylotenera, Rheinheimera, Marinagarivorans, Paraglaciecola, Pseudophaeobacter, Gaiella, Streptomyces and Kribbella sps., were retrieved. Kribbella sp. showed carboxylesterase activity and Streptomyces sp. showed carboxylesterase, triacylglycerol lipase and cutinase activities, that might be involved in PBSA degradation. A culturomic approach, adopted to isolate bacterial specimen from carcasses, led to the isolation of the bacterial strain, Vibrio sp. 01 tested for the capacity to promote the hydrolysis of the ester bonds. Granules of PBSA, incubated 82 d at 20 °C with Vibrio sp. 01, were characterized by scanning electron microscopy, infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry, showing fractures compared to the control sample, and hydrolysis of ester bonds. These preliminary results are encouraging for further investigation on the ability of the microbiome associated with plankton to biodegrade polyesters, such as PBSA, and increasing knowledge on microorganisms involved in bioplastic degradation in marine environment.

Dual Application of p-Nitrophenol Alkanoate-Based Assay for Soil Selection and Screening of Microbial Strains for Bioplastic Degradation

With an increase in the commercialization of bioplastics, the importance of screening for plastic-degrading strains and microbes has emerged. Conventional methods for screening such strains are time-consuming and labor-intensive. Therefore, we suggest a method for quickly and effectively screening plastic-degrading microbial strains through dual esterase assays for soil and isolated strains, using p-nitrophenyl alkanoates as substrates. To select microbe-abundant soil, the total amount of phospholipid fatty acids (PLFAs) included in each soil sample was analyzed, and esterase assays were performed for each soil sample to compare the esterase activity of each soil. In addition, by analyzing the correlation coefficients and sensitivity between the amount of PLFAs and the degree of esterase activity according to the substrate, it was confirmed that substrate pNP-C2 is the most useful index for soil containing several microbes having esterase activity. In addition, esterase assays of the isolated strains allowed us to select the most active strain as the degrading strain, and 16S rRNA results confirmed that it was Bacillus sp. N04 showed the highest degradation activity for polybutylene succinate (PBS) as measured in liquid culture for 7 days, with a degradation yield of 99%. Furthermore, Bacillus sp. N04 showed degradation activity against various bioplastics. We propose the dual application of p-nitrophenyl alkanoates as an efficient method to first select the appropriate soil and then to screen for plastic-degrading strains in it, and conclude that pNP-C2 in particular, is a useful indicator.

Fabrication of Soft Biodegradable Foam with Improved Shrinkage Resistance and Thermal Stability

The soft PBAT foam shows good flexibility, high elasticity, degradable nature, and it can be used as an environmental-friendly candidate for EVA and PU foams. Unfortunately, there are few reports on the application of PBAT as a soft foam. In this study, PBAT foam was fabricated by a pressure quenching method using CO2 as the blowing agent. A significant volume shrinkage of about 81% occurred, where the initial PBAT foam had an extremely high expansion ratio, of about 31 times. A 5-10 wt% PBS with high crystallinity was blended, and N2 with low gas solubility and diffusivity was mixed, with the aim of resisting foam shrinkage and preparing PBAT with a high final expansion ratio of 14.7 times. The possible mechanism behind this phenomenon was established, and the increased matrix modulus and decreased pressure difference within and outside the cell structure were the main reasons for the shrinkage resistance. The properties of PBAT and PBAT/PBS foams with a density of 0.1 g/cm3 were measured, based on the requirements for shoe applications. The 5-10 wt% PBS loading presented advantages in reducing thermal shrinkage at 75 °C/40 min, without compromising the hardness, elasticity, and the compression set, which ensures that PBAT/PBS foams have good prospects for use as soft foams.

PBAT is biodegradable but what about the toxicity of its biodegradation products?

CONTEXT

Poly(butylene adipate-co-terephthalate) (PBAT) is a biodegradable plastic. It was introduced to the plastics market in 1998 and since then has been widely used around the world. The main idea of this research is to perform quantum chemical calculations to study the potential toxicity of PBAT and its degradation products. We analyzed the electron transfer capacity to determine its potential toxicity. We found that biodegradable products formed with benzene rings are as good electron acceptors as PBAT and OOH•. Our results indicate that the biodegradation products are potentially as toxic as PBAT. This might explain why biodegradation products alter the photosynthetic system of plants and inhibit their growth. From this and other previous investigations, we can think that biodegradable plastics could represent a potential environmental risk.

METHODS

All DFT computations were performed using the Gaussian16 at M062x/6-311 + g(2d,p) level of theory without symmetry constraints. Electro-donating (ω-) and electro-accepting (ω +) powers were used as response functions.

Genetic Modifications in Bacteria for the Degradation of Synthetic Polymers: A Review

Synthetic polymers, commonly known as plastics, are currently present in all aspects of our lives. Although they are useful, they present the problem of what to do with them after their lifespan. There are currently mechanical and chemical methods to treat plastics, but these are methods that, among other disadvantages, can be expensive in terms of energy or produce polluting gases. A more environmentally friendly alternative is recycling, although this practice is not widespread. Based on the practice of the so-called circular economy, many studies are focused on the biodegradation of these polymers by enzymes. Using enzymes is a harmless method that can also generate substances with high added value. Novel and enhanced plastic-degrading enzymes have been obtained by modifying the amino acid sequence of existing ones, especially on their active site, using a wide variety of genetic approaches. Currently, many studies focus on the common aim of achieving strains with greater hydrolytic activity toward a different range of plastic polymers. Although in most cases the depolymerization rate is improved, more research is required to develop effective biodegradation strategies for plastic recycling or upcycling. This review focuses on a compilation and discussion of the most important research outcomes carried out on microbial biotechnology to degrade and recycle plastics.

Synthesis and Characterization of Poly(butylene glycol adipate-co-terephthalate/diphenylsilanediol adipate-co-terephthalate) Copolyester

The copolyester poly(butylene glycol adipate-co-terephthalate/diphenylsilanediol adipate-co-terephthalate) (PBDAT) was synthesized by the melt polycondensation method using terephthalic acid, adipic acid, 1,4-butanediol, and diphenylsilylene glycol as the raw materials. The molecular chain structure, thermal properties, thermal stability, mechanical properties, and degradation behaviors of the copolyesters were investigated. The results showed that the prepared PBDAT copolyesters exhibited good thermal stability and mechanical properties. With the increase in diphenylsilanediol (DPSD) content, the thermal stability of PBDAT and the melting temperature both increased. The tensile strength and elastic modulus of PBDAT also exhibited an increasing tend. When the DPSD content was 12.5% (PBDAT-12.5), the tensile strength, the elastic modulus, and elongation at break were 30.56 MPa, 238 MPa, and 219%, respectively. With the increase in diphenylsilanediol content, the hydrophilicity of PBDAT decreased, but PBDAT still shows good degradability and the thermal degradation T5% temperature was 355 °C. The thermal degradation of PBDAT was also improved.

Chlorogenic acid releasing microspheres enhanced electrospun conduits to promote peripheral nerve regeneration

Chlorogenic acid (CGA) has been confirmed as a polyphenol, and existing research has suggested the high bioactivity of CGA for therapeutic effects on a wide variety of diseases. Despite the existing reports of anti-inflammatory, antioxidant, and neuroprotective effects of CGA, the role and mechanism of CGA in facilitating the regeneration of peripheral nerve defects have been rarely investigated. Herein, a biodegradable polycaprolactone (PCL) conduit with embedded CGA-releasing GelMA microspheres (CGM/PCL) was successfully prepared and used for repairing a rate model with sciatic nerve defects. CGM and CGM/PCL conduits displayed high in vitro biocompatibility and can support the growth of cells for nerve regeneration. Furthermore, CGM/PCL conduits displayed high performance which is close to that of autologous nerve grafts in promoting in vivo PNI regeneration, compared with PCL conduits. The sciatic nerve functional index analysis, electrophysiological examination, and immunological analysis performed to evaluate the functional recovery of the injurious sciatic nerve of rats have indeed proved the favorable effects of CGM/PCL conduits. The result of this study not only aimed to explore CGA's contribution to nerve regeneration but also provided a new strategy for designing and preparing functional NGCs for PNI treatment.

Biodegradation of low-density polyethylene (LDPE) through application of indigenous strain Alcaligenes faecalis ISJ128

The resiliency of plastic products against microbial degradation in natural environment often creates devastating changes for humans, plants, and animals on the earth's surface. Biodegradation of plastics using indigenous bacteria may serve as a critical approach to overcome this resulting environmental stress. In the present work, a polyethylene degrading bacterium Alcaligenes faecalis strain ISJ128 (Accession No. MK968769) was isolated from partially degraded polyethylene film buried in the soil at plastic waste disposal site. The biodegradation studies were conducted by employing various methods such as hydrophobicity assessment of the strain ISJ128, measurement of viability and total protein content of bacterial biofilm attached to the polyethylene surface. The proliferation of bacterial cells on polyethylene film, as indicated by high growth response in terms of protein content (85.50 µg mL-1) and viability (1010 CFU mL-1), proposed reasonable suitability of our strain A. faecalis ISJ128 toward polyethylene degradation. The results of biodegradation assay revealed significant degradation (10.40%) of polyethylene film within a short period of time (i.e., 60 days), whereas no signs of degradation were seen in control PE film. A. faecalis strain ISJ128 also demonstrated a removal rate of 0.0018 day-1 along with half-life of 462 days. The scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy studies not only displayed changes on polyethylene surface but also altered level of intensity of functional groups and an increase in the carbonyl indexes justifying the degradation of polyethylene film due to bacterial activity. In addition, the secondary structure prediction (M fold software) of 16SrDNA proved the stable nature of the bacterial strain, thereby reflecting the profound scope of A. faecalis strain ISJ128 as a potential degrader for the eco-friendly disposal of polyethylene waste. Schematic representation of methodology.

Microorganisms that produce enzymes active on biodegradable polyesters are ubiquitous

Biodegradability standards measure ultimate biodegradation of polymers by exposing the material under test to a natural microbial inoculum. Available tests developed by the International Organization for Standardization (ISO) use inoculums sampled from different environments e.g. soil, marine sediments, seawater. Understanding whether each inoculum is to be considered as microbially unique or not can be relevant for the interpretation of tests results. In this review, we address this question by consideration of the following: (i) the chemical nature of biodegradable plastics (virtually all biodegradable plastics are polyesters) (ii) the diffusion of ester bonds in nature both in simple molecules and in polymers (ubiquitous); (iii) the diffusion of decomposers capable of producing enzymes, called esterases, which accelerate the hydrolysis of esters, including polyesters (ubiquitous); (iv) the evidence showing that synthetic polyesters can be depolymerized by esterases (large and growing); (v) the evidence showing that these esterases are ubiquitous (growing and confirmed by bioinformatics studies). By combining the relevant available facts it can be concluded that if a certain polyester shows ultimate biodegradation when exposed to a natural inoculum, it can be considered biodegradable and need not be retested using other inoculums. Obviously, if the polymer does not show ultimate biodegradation it must be considered recalcitrant, until proven otherwise.

A lesson from polybutylene succinate plastisphere to the discovery of novel plastic degrading enzyme genes in marine vibrios

Polybutylene succinate (PBS) is an eco-friendly green plastic. However, PBS was shown as being non-biodegradable in marine environments, and up until now, only a limited number of PBS-degrading marine microbes have been discovered. We first set up in vitro PBS- and PBSA (polybutylene succinate adipate)-plastispheres to characterize novel PBS-degrading marine microbes. Microbial growth and oxygen consumption were observed in both PBS- and PBSA-plastispheres enriched with natural seawater collected from Usujiri, Hokkaido, Japan, and Vibrionaceae and Pseudoalteromonadaceae were significantly enriched on these films. Further gene identification indicated that vibrios belonging to the Gazogenes clade possess genes related to a PBS degrading enzyme (PBSase). The PBS degradation assay for six Gazogenes clade vibrios identified Vibrio ruber, Vibrio rhizosphaerae, and Vibrio spartinae as being capable of degrading PBS. We further identified the gene responsible for PBSase from the type strain of V. ruber, and the purified recombinant vibrio PBSase was found to have low-temperature adaptation and was active under high NaCl concentrations. We also provided docking models between the vibrio PBSase and PBS and PBSA units to show how vibrio PBSase interacts with each substrate compared to the Acidovorax PBSase. These results could contribute to a more sustainable society through further utilization of PBS in marine environments and plastic recycling.

Enhancing biodegradation of PBAT through bio-stimulation using Pseudozyma jejuensis for effective plastic waste reduction

Polybutylene adipate-co-terephthalate (PBAT) is a flexible and biodegradable material that finds applications in mulching film and the food packaging industry. In this study, we aimed to address the global plastic waste problem by developing an improved biodegradation system for PBAT. Our focus was on utilizing the biodegradation capabilities of Pseudozyma jejuensis, a microorganism known for its ability to decompose Polycaprolactam (PCL). Through bio-stimulation, we aimed to enhance the growth mechanism of P. jejuensis and optimize PBAT biodegradation. Our results demonstrated significant structural changes in the PBAT film, as revealed by FT-IR analysis. Moreover, FE-SEM imaging exhibited evident surface erosion and pitting, indicating physical alterations due to biodegradation. These findings provide strong evidence for the efficiency of our developed biodegradation system. To fully harness the potential of this system and enable its practical implementation, further research is warranted to optimize and scale up the process. Our work contributes to the ongoing efforts to combat the global plastic waste crisis, offering a valuable solution for the efficient biodegradation of PBAT.

Effect of segmental motion on hydrolytic degradation of polyglycolide in electro-spun fiber mats

Recently, environmentally degradable polymers have received great attention from the perspective of sustaining the aquatic environment. To control the degradation behavior of solid polymer materials in an aqueous phase, it is crucial to better understand the thermal molecular motion of polymer chains in water. We herein focus on polyglycolide (PGA), which is one of the representative aliphatic polyesters that are hydrolytically degradable. Three kinds of fiber mats of PGA with different fiber diameters and comparable crystallinities were prepared using an electrospinning method. Our choice of fiber mats was because the ratio of the surface area, where the hydrolytic degradation starts to occur, to the volume was larger than that for the films. Dynamic mechanical analysis (DMA) enabled us to gain direct access to the dynamic glass transition temperature (Tgα) of PGA in the fiber mats both in dry gaseous nitrogen and liquid water. The Tgα value varied not only with the presence of water molecules, but also with the fiber diameter, or the specific surface area. The degradation behavior of PGA fiber mats was examined by immersing the samples in phosphate-buffered saline at various temperatures. When the segmental motion of PGA in the fiber mats was released, the apparent crystallinity of the mats increased, meaning that PGA amorphous chains were cleaved and thus partially eluted into the aqueous phase. It was also shown that partially cleaved chains crystallized.

Characterization of endophytic bacteriome diversity and associated beneficial bacteria inhabiting a macrophyte Eichhornia crassipes

Introduction

The endosphere of a plant is an interface containing a thriving community of endobacteria that can affect plant growth and potential for bioremediation. Eichhornia crassipes is an aquatic macrophyte, adapted to estuarine and freshwater ecosystems, which harbors a diverse bacterial community. Despite this, we currently lack a predictive understanding of how E. crassipes taxonomically structure the endobacterial community assemblies across distinct habitats (root, stem, and leaf).

Methods

In the present study, we assessed the endophytic bacteriome from different compartments using 16S rRNA gene sequencing analysis and verified the in vitro plant beneficial potential of isolated bacterial endophytes of E. crassipes.

Results and discussion

Plant compartments displayed a significant impact on the endobacterial community structures. Stem and leaf tissues were more selective, and the community exhibited a lower richness and diversity than root tissue. The taxonomic analysis of operational taxonomic units (OTUs) showed that the major phyla belonged to Proteobacteria and Actinobacteriota (> 80% in total). The most abundant genera in the sampled endosphere was Delftia in both stem and leaf samples. Members of the family Rhizobiaceae, such as in both stem and leaf samples. Members of the family Rhizobiaceae, such as Allorhizobium- Neorhizobium-Pararhizobium-Rhizobium were mainly associated with leaf tissue, whereas the genera Nannocystis and Nitrospira from the families Nannocystaceae and Nitrospiraceae, respectively, were statistically significantly associated with root tissue. Piscinibacter and Steroidobacter were putative keystone taxa of stem tissue. Most of the endophytic bacteria isolated from E. crassipes showed in vitro plant beneficial effects known to stimulate plant growth and induce plant resistance to stresses. This study provides new insights into the distribution and interaction of endobacteria across different compartments of E. crassipes Future study of endobacterial communities, using both culture-dependent and -independent techniques, will explore the mechanisms underlying the wide-spread adaptability of E. crassipesto various ecosystems and contribute to the development of efficient bacterial consortia for bioremediation and plant growth promotion.

Preparation and Properties of Poly(butylene adipate-co-terephthalate)/thermoplastic Hydroxypropyl Starch Composite Films Reinforced with Nano-Silica

The use of biodegradable plastics is gradually increasing, but its expensive cost limits promotion. In this study, poly(butylene adipate-co-terephthalate)/thermoplastic hydroxypropyl starch reinforced with nano-silica (PBAT/TPHS_g-SiO2) composite films with high hydroxypropyl starch content were prepared in a two-step process. The effect of reinforced thermoplastic hydroxypropyl starch on the mechanical, thermal, processing properties, and micromorphology of the composite films was investigated. The results showed that the tensile strength of the composite films was significantly improved by the addition of nano-silica, with 35% increase in horizontal tensile strength and 21% increase in vertical tensile strength after the addition of 4 phr of nano-silica. When the content of thermoplastic hydroxypropyl starch reinforced with nano-silica (TPHS_g-4SiO2) is 40%, the horizontal and vertical tensile strengths of the films are 9.82 and 12.09 MPa, respectively, and the elongation at break of the films is over 500%. Electron micrographs show that TPHS_g-4SiO2 is better homogeneously dispersed in the PBAT and exhibits a bi-continuous phase structure at a TPHS_g-4SiO2 content of 40%. In this study, the blowing PBAT/TPHS_g-4SiO2 composite films effectively reduce the cost and still show better mechanical properties, which are suitable for packaging applications.

General overview of biopolymers: structure and properties

Biopolymers are synthesized from a biological origin under natural phenomenon especially during their growth cycle, in the form of polymeric substances that portrays excellent properties such as flexibility, tensile strength, steadiness, reusability, and so on. The amalgamated form of two or more biopolymers leads to the formation of “biocomposites” with novel applications. Several mechanisms were identified for the effective production of biopolymers from diverse life forms such as microbial origin plant and animal origin. Based on their origin, biopolymer differs in their structure and functions. Biopolymers are preferred over chemically synthesized polymers due to their biodegradability and their impact on the environment. Biopolymers play a pivotal role in pharmaceutical industries. The biopolymers could be employed for, the administration of medicine as well as regenerative medicine to reach minimal immunogenicity and maximum pharmacological expressivity in a treated individual. Based on their properties biopolymers were exclusively used in medical devices, cosmaceuticals, and confectionaries, it is also used as additives in food industries, bio-sensors, textile industries, and wastewater treatment plants. Ecological support is of utmost concern nowadays due to the ever-expanding ramification over the planet by usage of plastic as packaging material, turning up scientists and researchers to focus on biodegradable biopolymer utilization. The miscibility-structural-property relation between every biopolymer must be focused on to improve the better environment. Specific biopolymers are designed for the betterment of agrarian and commoners of society. Advanced structural modifications, properties of biopolymers, and applications of biopolymers to achieve a greener environment were discussed in this chapter.

Complete bio-degradation of poly(butylene adipate-co-terephthalate) via engineered cutinases

Poly(butylene adipate-co-terephthalate) (PBAT), a polyester made of terephthalic acid (TPA), 1,4-butanediol, and adipic acid, is extensively utilized in plastic production and has accumulated globally as environmental waste. Biodegradation is an attractive strategy to manage PBAT, but an effective PBAT-degrading enzyme is required. Here, we demonstrate that cutinases are highly potent enzymes that can completely decompose PBAT films in 48 h. We further show that the engineered cutinases, by applying a double mutation strategy to render a more flexible substrate-binding pocket exhibit higher decomposition rates. Notably, these variants produce TPA as a major end-product, which is beneficial feature for the future recycling economy. The crystal structures of wild type and double mutation of a cutinase from Thermobifida fusca in complex with a substrate analogue are also solved, elucidating their substrate-binding modes. These structural and biochemical analyses enable us to propose the mechanism of cutinase-mediated PBAT degradation.

Enzymes' Power for Plastics Degradation

Plastics are everywhere in our modern way of living, and their production keeps increasing every year, causing major environmental concerns. Nowadays, the end-of-life management involves accumulation in landfills, incineration, and recycling to a lower extent. This ecological threat to the environment is inspiring alternative bio-based solutions for plastic waste treatment and recycling toward a circular economy. Over the past decade, considerable efforts have been made to degrade commodity plastics using biocatalytic approaches. Here, we provide a comprehensive review on the recent advances in enzyme-based biocatalysis and in the design of related biocatalytic processes to recycle or upcycle commodity plastics, including polyesters, polyamides, polyurethanes, and polyolefins. We also discuss scope and limitations, challenges, and opportunities of this field of research. An important message from this review is that polymer-assimilating enzymes are very likely part of the solution to reaching a circular plastic economy.

Biodegradation of polylactic acid by a mesophilic bacteria Bacillus safensis

A mesophilic bacterial strain, Bacillus safensis PLA1006, was isolated from landfill soil and was tested for growth on polylactic acid (PLA) emulsion medium. The strain formed clear zones on the medium and produced protease and lipase. The macroscopic morphology of the PLA films was not changed significantly after treatment with Bacillus safensis PLA1006 but the films were whitened. Weight loss of PLA films was about 8% after 30 days of incubation with Bacillus safensis PLA1006 in mineral salt medium. Scanning electron microscopy revealed etching on the surface of PLA film treated by Bacillus safensis PLA1006. This also caused an increase in hydrophilicity of the PLA films surface. Attenuated total reflectance - Fourier transform infrared spectroscopy analysis of PLA films after treated by Bacillus safensis PLA1006 showed no new absorption peaks but a decrease in the intensity of all absorption peaks. The hydrolysis products of PLA by the strain contained monomers and oligomers of lactic acid. Zymogram detection showed that proteases may play a role in the degradation of PLA.

Approaches in Sustainable, Biobased Multilayer Packaging Solutions

The depletion of fossil resources and the growing demand for plastic waste reduction has put industries and academic researchers under pressure to develop increasingly sustainable packaging solutions that are both functional and circularly designed. In this review, we provide an overview of the fundamentals and recent advances in biobased packaging materials, including new materials and techniques for their modification as well as their end-of-life scenarios. We also discuss the composition and modification of biobased films and multilayer structures, with particular attention to readily available drop-in solutions, as well as coating techniques. Moreover, we discuss end-of-life factors, including sorting systems, detection methods, composting options, and recycling and upcycling possibilities. Finally, regulatory aspects are pointed out for each application scenario and end-of-life option. Moreover, we discuss the human factor in terms of consumer perception and acceptance of upcycling.

Synthesis, Properties, and Biodegradability of Novel Sequence-Controlled Copolyesters Composed of Glycolic Acid, Dicarboxylic Acids, and C3 or C4 Diols

We have previously reported that sequence-controlled copolyesters such as poly((ethylene diglycolate) terephthalate) (poly(GEGT)) showed higher melting temperatures than those of the corresponding random copolymers and high biodegradability in seawater. In this study, to elucidate the effect of the diol component on their properties, a series of new sequence-controlled copolyesters composed of glycolic acid, 1,4-butanediol or 1,3-propanediol, and dicarboxylic acid units was studied. 1,4-Butylene diglycolate (GBG) and 1,3-trimethylene diglycolate (GPG) were prepared by the reactions of 1,4-dibromobutane or 1,3-dibromopropane with potassium glycolate, respectively. Polycondensation of GBG or GPG with various dicarboxylic acid chlorides produced a series of copolyesters. Terephthalic acid, 2,5-furandicarboxylic acid, and adipic acid were used as the dicarboxylic acid units. Among the copolyesters bearing terephthalate or 2,5-furandicarboxylate units, the melting temperatures (T_m) of the copolyesters containing 1,4-butanediol or 1,2-ethanediol units were substantially higher than those of the copolyester containing the 1,3-propanediol unit. Poly((1,4-butylene diglycolate) 2,5-furandicarboxylate) (poly(GBGF)) showed a T_m at 90 °C, while the corresponding random copolymer was reported to be amorphous. The glass-transition temperatures of the copolyesters decreased as the carbon number of the diol component increased. Poly(GBGF) was found to show higher biodegradability in seawater than that of poly(butylene 2,5-furandicarboxylate) (PBF). On the other hand, the hydrolysis of poly(GBGF) was suppressed in comparison with that of poly(glycolic acid). Thus, these sequence-controlled copolyesters have both improved biodegradability compared to PBF and lower hydrolyzability than PGA.

Accelerated degradation of plastic products via yeast enzyme treatment

Biodegradable plastics can solve the problem of unwanted plastics accumulating in the environment if they can be given the contradictory properties of durability in use and rapid degradation after use. Commercially available agricultural biodegradable mulch films are made from formulations containing polybutylene adipate-co-terephthalate (PBAT) to provide mechanical and UV resistance during the growing season. Although used films are ploughed into the soil using a tiller to promote decomposition, it is difficult if they remain durable. We showed that an enzyme produced by the leaf surface yeast Pseudozyma antarctica (PaE) degrades PBAT-containing films. In laboratory studies, PaE randomly cleaved the PBAT polymer chain and induced erosion of the film surface. In the field, commercial biodegradable films containing PBAT placed on ridges were weakened in both the warm and cold seasons by spraying the culture filtrate of P. antarctica. After the field was ploughed the next day, the size and total weight of residual film fragments decreased significantly (p < 0.05). Durable biodegradable plastics used in the field are degraded using PaE treatment and are broken down into small fragments by the plough. The resultant degradation products can then be more readily assimilated by many soil microorganisms.

The fate of conventional and potentially degradable gillnets in a seawater-sediment system

Abandoned gillnets in the marine environment represent a global environmental risk due to the ghost fishing caused by the nets. Degradation of conventional nylon gillnets was compared to that of nets made of polybutylene succinate co-adipate-co-terephthalate (PBSAT) that are designed to degrade more readily in the environment. Gillnet filaments were incubated in microcosms of natural seawater (SW) and marine sediments at 20 °C over a period of 36 months. Tensile strength tests and scanning electron microscopy analyses showed weakening and degradation of the PBSAT filaments over time, while nylon filaments remained unchanged. Pyrolysis-gas chromatography/mass spectrometry revealed potential PBSAT degradation products associated with the filament surfaces, while nylon degradation products were not detected by these analyses. Microbial communities differed significantly between the biofilms on the nylon and PBSAT filaments. The slow deterioration of the PBSAT gillnet filaments shown here may be beneficial and reduce the ghost fishing periods of these gillnets.

Enzymatic Degradation of the Most Common Aliphatic Bio-Polyesters and Evaluation of the Mechanisms Involved: An Extended Study

Commercial hydrolytic enzymes belonging to different subclasses (several lipases, proteinase k, cutinase) were investigated for their ability to degrade different aliphatic polyesters, i.e., poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA), two poly(caprolactone), having two different molecular weights, poly(lactic acid) (PLA) and poly(propylene carbonate) (PPC). The enzyme screening was first carried out by investigating the capacity of fully degrading the target polymers in 24 h, then weight loss measurements of selected polyesters and target enzymes were performed. Solid residues after enzyme degradation were characterized by proton nuclear magnetic resonance (¹H NMR), gel permeation chromatography (GPC), infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetry (TGA). Liquid fractions were studied via GPC, ¹H NMR and high-performance liquid chromatography (HPLC). PCL and PBSA were found to be the most biodegradable polyesters, under the conditions used in this study. PBS was fully degraded only by cutinase, whereas none of the tested enzymes were able to completely degrade PLA and PPC, in the conditions assessed here. Cutinase exhibited the highest hydrolytic activity on PBSA, while lipase from Candida sp. (CALB) on low molecular weight PCL. Chemical analyses on residual solids showed that the enzymatic degradation occurred homogeneously from the surface through an erosion mechanism and did not significantly affect the macromolecular structure and thermal stability. Cleaving action mode for each enzyme (endo- and/or exo-type) on the different polyesters were also proposed based on the evaluation of the degradation products in the liquid fraction.

Plastic Waste Management in India: Challenges, Opportunities, and Roadmap for Circular Economy

Plastic waste (PW) is one of the most rapid-growing waste streams in municipal solid waste all over the world. India has become a global player in the plastic value chain. Despite low consumption, domestic generation and imports create a significant burden on the overall waste management system, which requires in-depth understanding of the scenario and pathways that can mitigate the crisis. Although Indian researchers have widely researched technology-related issues in academic papers, a substantial knowledge gap exists in understanding the problem’s depth and possible solutions. This review article focuses on current plastic production, consumption, and waste generation in India. This review article mainly analyzes data and information regarding Indian PW management and highlights some critical issues such as reverse supply chain, effective PW management, source-specific recovery, and PW rules in India. Comprehensively, this review will help to identify implementable strategies for policymakers and research opportunities for future researchers in holistic PW management and recycling in India, focusing on the circular economy and sustainable development goals.

Non-Isothermal Crystallization of Titanium-Dioxide-Incorporated Rice Straw Fiber/Poly(butylene succinate) Biocomposites

In this work, titanium dioxide (TiO2)-incorporated rice straw fiber (RS)/poly(butylene succinate) (PBS) biocomposites were prepared by injection molding with different TiO2 powder loadings. The RS/PBS with 1 wt% TiO2 demonstrated the best mechanical properties, where the flexural strength and modulus increased by 30.34% and 28.39%, respectively, compared with RS/PBS. The non-isothermal crystallization of neat PBS, RS/PBS composites, and titanium-dioxide-incorporated RS/PBS composites was investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The non-isothermal crystallization data were analyzed using several theoretical models. The Avrami and Mo kinetic models described the non-isothermal crystallization behavior of neat PBS and the composites; however, the Ozawa model was inapplicable. The crystallization temperature (Tc), half-time of crystallization (t1/2), and kinetic parameters (FT) showed that the crystallizability followed the order: TiO2-incorporated RS/PBS composites > RS/PBS > PBS. The RS/PBS with 1 wt% TiO2 showed the best crystallization properties. The Friedman model was used to evaluate the effective activation energy of the non-isothermal crystallization of PBS and its composites. Rice straw fiber and TiO2 acted as nucleating agents for PBS. The XRD results showed that the addition of rice straw fiber and TiO2 did not substantially affect the crystal parameters of the PBS matrix. Overall, this study shows that RS and TiO2 can significantly improve the crystallization and mechanical properties of PBS composites.

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.

Immuno-modulatory Effects of Microparticles Formulated from Degradable Polystyrene Analogue

Environmental accumulation of non-degradable polystyrene (PS) microparticles from plastic waste poses potential adverse impact on marine life and human health. Herein, we formulate microparticles from a degradable polystyrene analogue (dePS) and comprehensively evaluate their immuno-modulatory characteristics. Both dePS copolymer and microparticles are chemically degradable under accelerated hydrolytic condition. In vitro studies show that dePS microparticles are non-toxic to three immortalized cell lines. While dePS microparticles do not induce macrophage polarization in vitro, dePS microparticles induce in vivo upregulation of both pro-inflammatory and anti-inflammatory biomarkers in immuno-competent mice, suggesting the coexistence of mixed phenotypes of macrophages in the host immune response to these microparticles. Interestingly, on day 7 post-injection, dePS microparticles induce a lower level of several immuno-modulatory biomarkers (MMPs activity, TNF-α, and arginase activity) compared to that of reference poly(lactic-co-glycolic acid) PLGA microparticles. Remarkably, compared to PS microparticles, dePS microparticles exhibit similar in vitro and in vivo bioactivity while acquiring additional chemical degradability. Overall, our research gains new insights into the host immune response to dePS microparticles and suggests that this degradable polystyrene analogue might be explored as an alternative material choice for biomedical and consumer care applications. This article is protected by copyright. All rights reserved.

Design of 2,5-furandicarboxylic based polyesters degraded in different environmental conditions: Comprehensive experimental and theoretical study

Nowadays, the promotion and application of aliphatic-aromatic copolyesters, such as poly (butylene adipate-co-terephthalate) (PBAT), are growing into a general trend. Although the structures of diacids exerted substantial impacts on degradation behavior, the underlying mechanisms have rarely been studied. In this work, 2,5-Furandicarboxylic acid was combined with succinic acid (PBSF), adipic acid (PBAF) and diglycolic acid (PBDF) to prepare three kinds of copolyesters. They showed unique degradation behaviors in buffer, enzyme environment and artificial seawater. These characteristics are closely related to the structural compositions of diacids. PBAFs displayed impressive biodegradability when catalyzed by Candida antarctica lipase B (CALB), while the more hydrophilic PBDFs exhibited faster hydrolysis in both buffer and artificial seawater. PBSFs, with hydrophobic and short segments, obtained a relatively slower rate of hydrolysis and enzymatic degradation. The reactivity sites and hydrolytic pathway were revealed by the combination of DFT calculation and Fukui function analysis. MD simulations, QM/MM optimizations and theozyme calculations showed that PBAF-CALB was prone to form a pre-reaction state, leading to the reduced energy barrier in the acylation process. This work revealed the effects of different structural features of diacids on polymer degradation and paved a way to design target biodegradable polymers in different degradation conditions.

Can anaerobic digestion be a suitable end-of-life scenario for biodegradable plastics? A critical review of the current situation, hurdles, and challenges

Growing concern regarding non-biodegradable plastics and the impact of these materials on the environment has promoted interest in biodegradable plastics. The intensification of separate biowastes collection in most European countries has also contributed to the development of biodegradable plastics, and the subject of their end-of-life is becoming a key issue. To date, there has been relatively little research to evaluate the biodegradability of biodegradable plastics by anaerobic digestion (AD) compared to industrial and home composting. However, anaerobic digestion is a particularly promising strategy for treating biodegradable organic wastes in the context of circular waste management. This critical review aims to provide an in-depth update of anaerobic digestion of biodegradable plastics by providing a summary of the literature regarding process performances, parameters affecting biodegradability, the microorganisms involved, and some of the strategies (e.g., pretreatment, additives, and inoculum acclimation) used to enhance the degradation rate of biodegradable plastics. In addition, a critical section is dedicated to suggestions and recommendations for the development of biodegradable plastics sector and their treatment in anaerobic digestion.

Strategies and progress in synthetic textile fiber biodegradability

Abstract

The serious issue of textile waste accumulation has raised attention on biodegradability as a possible route to support sustainable consumption of textile fibers. However, synthetic textile fibers that dominate the market, especially poly(ethylene terephthalate) (PET), resist biological degradation, creating environmental and waste management challenges. Because pure natural fibers, like cotton, both perform well for consumer textiles and generally meet certain standardized biodegradability criteria, inspiration from the mechanisms involved in natural biodegradability are leading to new discoveries and developments in biologically accelerated textile waste remediation for both natural and synthetic fibers. The objective of this review is to present a multidisciplinary perspective on the essential bio-chemo-physical requirements for textile materials to undergo biodegradation, taking into consideration the impact of environmental or waste management process conditions on biodegradability outcomes. Strategies and recent progress in enhancing synthetic textile fiber biodegradability are reviewed, with emphasis on performance and biodegradability behavior of poly(lactic acid) (PLA) as an alternative biobased, biodegradable apparel textile fiber, and on biological strategies for addressing PET waste, including industrial enzymatic hydrolysis to generate recyclable monomers. Notably, while pure PET fibers do not biodegrade within the timeline of any standardized conditions, recent developments with process intensification and engineered enzymes show that higher enzymatic recycling efficiency for PET polymer has been achieved compared to cellulosic materials. Furthermore, combined with alternative waste management practices, such as composting, anaerobic digestion and biocatalyzed industrial reprocessing, the development of synthetic/natural fiber blends and other strategies are creating opportunities for new biodegradable and recyclable textile fibers.

Article Highlights

Recent advances in the microbial synthesis of lactate-based copolymer

Due to the increasing environmental pollution of un-degradable plastics and the consumption of non-renewable resources, more attention has been attracted by new bio-degradable/based polymers produced from renewable resources. Polylactic acid (PLA) is one of the most representative bio-based materials, with obvious advantages and disadvantages, and has a wide range of applications in industry, medicine, and research. By copolymerizing to make up for its deficiencies, the obtained copolymers have more excellent properties. The development of a one-step microbial metabolism production process of the lactate (LA)-based copolymers overcomes the inherent shortcomings in the traditional chemical synthesis process. The most common lactate-based copolymer is poly(lactate-co-3-hydroxybutyrate) [P(LA-co-3HB)], within which the difference of LA monomer fraction will cause the change in the material properties. It is necessary to regulate LA monomer fraction by appropriate methods. Based on synthetic biology and systems metabolic engineering, this review mainly focus on how did the different production strategies (such as enzyme engineering, fermentation engineering, etc.) of P(LA-co-3HB) optimize the chassis cells to efficiently produce it. In addition, the metabolic engineering strategies of some other lactate-based copolymers are also introduced in this article. These studies would facilitate to expand the application fields of the corresponding materials.

Methane production and active microbial communities during anaerobic digestion of three commercial biodegradable coffee capsules under mesophilic and thermophilic conditions

Biodegradable plastics market is increasing these last decades, including for coffee capsules. Anaerobic digestion, as a potential end-of-life scenario for plastic waste, has to be investigated. For this purpose, mesophilic (38 °C) and thermophilic (58 °C) anaerobic digestion tests on three coffee capsules made up with biodegradable plastic (Beanarella®, Launay® or Tintoretto®) and spent coffee (control) were compared by their methane production and the microbial communities active during the process. Mesophilic biodegradation of the capsules was slow and did not reach completion after 100 days, methane production ranged between 67 and 127 NL (CH₄) kg^-1 (VS). Thermophilic anaerobic digestion resulted in a better biodegradation and reached completion around 100 days, methane productions were between 257 and 294 NL (CH₄) kg^-1 (VS). The microbial populations from the reactors fed with plastics versus spent coffee grounds were significantly different, under both the mesophilic and the thermophilic conditions. However, the different biodegradable plastics only had a small impact on the main microbial community composition at a similar operational temperature and sampling time. Interestingly, the genus Tepidimicrobium was identified as a potential key microorganisms involved in the thermophilic conversion of biodegradable plastic in methane.

Metagenome-Assembled Genomes of 12 Bacterial Species from Biofouled Plastic Fabrics Harbor Multiple Genes for Degradation of Hydrocarbons

We report the metagenome-assembled genomes (MAGs) of 12 different bacterial species recovered from environmental microbiomes associated with biofouled plastic fabrics. The MAGs have estimated sizes of 2.53 to 7.66 Mb with 3,229 to 9,289 proteins, 26.20% to 99.1% genome completeness, 48.9% to 72.6% G+C content, and multiple genes for hydrocarbon degradation.

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

As the global threat of plastic pollution has grown in scale and urgency, so have efforts to find sustainable and efficient solutions. Research conducted over the past few years has identified gut environments within insect larvae, including Tenebrio molitor (yellow mealworms), as microenvironments uniquely suited to rapid plastic biodegradation. However, there is currently limited understanding of how the insect host and its gut microbiome collaborate to create an environment conducive to plastic biodegradation. In this work, we provide evidence that T. molitor secretes one or more emulsifying factor(s) (30-100 kDa) that mediate plastic bioavailability. We also demonstrate that the insect gut microbiome secretes factor(s) (<30 kDa) that enhance respiration on polystyrene (PS). We apply these insights to culture PS-fed gut microbiome enrichments, with elevated rates of respiration and degradation compared to the unenriched gut microbiome. Within the enrichment, we identified eight unique gut microorganisms associated with PS biodegradation including Citrobacter freundii, Serratia marcescens, and Klebsiella aerogenes. Our results demonstrate that both the mealworm itself and its gut microbiome contribute to accelerated plastic biodegradation. This work provides new insights into insect-mediated mechanisms of plastic degradation and potential strategies for cultivation of plastic-degrading microorganisms in future investigations and scale-up.

Biodegradable Plastics: Standards, Policies, and Impacts

Plastics are ubiquitous in our society. They are in our phones, clothes, bottles, and cars. Yet having improved our lives considerably, they now threaten our environment and our health. The associated carbon emissions and persistency of plastics challenge the fragile balance of many ecosystems. One solution is using biodegradable plastics. Ideally, such plastics are easily assimilated by microorganisms and disappear from our environment. This can help reduce the problems of climate change, microplastics, and littering. However, biodegradable plastics are still only a tiny portion of the global plastics market and require further efforts in research and commercialization. Here, a critical overview of the state of the art of biodegradable plastics is given. Using a material flow analysis, the challenges of the plastic market are highlighted, and with it the large market potential of biodegradable plastics. The environmental and socio-economic impact of plastics, government policies, standards and certifications, physico-chemical properties, and analytical techniques are covered. The Review concludes with a personal outlook on the future of bioplastics, based on our own experience with their development and commercialization.

The potential of cold-adapted microorganisms for biodegradation of bioplastics

Due to the extensive use of plastics, their quantity in the environment is constantly increasing, which creates a global problem. In the present study, we sought to isolate, test and identify Antarctic microorganisms which possess the ability to biodegrade bioplastics such as poly(ε-caprolactone) (PCL), poly(butylene succinate) (PBS) and poly(butylene succinate-co-butylene adipate) (PBSA) at low temperatures. 161 bacterial and 38 fungal isolates were isolated from 22 Antarctic soil samples. Among them, 92.16% of bacterial and 77.27% of fungal isolates formed a clear zone on emulsified PBSA, 98.04% and 81.82% on PBS and 100% and 77.27% on PCL as an additive to minimal medium at 20 °C. Based on the 16S and 18S rRNA sequences, bacterial strains were identified as species belonging to Pseudomonas and Bacillus and fungal strains as species belonging to Geomyces, Sclerotinia, Fusarium and Mortierella, while the yeast strain was identified as Hansenula anomala. In the biodegradation process conducted under laboratory conditions at 14, 20 and 28 °C, Sclerotinia sp. B11IV and Fusarium sp. B3'M strains showed the highest biodegradation activity at 20 °C (49.68% for PBSA and 33.7% for PCL, 45.99% for PBSA and 49.65% for PCL, respectively). The highest biodegradation rate for Geomyces sp. B10I was noted at 14 °C (25.67% for PBSA and 5.71% for PCL), which suggested a preference for lower temperatures (at 20 °C the biodegradation rate was only 11.34% for PBSA, and 4.46% for PCL). These data showed that microorganisms isolated from Antarctic regions are good candidates for effective plastic degradation at low temperatures.

Seawater degradation of PLA accelerated by water-soluble PVA

In order to promote the degradation of PLA in seawater, a series of seawater-degradable polyester blends PVA/PLA were prepared by blending biodegradable polylactic acid (PLA) with water-soluble modified polyvinyl alcohol (PVA) in this paper. ADR 4370S was introduced to bring a certain degree of improvement in compatibility of PVA/PLA blends. The results of degradation test in natural seawater for 180 days show that the weight loss of PVA/PLA blends in seawater is much higher compared with that of pure PLA. PVA can be used as an effective hydrolysis accelerator for PLA matrix, helping to significantly reduce the molecular weight of PLA. The channels caused by dissolution/swelling of PVA facilitate the entry of water and microorganisms into the materials to contact with PLA, thereby promoting the degradation process of PLA matrix itself. Thus, both dissolution/swelling of PVA and degradation of PLA occur in PVA/PLA blends, and the degree of rapid dissolution of PVA in the early stage determines the degree of degradation of PLA.

Biodegradation mechanism of polycaprolactone by a novel esterase MGS0156: a QM/MM approach

Nowadays micro-plastic pollution has become one of the most serious global environmental problems. A potential strategy in managing micro-plastic waste is enzyme-catalyzed degradation. MGS0156 is a hydrolase screened from environmental metagenomes, which can efficiently degrade commercial plastics such as polycaprolactone, polylactide, etc. Here a combined molecular dynamics, molecular mechanics Poisson-Boltzmann surface area, and quantum mechanics/molecular mechanism method was used to reveal the enzymatic depolymerization mechanism. By systematically analyzing the binding processes of nine oligomers (from a monomer to tetramer), we found that longer oligomers have relatively stronger binding energy. The degradation process involves two concerted elementary steps: triad-assisted nucleophilic attack and C-O bond cleavage. C-O bond cleavage is the rate determining step with an average barrier of 15.7 kcal mol-1, which is consistent with the experimentally determined kcat (1101 s-1, corresponds to 13.3 kcal mol-1). The electrostatic influence analysis of twenty amino acids highlights His231 and Asp237 as potential mutation targets for designing more efficient MGS0156 mutants.

Soil Microbial Communities Associated With Biodegradable Plastic Mulch Films

Agricultural plastic mulch films provide a favorable soil microclimate for plant growth, improving crop yields. Biodegradable plastic mulch films (BDMs) have emerged as a sustainable alternative to widely used non-biodegradable polyethylene (PE) films. BDMs are tilled into the soil after use and are expected to biodegrade under field conditions. However, little is known about the microbes involved in biodegradation and the relationships between microbes and plastics in soils. In order to capture the consortium of soil microbes associated with (and thus likely degrading) BDMs, agriculturally-weathered plastics from two locations were studied alongside laboratory enrichment experiments to assess differences in the microbial communities associated with BDMs and PE films. Using a combination of amplicon sequencing and quantitative PCR (qPCR), we observed that agriculturally-weathered plastics hosted an enrichment of fungi and an altered bacterial community composition compared to the surrounding soil. Notably, Methylobacterium, Arthrobacter, and Sphingomonas were enriched on BDMs compared to non-biodegradable PE. In laboratory enrichment cultures, microbial consortia were able to degrade the plastics, and the composition of the microbial communities was influenced by the composition of the BDMs. Our initial characterization of the microbial communities associated with biodegradable plastic mulch films, or the biodegradable "plastisphere," lays the groundwork for understanding biodegradation dynamics of biodegradable plastics in the environment.