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Abstract: We isolated 5 mesophilic microorganisms that form clear zones around the colony on an opaque medium containing the aliphatic–aromatic copolyester poly(60 mol% butylene adipate-co-40 mol% butylene terephthalate) (PBAT). Among all strains, the fungal strain NKCM1712 degraded PBAT at the fastest rate (3.5 ± 0.3 μg cm−2 h−1). Genetic and morphological analyses revealed that this strain was closely related to Isaria fumosorosea (phylum Ascomycota). Mass spectroscopic analysis revealed that the degradation products were T, AB, TB, BAB, and ABT (T, terephthalic acid unit; A, adipic acid unit; B, 1,4-butanediol unit)] in the culture of the strain that used PBAT as the sole carbon source. Furthermore, the PBAT degradation ability of this strain in terms of BOD suggested that it could utilize the PBAT degradation products as growth substrates. This is the first report of a mesophilic strain that can mineralize an aliphatic–aromatic polyester into carbon dioxide on its own. [Copyright &y& Elsevier]

Ideal biodegradable polymers have high durability during use and high degradability in the natural environment it enters after use. A trigger system that uses external stimuli to change the chemical properties of a polymer or directly degrade the polymer to low molecular weight compounds is suitable for controlling the biodegradability of a polymer. In this study, we adopted the reductive cleavage of disulfide bonds as a trigger to control the biodegradability of polymers. We synthesized polyesters with disulfide bonds and demonstrated that the environmental biodegradability of these polymers could be triggered by cleavage of the disulfide bonds in a reductive environment. [ABSTRACT FROM AUTHOR]

A DNA fragment carrying the gene encoding poly(3-hydroxybutyrate) [P(3HB)] depolymerase was cloned from the genomic DNA of the marine bacterium Shewanella sp. strain JKCM-AJ-6,1α (wild-type strain) from seawater. The gene was 2049 bp and encoded 683-amino acids protein with a molecular mass of 70,382 Da. A sequence homology revealed that the deduced protein contains a signal peptide, catalytic domain (CD), fibronectin type III linker domain (LD), and two substrate-binding domains (SBDs). Meanwhile, a P(3HB) depolymerase purified from wild-type strain (wPhaZ She ) had a smaller molecular mass (47 kDa) because it lacked the SBDs, compared with calculated one based on the sequence. wPhaZ She was unstable above 15 °C and had relatively high enzymatic activity in the presence of 0.5 M NaCl, demonstrating that the enzyme is thermolabile and halotolerant. In addition, there was no decrease in the activity by self-inhibition. In contrast, a recombinant form of the enzyme (rbPhaZ She ) produced in Escherichia coli BL21 had a stronger binding affinity for P(3HB) and exhibited self-inhibition. These results demonstrate that a truncated form P(3HB) depolymerase lacking SBDs (wPhaZ She ) has an advantage for P(3HB) degradation in marine environments with relatively high NaCl concentrations owing to a less self-inhibitory effect. [ABSTRACT FROM AUTHOR]

• The enzymatic degradation tests of PHBH fibers were conducted using PHB depolymerase. • The enzymatic degradation rate of PHBH fibers decreased with increasing drawing ratio. • Solid and highly-ordered structures were examined by DSC, SAXS, WAXD measurements. • The degradation rate from fiber cross-section was then quantified for the first time. • The degradation rate of flat-on lamellar crystals was larger than that of edge-on. In this study, the relationship between the crystal orientation and enzymatic degradation rate of poly(3-hydroxybutyrate- co -3-hydroxyhexanoate) (PHBH) was investigated. The enzymatic degradation rates of melt-spun PHBH fibers were quantified via PHB depolymerase from Ralstonia pickettii T1, and the degradation rate decreased with increasing drawing ratio. The solid structure was investigated via differential scanning calorimetry and small-angle X-ray scattering, and kinetic analysis was performed, indicating that the degradation rate was affected not only by crystallinity and lamellar thickness but also by highly ordered structure. The highly ordered structure was examined via wide-angle X-ray diffraction. The enzymatic degradation rate from the fiber cross-sections was then quantified for the first time, and it increased with drawing ratio and was larger than that from the fiber sides. This result showed that the degradation rate varied depending on the crystal orientation. Furthermore, an enzymatic degradation test of PHBH ring-banded spherulites was conducted, and it was found that the degradation rate of flat-on lamellar crystals was greater than that of edge-on lamellar crystals. This is the first study to quantitatively evaluate the relationship between the crystal orientation and the enzymatic degradation rate. [ABSTRACT FROM AUTHOR]

• Poly(butylene succinate)(PBS) biodegrades very slowly in marine environments. • PBS with 16-hydroxyhexadecanoic acid (16HHD) and PCL enhances marine biodegradability. • PBS with 16HHD and PCL shows 90.4 % and 83.2 % biodegradability in marine conditions. One potential solution for reducing marine pollution from plastic waste is to replace conventional plastics with biodegradable alternatives. However, most chemosynthetically biodegradable aliphatic polyesters, such as poly(butylene succinate) (PBS), exhibit extremely slow biodegradation rates in marine environments. To address this problem, we present a novel method to enhance the marine biodegradability of PBS by blending it with 10 wt.% of 16-hydroxyhexadecanoic acid (16HHD) and poly(ε -caprolactone) (PCL). The weight loss rates of the PBS samples with 16HHD and PCL were 18.4- and 7.8-times faster than that of pristine PBS. Scanning electron micrographs of PBS blended with 16HHD and PCL after oceanic incubation for four months showed a rough surface, suggesting that enzymatic degradation occurred. Additionally, unlike pristine PBS, samples with 16HHD and PCL demonstrated biochemical oxygen demand (BOD) biodegradabilities of 90.4 % and 83.2 %, respectively, under marine conditions. Analysis of the microbial community of BOD testing using 16S ribosomal RNA gene sequencing indicated that the addition of 16HHD and PCL changed the microbial community compared to pristine PBS. These findings demonstrate how blending PBS with 16HHD and PCL enhances its marine biodegradability, thereby offering a promising avenue for addressing plastic pollution in marine ecosystems. [Display omitted] [ABSTRACT FROM AUTHOR]

• CTA (non-biodegradable) was coated onto PHBH (biodegradable) films. • Deacetylation of CTA by weak alkali is a degradation initiation function. • The coated films were deacetylated under weakly alkaline seawater conditions. • Finally, the deacetylated coated PHBH films begun to be degraded. A non-biodegradable polymer (cellulose triacetate; CTA) was coated on the surface of a biodegradable polymer film (poly(3-hydroxybutylate- co -3-hydroxyhexanoate); PHBH), and the multilayer coated films were characterized using microscopy and spectroscopic techniques. The enzymatic degradability of the CTA-coated PHBH films was compared with that of non-coated PHBH films in the presence of an enzyme mixture (cellulase and PHB depolymerase). Non-coated PHBH films were effectively degraded; however, the CTA-coated films were only slightly degraded, indicating that the CTA coating could suppress PHBH biodegradation during use. Surface-deacetylated coated films (with a degree of substitution of 1.3) could be degraded by the same enzyme mixture, indicating that the deacetylation of CTA in an alkaline environment can trigger the degradation of PHBH. Furthermore, degradation tests in seawater demonstrated that CTA was deacetylated under weakly alkaline seawater conditions, and the degradation of cellulose acetate on the surface exposed the PHBH underneath, thereby allowing PHBH degradation. Overall, the results suggest that CTA coatings can effectively serve to initiate the biodegradation of PHBH when released into the ocean. [ABSTRACT FROM AUTHOR]

We report for the first time the mesophilic poly(ethylene succinate)(PESu)-degrading microorganisms isolated from aquatic and soil environments. The degrading isolates were classified into two groups, Gram-positive bacterium and fungus. Phylogenetic analysis revealed that the degrading bacteria belong to the genera Bacillus and Paenibacillus. Thus, PESu may be degraded by very limited species in natural environments. Furthermore, strain KT 1012 which could degrade PESu film at the fastest rate among the degrading bacteria in this study was characterized in detail. The DNA G+C content was 40.4 mol% and iso-C15:0 was the major fatty acid. The temperature optima for growth was approximately 40–45 °C. The phenotypic properties and the phylogenetic inference indicate that strain KT1012 is a related species to Bacillus pumilus. Strain KT1012 did not hydrolyze poly(lactic acid), poly(butylene succinate), poly(3-hydoroxybutyrate) but hydrolyzed PESu, poly(∊-caprolactone) films and olive oil. Strain KT1012 exhibited a high PESu hydrolytic activity in liquid culture when it was cultivated on a nutrient rich medium such as LB medium, suggesting that the hydrolytic activity is not expressed inducibly but constitutively in strain KT1012. [Copyright &y& Elsevier]

• Five poly(ω -hydroxyalkanoate) (P ω HA)s with varying numbers of methylene units were synthesized by ring opening polymerization of corresponding lactones. • The thermal properties, crystallinity, and mechanical properties of PωHAs were evaluated by TGA, DSC, WAXD measurements, and tensile test, respectively. • The clear-zone formation testing exhibits that the PPdL-degrading enzyme was not found, suggesting that the primary structure of PωHAs can endure enzymatic hydrolysis. • The BOD biodegradation testing of the hydrolysates of PωHAs revealed that they were metabolized by environmental microorganisms. • PVL, PCL, PEL, and POL showed BOD biodegradability, whereas PPdL did not. Poly(ε -caprolactone) (PCL), a type of liner poly(ω -hydroxyalkanoate)s (P ω HA)s, is a commercially available biodegradable polymer. The series of P ω HAs with different number of methylene units has been also regarded to be a biodegradable polymer. Although the chemical structure of P ω HAs strongly affects their biodegradability, the effect of the number of methylene units in P ω HAs on their biodegradability has not yet been evaluated. In this study, we synthesized five P ω HAs, poly(δ -valerolactone) (PVL; n = 4), PCL (n = 5), poly(ζ -enantholactone) (PEL; n = 6), poly(η -octalactone) (POL; n = 7), and poly(ω -pentadecanolactone) (PPdL) (n = 14); subsequently, we evaluated their biodegradability via clear-zone formation and biochemical oxygen demand (BOD) biodegradation testing. PVL, PCL, PEL, and POL and their hydrolysates showed good BOD biodegradability, whereas PPdL did not show BOD biodegradability despite the biodegradability of its hydrolysate with soil inocula. These results indicate that the number of methylene units in P ω HAs affects their biodegradability. [Display omitted] [ABSTRACT FROM AUTHOR]

• PHA Melt-spun fibers (undrawn and drawn fibers) after enzymatic degradation were analyzed by SEM and TEM. • On undrawn fibers, lamellar crystals were unraveled on undrawn fibers at the enzymatic degradation front owing to degradation of the amorphous regions between the lamellar crystals. • On drawn fibers, lamellar stacking structures were degraded without unraveling of lamellar crystals at the degradation front. Enzymatic degradation of the lamellar stacking structures of two types of poly[(R)-3-hydroxybutyrate- co -(R)-3-hydroxyvalerate] melt-spun fibers (undrawn and drawn fibers) was analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images of undrawn fibers showed that enzymatic degradation proceeded from the amorphous regions of spherulites on the surface and in the interior of the fibers. In addition, the lamellar crystals of undrawn fibers unraveled when the amorphous regions between the lamellar crystals were preferentially degraded. In contrast, on the drawn fibers, periodic stacking structures of lamellar crystals with a thickness of approximately 300 nm were observed at the initial stage of degradation. Some of these lamellar stacking structures were connected in the drawing direction. Furthermore, SEM images showed that the periodic lamellar stacking structures with thickness of approximately 2 µm appeared as degradation proceeded. TEM images showed that the lamellar crystals of the periodic stacking structures did not unravel at the enzymatic degradation front because the amorphous regions and lamellar crystals were degraded simultaneously, which was attributed to the strong connection between the lamellar crystals of the periodic lamellar stacking structures through tie molecules. [ABSTRACT FROM AUTHOR]

Abstract Since the use of biodegradable polymers for food packaging is becoming popular, it is important to investigate the biodegradable-polymer-hydrolyzing potential of microorganisms in fermented foods. Here, we focused on 4 Japanese washed-rind cheeses. Metagenomic analyses revealed that microbiota in the 4 Japanese washed-rind cheeses was composed of bacteria classified into 515 operational taxonomic units (OTUs) and fungi classified into 74 OTUs. Remarkably, a considerable number of marine bacteria were identified in 3 of 4 cheeses. Further, we isolated a poly(3-hydroxybutyrate) (P(3HB))-degrading bacterium, designated as strain MC1, from one of the cheeses—Muchuri. The strain was a gram-negative, rod-shaped bacterium. It grew well and formed a large clear zone on P(3HB)-containing medium at a temperature range of 30–37 °C, while it did not degrade P(3HB) at 4 °C. The phenotypic properties and phylogenetic inference indicated that strain MC1 is related to Alcanivorax dieselolei B-5T, which is a marine inhabitant. Our study demonstrated that MC1 degrades P(3HB) and that components in cheese promote the degradation of P(3HB) while nutrient-rich conditions suppress it. This suggests that packaging material made of P(3HB) for cheeses could be used under low temperatures and nutrient-rich conditions. Highlights • Microbiota in the 4 Japanese cheeses was composed of bacteria classified into 515 OTUs, and fungi classified into 74 OTUs. • A considerable number of marine bacteria were contained in 3 of 4 cheeses. • A P(3HB)-degrading bacterium strain MC1 related to marine bacterium Alcanivorax was isolated from one of 4 cheeses. • Components in cheese promoted the degradation of P(3HB) while nutrient-rich conditions suppressed it. [ABSTRACT FROM AUTHOR]

• Biodegradation by microorganisms depended on the position of the functional group on the cyclohexane ring. • Polyesters containing cyclohexane rings were prepared from biodegradable cyclohexane monomers. • Some polyesters containing cyclohexane rings were hydrolyzed to water-soluble products by bacterial degradation. • Microorganisms could not mineralize the solid state of polyesters containing cyclohexane rings. The introduction of cyclohexane rings endows polymers with excellent thermal and mechanical properties. Although cyclohexane rings have been incorporated into biodegradable polymers via copolymerization to improve their properties, their biodegradability has not been thoroughly investigated. In this study, we evaluated the biodegradability of ten cyclohexane ring-containing monomers as hydrolysates by biochemical oxygen demand (BOD) biodegradation testing to evaluate whether they can be used for biodegradable polyesters. These biodegradable monomers were polymerized with 1,4-butanediol and succinic acid to the corresponding polyesters containing cyclohexane rings. The biodegradability of these polyesters was investigated using clear-zone formation and BOD biodegradation testing. The clear-zone formation testing revealed the presence of microorganisms producing cyclohexane ring-containing polyester-degrading enzymes in eight polyesters with cyclohexane rings. Meanwhile, the respective polyesters did not exhibit BOD biodegradability despite the successful mineralization of the corresponding constituents. Overall, these findings indicate that the constituents exhibiting BOD biodegradability can be used as biodegradable building blocks. [ABSTRACT FROM AUTHOR]

• The strain YKCMOAS1 degrades poly(ethylene succinate) (PESu) films in seawater. • Initiation is triggered by surface wear of endospore-encapsulated PESu. • YKCMOAS1 encodes a polyester hydrolyzing enzyme homologous with a Bacillus protein. • PESu is degraded within ∼400 d with endospores vs. 7.7 years without endospores. • Other microorganisms mineralized the water-soluble degradation products in ∼10 d. Currently, commercially available biodegradable plastics are not well controlled in terms of the rate and timing of biodegradation. To overcome these challenges, several methods have been proposed. Herein, we propose a new system for controlling the onset and degradation rate of plastic biodegradation by encapsulating endospores of degrading microorganisms into plastics with typically slow biodegradation rates. Endospores of bacterial strain YKCMOAS1 germinated and initiated biodegradation when triggered by surface wear of an aliphatic biodegradable polyester, poly(ethylene succinate) (PESu). The weight loss rate of endospore-containing PESu film immersed in seawater was approximately 7-fold faster than that of PESu film without endospores. The YKCMOAS1 strain used in this study grew in seawater and showed PESu film-degrading activity in a marine mineral medium. Based on the weight loss rate of the endospore-containing PESu films, they were estimated to have completely degraded into water-soluble compounds within approximately 400 d Meanwhile, the biochemical oxygen demand degradation test revealed that the water-soluble products from PESu, which were produced by the vegetative cells were completely biodegraded within 10 d Taken together, these results indicate that material hydrolysis by bacterial strain YKCMOAS1 was triggered by material wear, followed by rapid biodegradation. This is the first report of the application of bioaugmentation to the stable expression of environmental degradation of biodegradable plastics. These results might provide insight into the design concept of novel biodegradable plastics that not only exhibit environmentally independent biodegradation, but also allow control of the onset time. [ABSTRACT FROM AUTHOR]

Biodegradable plastics may be a solution for eliminating large marine plastic debris, such as fishing gear, which causes environmental damage. The biodegradable polyester poly(ε-caprolactone) (PCL) is degraded in various environments; however, no reports have examined PCL-degrading microbes inhabiting coastal environments, despite the fact that marine plastic debris accumulates in this environment. Therefore, in this study, we isolated a PCL-degrading bacterium (strain TKCM 64) from marine plastic debris in coastal seawater (Okinoshima Park, Chiba, Japan) for the first time. Genetic and biochemical analyses showed that strain TKCM 64 was closely related to Pseudomonas pachastrellae JCM12285 T . The maximum specific growth rate (0.4 h −1 ) of the isolate was observed in the absence of NaCl at 30 °C, and the strain was able to grow, even at 1.20 M NaCl, suggesting that the strain could belong to a marine species showing halotolerance. Strain TKCM 64 degraded PCL film at a rate of 1.39 ± 0.09 mg cm −2 ·day −1 . The strain showed PCL hydrolytic activity, which was induced in the presence of PCL and its hydrolysate: 6-hydroxyhexanoic acid (6HH), in addition to a major component of cutin, 16-hydroxyhexadecanoic acid. Thus, we concluded that the PCL hydrolysate 6HH, as an analog of cutin hydrolysate, functioned as an inducer of a PCL hydrolase that is a kind of cutinase in strain TKCM 64. In addition, Pseudomonas pachastrellae was found to be a key bacterial species involved in PCL degradation in coastal environments. [ABSTRACT FROM AUTHOR]

Development of novel biodegradable monomers is indispensable for affording high-performance biodegradable polymers. In addition, a monomer that is synthesized from biomass is preferable as this enhances the overall sustainability of the resulting biodegradable polymer. Bio-based polyoxabicyclates (POBCs) comprising oxabicyclodicarboxylic anhydride (OBCA), which are flexible and transparent materials, were derived from an inedible bio-based chemical, i.e. furfural. Herein, we evaluated the biodegradability of the POBCs using biochemical oxygen demand (BOD)-biodegradation testing and the clear-zone formation method. We observed that the environmental biodegradability of the POBCs depended on the length of diol methylene units. The BOD biodegradabilities of POBCs comprising 1,3-propanediol, 1,4-butanediol, and 1,10-decanediol were more than 85%. Furthermore, two bacteria formed a clear zone on the emulsified medium containing POBC with 1,4-butanediol. These results indicated that OBCA could be adopted as a novel biodegradable monomer. [ABSTRACT FROM AUTHOR]

• Four types of PHA films were oxidized via photo-activated chlorine dioxide radical. • The reactivity of the oxidation is affected by the presence of the side chain. • No significant changes in mechanical properties were observed. • The enzymatic degradability of some of the oxidized PHA films was reduced. • The initial biodegradation rate of the oxidized films in seawater was slightly reduced. Polyhydroxyalkanoates (PHAs) are novel candidates for biodegradable plastics, and hydrophobic surfaces have been modified to improve their dyeability and adhesion to other materials. In this study, surface oxidation by photoactivated chlorine dioxide radicals was carried out on four types of PHA films with different molecular structures to investigate whether the number of introduced functional groups changes. Whether the mechanical properties, crystallinity, enzymatic degradability, and biodegradability in seawater were changed by oxidation was also investigated. It was found that the number of functional groups decreased in the polymer having monomer units without side chains, indicating that the reactivity of the oxidation is affected by the presence of the side chain. No significant changes in mechanical properties and crystallinity were observed. The enzymatic degradability of some of the oxidized PHA films was significantly reduced because it did not match the substrate specificity of the catalytic domain of a PHA depolymerase due to changes in the molecular structure caused by oxidation. In a biodegradation test using seawater, the initial biodegradation rate of the oxidized films was slightly reduced, suggesting that the oxidation may affect the biodegradation of microorganisms in the environment. [ABSTRACT FROM AUTHOR]

Although some poly( n -alkylene n -alkylenedionate) (PAAD)s are believed to be biodegraded easily, others are barely degraded. However, comparative studies of biodegradability have been limited to only a few types of typical PAADs. Therefore, in this study, we prepared nine poly(butylene n -alkylenedioate) (PBAD)s having 2–10 methylene units in the dicarboxylic acid and evaluated the biodegradability of these PBADs by biochemical oxygen demand (BOD)-biodegradation testing. The frequencies of the degrading microorganisms in 19 sites varied with the structure of PBADs. Additionally, BOD-biodegradation rates of PBSu and PBDd were much lower than those other PBADs. Thus, the environmental degradability of PBADs could be related to the frequencies of species that produced the degrading enzymes. Phylogenetic analysis of PBAD-degrading isolates and related species revealed that various bacterial taxa composed of five phyla were involved in environmental degradation of PBADs. [ABSTRACT FROM AUTHOR]

A compression-molded green composite material comprising of bacterially synthesized poly(3-hydroxybutyrate- co -3-hydroxyhexanoate) [P(3HB- co -3HHx)] and short kenaf fibers (KF) was prepared in the present study. Accordingly, P(3HB- co -3HHx) was produced by the Cupriavidus necator Re2058/pCB113 using the palm oil as the sole carbon source, while the polyhydroxyalkanoate (PHA) copolymer with ∼99% purity was recovered from the bacterial cells using a newly reported solvent-free biological recovery method. Experimental results showed that P(3HB- co -3HHx) containing 30 wt % KF possessed the highest flexural strength and similar or better comparable mechanical performance compared to that of the low density polyethylene (LDPE), LDPE/KF composites and high density polyethylene (HDPE). Water absorption and soil burial tests were also performed to evaluate the durability of the P(3HB- co -3HHx)/KF composites. As compared to that of the pristine P(3HB- co -3HHx), it was determined that P(3HB- co -3HHx)/KF composites demonstrated higher water absorption percentage and showed higher percentage of weight loss during the soil degradation study. Burkholderia sp., Streptomyces sp., Amycolatopsis sp. and Streptacidiphilus sp. that involved in the biodegradation of P(3HB- co -3HHx)/KF composites during the soil degradation study were successfully isolated and characterized. These species had the capability to degrade the composite material in vitro . [ABSTRACT FROM AUTHOR]

The use of biodegradable plastic films made of poly(butylene adipate- co -terephthalate) (PBAT) to improve crop production has been proposed. Because the film after use is expected to be degraded on site, it is important to understand the biodegradation mechanism of PBAT in aerobic and mild temperature conditions. We therefore isolated three PBAT-degrading strains, NKCM3201, NKCM3202, and NKCM3101, from soil environments. Phylogenetic analysis revealed that the strains are closely related to Bacillus pumilus . Strain NKCM3201, which degraded PBAT film at the fastest rate (12.2 μg/day/cm 2 ) and grew well at 30 °C to 40 °C in aerobic conditions, was selected for further analysis. We cloned the 648-bp coding region of the PBAT hydrolase (PBATH Bp ) gene, which encodes a 215-amino acid protein containing a signal peptide of 34 residues. Mutation analyses revealed that PBATH Bp belongs to the serine hydrolase superfamily, with a catalytic triad composed of Ser77, Asp133, and His156. Homology 3D modeling of PBATH Bp using Bacillus subtilis 168 lipase as a template showed that the enzyme belongs to the α/β hydrolase fold family, which lack a lid domain on its surface. PBATH Bp hydrolyzed PBAT, poly(butylene succinate- co -adipate) (PBSA), poly(ethylene succinate) (PESu), and polycaprolactone (PCL) films at a degradation rate of 14.3, 3.3 × 10 2 , 7.0 × 10 2 , and 1.1 × 10 2 μg/cm 2 /day, respectively. Liquid chromatography-mass spectrometry analysis of degradation products from PBAT revealed that PBATH Bp hydrolyses ester bonds between butanediol and terephthalate (B-T bonds) at much slower rates than ester bonds between adipate and butanediol. This ester bond preference may explain the very slow PBAT degradation rate compared to PBSA, PESu, and PCL. This is the first report of a PBAT hydrolase from an aerobic mesophilic bacterium, and may contribute to our understanding of PBAT biodegradation under mild temperature conditions. [ABSTRACT FROM AUTHOR]

• Biodegradable polyesters were selected to produce microbeads as alternatives to conventional microbeads. • Manufactured polyester microbeads have comparable compression strengths to those of commonly used microbeads. • PBSA and P(3HB) microbeads have good biodegradability under marine conditions. The conventional microbeads in cosmetics and personal care products comprise non-biodegradable plastics, which pollute the marine environment. In the present study, we used a simple melt-homogenizing method to manufacture microbeads from four biodegradable polyesters, i.e., poly(butylene succinate) (PBS), poly(butylene succinate adipate) (PBSA), poly(lactic acid) (PLA), and poly[(R)-3-hydroxybutyrate] (P(3HB)). We then determined the morphology, compression properties, and biodegradability of each polyester. The microbeads ranged in size from 25 to 200 μm, were almost spherical, and had smooth surfaces, as verified by scanning electron microscopy (SEM). The single microbeads were subjected to compression tests because their mechanical properties are correlated to their sensory performance. The compression strengths of the four plastic microbeads, which were comparable to those of commonly used microbeads such as polyethylene and polypropylene, were widely distributed. In particular, the PBSA and P(3HB) microbeads were readily biodegradable, as evaluated by enzymatic degradation and sea water degradation tests, indicating their potential as alternatives to conventional microbeads. [ABSTRACT FROM AUTHOR]

We investigated changes in soil microbiota associated with the degradation of poly(butylene adipate- co -terephthalate) (PBAT) film at 30 °C using a polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method. The analysis revealed that fungal flora in soil in the vicinity of film surface (FS) drastically changed after incubation for 7 months. Phylogenetic analysis showed that fungi belonging to the phylum Ascomycota were enriched on the FS. In addition, the presence of PBAT affected the growth of specific fungal species in bulk soil (BS). On the other hand, compositions of the bacterial flora formed in both BS and FS were not strongly influenced by the presence of PBAT. Plant growth-promoting rhizobacteria (PGPR), genera Azospirillum and Mesorhizobium , were detected in both environments, i.e., in BS and FS, during the course of 7-month incubation. In terms of plant growth, the growth of Brassica rapa var. chinensis was not negatively affected in BS after 7 month compared with that in the control soil (CS), indicating that changes in the soil microbiota because of the addition of PBAT have little influence on the growth of B . rapa var. chinensis . [ABSTRACT FROM AUTHOR]

A poly[(R)-3-hydroxybutyrate] [P(3HB)]-degrading bacterium (strain JKCM-AJ-6,1α) was isolated from coastal seawater near the port of Yaizu, Suruga Bay, Japan. The strain grew well in a marine mineral medium supplemented with P(3HB) powder as the sole carbon source. Phylogenetic analysis revealed that the strain JKCM-AJ-6,1α belonged to the genus Shewanella . The isolate was unable to grow at temperatures above 50 °C, and the optimum range of growth temperatures was 30 °C–37 °C; however, the optimum temperature for degradation of P(3HB) was 15 °C. The maximum specific growth rate (μ = 1.0 h −1 ) was attained at a NaCl concentration of 0.2 M, but the strain was able to grow even in the presence of 0.8 M NaCl. This suggests that the strain is a typical marine bacterium. This is the first report showing P(3HB) depolymerase activity in a member of the genus Shewanella . It is concluded that the genus Shewanella may be one of the key bacterial groups involved in the P(3HB) cycle in marine environments. [ABSTRACT FROM AUTHOR]

Abstract: We isolated 12 poly(butylene succinate) (PBSu)-degrading fungi from various soil environments. Among the isolates, the NKCM1706 strain exhibited the fastest degradation rate for the PBSu film (10.5μgcm−2 h−1). Phylogenetic analysis revealed that this strain is closely related to Aspergillus fumigatus (internal transcribed spacer (ITS) identity, 100%). Further, this strain exhibited PBSu-hydrolytic activity in the presence of poly(ɛ-caprolactone) (PCL), PBSu, and poly(butylene succinate-co-adipate) (PBSA). On adding this strain into the soil sample, the PBSu degradation rate accelerated approximately sixfold, suggesting that this strain plays a crucial role in PBSu degradation in actual soil environments. In addition to PBSu, the NKCM1706 strain could degrade PBSA, poly(ethylene succinate) (PESu), poly(3-hydroxybutyrate) (P(3HB)), and PCL. [Copyright &y& Elsevier]

Abstract: Twenty fungi, which all formed a clear zone around the colony on a poly(ethylene succinate) (PESu)-containing medium, were isolated from various environmental samples. Mesophilic strain NKCM1003, with the highest PESu hydrolytic activity among all the isolates, degraded a PESu film at the rate of 21±2μg/cm2/h when it was aerobically incubated at 30°C on a medium containing PESu as the sole carbon source. SEM observations showed that the strain gradually degraded the film starting from the amorphous regions of the surface. Phylogenetic analysis revealed that the strain was closely related to the species Aspergillus clavatus. Zymogram analysis suggested that the secreted enzyme with PESu hydrolytic activity is a P(3HB) depolymerase. The strain also utilized the enzymatic products of PESu, permitting it to grow well. These results indicate that the strain NKCM1003 plays an important role in the PESu-degrading process in the field. [Copyright &y& Elsevier]

• PBADs composed of long-methylene chains and PE have similar thermal and mechanical properties. • PBADs were hydrolyzed to water-soluble products by bacterial degradation. • The hydrolysates of PBADs are easily metabolized by microorganisms. • PBADs composed of long-methylene chains are poorly metabolized by microorganisms. Poly(butylene n -alkylenedionate)s (PBADs), which are polymers that are potentially biodegradable in various environments, exhibit excellent thermal and mechanical properties similar to those of polyethylene because of their long alkyl chains. However, although it has not yet been experimentally verified, it is known that differences in the alkyl chain length affect the biodegradability of PBADs. In this study, we synthesized PBADs with alkylene diacid units, with the number of methylene chains ranging from 11 to 14. We subsequently investigated the relationship between their biodegradability via clear-zone formation and BOD-biodegradation testing and their physical properties, including their structural characteristics, using instrumental analysis. Although the monomers 1,4-butanediol (BD) and α,ω-dicarboxylic acids (DCA) exhibited good biochemical oxygen demand (BOD)-biodegradability, PBADs did not, indicating that PBADs with 11–14 methylene chains do not readily degrade in natural environments. [ABSTRACT FROM AUTHOR]

• Mesophilic actinobacterium Rhodococcus fascians NKCM2511 biodegrades PBAT. • The gene pbath Rf responsible for PBAT degradation was cloned from this strain. • The protein product of pbath Rf , PBATH Rf , degraded PBAT films. • PBATH Rf properties enable biodegradation of PBAT in the actual field conditions. Poly(butylene adipate- co -terephthalate) (PBAT) possesses excellent film-forming ability and biodegradability. Therefore, it is considered to be a promising mulching film material that eliminates the need for recovery. In the applications that require PBAT degradation in the field after use, it is important to understand the biodegradation mechanism at moderate temperatures. We have previously isolated from the soil the mesophilic actinobacteria Rhodococcus fascians NKCM2511 that biodegraded PBAT under moderate temperature conditions (20–30 °C). In this study, to clarify the mechanism of PBAT degradation by the strain NKCM2511, a DNA fragment carrying the gene pbath Rf responsible for the PBAT degradation activity was cloned. The gene encoded a 216-amino-acid-long protein designated as PBATH Rf. Homology modeling revealed that PBATH Rf belongs to the α/β hydrolase fold family, lacking the lid domain covering the active site. PBATH Rf degraded PBAT film at 30 °C at the rate of 0.10 ± 0.03 mg/cm2/d and was capable of degrading several other aliphatic polyester films. Liquid chromatography revealed that PBATH Rf preferentially cleaved the ester bond between 1,4-butanediol and adipic acid rather than that between 1,4-butanediol and terephthalic acid (T). This characteristic of PBATH Rf may explain the low degradation rate of the aliphatic - aromatic copolyester PBAT, compared to the rate of degradation of aliphatic polyesters without T. In addition, liquid chromatography showed that PBATH Rf released T, mono(2-hydroxyethyl) terephthalic acid, and bis(2-hydroxybutyl) terephthalate from an amorphous poly(ethylene terephthalate) (PET) film. However, no significant change in the PET film surface after the treatment with PBATH Rf was found by scanning electron microscopy. This is the first report of an enzyme from the mesophilic actinobacteria Rhodococcus fascians that can hydrolyze various polyesters, including PBAT, and catalyze hydrolysis on the surface of an amorphous PET film. This study also provides insight into the biodegradation mechanism of PBAT in the actual field as it describes an enzyme from a naturally occurring organism that acts in the medium temperature range. [ABSTRACT FROM AUTHOR]

• A plastic-degrading microbe was isolated from plastisphere on marine plastic debris. • The strain was a marine species belonging to the genus Nocardioides. • The isolate formed biofilm on plastics and degraded P(3HB) efficiently. • Genetic analysis revealed that it had a P(3HB) depolymerase gene on the genome. Plastic debris surfaces in marine environments provide novel habitats for marine microbes. This type of microbial community is known as a "plastisphere". Prior metagenomic analyses of plastispheres suggest that the surface of marine plastic debris contain plastic-degrading microbes. Here, we focus on plastisphere as a microbial source. We isolated strain OK12 from plastic bag debris collected from a beach in Japan. The strain grew on a mineral medium supplemented with poly(3-hydroxybutyrate) [P(3HB)] as the sole carbon source. Genetic and biochemical analyses demonstrated that the strain belongs to the genus Nocardioides. In addition, the average nucleotide identity value of the two genomes of the strain OK12 and Nocardioides marinisabuli DSM 18965, a marine species, was 98.3 %, above the 95 % threshold. The strain did not grow above 50 °C, and the optimum temperature for growth was 30 °C. The strain grew and degraded P(3HB) in a broad range of NaCl concentrations (0.01–2.4 M), whereas it did not grow without NaCl, suggesting that the strain is a marine species. The strain degraded the P(3HB) film at a fast rate, despite the fact that the P(3HB) degrading activity in the culture supernatant was low. The strain formed biofilms on the P(3HB) and polypropylene film surfaces. This biofilm formation may have helped the strain to degrade P(3HB). [ABSTRACT FROM AUTHOR]

• A mesophilicactinobacteria, which degrades poly(butylene adipate- co -terephthalate) (PBAT) was isolated from soil. • The isolate grew only in aerobic conditions and degraded PBAT in the temperature range of 20 ˚C to 30 ˚C. • BOD biodegradation testing with the strain revealed it could mineralize PBAT to CO 2. An aliphatic aromatic copolyester, poly(butylene adipate- co -terephthalate) (PBAT) is a chemically synthetic and biodegradable polymer that exhibits good mechanical properties, similar to those of low-density polyethylene (LDPE), and can be a replacement for LDPE as biodegradable mulch films in the agricultural field. Biodegradability of PBAT is stable at high temperature conditions (50 – 60 ˚C) such as compost environments compared to mild temperature conditions (25 – 37 ˚C) such as soil environments. Considering that PBAT could be used in biodegradable agricultural applications such as mulching film, it is important to investigate the biodegradation mechanism at mild temperatures. In this study, a PBAT-degrading bacterium isolated from a soil environment, designated as strain NKCM 2511, was studied in detail. Genetic and biochemical analysis revealed that the strain belongs to the genus Rhodococcus in the phylum Actinobacteria. The strain grew only in aerobic conditions and formed a clear zone on a PBAT containing plate in the temperature range of 20 ˚C to 30 ˚C. Based on biochemical oxygen demand (BOD) biodegradation testing, among 3 PBAT components, adipicacid and terephthalic acid resulted in low growth rate of the strains (5 % and 7 %, incubated at 25 °C for 20 days), whereas 1,4-butanediol resulted in good growth of the strains (55 %). The low BOD biodegradation rate of PBAT by this strain (7 %) may be due to such low rates of terephthalic and adipic acid. Additionally, the PBAT degradation rate was proportional to the growth rate in the presence of various carbon sources. Therefore, the strain was an aerobically mesophilic PBAT-degrading bacterium that expressed the PBAT-degrading enzyme constitutively. To our knowledge, this is the first report on a PBAT-degrading actinobacterial strain in mild conditions. This study provides information to better understand the biodegradation mechanism of PBAT under mild conditions such as in fields. [ABSTRACT FROM AUTHOR]