Enzymatic degradation of polyester films by a cutinase-like enzyme from Pseudozyma antarctica: surface plasmon resonance and atomic force microscopy study

Enzymatic degradation of polylactic acid (PLA)

Environmental concerns arising from the increasing use of polluting plastics highlight polylactic acid (PLA) as a promising eco-friendly alternative. PLA is a biodegradable polyester that can be produced through the fermentation of renewable resources. Together with its excellent properties, suitable for a wide range of applications, the use of PLA has increased significantly over the years and is expected to further grow. However, insufficient degradability under natural conditions emphasizes the need for the exploration of biodegradation mechanisms, intending to develop more efficient techniques for waste disposal and recycling or upcycling. Biodegradation occurs through the secretion of depolymerizing enzymes, mainly proteases, lipases, cutinases, and esterases, by various microorganisms. This review focuses on the enzymatic degradation of PLA and presents different enzymes that were isolated and purified from natural PLA-degrading microorganisms, or recombinantly expressed. The review depicts the main characteristics of the enzymes, including recent advances and analytical methods used to evaluate enantiopurity and depolymerizing activity. While complete degradation of solid PLA particles is still difficult to achieve, future research and improvement of enzyme properties may provide an avenue for the development of advanced procedures for PLA degradation and upcycling, utilizing its building blocks for further applications as envisaged by circular economy principles. KEY POINTS: • Enzymes can be promisingly utilized for PLA upcycling. • Natural and recombinant PLA depolymerases and methods for activity evaluation are summarized. • Approaches to improve enzymatic degradation of PLA are discussed.

Enzymatic Degradation Behavior of Self-Degradable Lipase-Embedded Aliphatic and Aromatic Polyesters and Their Blends

Over the past decade, the preparation of novel materials by enzyme-embedding into biopolyesters has been proposed as a straightforward method to produce self-degrading polymers. This paper reports the preparation and enzymatic degradation of extruded self-degradable films of three different biopolyesters: poly(lactic acid) (PLA), poly(butylene adipate-co-terephthalate) (PBAT), and poly(butylene succinate) (PBS), as well as three binary/ternary blends. Candida antarctica lipase B (CalB) has been employed for the enzyme-embedding procedure, and to the best of our knowledge, the use of this approach in biopolyester blends has not been reported before. The three homopolymers exhibited differentiated degradation and suggested a preferential attack of CalB on PBS films over PBAT and PLA. Moreover, the self-degradable films obtained from the blends showed slow degradation, probably due to the higher content in PLA and PBAT. These observations pave the way for exploring enzymes capable of degrading all blend components or an enzymatic mixture for blend degradation.

Myco-remediation of plastic pollution: current knowledge and future prospects

To date, enumerable fungi have been reported to participate in the biodegradation of several notorious plastic materials following their isolation from soil of plastic-dumping sites, marine water, waste of mulch films, landfills, plant parts and gut of wax moth. The general mechanism begins with formation of hydrophobin and biofilm proceding to secretion of specific plastic degarding enzymes (peroxidase, hydrolase, protease and urease), penetration of three dimensional substrates and mineralization of plastic polymers into harmless products. As a result, several synthetic polymers including polyethylene, polystyrene, polypropylene, polyvinyl chloride, polyurethane and/or bio-degradable plastics have been validated to deteriorate within months through the action of a wide variety of fungal strains predominantly Ascomycota (Alternaria, Aspergillus, Cladosporium, Fusarium, Penicillium spp.). Understanding the potential and mode of operation of these organisms is thus of prime importance inspiring us to furnish an up to date view on all the presently known fungal strains claimed to mitigate the plastic waste problem. Future research henceforth needs to be directed towards metagenomic approach to distinguish polymer degrading microbial diversity followed by bio-augmentation to build fascinating future of waste disposal.

Enhanced biodegradable polyester film degradation in soil by sequential cooperation of yeast-derived esterase and microbial community

The degradation of biodegradable plastics poses a significant environmental challenge and requires effective solutions. In this study, an esterase derived from a phyllosphere yeast Pseudozyma antarctica (PaE) enhanced the degradation and mineralization of poly(butylene succinate-co-adipate) (PBSA) film in soil. PaE was found to substitute for esterases from initial degraders and activate sequential esterase production from soil microbes. The PBSA film pretreated with PaE (PBSA-E) rapidly diminished and was mineralized in soil until day 55 with high CO2 production. Soil with PBSA-E maintained higher esterase activities with enhancement of microbial abundance, whereas soil with inactivated PaE-treated PBSA film (PBSA-inact E) showed gradual degradation and time-lagged esterase activity increases. The fungal genera Arthrobotrys and Tetracladium, as possible contributors to PBSA-film degradation, increased in abundance in soil with PBSA-inact E but were less abundant in soil with PBSA-E. The dominance of the fungal genus Fusarium and the bacterial genera Arthrobacter and Azotobacter in soil with PBSA-E further supported PBSA degradation. Our study highlights the potential of PaE in addressing concerns associated with biodegradable plastic persistence in agricultural and environmental contexts.

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.

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.

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.

Biodegradation of Biodegradable Polymers in Mesophilic Aerobic Environments

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

Ten decadal advances in fungal biology leading towards human well-being

Fungi are an understudied resource possessing huge potential for developing products that can greatly improve human well-being. In the current paper, we highlight some important discoveries and developments in applied mycology and interdisciplinary Life Science research. These examples concern recently introduced drugs for the treatment of infections and neurological diseases; application of -OMICS techniques and genetic tools in medical mycology and the regulation of mycotoxin production; as well as some highlights of mushroom cultivaton in Asia. Examples for new diagnostic tools in medical mycology and the exploitation of new candidates for therapeutic drugs, are also given. In addition, two entries illustrating the latest developments in the use of fungi for biodegradation and fungal biomaterial production are provided. Some other areas where there have been and/or will be significant developments are also included. It is our hope that this paper will help realise the importance of fungi as a potential industrial resource and see the next two decades bring forward many new fungal and fungus-derived products.

Disruption of protease A and B orthologous genes in the basidiomycetous yeast Pseudozyma antarctica GB-4(0) yields a stable extracellular biodegradable plastic-degrading enzyme

The yeast Pseudozyma antarctica (currently designated Moesziomyces antarcticus) secretes a xylose-induced biodegradable plastic-degrading enzyme (PaE). To suppress degradation of PaE during production and storage, we targeted the inhibition of proteolytic enzyme activity in P. antarctica. Proteases A and B act as upper regulators in the proteolytic network of the model yeast, Saccharomyces cerevisiae. We searched for orthologous genes encoding proteases A and B in the genome of P. antarctica GB-4(0) based on the predicted amino acid sequences. We found two gene candidates, PaPRO1 and PaPRO2, with conserved catalytically important domains and signal peptides indicative of vacuolar protease function. We then prepared gene-deletion mutants of strain GB-4(0), ΔPaPRO1 and ΔPaPRO2, and evaluated PaE stability in culture by immunoblotting analysis. Both mutants exhibited sufficient production of PaE without degradation fragments, while the parent strain exhibited the degradation fragments. Therefore, we concluded that the protease A and B orthologous genes are related to the degradation of PaE. To produce a large quantity of PaE, we made a PaPRO2 deletion mutant of a PaE-overexpression strain named XG8 by introducing a PaE high-production cassette into the strain GB-4(0). The ΔPaPRO2 mutant of XG8 was able to produce PaE without the degradation fragments during large-scale cultivation in a 3-L jar fermenter for 3 days at 30°C. After terminating the agitation, the PaE activity in the XG8 ΔPaPRO2 mutant culture was maintained for the subsequent 48 h incubation at 25°C regardless of remaining cells, while activity in the XG8 control was reduced to 55.1%. The gene-deleted mutants will be useful for the development of industrial processes of PaE production and storage.

Construction of a Pseudozyma antarctica strain without foreign DNA sequences (self-cloning strain) for high yield production of a biodegradable plastic-degrading enzyme

The basidiomycetous yeast Pseudozyma antarctica GB-4(0) esterase (PaE) is a promising candidate for accelerating degradation of used biodegradable plastics (BPs). To increase safety and reduce costs associated with the use of PaE, we constructed a self-cloning strain with high-PaE productivity. A Lys12 gene (PaLYS12)-deleted lysine auxotroph strain GB4-(0)-L1 was obtained from GB-4(0) by ultraviolet mutagenesis and nystatin enrichment. Subsequently, the PaE gene (PaCLE1) expression cassette consisting of GB-4(0)-derived PaCLE1, under the control of a xylose-inducible xylanase promoter with PaLYS12, was randomly introduced into the GB4-(0)-L1 genome. A PaE high-producing strain, PGB474, was selected from among the transformants by high throughput double-screening based on its ability to degrade emulsified polybutylene succinate-co-adipate. Quantitative PCR revealed that four copies of the PaE gene expression cassette were introduced into the PGB474 genome. PGB474 produced 2.0 g/L of PaE by xylose-fed-batch cultivation using a 3-L jar fermentor for 72 h.

Disease severity enhancement by an esterase from non-phytopathogenic yeast Pseudozyma antarctica and its potential as adjuvant for biocontrol agents

The phylloplane yeast Pseudozyma antarctica secretes an esterase, named PaE, and xylanase when cultivated with xylose. We previously observed that the lipophilic layer of Micro-Tom tomato leaves became thinner after the culture filtrate treatment. The leaves developed reduced water-holding ability and became wilted. In this study, the purified enzymes were spotted on Micro-Tom leaves. PaE, but not xylanase, thinned the lipophilic layer of leaves and decreased leaf resistance to the phytopathogenic fungus Botrytis cinerea. Disease severity increased significantly in detached leaves and potted plants treated with the culture filtrate and B. cinerea spores compared with those treated with inactivated enzyme and B. cinerea alone. Spore germination ratios, numbers of penetrating fungal hyphae in the leaves, and fungal DNA contents also increased significantly on the detached leaves. Japanese knotweed (Fallopia japonica), a serious invasive alien weed in Europe and North America, also became susceptible to infection by the rust pathogen Puccinia polygoni-amphibii var. tovariae following the culture filtrate treatment. The culture filtrate treatment increased disease development in plants induced by both phytopathogenic fungi. Our results suggest that P. antarctica culture filtrate could be used as an adjuvant for sustainable biological weed control using phytopathogenic fungi.

Light-Addressable Potentiometric Sensors Using ZnO Nanorods as the Sensor Substrate for Bioanalytical Applications

Light-addressable potentiometric sensors (LAPS) are of great interest in bioimaging applications such as the monitoring of concentrations in microfluidic channels or the investigation of metabolic and signaling events in living cells. By measuring the photocurrents at electrolyte-insulator-semiconductor (EIS) and electrolyte-semiconductor structures, LAPS can produce spatiotemporal images of chemical or biological analytes, electrical potentials and impedance. However, its commercial applications are often restricted by their limited AC photocurrents and resolution of LAPS images. Herein, for the first time, the use of 1D semiconducting oxides in the form of ZnO nanorods for LAPS imaging is explored to solve this issue. A significantly increased AC photocurrent with enhanced image resolution has been achieved based on ZnO nanorods, with a photocurrent of 45.7 ± 0.1 nA at a light intensity of 0.05 mW, a lateral resolution as low as 3.0 μm as demonstrated by images of a PMMA dot on ZnO nanorods and a pH sensitivity of 53 mV/pH. The suitability of the device for bioanalysis and bioimaging was demonstrated by monitoring the degradation of a thin poly(ester amide) film with the enzyme α-chymotrypsin using LAPS. This simple and robust route to fabricate LAPS substrates with excellent performance would provide tremendous opportunities for bioimaging.

Enzymatic degradation of poly-butylene succinate-co-adipate film in rice husks by yeast Pseudozyma antarctica in indoor conditions

Agricultural mulch films made from biodegradable polymers (BP) have been used to decrease the burden of plastic waste recovery and recycling. However, their degradations depend largely on environmental conditions and sometimes do not proceed as desired. Yeast strains of Pseudozyma antarctica often isolated from rice husks were found to secrete an esterase to degrade BP films. Poly-butylene succinate-co-adipate (PBSA) films buried in unsterilized rice husks with 60% (w/w) moisture degraded rapidly compared to that buried in field soil. The type strain of P. antarctica JCM 10317 added as cell suspension onto sterilized rice husks with PBSA film grew rapidly forming filamentous growth on the surface of rice husks and films. BP-degrading enzyme secreted by the growing cells was adsorbed on the surface of film and decomposed the film. Addition of rice husk-derived P. antarctica strains also showed BP film degradation activity in sterilized rice husks. In the light of these findings, we suggest that techniques for disposal of used BPs which combine plastics with unutilized residual plant materials piled at the side of agricultural fields be developed.

Photo-triggered enzymatic degradation of biodegradable polymers

Control over the initiation of enzymatic degradation of biodegradable polymers was demonstrated by tuning the solid-molten state of a surface coated azo-compound with light irradiation.

Isolation and screening of biopolymer-degrading microorganisms from northern Thailand

Forty agricultural soils were collected from Chiang Mai and Lampang provinces in northern Thailand. Bacteria, actinomycetes and fungi were isolated and screened for their ability to degrade polylactic acid (PLA), polycaprolactone (PCL) and poly(butylene succinate) (PBS) by the agar diffusion method. Sixty-seven actinomycetes, seven bacteria and five fungal isolates were obtained. The majority of actinomycetes were Streptomyces based on morphological characteristic, chemotaxonomy and 16S rRNA gene data. Seventy-nine microorganisms were isolated from 40 soil samples. Twenty-six isolates showed PLA-degradation (32.9 %), 44 isolates showed PBS-degradation (55.7 %) and 58 isolates showed PCL-degradation (73.4 %). Interestingly, 16 isolates (20.2 %) could degrade all three types of bioplastics used in this study. The Amycolatopsis sp. strain SCM_MK2-4 showed the highest enzyme activity for both PLA and PCL, 0.046 and 0.023 U/mL, respectively. Moreover, this strain produced protease, esterase and lipase on agar plates. Approximately, 36.7 % of the PLA film was degraded by Amycolatopsis sp. SCM_MK2-4 after 7 days of cultivation at 30 °C in culture broth.

Assessment of epiphytic yeast diversity in rice (Oryza sativa) phyllosphere in Thailand by a culture-independent approach

The epiphytic yeast diversity in rice phyllosphere in Thailand was investigated by a culture-independent technique based on the RFLP pattern and the sequence of the D1/D2 domain of the large subunit rRNA gene. Forty-four samples of rice leaf were collected randomly from six provinces. The DNA was extracted from leaf washing samples and the D1/D2 domain was amplified using PCR technique. The PCR products were cloned and then screened by colony PCR. Of total 1121 clones, 451 clones (40.2 %) revealed the D1/D2 domain sequences closely related to sequences of yeasts in GenBank, and they were clustered into 45 operational taxonomic units (OTUs) at 99 % homology. Of total yeast related clones, 329 clones (72.9 %) were identified as nine known yeast species, which consisted of 314 clones (8 OTUs) in the phylum Basidiomycota including Bullera japonica, Pseudozyma antarctica, Pseudozyma aphidis, Sporobolomyces blumeae, Sporobolomyces carnicolor and Sporobolomyces oryzicola and 15 clones (6 OTUs) in the phylum Ascomycota including Metschnikowia koreensis, Meyerozyma guilliermondii and Wickerhamomyces anomalus. The D1/D2 sequences (122 clones) that could not be identified as known yeast species were closest to 3 and 14 species in Ascomycota and Basidiomycota, respectively, some of which may be new yeast species. The most predominant species detected was P. antarctica (42.6 %) followed by B. japonica (25.9 %) with 63.6 and 22.7 % frequency of occurrence, respectively. The results of OTU richness of each sampling location revealed that climate condition and sampling location could affect epiphytic yeast diversity in rice phyllosphere.

Purification, characterization, and cloning of the gene for a biodegradable plastic-degrading enzyme from Paraphoma-related fungal strain B47-9

Paraphoma-related fungal strain B47-9 secreted a biodegradable plastic (BP)-degrading enzyme which amounted to 68 % (w/w) of the total secreted proteins in a culture medium containing emulsified poly(butylene succinate-co-adipate) (PBSA) as sole carbon source. The gene for this enzyme was found to be composed of an open reading frame consisting of 681 nucleotides encoding 227 amino acids and two introns. Southern blot analysis showed that this gene exists as a single copy. The deduced amino acid sequence suggested that this enzyme belongs to the cutinase (E.C.3.1.1.74) family; thus, it was named P araphoma-related fungus cutinase-like enzyme (PCLE). It degraded various types of BP films, such as poly(butylene succinate), PBSA, poly(butylene adipate-co-terephthalate), poly(ε-caprolactone), and poly(DL-lactic acid). It has a molecular mass of 19.7 kDa, and an optimum pH and temperature for degradation of emulsified PBSA of 7.2 and 45 °C, respectively. Ca(2+) ion at a concentration of about 1.0 mM markedly enhanced the degradation of emulsified PBSA.