The potential of cold-adapted microorganisms for biodegradation of bioplastics

Integrated assessment of the chemical, microbiological and ecotoxicological effects of a bio-packaging end-of-life in compost

The present study aimed to i) assess the disintegration of a novel bio-packaging during aerobic composting (2 and 6 % tested concentrations) and evaluate the resulting compost ii) analyse the ecotoxicity of bioplastics residues on earthworms; iii) study the microbial communities during composting and in 'earthworms' gut after their exposure to bioplastic residues; iv) correlate gut microbiota with ecotoxicity analyses; v) evaluate the chemico-physical characterisation of bio-packaging after composting and earthworms' exposure. Both tested concentrations showed disintegration of bio-packaging close to 90 % from the first sampling time, and compost chemical analyses identified its maturity and stability at the end of the process. Ecotoxicological assessments were then conducted on Eisenia fetida regarding fertility, growth, genotoxic damage, and impacts on the gut microbiome. The bioplastic residues did not influence the earthworms' fertility, but DNA damages were measured at the highest bioplastic dose tested. Furthermore bioplastic residues did not significantly affect the bacterial community during composting, but compost treated with 2 % bio-packaging exhibited greater variability in the fungal communities, including Mortierella, Mucor, and Alternaria genera, which can use bioplastics as a carbon source. Moreover, bioplastic residues influenced gut bacterial communities, with Paenibacillus, Bacillus, Rhizobium, Legionella, and Saccharimonadales genera being particularly abundant at 2 % bioplastic concentration. Higher concentrations affected microbial composition by favouring different genera such as Pseudomonas, Ureibacillus, and Streptococcus. For fungal communities, Pestalotiopsis sp. was found predominantly in earthworms exposed to 2 % bioplastic residues and is potentially linked to its role as a microplastics degrader. After composting, Attenuated Total Reflection analysis on bioplastic residues displayed evidence of ageing with the formation of hydroxyl groups and amidic groups after earthworm exposure.

Timeframe of aerobic biodegradation of bioplastics differs under standard conditions and conditions simulating technological composting with biowaste

To determine the actual timeframe of biodegradation, bioplastics (BPs) (based on polylactic acid (PLA), starch (FS), polybutylene succinate (PBS), cellulose (Cel)) were degraded with biowaste (B), which simulates real substrate technological conditions during composting. For comparison, standard conditions (with mature compost (C)) were also applied. The 90-day aerobic tests, both with C or B, were carried out at 58 ± 2 °C. This comparison enables understanding of how BPs behave in real substrate conditions and how C and B affect the time or completeness of degradation based on oxygen consumption (OC) for BPs, the ratio of OC to theoretical oxygen consumption (OC/Th-O2), and the decrease in volatile solids (VS). Additionally, for deeper insight into the biodegradation process, microscopic, microbial (based on 16S rDNA), FTIR, and mechanical (tensile strength, elongation at break) analyses were performed. There was no association between the initial mechanical properties of BPs and the time necessary for their biodegradation. BPs lost their mechanical properties and remained visible for a shorter time when degraded with C than with B. OC for Cel, FS, PLA, and PBS biodegradation was 1143, 1654, 1748, and 1211g O2/kg, respectively, which amounted to 83, 70, 69, and 60% of the theoretical OC (Th-O2), respectively. Intensive OC took place at the same time as an intensive decrease in VS content. With C, Cel was most susceptible to biodegradation (completely biodegrading within 11 days), and PLA was least susceptible (requiring 70 days for complete biodegradation). With B, however, the time required for biodegradation was generally longer, and the differences in the time needed for complete biodegradation were smaller, ranging from 45 d (FS) to 75 d (PLA). The use of C or B had the greatest effect on Cel biodegradation (10 d vs 62 d, respectively), and the least effect on PLA (70 d vs 75 d). Specific bacterial and fungal community structures were identified as potential BP biodegraders; the communities depended on the type of BPs and the substrate conditions. In conclusion, the time needed for biodegradation of these BPs varied widely depending on the specific bioplastic and the substrate conditions; the biodegradability decreased in the following order: Cel ≫ FS ≫ PBS ≫ PLA with C and FS ≫ Cel = PBS ≫ PLA with B. The biodegradability ranking of BPs with B was assumed to be ultimate as it simulates the real substrate conditions during composting. However, all of the BPs completely biodegraded in less than 90 days.

Biodegradation: the best solution to the world problem of discarded polymers

The widespread use of polymers has made our lives increasingly convenient by offering a more convenient and dependable material. However, the challenge of efficiently decomposing these materials has resulted in a surge of polymer waste, posing environment and health risk. Currently, landfill and incineration treatment approaches have notable shortcomings, prompting a shift towards more eco-friendly and sustainable biodegradation approaches. Biodegradation primarily relies on microorganisms, with research focusing on both solitary bacterial strain and multi-strain communities for polymer biodegradation. Furthermore, directed evolution and rational design of enzyme have significantly contributed to the polymer biodegradation process. However, previous reviews often undervaluing the role of multi-strain communities. In this review, we assess the current state of these three significant fields of research, provide practical solutions to issues with polymer biodegradation, and outline potential future directions for the subject. Ultimately, biodegradation, whether facilitated by single bacteria, multi-strain communities, or engineered enzymes, now represents the most effective method for managing waste polymers.

Biodegradation of polystyrene (PS) and polypropylene (PP) by deep-sea psychrophilic bacteria of Pseudoalteromonas in accompany with simultaneous release of microplastics and nanoplastics

Plastics dumped in the environment are fragmented into microplastics by various factors (UV, weathering, mechanical abrasion, animal chewing, etc.). However, little is known about plastic fragmentation and degradation mediated by deep-sea microflora. To obtain deep-sea bacteria that can degrade plastics, we enriched in situ for 1 year in the Western Pacific using PS as a carbon source. Subsequently, two deep-sea prevalent bacteria of the genus Pseudoalteromonas (Pseudoalteromonas lipolytica and Pseudoalteromonas tetraodonis) were isolated after 6 months enrichment in the laboratory under low temperature (15 °C). Both showed the ability to degrade polystyrene (PS) and polypropylene (PP), and biodegradation accelerated the generation of micro- and nanoplastics. Plastic biodegradation was evidenced by the formation of carboxyl and carboxylic acid groups, heat resistance decrease and plastic weight loss. After 80 days incubation at 15 °C, the microplastic concentration of PS and PP could be up to 1.94 × 107/L and 5.83 × 107/L, respectively, and the proportion of nanoplastics (< 1 μm) could be up to 65.8 % and 73.6 %. The film weight loss were 5.4 % and 4.5 % of the PS films, and 2.3 % and 1.8 % of the PP films by P. lipolytica and P. tetraodonis, respectively; thus after discounting the weight loss of microplastics, the only 3.9 % and 2.8 % of the PS films, and 1.3 % and 0.7 % of the PP films, respectively, were truly degraded by the two bacteria respectively after 80 days of incubation. This study highlights the role of Pseudoalteromonas in fragmentation and degradation of plastics in cold dark pelagic deep sea.

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.

Exploring the hidden environmental pollution of microplastics derived from bioplastics: A review

Bioplastics might be an ecofriendly alternative to traditional plastics. However, recent studies have emphasized that even bioplastics can end up becoming micro- and nano-plastics due to their degradation under ambient environmental conditions. Hence, there is an urgent need to assess the hidden environmental pollution caused by bioplastics. However, little is known about the evolutionary trends of bibliographic data, degradation pathways, formation, and toxicity of micro- and nano-scaled bioplastics originating from biodegradable polymers such as polylactic acid, polyhydroxyalkanoates, and starch-based plastics. Therefore, the prime objective of the current review was to investigate evolutionary trends and the latest advancements in the field of micro-bioplastic pollution. Additionally, it aims to confront the limitations of existing research on microplastic pollution derived from the degradation of bioplastic wastes, and to understand what is needed in future research. The literature survey revealed that research focusing on micro- and nano-bioplastics has begun since 2012. This review identifies novel insights into microbioplastics formation through diverse degradation pathways, including photo-oxidation, ozone-induced degradation, mechanochemical degradation, biodegradation, thermal, and catalytic degradation. Critical research gaps are identified, including defining optimal environmental conditions for complete degradation of diverse bioplastics, exploring micro- and nano-bioplastics formation in natural environments, investigating the global occurrence and distribution of these particles in diverse ecosystems, assessing toxic substances released during bioplastics degradation, and bridging the disparity between laboratory studies and real-world applications. By identifying new trends and knowledge gaps, this study lays the groundwork for future investigations and sustainable solutions in the realm of sustainable management of bioplastic wastes.

Bacterial degradation kinetics of poly(Ɛ-caprolactone) (PCL) film by Aquabacterium sp. CY2-9 isolated from plastic-contaminated landfill

Despite the identification of numerous bioplastic-degrading bacteria, the inconsistent rate of bioplastic degradation under differing cultivation conditions limits the intercomparison of results on biodegradation kinetics. In this study, we isolated a poly (Ɛ-caprolactone) (PCL)-degrading bacterium from a plastic-contaminated landfill and determined the principle-based biodegradation kinetics in a confined model system of varying cultivation conditions. Bacterial degradation of PCL films synthesized by different polymer number average molecular weights (M_n) and concentrations (% w/v) was investigated using both solid and liquid media at various temperatures. As a result, the most active gram-negative bacterial strain at ambient temperature (28 °C), designated CY2-9, was identified as Aquabacterium sp. Based on 16 S rRNA gene analysis. A clear zone around the bacterial colony was apparently exhibited during solid cultivation, and the diameter sizes increased with incubation time. During biodegradation processes in the PCL film, the thermal stability declined (determined by TGA; weight changes at critical temperature), whereas the crystalline proportion increased (determined by DSC; phase transition with temperature increment), implying preferential degradation of the amorphous region in the polymer structure. The surface morphologies (determined by SEM; electron optical system) were gradually hydrolyzed, creating destruction patterns as well as alterations in functional groups on film surfaces (determined by FT-IR; infrared spectrum of absorption or emission). In the kinetic study based on the weight loss of the PCL film (4.5 × 10⁴ Da, 1% w/v), ∼1.5 (>±0.1) × 10^-1 day^-1 was obtained from linear regression for both solid and liquid media cultivation at 28 °C. The biodegradation efficiencies increased proportionally by a factor of 2.6-7.9, depending on the lower polymer number average molecular weight and lower concentration. Overall, our results are useful for measuring and/or predicting the degradation rates of PCL films by microorganisms in natural environments.

Discovery of plastic-degrading microbial strains isolated from the alpine and Arctic terrestrial plastisphere

Increasing plastic production and the release of some plastic in to the environment highlight the need for circular plastic economy. Microorganisms have a great potential to enable a more sustainable plastic economy by biodegradation and enzymatic recycling of polymers. Temperature is a crucial parameter affecting biodegradation rates, but so far microbial plastic degradation has mostly been studied at temperatures above 20°C. Here, we isolated 34 cold-adapted microbial strains from the plastisphere using plastics buried in alpine and Arctic soils during laboratory incubations as well as plastics collected directly from Arctic terrestrial environments. We tested their ability to degrade, at 15°C, conventional polyethylene (PE) and the biodegradable plastics polyester-polyurethane (PUR; Impranil®); ecovio® and BI-OPL, two commercial plastic films made of polybutylene adipate-co-terephthalate (PBAT) and polylactic acid (PLA); pure PBAT; and pure PLA. Agar clearing tests indicated that 19 strains had the ability to degrade the dispersed PUR. Weight-loss analysis showed degradation of the polyester plastic films ecovio® and BI-OPL by 12 and 5 strains, respectively, whereas no strain was able to break down PE. NMR analysis revealed significant mass reduction of the PBAT and PLA components in the biodegradable plastic films by 8 and 7 strains, respectively. Co-hydrolysis experiments with a polymer-embedded fluorogenic probe revealed the potential of many strains to depolymerize PBAT. Neodevriesia and Lachnellula strains were able to degrade all the tested biodegradable plastic materials, making these strains especially promising for future applications. Further, the composition of the culturing medium strongly affected the microbial plastic degradation, with different strains having different optimal conditions. In our study we discovered many novel microbial taxa with the ability to break down biodegradable plastic films, dispersed PUR, and PBAT, providing a strong foundation to underline the role of biodegradable polymers in a circular plastic economy.

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.

A polyesterase from the Antarctic bacterium Moraxella sp. degrades highly crystalline synthetic polymers

The uncontrolled release of plastics in the environment has rendered them ubiquitous around the planet, threatening the wildlife and human health. Biodegradation and valorization of plastics has emerged as an eco-friendly alternative to conventional management techniques. Discovery of novel polymer-degrading enzymes with diversified properties is hence an important task in order to explore different operational conditions for plastic-waste upcycling. In the present study, a barely studied psychrophilic enzyme (MoPE) from the Antractic bacterium Moraxella sp. was heterologously expressed, characterized and its potential in polymer degradation was further investigated. Based on its amino acid composition and structure, MoPE resembled PET-degrading enzymes, sharing features from both mesophilic and thermophilic homologues. MoPE hydrolyzes non-biodegradable plastics, such as polyethylene terephthalate and polyurethane, as well as biodegradable synthetic polyesters, such as polycaprolactone, polyhydroxy butyrate, polybutylene succinate and polylactic acid. The mass fraction crystallinity of the aliphatic polymers tested ranged from 11% to 64% highlighting the potential of the enzyme to hydrolyze highly crystalline plastics. MoPE was able to degrade different types of amorphous and semi-crystalline PET, releasing water-soluble monomers and showed synergy with a feruloyl esterase of the tannase family for the release of terephthalic acid. Based on the above, MoPE was characterized as a versatile psychrophilic polyesterase demonstrating a broad-range plastics degradation potential.

Identification of novel extracellular putative chitinase and hydrolase from Geomyces sp. B10I with the biodegradation activity towards polyesters

Cold-adapted filamentous fungal strain Geomyces sp. B10I has been reported to decompose polyesters such as poly(e-caprolactone) (PCL), poly(butylene succinate) (PBS) and poly(butylene succinate-co-butylene adipate) (PBSA). Here, we identified the enzymes of Geomyces sp. B10I, which appear to be responsible for its biodegradation activity. We compared their amino acid sequences with sequences of well-studied fungal enzymes. Partial purification of an extracellular mixture of the two enzymes, named hydrGB10I and chitGB10I, using ammonium sulfate precipitation and ionic exchange chromatography gave 14.16-fold purity. The amino acid sequence of the proteins obtained from the MALDI-TOF analysis determined the molecular mass of 77.2 kDa and 46.5 kDa, respectively. Conserved domain homology analysis revealed that both proteins belong to the class of hydrolases; hydrGB10I belongs to the glycosyl hydrolase 81 superfamily, while chitGB10I contains the domain of the glycosyl hydrolase 18 superfamily. Phylogenetic analysis suggests a distinct nature of the hydrGB10I and chitGB10I of Geomyces sp. B10I when compared with other fungal polyester-degrading enzymes described to date.