Back to the Future: Decomposability of a Biobased and Biodegradable Plastic in Field Soil Environments and Its Microbiome under Ambient and Future Climates

PHA Microplastic Aging Decreases N2O Sink Capacity: Released γ-Butyrolactone Decouples Denitrifying Electron Transfer and Oxidative Phosphorylation

Bacterial denitrification is a main pathway for soil N2O sinks, which is crucial for assessing and controlling N2O emissions. Biobased polyhydroxyalkanoate (PHA) microplastic particles (MPs) degrade slowly in conventional environments, remaining inert for extended periods. However, the impacts of PHA microplastic aging on the bacterial N2O sink capacity before degradation remain poorly understood. Here, the soil model strain Paracoccus denitrificans was exposed to 0.05-0.5% (w/w) virgin and aged PHA MPs. Although no significant changes in the molecular weights were observed, aged PHA MPs hindered cell growth and N2O reduction rates, leading to a surge in N2O emissions. 1H NMR spectroscopy and UPLC-QTOF-MS analysis identified γ-butyrolactone as the key component released from aged PHA MPs. Metabolic verifications at the cellular level confirmed its inhibition on the N2O sink and ATP synthesis. The γ-butyrolactone that protonated and hydrolyzed spontaneously in the periplasm would compete for protons with ATPase and destroy the coupling between denitrifying electron transfer and oxidative phosphorylation. Consequently, energy-deficient cells reduced the electron supply for N2O reduction, which did not contribute to energy conservation. This work unveils a novel mechanism by which PHA microplastic aging impairs the bacterial N2O sink and highlights the need to consider environmental risks posed by biobased microplastic aging.

Feels Like Home: A Biobased and Biodegradable Plastic Offers a Novel Habitat for Diverse Plant Pathogenic Fungi in Temperate Forest Ecosystems

Poly(butylene succinate-co-adipate) (PBSA), a biodegradable plastic, is significantly colonized and degraded by soil microbes under natural field conditions, especially by fungal plant pathogens, raising concerns about potential economic losses. This study hypothesizes that the degradation of biodegradable plastics may increase the presence and abundance of plant pathogens by serving as an additional carbon source, ultimately posing a risk to forest ecosystems. We investigated (i) fungal plant pathogens during the exposure of PBSA in European broadleaved and coniferous forests (two forest types), with a specific focus on potential risk to tree health, and (ii) the response of such fungi to environmental factors, including tree species, soil pH, nutrient availability, moisture content, and the physicochemical properties of leaf litter layer. Next-generation sequencing (NGS) revealed that PBSA harbored a total of 318 fungal plant pathogenic amplicon sequence variants (ASVs) belonging to 108 genera. Among the identified genera (Alternaria, Nectria, Phoma, Lophodermium, and Phacidium), some species have been reported as causative agents of tree diseases. Plenodomus was present in high relative abundances on PBSA, which have not previously been associated with disease in broadleaved and coniferous forests. Furthermore, the highest number of fungal plant pathogens were detected at 200 days of PBSA exposure (112 and 99 fungal plant pathogenic ASV on PBSA degraded under Q. robur and F. sylvatic-dominated forest, respectively), which was double compared mature leaves and needles from the same forest sites. These findings suggest that PBSA attracts fungal plant pathogens in forests as an additional carbon source, potentially leading to increased disease outbreaks and disrupting the stability of forest ecosystems. The fungal plant pathogenic community compositions were mainly shaped by forest type, PBSA exposure time, site locations, leaf litter layer water content, and N:P ratio from leaf litter layer in both forest types. This study provides valuable insights into the potential risks posed by biodegradable plastic degradation in forests after 200 and 400 days of exposure, respectively. Further comprehensive evaluations of their effects on tree health and ecosystems, ideally on a long-term basis, are needed. These evaluations should include integrating microbial investigation, soil health monitoring, and ecosystem interaction assessments. Nevertheless, it should be noted that our interpretation of plant pathogens is solely based on high-throughput sequencing, bioinformatics, and annotation tools.

Unveiling the impacts of biodegradable microplastics on cadmium toxicity, translocation, transformation, and metabolome in lettuce

Biodegradable microplastics (BMPs) may impact the environmental fate and ecotoxicity of Cd, but the effect mechanism in soil-plant system remain poorly understood. This study investigated the impact of BMPs (poly(lactic acid) (PLA) and poly(butylene adipate terephthalate) (PBAT) microplastics) on the Cd toxicity, translocation, transformation, and metabolome in lettuce (Lactuca sativa L.) by pot experiments. The results show that co-exposure to BMPs and Cd synergistically inhibited the shoot growth. 0.2 % PLA MPs enhanced but 2.5 % PLA MPs inhibited the photosynthesis; however, the dose of PBAT MPs was negatively correlated with the content of chlorophyll a. Moreover, the presence of 2.5 % PBAT MPs increased the nitrate content of leaves by 9.5 % compared to single Cd exposure. The partial least squares path model (PLS-PM) indicates that BMPs exacerbated the inhibitory effects of Cd on lettuce growth. PLA MPs enhanced K, Ca, Cu, and Zn accumulation in root stele, whereas PBAT MPs promoted Fe and Mn enrichment in epidermis. Furthermore, co-exposure resulted in higher inorganic and water-soluble Cd proportions in shoots. PLA MPs elevated Cd contents in cell wall fractions of both roots and shoots, while PBAT MPs increased Cd contents in shoot cell walls and root cells and soluble Cd ratio in shoots. BMPs enhanced Cd toxicity and bioaccumulation by downregulating the expression of ABC transporters and phenylpropanoid biosynthesis pathways, and the relative abundance of related metabolites.

A state-of-the-art review of environmental behavior and potential risks of biodegradable microplastics in soil ecosystems: Comparison with conventional microplastics

As the use of biodegradable plastics becomes increasingly widespread, their environmental behaviors and impacts warrant attention. Unlike conventional plastics, their degradability predisposes them to fragment into microplastics (MPs) more readily. These MPs subsequently enter the terrestrial environment. The abundant functional groups of biodegradable MPs significantly affect their transport and interactions with other contaminants (e.g., organic contaminants and heavy metals). The intermediates and additives released from depolymerization of biodegradable MPs, as well as coexisting contaminants, induce alterations in soil ecosystems. These processes indicate that the impacts of biodegradable MPs on soil ecosystems might significantly diverge from conventional MPs. However, an exhaustive and timely comparison of the environmental behaviors and effects of biodegradable and conventional MPs within soil ecosystems remains scarce. To address this gap, the Web of Science database and bibliometric software were utilized to identify publications with keywords containing biodegradable MPs and soil. Moreover, this review comprehensively summarizes the transport behavior of biodegradable MPs, their role as contaminant carriers, and the potential risks they pose to soil physicochemical properties, nutrient cycling, biota, and CO2 emissions as compared with conventional MPs. Biodegradable MPs, due to their great transport and adsorption capacity, facilitate the mobility of coexisting contaminants, potentially inducing widespread soil and groundwater contamination. Additionally, these MPs and their depolymerization products can disrupt soil ecosystems by altering physicochemical properties, increasing microbial biomass, decreasing microbial diversity, inhibiting the development of plants and animals, and increasing CO2 emissions. Finally, some perspectives are proposed to outline future research directions. Overall, this study emphasizes the pronounced effects of biodegradable MPs on soil ecosystems relative to their conventional counterparts and contributes to the understanding and management of biodegradable plastic contamination within the terrestrial ecosystem.

Research progress on degradation of biodegradable micro-nano plastics and its toxic effect mechanism on soil ecosystem

Biodegradable plastics (BPs) are known to decompose into micro-nano plastics (BMNPs) more readily than conventional plastics (CPs). Given the environmental risks posed by BMNPs in soil ecosystems, their impact has garnered increasing attention. However, research focusing on the toxic effects of BMNPs on soils remains relatively limited. The degradation process and duration of BMNPs in soil are influenced by numerous factors, which directly impact the toxic effects of BMNPs. This highlights the urgent need for further research. In this context, this review delineates the classification of BPs, investigates the degradation processes of BPs along with their influencing factors, summarizes the toxic effects on soil ecosystems, and explores the potential mechanisms that underlie these toxic effects. Finally, it provides an outlook on related research concerning BMNPs in soil. The results indicate that specific BMNPs release additives at a faster rate during decomposition, degradation, and aging, with certain compounds exhibiting increased bioavailability. Importantly, a substantial body of research has shown that BMNPs generally manifest more pronounced toxic effects in comparison to conventional micro-nano plastics (CMNPs). The toxic effects associated with BMNPs encompass a decline in soil quality and microbial biomass, disruption of nutrient cycling, inhibition of plant root growth, and negative impacts on invertebrate reproduction, survival, and fertilization rates. The rough and complex surfaces of BMNPs contribute to increased mechanical damage to tested organisms, enhance absorption by microorganisms, and disrupt normal physiological functions. Notably, the toxic effects of BMNPs on soil ecosystems are influenced by factors including concentration, type of BMNPs, exposure conditions, degradation products, and the nature of additives used. Therefore, it is crucial to standardize detection technologies and toxicity testing conditions for BMNPs. In conclusion, this review provides scientific evidence that supports effective prevention and management of BMNP pollution, assessment of its ecological risks, and governance of BMNPs-related products.

Wet-dry or freeze-thaw alternation can regulate the impacts of farmland plastic pollution on soil bacterial communities and functions

The persistence of farmland plastic pollution has raised significant concerns regarding its potential long-term impacts on soil health in the context of global climate change. However, there are still gaps in the understanding of the impacts of plastic residues on soil microbial communities and functions in agricultural environments under unstable and extreme climatic conditions. In this study, the effects of plastic residues (two types and three shapes) on farmland soil bacterial communities and functions across varying environmental conditions were investigated through microscopic experiments. The results revealed that plastic residues subjected to wet-dry or freeze-thaw alternations exhibited greater degradation compared to those under natural conditions. The effects of plastic residue types and shapes on soil bacterial diversity and function were regulated by environmental factors. The plastic residues significantly reduced the stability of the bacterial network under natural condition (P < 0.05), whereas the opposite phenomenon was observed under wet-dry or freeze-thaw alternating conditions. Compared to under natural condition, lower numbers of bacterial functional pathways exhibiting significant differences due to plastic residues were observed under wet-dry or freeze-thaw alternating conditions. Significant associations were observed between soil bacterial communities and functions and various soil physicochemical properties under natural conditions (P < 0.05), and most of these associations were attenuated in the wet-dry or freeze-thaw alternations. This study demonstrated the potential impacts of plastic pollution on farmland soil microbiomes, which could be modulated by both residue characteristics and climatic conditions. Specifically, extreme environments could mitigate plastic-pollution-driven influences on soil microbiomes.

Biodegradation of poly(butylene adipate terephthalate) and poly(vinyl alcohol) within aquatic pathway

Understanding the environmental fate of biodegradable plastics in aquatic systems is crucial, given the alarming amount of plastic waste and microplastic particles transported through aquatic pathways. In particular, there is a need to analyze the biodegradation of commercialized biodegradable plastics upon release from wastewater treatment plants into natural aquatic systems. This study investigates the biodegradation behaviors of poly(butylene adipate terephthalate) (PBAT) and poly(vinyl alcohol) (PVA) in wastewater, freshwater, and seawater. Biodegradation of PBAT and PVA assessed through biochemical oxygen demand (BOD) experiments and microcosm tests revealed that the type of aquatic system governs the biodegradation behaviors of each plastic, with the highest biodegradation rate achieved in wastewater for both PBAT and PVA (25.6 and 32.2 % in 30 d, respectively). Plastic release pathway from wastewater into other aquatic systems simulated by sequential incubation in different microcosms suggested that PBAT exposed to wastewater and freshwater before reaching seawater was more prone to degradation than when directly exposed to seawater. On the other hand, PVA displayed comparable biodegradation rate regardless of whether it was directly exposed to seawater or had passed through other environments beforehand. Metagenome amplicon sequencing of 16S rRNA genes revealed distinct community shifts dependent on the type of plastics in changing environments along the simulated aquatic pathway. Several bacterial species putatively implicated in the biodegradation of PBAT and PVA are discussed. Our findings underscore the significant influence of pollution routes on the biodegradation of PBAT and PVA, highlighting the potential for wastewater treatment to facilitate rapid degradation compared to direct exposure to pristine aquatic environments.

Soil viral-host interactions regulate microplastic-dependent carbon storage

Microplastic is globally regarded as an important factor impacting biogeochemical cycles, yet our understanding of such influences is limited by the uncertainties of intricate microbial processes. By multiomics analysis, coupled with soil chemodiversity characterization and microbial carbon use efficiency (CUE), we investigated how microbial responses to microplastics impacted soil carbon cycling in a long-term field experiment. We showed that biodegradable microplastics promoted soil organic carbon accrual by an average of 2.47%, while nondegradable microplastics inhibited it by 17.4%, as a consequence of the virus-bacteria coadaptations to the microplastics disturbance. In the relevant functional pathways, nondegradable microplastics significantly (P < 0.05) enhanced the abundance and transcriptional activity related to complex carbohydrate metabolism, whereas biodegradable microplastics significantly (P < 0.05) promoted functions involved in amino acid metabolism and glycolysis. Accordingly, viral lysis enhanced in nondegradable microplastics treatments to introduce more complex organic compounds to soil dissolved organic matters, thus benefiting the oligotrophs with high carbon metabolic capabilities in exploitation competition. In contrast, biodegradable microplastics enriched viral auxiliary metabolic genes of carbon metabolism through "piggyback-the-winner" strategy, conferring to dominant copiotrophs, enhanced substrate utilization capabilities. These virus-host interactions were also demonstrated in the corresponding soil plastisphere, which would alter microbial resource allocation and metabolism via CUE, affecting carbon storage consequently. Overall, our results underscore the importance of viral-host interactions in understanding the microplastics-dependent carbon storage in the soil ecosystem.

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

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

Microplastic pollution promotes soil respiration: A global-scale meta-analysis

Microplastic (MP) pollution likely affects global soil carbon (C) dynamics, yet it remains uncertain how and to what extent MP influences soil respiration. Here, we report on a global meta-analysis to determine the effects of MP pollution on the soil microbiome and CO2 emission. We found that MP pollution significantly increased the contents of soil organic C (SOC) (21%) and dissolved organic C (DOC) (12%), the activity of fluorescein diacetate hydrolase (FDAse) (10%), and microbial biomass (17%), but led to a decrease in microbial diversity (3%). In particular, increases in soil C components and microbial biomass further promote CO2 emission (25%) from soil, but with a much higher effect of MPs on these emissions than on soil C components and microbial biomass. The effect could be attributed to the opposite effects of MPs on microbial biomass vs. diversity, as soil MP accumulation recruited some functionally important bacteria and provided additional C substrates for specific heterotrophic microorganisms, while inhibiting the growth of autotrophic taxa (e.g., Chloroflexi, Cyanobacteria). This study reveals that MP pollution can increase soil CO2 emission by causing shifts in the soil microbiome. These results underscore the potential importance of plastic pollution for terrestrial C fluxes, and thus climate feedbacks.

A strong hydrogen bond bridging interface based on tannic acid for improving the performance of high-filled bamboo fibers/poly (butylene succinate-co-butylene adipate) (PBSA)biocomposites

Natural plant fiber-reinforced bio-based polymer composites are widely attracting attention because of their economical, readily available, low carbon, and biodegradable, and showing promise in gradually replacing petroleum-based composites. Nevertheless, the fragile interfacial bonding between fiber and substrate hinders the progression of low-cost and abundant sustainable high-performance biocomposites. In this paper, a novel high-performance sustainable biocomposite was built by introducing a high density strong hydrogen-bonded bridging interface based on tannic acid (TA) between bamboo fibers (BFs) and PBSA. Through comprehensive analysis, this strategy endowed the biocomposites with better mechanical properties, thermal stability, dynamic thermo-mechanical properties and water resistance. The optimum performance of the composites was achieved when the TA concentration was 2 g/L. Tensile strength as well as modulus, flexural strength as well as modulus, and impact strength improved by 22 %, 10 %, 15 %, 35 %, and 25 % respectively. Additionally, the initial degradation temperature(Tonset) and maximum degradation temperature(Tmax) increased by 12.07 °C and 14.8 °C respectively. The maximum storage modulus(E'), room temperature E', and loss modulus(E")elevated by 199 %, 75 %, and 181 % respectively. Moreover, the water absorption rate decreased by 59 %. The strong hydrogen-bonded bridging interface serves as a novel model and theory for biocomposite interface engineering. At the same time, it offers a promising future for the development of high performance sustainable biocomposites with low cost and abundant biomass resources and contributes to their wide application in aerospace, automotive, biomedical and other field.

Effects of photoaging on structure and characteristics of biofilms on microplastic in soil: Biomass and microbial community

Understanding of the environmental behaviors of microplastics is limited by a lack of knowledge about how photoaging influences biofilm formation on microplastics in soil. Here, original microplastics (OMPs) and photoaged-microplastics (AMPs) were incubated in soil to study the effect of photoaging on formation and characteristics of biofilm on the poly (butylene succinate) microplastics. Because photoaging decreased the hydrophobicity of the microplastic, the biomass of biofilm on the OMPs was nearly twice that on the AMPs in the early stage of incubation. However, the significance of the substrate on biomass in the biofilm declined as the plastisphere developed. The bacterial communities in the plastisphere were distinct from, and less diverse than, those in surrounding soil. The dominant genera in the OMPs and AMPs plastispheres were Achromobacter and Burkholderia, respectively, indicating that photoaging changed the composition of the bacterial community of biofilm at the genus level. Meantime, photoaging decreased the complexity and stability of the plastisphere bacterial community network. Results of Biolog ECO-microplate assays and functional prediction from amplicons showed that photoaging treatment enhanced the carbon metabolic capacity of the microplastic biofilm. This study provides new insights into the formation of plastispheres in soil.

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.

Differential fungal assemblages and functions between the plastisphere of biodegradable and conventional microplastics in farmland

The heterogeneity of plastisphere and soil can lead to variation in microbiome, potentially impacting soil functions. Current studies of the plastisphere have mainly focused on bacterial communities, and fungal communities are poorly understood. Biodegradable and conventional microplastics may recruit specific microbial taxa due to their different biodegradability. Herein, we collected polyethylene (PE) and polybutylene adipate terephthalate/polylactide (PBAT/PLA) microplastics in farmland (Hebei, China) and characterized the fungal community in PE and PBAT/PLA plastisphere. Results from high-throughput sequencing showed significantly lower alpha diversity and distinct composition of fungal community in PBAT/PLA plastisphere compared to PE plastisphere. Additionally, the PBAT/PLA plastisphere demonstrated a significant enrichment of fungal taxa with potential plastic-degrading capability such as Nectriaceae, Pleosporaceae and Didymellaceae. The stochasticity of drift (28.7-43.5 %) and dispersal limitation (38.6-39.4 %) were dominant in the assembly of PE and PBAT/PLA plastisphere fungal community. Higher stable and more complex network in PBAT/PLA plastispheres were observed as compared to PE plastisphere. Besides, the total relative abundance of plant and animal pathogens were higher in PBAT/PLA plastisphere than that in PE plastisphere, suggesting that biodegradable microplastics may pose a higher threat to soil health. This study contributes to our understanding of the characteristics of plastisphere fungal communities in soil environments and the associated risks to terrestrial ecosystems resulting from microplastic accumulation.

Distinct influence of conventional and biodegradable microplastics on microbe-driving nitrogen cycling processes in soils and plastispheres as evaluated by metagenomic analysis

Plastic mulching is one of the large contributors to microplastic (MP) accumulation in agricultural landscapes. However, the effects of conventional (PE-MPs) and biodegradable MPs (BMPs) on microbial functional and genomic information encoding nitrogen (N) cycling have yet to be addressed. Here, a soil microcosmic experiment was conducted by adding PE-MPs and BMPs to a Mollisol at dosage of 5% (w/w) followed by incubation for 90 days. The soils and MPs were examined by metagenomics and genome binning methods. The results revealed that BMPs harbored rougher surfaces and induced stronger alterations in microbial functional and taxonomic profiles in the soil and plastisphere than PE-MPs. In comparison to their respective soils, the plastispheres of PE-MPs and BMPs stimulated the processes of N fixation, N degradation and assimilatory nitrate reduction (ANRA) and reduced the gene abundances encoding nitrification and denitrification, in which BMPs induced stronger influences than PE-MPs. Ramlibacter mainly drove the differences in N cycling processes between the soils containing two types of MPs and was further enriched in the BMP plastisphere. Three high-quality genomes were identified as Ramlibacter stains with higher abundances in the plastisphere of BMP than that of PE-MP. These Ramlibacter strains had the metabolic capacities of N fixation, N degradation, ANRA and ammonium transport, which were potentially attributed to their biosynthesis and the accumulation of soil NH₄⁺-N. Taken together, our results highlight the genetic mechanisms of soil N bioavailability in the presence of biodegradable MPs, which have important implications for maintaining sustainable agriculture and controlling microplastic risk.

Fate of a biodegradable plastic in forest soil: Dominant tree species and forest types drive changes in microbial community assembly, influence the composition of plastisphere, and affect poly(butylene succinate-co-adipate) degradation

Poly(butylene succinate-co-adipate) (PBSA) degradation and its plastisphere microbiome in cropland soils have been studied; however, such knowledge is limited in the case of forest ecosystems. In this context, we investigated: i) the impact of forest types (conifer and broadleaved forests) on the plastisphere microbiome and its community assembly, ii) their link to PBSA degradation, and iii) the identities of potential microbial keystone taxa. We determined that forest type significantly affected microbial richness (F = 5.26-9.88, P = 0.034 to 0.006) and fungal community composition (R² = 0.38, P = 0.001) of the plastisphere microbiome, whereas its effects on microbial abundance and bacterial community composition were not significant. The bacterial community was governed by stochastic processes (mainly homogenizing dispersal), whereas the fungal community was driven by both stochastic and deterministic processes (drift and homogeneous selection). The highest molar mass loss was found for PBSA degraded under Pinus sylvestris (26.6 ± 2.6 to 33.9 ± 1.8 % (mean ± SE) at 200 and 400 days, respectively), and the lowest molar mass loss was found under Picea abies (12.0 ± 1.6 to 16.0 ± 0.5 % (mean ± SE) at 200 and 400 days, respectively). Important fungal PBSA decomposers (Tetracladium) and atmospheric dinitrogen (N₂)-fixing bacteria (symbiotic: Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium and Methylobacterium and non-symbiotic: Mycobacterium) were identified as potential keystone taxa. The present study is among the first to determine the plastisphere microbiome and its community assembly processes associated with PBSA in forest ecosystems. We detected consistent biological patterns in the forest and cropland ecosystems, indicating a potential mechanistic interaction between N₂-fixing bacteria and Tetracladium during PBSA biodegradation.

Degradation of Bio-Based and Biodegradable Plastic and Its Contribution to Soil Organic Carbon Stock

Expanding the use of environmentally friendly materials to protect the environment is one of the key factors in maintaining a sustainable ecological balance. Poly(butylene succinate-co-adipate) (PBSA) is considered among the most promising bio-based and biodegradable plastics for the future with a high number of applications in soil and agriculture. Therefore, the decomposition process of PBSA and its consequences for the carbon stored in soil require careful monitoring. For the first time, the stable isotope technique was applied in the current study to partitioning plastic- and soil-originated C in the CO₂ released during 80 days of PBSA decomposition in a Haplic Chernozem soil as dependent on nitrogen availability. The decomposition of the plastic was accompanied by the C loss from soil organic matter (SOM) through priming, which in turn was dependent on added N. Nitrogen facilitated PBSA decomposition and reduced the priming effect during the first 6 weeks of the experiment. During the 80 days of plastic decomposition, 30% and 49% of the released CO₂ were PBSA-derived, while the amount of SOM-derived CO₂ exceeded the corresponding controls by 100.2 and 132.3% in PBSA-amended soil without and with N fertilization, respectively. Finally, only 4.1% and 5.4% of the PBSA added into the soil was mineralized to CO₂, in the treatments without and with N amendment, respectively.

Bacterial dynamics during the burial of starch-based bioplastic and oxo-low-density-polyethylene in compost soil

BACKGROUND

Plastic waste accumulation is one of the main ecological concerns in the past decades. A new generation of plastics that are easier to degrade in the environment compared to conventional plastics, such as starch-based bioplastics and oxo-biodegradable plastics, is perceived as a solution to this issue. However, the fate of these materials in the environment are unclear, and less is known about how their presence affect the microorganisms that may play a role in their biodegradation. In this study, we monitored the dynamics of bacterial community in soil upon introduction of commercial carrier bags claimed as biodegradable: cassava starch-based bioplastic and oxo-low-density polyethylene (oxo-LDPE). Each type of plastic bag was buried separately in compost soil and incubated for 30, 60, 90, and 120 days. Following incubation, soil pH and temperature as well as the weight of remaining plastics were measured. Bacterial diversity in soil attached to the surface of remaining plastics was analyzed using Illumina high-throughput sequencing of the V3-V4 region of 16SrRNA gene.

RESULTS

After 120 days, the starch-based bioplastic weight has decreased by 74%, while the oxo-LDPE remained intact with only 3% weight reduction. The bacterial composition in soil fluctuated over time with or without the introduction of either type of plastic. While major bacterial phyla remained similar for all treatment in this study, different types of plastics led to different soil bacterial community structure. None of these bacteria were abundant continuously, but rather they emerged at specific time points. The introduction of plastics into soil increased not only the population of bacteria known for their ability to directly utilize plastic component for their growth, but also the abundance of those that may interact with direct degraders. Bacterial groups that are involved in nitrogen cycling also arose throughout burial.

CONCLUSIONS

The introduction of starch-based bioplastic and oxo-LDPE led to contrasting shift in soil bacterial population overtime, which may determine their fate in the environment.

Effects of polylactic acid (PLA) and polybutylene adipate-co-terephthalate (PBAT) biodegradable microplastics on the abundance and diversity of denitrifying and anammox bacteria in freshwater sediment

Microplastics (MPs) have been widely distributed on Earth and have drawn global concern for freshwater and marine ecosystems. Biodegradable plastics have risen in popularity to replace nonbiodegradable plastics all over the world. The effects of biodegradable plastics on denitrifying and anammox bacteria in freshwater sediment remain largely unknown. In this study, water column reactors containing polylactic acid (PLA) or polybutylene adipate-co-terephthalate (PBAT) MPs in sediment were established to simulate lake ecosystems and analyze the effects of biodegradable MPs on sedimentary nitrogen transformation microorganisms. The total organic carbon (TOC) concentrations in the PLA and PBAT groups were slightly higher than those in the control group, which might be related to the slow degradation of these two plastics. Denitrifying and anammox bacterial diversities decreased after adding MPs to sediments for 30 days, and the dominant OTUs of these two bacteria were differentiated from the control. The abundance levels of nirS denitrifying and anammox bacteria on the PLA MP surface were significantly higher than those in the other groups (P < 0.05), but they were lower in the PBAT groups than in the other groups. As an excellent electron donor for the denitrification process, lactic acid release from PLA degradation resulted in the enrichment of denitrifying and anammox bacteria on the MP surfaces. However, PBAT led to various responses of bacteria in an anaerobic environment. In addition, the redundancy analysis results indicated that total phosphorus, TOC and nitrate were strongly negatively correlated with the abundance levels of denitrifying and anammox bacteria. Our findings provided insight into the effects of MPs, especially the biodegradable ones, on sedimentary nitrogen-transformation bacteria.

Future climate change enhances the complexity of plastisphere microbial co-occurrence networks, but does not significantly affect the community assembly

Biobased and biodegradable plastics have been intensively used in agriculture as mulching films. They provide a distinctive habitat for soil microbes, yet much less is known about the community assembly and interactions of plastisphere microbiota in soils under future climate change. For the first time, we explored the relative importance of ecological processes and the co-occurrence networks of plastic-associated microbes under ambient and future climates. The drift primarily dominated the community assembly of bacteria and fungi after 180D and 328D incubation in both climate regimes. The neutral community model prediction indicated that the migration rate of the plastisphere community in the later decay phase was lower than that in the early decay phase, contributing to the generation of the specific niches. Furthermore, future climate promoted the complexity and modularity of plastic-associated microbial networks: more competition and cooperation were observed in bacteria (or inter-kingdom) and fungi under future climate conditions, respectively. Overall, our findings strengthened the understanding of ecological processes and interplay of plastisphere microbiota during plastic biodegradation in soils under ambient and future climate regimes.

Past, present, and future perspectives of biodegradable films for soil: A 30-year systematic review

Based on the Web of Science Core Collection (WOSCC) database, the academic works published in the past 30 years on biodegradable films for soil were analyzed. In order to ensure the rigor of this experiment, this paper is based on the mathematical double matrix model VOS Viewer software and CiteSpace software. This work shows that publications of biodegradable films for soil are increasing year by year; polymer science is the hottest subject in the field of biodegradable films for soil; China and the United States are the countries with the most significant number of publications in this field, has an important position; Washington State University is the most published institution. This study further identifies and reveals the essential characteristics, research strength, knowledge structure, main research fields, and research hotspots in the late stage of the field of biodegradable films for soil and introduces the Activity Index (AI) and the Attractive Index (AAI), thereby assessing trends and performance in different countries. The paper also further illustrates the importance of biodegradable films by presenting field trials using biodegradable films on different plants. The research in the field of biodegradable films for soil is divided into four categories: “The research field of degradation,” “The effect of biodegradable film on soil,” “Performance and mechanism of the biodegradable film,” and “Effects of biodegradable film on crop growth and development.”. The study can be seen as a microcosm of the development of biodegradable films for soils, which will help researchers quickly identify their general patterns. Readers can better understand the changes and development trends in this field in the past 30 years and provide references for future research.

Dark side of a bio-based and biodegradable plastic? Assessment of pathogenic microbes associated with poly(butylene succinate-co-adipate) under ambient and future climates using next-generation sequencing

Bio-based and biodegradable plastic mulching films have been proposed to replace the non-biodegradable plastic mulch films to solve plastic pollution problems in agricultural soils. However, the impact of bio-based and biodegradable plastics on plant and human health remains largely unexplored. Here, we aimed to assess the risk under field conditions of a bio-based and biodegradable poly(butylene succinate-co-adipate; PBSA), a widely used mulching film as carrier of potential pathogenic microorganisms (bacteria and fungi) at ambient and future climate conditions. Overall, we affiliated 64 fungal and 11 bacterial operational taxonomic units (OTUs) as pathogens by using Next-Generation Sequencing approach. Our results revealed that PBSA hosted at least 53 plant pathogens, of which 51 were classified as fungi, while the other two were bacteria. Most fungal plant pathogens were able to withstand the anticipated future climate changes. We detected 13 fungal and eight bacterial OTUs, which were classified as opportunistic human pathogens. Only one bacterial OTU (Enterococcus faecium) was assigned to a human pathogen. While future climate conditions only significantly impacted on the presence and frequency of detection of few pathogens, incubation time was found to significantly impacted on nine pathogens. This result demonstrates the temporal dynamics of pathogens associated with PBSA. The threats to plant and human health were discussed. We emphasize that the risks to human health are relatively low because we mainly found opportunistic pathogens associated with PBSA and the amount are comparable to the plant debris. However, the risks to plant health may be considered as moderate because many plant pathogens were discovered and/or enriched in PBSA. Furthermore, in soil environments, the pathogenic risk of plastic is highly depending on the surrounding soil pathobiome where plastic is being decomposed.

Sustainably Recycling and Upcycling of Single-Use Plastic Wastes through Heterogeneous Catalysis

The huge amount of plastic waste has caused a series of environmental and economic problems. Depolymerization of these wastes and their conversion into desired chemicals have been regarded as a promising route for dealing with these issues, which strongly relies on catalysis for C-C and C-O bond cleavage and selective transformation. Here, we reviewed recent developments in catalysis systems for dealing with single-use plastics, such as polyethylene, polypropylene, and polyethylene glycol terephthalate. The recycling processes of depolymerization into original monomers and conversion into other economic-incentive chemicals were systemically discussed. Rational designs of catalysts for efficient conversion were particularly highlighted. Overall, improving the tolerance of catalysts to impurities in practical plastics, reducing the economic cost during the catalytic depolymerization process, and trying to obtain gaseous hydrogen from plastic wastes are suggested as the developing trends in this field.

Links among Microbial Communities, Soil Properties and Functions: Are Fungi the Sole Players in Decomposition of Bio-Based and Biodegradable Plastic?

The incomplete degradation of bio-based and biodegradable plastics (BBPs) in soils causes multiple threats to soil quality, human health, and food security. Plastic residuals can interact with soil microbial communities. We aimed to link the structure and enzyme-mediated functional traits of a microbial community composition that were present during poly (butylene succinate-co-butylene adipate (PBSA) decomposition in soil with (PSN) and without (PS) the addition of nitrogen fertilizer ((NH₄)₂SO₄). We identified bacterial (Achromobacter, Luteimonas, Rhodanobacter, and Lysobacter) and fungal (Fusarium, Chaetomium, Clonostachys, Fusicolla, and Acremonium) taxa that were linked to the activities of ß-glucosidase, chitinase, phosphatase, and lipase in plastic-amended soils. Fungal biomass increased by 1.7 and 4 times in PS and PSN treatment, respectively, as compared to non-plastic amended soil. PBSA significantly changed the relationships between soil properties (C: N ratio, TN, and pH) and microbial community structure; however, the relationships between fungal biomass and soil enzyme activities remained constant. PBSA significantly altered the relationship between fungal biomass and acid phosphatase. We demonstrated that although the soil functions related to nutrient cycling were not negatively affected in PSN treatment, potential negative effects are reasoned by the enrichment of plant pathogens. We concluded that in comparison to fungi, the bacteria demonstrated a broader functional spectrum in the BBP degradation process.

Differences in the Plastispheres of Biodegradable and Non-biodegradable Plastics: A Mini Review

There has been a steady rise in the production and disposal of biodegradable plastics. Unlike the microorganisms present in the biofilms on non-biodegradable plastic surfaces (the “plastisphere”), the plastisphere of biodegradable plastic has not been well-characterized. As the polymer structure of biodegradable plastic has a higher microbial affinity than that of non-biodegradable plastic, their plastispheres are assumed to be different. This review summarizes the reported differences in microbial communities on the surface of biodegradable and non-biodegradable plastics, discusses the driving forces behind these differences, and discusses the potential environmental risks. Overall, the plastisphere biomass on the surface of non-biodegradable plastic was observed to be lower than that of biodegradable plastic. The community structure of microbes in both plastispheres was diverse, mainly due to the properties of the plastic surface, such as surface charge, hydrophilicity/hydrophobicity, roughness, and bioavailability of polymer components for microbes. Further research should focus on developing biodegradable plastic that degrade faster in the environment, revealing the mechanism of enrichment of ARGs and potential pathogens on plastics, and understanding the potential influence of plastispheres on the evolution and selection of plastic-degrading microbial potential.

Key knowledge gaps for One Health approach to mitigate nanoplastic risks

There are increasing concerns over the threat of nanoplastics to environmental and human health. However, multidisciplinary barriers persist between the communities assessing the risks to environmental and human health. As a result, the hazards and risks of nanoplastics remain uncertain. Here, we identify key knowledge gaps by evaluating the exposure of nanoplastics in the environment, assessing their bio-nano interactions, and examining their potential risks to humans and the environment. We suggest considering nanoplastics a complex and dynamic mixture of polymers, additives, and contaminants, with interconnected risks to environmental and human health. We call for comprehensive integration of One Health approach to produce robust multidisciplinary evidence to nanoplastics threats at the planetary level. Although there are many challenges, this holistic approach incorporates the relevance of environmental exposure and multi-sectoral responses, which provide the opportunity to identify the risk mitigation strategies of nanoplastics to build resilient health systems.

Nitrogen fixing bacteria facilitate microbial biodegradation of a bio-based and biodegradable plastic in soils under ambient and future climatic conditions

We discovered a biological mechanism supporting microbial degradation of bio-based poly(butylene succinate-co-adipate) (PBSA) plastic in soils under ambient and future climates. Here, we show that nitrogen-fixing bacteria facilitate the microbial degradation of PBSA by enhancing fungal abundance, accelerating plastic-degrading enzyme activities, and shaping/interacting with plastic-degrading fungal communities.

Identification of Microorganisms Dwelling on the 19th Century Lanna Mural Paintings from Northern Thailand Using Culture-Dependent and -Independent Approaches

Simple Summary

In this study, we compared microbial communities in Lanna mural paintings in temples with different numbers of visitors using culture-dependent and culture independent approaches. The results showed that microorganisms could damage the colors that are used on murals. The process of degradation involved the production of organic acids and formation of the calcium crystal. Furthermore, we found that the site with higher number of visitors is associated with microbial contamination from humans while the site with lower number of visitors had higher saprotroph population. Further research into these microorganisms, their activities and functional roles may provide crucial information to aid the preservation of mural paintings.

Abstract

Lanna painting is a unique type of painting in many temples in the Northern Thai region. Similar to most mural paintings, they usually decay over time partly due to the activity of microbes. This study aimed to investigate the microorganisms from two Lanna masterpiece paintings in two temples that differ in the numbers of visitors using both culture-dependent and -independent approaches. The microorganisms isolated from the murals were also tested for the biodeterioration activities including discoloration, acid production and calcium precipitation. Most microorganisms extracted from the paintings were able to discolor the paints, but only fungi were able to discolor, produce acids and precipitate calcium. The microorganism communities, diversity and functional prediction were also investigated using the culture-independent method. The diversity of microorganisms and functional prediction were different between the two temples. Gammaproteobacteria was the predominant group of bacteria in both temples. However, the fungal communities were different between the two temples as Aspergillus was the most abundant genus in the site with higher number of visitors [Buak Krok Luang temple (BK)]. Conversely, mural paintings at Tha Kham temple (TK) were dominated by the Neodevriesia genera. We noticed that a high number of visitors (Buak Krok Luang) was correlated with microbial contamination from humans while the microbial community at Tha Kham temple had a higher proportion of saprotrophs. These results could be applied to formulate a strategy to mitigate the amount of tourists as well as manage microorganism to slow down the biodeterioration process.

A critical review on microbial degradation of petroleum-based plastics: quantitatively effects of chemical addition in cultivation media on biodegradation efficiency

Petroleum-based plastics (PBP) with different properties have been developed to suit various needs of modern lives. Nevertheless, these well-developed properties also present the double-edged sword effect that significantly threatens the sustainability of the environment. This work focuses on the impact of microbial cultivating conditions (the elementary compositions and temperature) to provide insightful information for the process optimization of microbial degradation. The major elementary compositions in cultivation media and temperature from the literature were radically reviewed and assessed using the constructed supervised machine learning algorithm. Fifty-two literatures were collected as a training dataset to investigate the impact of major chemical elements and cultivation temperature upon PBP biodegradation. Among six singular parameters (NH₄⁺, K⁺, PO₄^3-, Mg²⁺, Ca²⁺, and temperature) and thirty corresponding binary parameters, four singular (NH₄⁺, K⁺, PO₄^3-, and Mg²⁺) and six binary parameters (NH₄⁺/K⁺, NH₄⁺/PO₄^3-, NH₄⁺/Ca²⁺, K⁺/PO₄^3-, PO₄^3-/Mg²⁺, Mg²⁺/Temp) were identified as statistically significant towards microbial degradation through analysis of variance (ANOVA). The binary effect (PO₄^3-/Mg²⁺) is found to be the most statistically significant towards the microbial degradation of PBP. The concentration range, which locates at 0.1-0.6 g/L for Mg²⁺ and 0-2.8 g/L for PO₄^3-, was identified to contribute to the maximum PBP biodegradation. Among all the investigated elements, Mg²⁺ is the only element that is statistically and significantly associated with the variations of cultivation temperature. The optimal preparation conditions within ± 20% uncertainties based upon the range of collected literature reports are recommended. Five representative cultivation elementary compositions (NH₄⁺, K⁺, PO₄^3-, Mg²⁺, and Ca²⁺) and temperature were reviewed from fifty two different literature reports to investigate their impacts on the microbial degradation of PBP using supervised machine learning algorithm. The optimal cultivation conditions based upon collected literature reports to achieve biodegradation over 80% were identified.