Ecology and risks of the global plastisphere as a newly expanding microbial habitat

Effects of soil microplastic heterogeneity on plant growth vary with species and microplastic types

Microplastics are heterogeneously distributed in soils. However, it is unknown whether soil microplastic heterogeneity affects plant growth and root foraging responses and whether such effects vary with plant species and microplastic types. We grew each of seven herbaceous species (Platycodon grandiflorus, Trifolium repens, Portulaca oleracea, Medicago sativa, Taraxacum mongolicum, Perilla frutescenst, and Paspalum notatum) in heterogeneous soil (patches without microplastics and patches with 0.2 % microplastics) and homogeneous soil (patches with 0.1 % microplastics). Three microplastic types were tested: polypropylene (PP), polyacrylonitrile (PAN), and polyester (PET). P. frutescens showed no response to soil microplastic heterogeneity. For P. grandiflora, microplastic heterogeneity tended to decrease its biomass (total, shoot and root) when the microplastic was PAN and also shoot biomass when it was PET, but had no effect when it was PP. For T. repens, microplastic heterogeneity promoted biomass when PAN was used, decreased total and root biomass when PET was used, but showed no effect when PP was used. Microplastic heterogeneity increased biomass of P. oleracea and decreased that of M. sativa when PET was used, but had no effect when PP or PAN was used. For T. mongolicum, microplastic heterogeneity reduced biomass when the microplastic was PAN, tended to increase total and root biomass when it was PP, but showed no effect when it was PET. For P. notatum, microplastic heterogeneity increased biomass when the microplastic was PP, decreased it when PET was used, but had no effect when PAN was used. However, biomass of none of the seven species showed root foraging responses at the patch level. Therefore, soil microplastic heterogeneity can influence plant growth, but such effects depend on species and microplastic types and are not associated with root foraging. Our findings highlight the roles of soil microplastic heterogeneity, which may influence species interactions and community structure and productivity.

Enhancing biodegradation efficiency of PLA/PBAT-ST20 bioplastic using thermophilic bacteria co-culture system: New insight from structural characterization, enzyme activity, and metabolic pathways

The rising utilization of PLA/PBAT-ST20 presents potential ecological risks stemming from its casual disposal and incomplete degradation. To solve this problem, this study investigated the degradation capabilities of PLA/PBAT-ST20 by a co-culture system comprising two thermophilic bacteria, Pseudomonas G1 and Kocuria G2, selected and identified from the thermophilic phase of compost. Structural characterization results revealed that the strains colonized the PLA/PBAT-ST20's surface, causing holes and cracks, with an increase in the carbonyl index (CI) and polydispersity index (PDI), indicating oxidative degradation. Enzyme activity results demonstrated that the co-culture system significantly enhanced the secretion and activity of proteases and lipases, promoting the breakdown of ester bonds. LC-QTOF-MS results showed that various intermediate products were obtained after degradation, ultimately participating in the TCA cycle (ko00020), further completely mineralized. Additionally, after 15-day compost, the co-culture system achieved a degradation rate of 72.14 ± 2.1 wt% for PBAT/PLA-ST20 films, with a decrease in the abundance of plastic fragments of all sizes, demonstrating efficient degradation of PLA/PBAT-ST20 films. This study highlights the potential of thermophilic bacteria to address plastic pollution through biodegradation and emphasizes that the co-culture system could serve as an ideal solution for the remediation of PLA/PBAT plastics.

Phototrophs as the central components of the plastisphere microbiome in coastal environments

Upon entering the marine environment, plastics are colonized by a plethora of microorganisms to form a plastisphere, influencing the fate and transport of the plastic debris and the health of marine ecosystems. The assembly of marine plastisphere is generally believed to be dominated by stochastic processes. However, it remains elusive whether microbial interaction in the assembly of plastisphere microbial communities is conserved or not. We analyzed the plastisphere microbiomes of 137 plastic debris samples from intertidal zones at different geographical locations and habitats (seagrass, coral, mangrove, beach, and open ocean) and compared them with the surrounding sediment and seawater microbiomes. Microbial community structures of the plastisphere from different locations were more similar to each other but differed substantially from the surrounding sediment and water microbiomes, implying a common mechanism of plastisphere assembly. We used different machine learning algorithms (Multinomial Logistic Regression, Support Vector Machine, Decision Trees, Random Forest, and Artificial Neural Networks) to classify plastic debris samples with high sensitivity based on the microbiome composition. Eukaryotic and prokaryotic phototrophic organisms such as green algae, diatoms, and cyanobacteria, were found to be enriched on the plastic surfaces. Network analysis revealed the central role of the phototrophic organisms in the formation and sustenance of the plastispheres. We found that phototrophs served as core members interacting strongly with heterotrophic organisms in marine plastisphere, irrespective of the sampling location, habitats, and polymer types. This would explain the stochastic assembly of the plastisphere along with conserved properties driven by the phototrophs in the surrounding environment. Our results highlight the importance of phototrophic organisms in shaping the marine plastisphere microbial communities.

Polyhydroxybutyrate Plastics Show Rapid Disintegration and More Straightforward Biogeochemical Impacts than Polyethylene under Marine Biofragmentation

Although massive studies have investigated the spatiotemporally occurring marine plastisphere, a new microbial ecosystem colonizing the surfaces of plastics, the resulting biofragmentation process and impacts of plastics on biogeochemical cycles remain largely unknown. Here, we leverage synchrotron-based Fourier transform infrared spectromicroscopy (FTIR mapping) and metagenomic sequencing to explore independent marine microcosms amended with petroleum-based polyethylene (PE) and biobased polyhydroxybutyrate (PHB) plastic films. FTIR mapping results demonstrate unequal fragmentation scenarios by which the PE plastic rarely releases oxidized fragments while PHB disintegrates quickly, gradually forming fragments composed of extracellular polymeric substances resembling plastic films. Metagenomic analysis shows the critical role of hydrocarbonoclastic lineages in the biodegradation of the two plastics by the fatty acid degradation pathway, where the PE plastics host different microbial trajectories between the plastisphere (dominated by Alcanivorax) and surrounding seawater. In contrast, the PHB addition demonstrates decreased microbial richness and diversity, consistent community composition (dominated by Phaeobacter and Marinobacter), and apparently stimulated sulfur cycle and denitrification pathways in both the plastisphere and surrounding seawater. Our study gives scientific evidence on the marine biotic processes distinguishing petroleum- and biobased plastics, highlighting marine PHB input exerting straightforward impacts on the water phase and deserving critical management practices.

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.

Biomass waste-assisted micro(nano)plastics capture, utilization, and storage for sustainable water remediation

Micro(nano)plastics (MNPs) have become a significant environmental concern due to their widespread presence in the biosphere and potential harm to ecosystems and human health. Here, we propose for the first time a MNPs capture, utilization, and storage (PCUS) concept to achieve MNPs remediation from water while meeting economically productive upcycling and environmentally sustainable plastic waste management. A highly efficient capturing material derived from surface-modified woody biomass waste (M-Basswood) is developed to remove a broad spectrum of multidimensional and compositional MNPs from water. The M-Basswood delivered a high and stable capture efficiency of >99.1% at different pH or salinity levels. This exceptional capture performance is driven by multiscale interactions between M-Basswood and MNPs, involving physical trapping, strong electrostatic attractions, and triggered MNPs cluster-like aggregation sedimentation. Additionally, the in vivo biodistribution of MNPs shows low ingestion and accumulation of MNPs in the mice organs. After MNPs remediation from water, the M-Basswood, together with captured MNPs, is further processed into a high-performance composite board product where MNPs serve as the glue for utilization and storage. Furthermore, the life cycle assessment (LCA) and techno-economic analysis (TEA) results demonstrate the environmental friendliness and economic viability of our proposed full-chain PCUS strategy, promising to drive positive change in plastic pollution and foster a circular economy.

Emerging contaminants: A One Health perspective

Environmental pollution is escalating due to rapid global development that often prioritizes human needs over planetary health. Despite global efforts to mitigate legacy pollutants, the continuous introduction of new substances remains a major threat to both people and the planet. In response, global initiatives are focusing on risk assessment and regulation of emerging contaminants, as demonstrated by the ongoing efforts to establish the UN's Intergovernmental Science-Policy Panel on Chemicals, Waste, and Pollution Prevention. This review identifies the sources and impacts of emerging contaminants on planetary health, emphasizing the importance of adopting a One Health approach. Strategies for monitoring and addressing these pollutants are discussed, underscoring the need for robust and socially equitable environmental policies at both regional and international levels. Urgent actions are needed to transition toward sustainable pollution management practices to safeguard our planet for future generations.

Exploring untapped bacterial communities and potential polypropylene-degrading enzymes from mangrove sediment through metagenomics analysis

The versatility of plastic has resulted in huge amounts being consumed annually. Mismanagement of post-consumption plastic material has led to plastic waste pollution. Biodegradation of plastic by microorganisms has emerged as a potential solution to this problem. Therefore, this study aimed to investigate the microbial communities involved in the biodegradation of polypropylene (PP). Mangrove soil was enriched with virgin PP sheets or chemically pretreated PP comparing between 2 and 4 months enrichment to promote the growth of bacteria involved in PP biodegradation. The diversity of the resulting microbial communities was accessed through 16S metagenomic sequencing. The results indicated that Xanthomonadaceae, unclassified Gaiellales, and Nocardioidaceae were promoted during the enrichment. Additionally, shotgun metagenomics was used to investigate enzymes involved in plastic biodegradation. The results revealed the presence of various putative plastic-degrading enzymes in the mangrove soil, including alcohol dehydrogenase, aldehyde dehydrogenase, and alkane hydroxylase. The degradation of PP plastic was determined using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), and Water Contact Angle measurements. The FTIR spectra showed a reduced peak intensity of enriched and pretreated PP compared to the control. SEM images revealed the presence of bacterial biofilms as well as cracks on the PP surface. Corresponding to the FTIR and SEM analysis, the water contact angle measurement indicated a decrease in the hydrophobicity of PP and pretreated PP surface during the enrichment.

Persistence of 'wet wipes' in beach sand: An unrecognised reservoir for localised E. coli contamination

The flushing of wet wipes down toilets leads to blockages of sewerage systems. This, together with unregulated sewage discharge, often results in increasing numbers of wet wipes washing up onto beaches. However, it is unclear how long wet wipes can persist on the beach and whether they pose a prolonged public health risk if contaminated by E. coli. In this mesocosm study, three types of wet wipes (plastic containing, and home and commercially compostable) colonised with E. coli were buried in beach sand and their degradation, tensile strength, and concentration of E. coli was quantified over 15 weeks. Wet wipes containing plastic remained largely intact for 15 weeks, whilst both compostable wet wipes fragmented and degraded. Importantly, E. coli persisted on all three wet wipe types, representing localised reservoirs of E. coli in the sand, which could present a human health risk at the beach.

The "Microplastome" - A Holistic Perspective to Capture the Real-World Ecology of Microplastics

Microplastic pollution, an emerging pollution issue, has become a significant environmental concern globally due to its ubiquitous, persistent, complex, toxic, and ever-increasing nature. As a multifaceted and diverse suite of small plastic particles with different physicochemical properties and associated matters such as absorbed chemicals and microbes, future research on microplastics will need to comprehensively consider their multidimensional attributes. Here, we introduce a novel, conceptual framework of the "microplastome", defined as the entirety of various plastic particles (<5 mm), and their associated matters such as chemicals and microbes, found within a sample and its overall environmental and toxicological impacts. As a novel concept, this paper aims to emphasize and call for a collective quantification and characterization of microplastics and for a more holistic understanding regarding the differences, connections, and effects of microplastics in different biotic and abiotic ecosystem compartments. Deriving from this lens, we present our insights and prospective trajectories for characterization, risk assessment, and source apportionment of microplastics. We hope this new paradigm can guide and propel microplastic research toward a more holistic era and contribute to an informed strategy for combating this globally important environmental pollution issue.