A roadmap for a Plastisphere

Biofilms in plastisphere from freshwater wetlands: Biofilm formation, bacterial community assembly, and biogeochemical cycles

Microorganisms can colonize to the surface of microplastics (MPs) to form biofilms, termed "plastisphere", which could significantly change their physiochemical properties and ecological roles. However, the biofilm characteristics and the deep mechanisms (interaction, assembly, and biogeochemical cycles) underlying plastisphere in wetlands currently lack a comprehensive perspective. In this study, in situ biofilm formation experiments were performed in a park with different types of wetlands to examine the plastisphere by extrinsic addition of PVC MPs in summer and winter, respectively. Results from the spectroscopic and microscopic analyses revealed that biofilms attached to the MPs in constructed forest wetlands contained the most abundant biomass and extracellular polymeric substances. Meanwhile, data from the high-throughput sequencing showed lower diversity in plastisphere compared with soil bacterial communities. Network analysis suggested a simple and unstable co-occurrence pattern in plastisphere, and the null model indicated increased deterministic process of heterogeneous selection for its community assembly. Based on the quantification of biogeochemical cycling genes by high-throughput qPCR, the relative abundances of genes involving in carbon degradation, carbon fixation, and denitrification were significantly higher in plastisphere than those of soil communities. This study greatly enhanced our understanding of biofilm formation and ecological effects of MPs in freshwater wetlands.

Freshwater plastisphere: a review on biodiversity, risks, and biodegradation potential with implications for the aquatic ecosystem health

The plastisphere, a unique microbial biofilm community colonizing plastic debris and microplastics (MPs) in aquatic environments, has attracted increasing attention owing to its ecological and public health implications. This review consolidates current state of knowledge on freshwater plastisphere, focussing on its biodiversity, community assembly, and interactions with environmental factors. Current biomolecular approaches revealed a variety of prokaryotic and eukaryotic taxa associated with plastic surfaces. Despite their ecological importance, the presence of potentially pathogenic bacteria and mobile genetic elements (i.e., antibiotic resistance genes) raises concerns for ecosystem and human health. However, the extent of these risks and their implications remain unclear. Advanced sequencing technologies are promising for elucidating the functions of plastisphere, particularly in plastic biodegradation processes. Overall, this review emphasizes the need for comprehensive studies to understand plastisphere dynamics in freshwater and to support effective management strategies to mitigate the impact of plastic pollution on freshwater resources.

The soil plastisphere

Understanding the effects of plastic pollution in terrestrial ecosystems is a priority in environmental research. A central aspect of this suite of pollutants is that it entails particles, in addition to chemical compounds, and this makes plastic quite different from the vast majority of chemical environmental pollutants. Particles can be habitats for microbial communities, and plastics can be a source of chemical compounds that are released into the surrounding environment. In the aquatic literature, the term 'plastisphere' has been coined to refer to the microbial community colonizing plastic debris; here, we use a definition that also includes the immediate soil environment of these particles to align the definition with other concepts in soil microbiology. First, we highlight major differences in the plastisphere between aquatic and soil ecosystems, then we review what is currently known about the soil plastisphere, including the members of the microbial community that are enriched, and the possible mechanisms underpinning this selection. Then, we focus on outlining future prospects for research on the soil plastisphere.

Lake plastisphere as a new biotope in the Anthropocene: Potential pathogen colonization and distinct microbial functionality

The not-homogenous microplastics (MPs) distribution in freshwaters results in distinct microbial communities. Yet knowledge regarding plastisphere in metabolic pathways and element cycling behaviors remains limited. In this study, we collected MPs from 15 sampling sites in the Taihu Lake in China, and found that MPs were widely distributed in this freshwater lake, and dominantly composed of fibrous polyethylene terephthalate. Based on the metagenomic analysis, we found that MPs were colonized by Bacteroidia, Alpha-Proteobacteria, and Bacilli as a filter, but depleted in Verrucomicrobiae. Potential pathogens of plant eudicots and monocots were significantly enriched in plastisphere. Predicted functional profiles involved in the metabolism of other amino acids, biosynthesis of other secondary metabolites, and glycan biosynthesis and metabolism were overrepresented in plastisphere. Regarding elemental cycling, functional genes related to nitrogen fixation and nitrification showed 39.6% and 67.5% decline in plastisphere, whereas the genes involved in denitrification and nitrate reduction were significantly enriched. For sulfur cycles, the plastisphere exhibited higher sulfate reduction and sulfur oxidation system activities. Additionally, the taxonomic compositions and predicted functions in the plastispheres were mainly driven by the stochastic processes, while the deterministic processes were more important for the planktonic communities. The distinctions in the microbial composition, the predicted functionality, and the underly mechanisms between plastisphere and planktonic communities illustrated the unique ecology of the new anthropogenic-related plastisphere ecosystems.

Microbial colonization patterns and biodegradation of petrochemical and biodegradable plastics in lake waters: insights from a field experiment

Introduction

Once dispersed in water, plastic materials become promptly colonized by biofilm-forming microorganisms, commonly known as plastisphere.

Methods

By combining DNA sequencing and Confocal Laser Scanning Microscopy (CLSM), we investigated the plastisphere colonization patterns following exposure to natural lake waters (up to 77 days) of either petrochemical or biodegradable plastic materials (low density polyethylene - LDPE, polyethylene terephthalate - PET, polylactic acid - PLA, and the starch-based MaterBi® - Mb) in comparison to planktonic community composition. Chemical composition, water wettability, and morphology of plastic surfaces were evaluated, through Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), and static contact angle analysis, to assess the possible effects of microbial colonization and biodegradation activity.

Results and Discussion

The phylogenetic composition of plastisphere and planktonic communities was notably different. Pioneering microbial colonisers, likely selected from lake waters, were found associated with all plastic materials, along with a core of more than 30 abundant bacterial families associated with all polymers. The different plastic materials, either derived from petrochemical hydrocarbons (i.e., LDPE and PET) or biodegradable (PLA and Mb), were used by opportunistic aquatic microorganisms as adhesion surfaces rather than carbon sources. The Mb-associated microorganisms (i.e. mostly members of the family Burkholderiaceae) were likely able to degrade the starch residues on the polymer surfaces, although the Mb matrix maintained its original chemical structure and morphology. Overall, our findings provide insights into the complex interactions between aquatic microorganisms and plastic materials found in lake waters, highlighting the importance of understanding the plastisphere dynamics to better manage the fate of plastic debris in the environment.

Bacterial Colonization of Microplastics at the Beaches of an Oceanic Island, Tenerife, Canary Islands

(1) Isolated systems, such as oceanic islands, are increasingly experiencing important problems related to microplastic debris on their beaches. The formation of microbial biofilm on the surface of microplastics present in marine environments provides potential facilities for microorganisms to survive under the biofilm. Moreover, microplastics act as a vehicle for the dispersion of pathogenic organisms, constituting a new route of exposure for humans. (2) In this study, the microbial content (FIO and Vibrio spp. and Staphylococcus aureus) of microplastics (fragments and pellets) collected from seven beaches of the oceanic island of Tenerife, in the Canary Islands (Spain), was determined. (3) Results showed that Escherichia coli was present in 57.1% of the fragments and 28.5% of the pellets studied. In the case of intestinal Enterococci, 85.7% of the fragments and 57.1% of the pellets tested positive for this parameter. Finally, 100% of the fragments and 42.8% of the pellets analyzed from the different beaches contained Vibrio spp. (4) This study shows that microplastics act as reservoirs of microorganisms that can increase the presence of bacteria indicating faecal and pathogenic contamination in bathing areas.

Metagenomic insights into environmental risk of field microplastics in an urban river

Microplastics (MPs) are emerging as anthropogenic vectors for the colonization and transportation of microbial communities in aquatic ecosystems. However, the composition of the microbiome and its environmental risk on field MPs at watershed scale has rarely been explored. Here, geographical distributions of microbiome, antibiotic resistance genes (ARGs) and virulence factors (VFs) on field MPs at watershed scale were characterized and their potential environmental risks were evaluated based on the data from metagenomic analyzes. The succession of microbial communities on MPs was observed along the watershed, and some ARGs and VFs were significantly enriched on MPs in urban region in comparison with rural region. Potential environmental risk of MPs conducted by Projection Pursuit Regression model in midstream (peri-urban region) and downstream (urban region) were significantly higher than that in upstream (rural region), and exhibit close relationships with MPs concentration and water velocity. Furthermore, our source tracking results demonstrated that the microbiome, ARGs and VFs in urban region MPs were largely derived from rural region MPs. Our results caution us that special attention should be paid to the risks posed by MPs in urban water bodies, and highlight the threat of MPs from rural upstream areas.

Estuarine plastisphere as an overlooked source of N2O production

“Plastisphere”, microbial communities colonizing plastic debris, has sparked global concern for marine ecosystems. Microbiome inhabiting this novel human-made niche has been increasingly characterized; however, whether the plastisphere holds crucial roles in biogeochemical cycling remains largely unknown. Here we evaluate the potential of plastisphere in biotic and abiotic denitrification and nitrous oxide (N₂O) production in estuaries. Biofilm formation provides anoxic conditions favoring denitrifiers. Comparing with surrounding bulk water, plastisphere exhibits a higher denitrifying activity and N₂O production, suggesting an overlooked N₂O source. Regardless of plastisphere and bulk water, bacterial and fungal denitrifications are the main regulators for N₂O production instead of chemodenitrification. However, the contributions of bacteria and fungi in the plastisphere are different from those in bulk water, indicating a distinct N₂O production pattern in the plastisphere. These findings pinpoint plastisphere as a N₂O source, and provide insights into roles of the new biotope in biogeochemical cycling in the Anthropocene.

The roles of marine plastisphere in global nitrogen cycling are largely unknown. Here, the authors indicate that the plastisphere could act as a potential source of N2O production, which is mainly regulated by the biotic denitrification

SEM/EDX analysis of stomach contents of a sea slug snacking on a polluted seafloor reveal microplastics as a component of its diet

Understanding the impacts of microplastics on living organisms in aquatic habitats is one of the hottest research topics worldwide. Despite increased attention, investigating microplastics in underwater environments remains a problematic task, due to the ubiquitous occurrence of microplastic, its multiple modes of interactions with the biota, and to the diversity of the synthetic organic polymers composing microplastics in the field. Several studies on microplastics focused on marine invertebrates, but to date, the benthic sea slugs (Mollusca, Gastropoda, Heterobranchia) were not yet investigated. Sea slugs are known to live on the organisms on which they feed on or to snack while gliding over the sea floor, but also as users of exogenous molecules or materials not only for nutrition. Therefore, they may represent a potential biological model to explore new modes of transformation and/or management of plastic, so far considered to be a non-biodegradable polymer. In this study we analysed the stomachal content of Bursatella leachii, an aplysiid heterobranch living in the Mar Piccolo, a highly polluted coastal basin near Taranto, in the northern part of the Ionian Sea. Microplastics were found in the stomachs of all the six sampled specimens, and SEM/EDX analyses were carried out to characterize the plastic debris. The SEM images and EDX spectra gathered here should be regarded as a baseline reference database for future investigations on marine Heterobranchia and their interactions with microplastics.

Plant-Oil-Based Fibre Composites for Boat Hulls

Plant-oil-based fibre composites for boat hulls are an interesting and growing group of materials. Although many problems are to be tackled at different stages of their preparation, the green composites are already successfully commercialised. Within this paper, the most important chemical and physical characteristics of both natural fibres and sustainable resins are provided in the form of a comprehensive review. Finally, the complex issue of interactions filler-matrix is considered.

Microplastic Extraction from the Sediment Using Potassium Formate Water Solution (H2O/KCOOH)

Microplastics (MPs) are considered an important stratigraphic indicator, or ‘technofossils’, of the Anthropocene. Research on MP abundance in the environment has gained much attention but the lack of a standardized procedure has hindered the comparability of the results. The development of an effective and efficient method of MP extraction from the matrix is crucial for the proper identification and quantifying analysis of MPs in environmental samples. The procedures of density separation used currently have various limitations: high cost of reagents, limited solution density range, hazardous reagents, or a combination of the above. In this research, a procedure based on density separation with the use of potassium formate water solution (H2O/KCOOH) in controlled conditions was performed. Experimental sediment mixtures, spiked with polyethylene (PE), polystyrene (PS), polyurethane (PUR) and polyethylene terephthalate (PET) particles were prepared and an extraction procedure was tested in the context of a weight-based quantitative analysis of MPs. This article discusses the effectiveness and safety of the method. It additionally provides new information on the interactions between MP particles and the mineral matter of the sediment. Results were acquired with the use of instrumental methods, namely thermogravimetry (TG), Fourier Transform Infrared (FTIR) spectroscopy, Field Emission Scanning Electron microscopy and Energy Dispersive spectrometry (SEM/EDS), as well as X-ray fluorescence (XRF) analysis.

The ecology of the plastisphere: Microbial composition, function, assembly, and network in the freshwater and seawater ecosystems

Microplastics provide a unique habitat for microorganisms, forming the plastisphere. Yet the ecology of the plastisphere, including the microbial composition, functions, assembly processes, and interaction networks, needs to be understood. Here, we collected microplastics and their surrounding water samples in freshwater and seawater ecosystems. The bacterial and fungal communities of the plastisphere and the aquatic environment were studied based on 16S and internal transcribed spacer (ITS) high-throughput sequencing. We found that the plastisphere had a distinct microbial community and recruited a noteworthy proportion of unique species compared to the aquatic environment community, potentially altering ecosystem microbial community and causing microbial invasion. Using a random-forest machine-learning model, we identified a group of biomarkers that could best distinguish the plastisphere from the aquatic environment. Significant differences exist in microbial functions between the plastisphere and the aquatic environment, including functions of pathogenicity, compound degradation, as well as functions related to the cycling of carbon, nitrogen, and sulfur. And these functional differences were expressed differently in freshwater and seawater ecosystems. The oxidation-reduction potential, salinity, the concentrations of nitrogen-related ions (NO₃^-, NO₂^-, and NH₄⁺), and the concentration of dissolved organic carbon in the surrounding environment drive the variation of the plastisphere. But environmental physicochemical properties explain less of the microbial community variation in the plastisphere than that in the aquatic environment. Niche-based processes govern the assembly of the plastisphere community, while neutral-based processes dominate the community assembly of the aquatic environment. Furthermore, compared to the aquatic environment, the plastisphere has a network of less complexity, more modules, higher modularity, and more competitive links in freshwater ecosystems, but the pattern is reversed in seawater ecosystems. Altogether, the microbial ecology of the new anthropogenic ecosystem-plastisphere-is unique and exerts different effects in freshwater and seawater ecosystems.

The Proposal and Necessity of the Numerical Description of Nano- and Microplastics' Surfaces (Plastisphere)

The constantly growing amount of synthetic materials < 5 mm, called microplastics (MPs), is fragmented in the environment. Thus, their surface, Plastisphere, is substantially increasing forming an entirely new ecological niche. It has already been extensively studied by microbiologists observing the biofilm and by material scientists interested in the weathering of polymer materials. This paper aims to construct a bridge between the physical and chemical description of the Plastisphere and its microbiological and ecological significance. Various algorithms, based on the analysis of pictures obtained by scanning electron microscopy (SEM), are proposed to describe in detail the morphology of naturally weathered polymers. In particular, one can study the size and distribution of fibres in a standard filter, search the synthetic debris for mapping, estimate the grain size distribution, quantitatively characterize the different patterns of degradation for polymer spheres and ghost nets, or calculate the number of pores per surface. The description and visualization of a texture, as well as the classification of different morphologies present on a surface, are indispensable for the comprehensive characterization of weathered polymers found inside animals (e.g., fishes). All these approaches are presented as case studies and discussed within this work.