Environmental Factors Support the Formation of Specific Bacterial Assemblages on Microplastics

Plastic-Degrading Potential across the Global Microbiome Correlates with Recent Pollution Trends

Biodegradation is a plausible route toward sustainable management of the millions of tons of plastic waste that have accumulated in terrestrial and marine environments. However, the global diversity of plastic-degrading enzymes remains poorly understood. Taking advantage of global environmental DNA sampling projects, here we constructed hidden Markov models from experimentally verified enzymes and mined ocean and soil metagenomes to assess the global potential of microorganisms to degrade plastics. By controlling for false positives using gut microbiome data, we compiled a catalogue of over 30,000 nonredundant enzyme homologues with the potential to degrade 10 different plastic types. While differences between the ocean and soil microbiomes likely reflect the base compositions of these environments, we find that ocean enzyme abundance increases with depth as a response to plastic pollution and not merely taxonomic composition. By obtaining further pollution measurements, we observed that the abundance of the uncovered enzymes in both ocean and soil habitats significantly correlates with marine and country-specific plastic pollution trends. Our study thus uncovers the earth microbiome's potential to degrade plastics, providing evidence of a measurable effect of plastic pollution on the global microbial ecology as well as a useful resource for further applied research. IMPORTANCE Utilization of synthetic biology approaches to enhance current plastic degradation processes is of crucial importance, as natural plastic degradation processes are very slow. For instance, the predicted lifetime of a polyethylene terephthalate (PET) bottle under ambient conditions ranges from 16 to 48 years. Moreover, although there is still unexplored diversity in microbial communities, synergistic degradation of plastics by microorganisms holds great potential to revolutionize the management of global plastic waste. To this end, the methods and data on novel plastic-degrading enzymes presented here can help researchers by (i) providing further information about the taxonomic diversity of such enzymes as well as understanding of the mechanisms and steps involved in the biological breakdown of plastics, (ii) pointing toward the areas with increased availability of novel enzymes, and (iii) giving a basis for further application in industrial plastic waste biodegradation. Importantly, our findings provide evidence of a measurable effect of plastic pollution on the global microbial ecology.

Exposure to heavy metal and antibiotic enriches antibiotic resistant genes on the tire particles in soil

The widespread occurrence of tire particles (TPs) in soils has attracted considerable attention due to their potential threats. The assemblage of bacteria and associated antibiotic resistant genes (ARGs) on TPs is yet largely unknown, especially under the stress of soil pollutants. In the present study, TPs were incubated in soils with or without the stress of heavy metal (Cu²⁺) or/and antibiotic (tetracycline), and bacterial community and ARG profile on TPs and in soils were explored using high-throughput sequencing and high-throughput quantitative PCR. Results indicated that bacterial community structure on TPs was significantly different from the surrounding soils, with a lower diversity, and significantly shifted by heavy metal and antibiotic exposure. Additionally, a diverse set of ARGs were detected on TPs, and their abundances were significantly increased under the stress of heavy metal and antibiotic, revealing a strong synergistic effect. Moreover, a good fit was observed for the correlation between bacterial community and ARG profile on TPs. Taken together, this study, for the first time, demonstrates that TPs can provide a novel niche for soil bacteria and soil resistome, and heavy metal and antibiotic exposure may potentially increase the abundance of ARGs on TPs, threatening soil ecosystems and human health.

Soil pH has a stronger effect than arsenic content on shaping plastisphere bacterial communities in soil

Microplastic (MP) pollution is widespread in various ecosystems and is colonized by microbes that form biofilms with compositions and functions. However, compared with aquatic environments, the soil environment has been poorly studied in terms of the taxonomic composition of microbial communities and the factors influencing the community structure of microbes in the plastisphere. In the present study, a microcosm experiment was conducted to investigate the plastisphere bacterial communities of MP (polyvinyl chloride, PVC) in soils with different pH (4.62, 6.5, and 7.46) and arsenic (As) contents (13 and 74 mg kg^-1). Bacterial communities in the plastisphere were dominated by Proteobacteria and Firmicutes, with distinct compositions and structures compared with soil bacterial communities. Soil pH and As content significantly affected the plastisphere bacterial communities. Constrained analysis of principal coordinates and a structural equation model demonstrated that soil pH had a stronger influence on the dissimilarity and diversity of bacterial communities than did soil As content. Soil pH affected As speciation in soil and on MP. The concentration of dimethylarsinic acid (DMA) was significantly higher on MP than that in soil, indicating that As methylation occurred on MP. These results suggest that environmental fluctuations govern plastisphere bacterial communities with cascading effects on biogeochemical cycling of As in the soil ecosystems.

Biofilm-Developed Microplastics As Vectors of Pollutants in Aquatic Environments

Microplastics are a big and growing part of global pollution, which has aroused increasing concern in recent years because of their large amount, wide distribution, and adverse effects. Microplastics can sorb various pollutants from aquatic environments and act as vectors of pollutants. Most studies mainly focused on the virgin microplastics. However, microplastics in environments can be easily colonized by microorganisms, and form biofilm, which will influence the behaviors and potential risks of microplastics. The formation of biofilm on microplastics and its effects on their properties have been studied before, but their sorption and transport behaviors, and potential risks for pollutants' transfer have not been reviewed. In this paper, the role of biofilm-developed microplastics as vectors of pollutants was thoroughly analyzed and summarized. First, the formation of biofilm on microplastics, the compositions of microorganisms in biofilm, the influencing factors, and the property changes of microplastics after biofilm attachment are thoroughly reviewed. Second, the sorption of pollutants onto biofilm-developed microplastics is discussed. Third, the role of biofilm-developed microplastics as vector of pollutants are analyzed. We concluded that microplastics could provide unique substrates for microorganisms. Biofilm-developed microplastics can sorb more pollutants than the virgin ones, then act as vectors to introduce pollutants and attached microorganisms to aquatic environments and to organisms.

Biogeography rather than substrate type determines bacterial colonization dynamics of marine plastics

Since the middle of the 20th century, plastics have been incorporated into our everyday lives at an exponential rate. In recent years, the negative impacts of plastics, especially as environmental pollutants, have become evident. Marine plastic debris represents a relatively new and increasingly abundant substrate for colonization by microbial organisms, although the full functional potential of these organisms is yet to be uncovered. In the present study, we investigated plastic type and incubation location as drivers of marine bacterial community structure development on plastics, i.e., the Plastisphere, via 16S rRNA amplicon analysis. Four distinct plastic types: high-density polyethylene (HDPE), linear low-density polyethylene (LDPE), polyamide (PA), polymethyl methacrylate (PMMA), and glass-slide controls were incubated for five weeks in the coastal waters of four different biogeographic locations (Cape Verde, Chile, Japan, South Africa) during July and August of 2019. The primary driver of the coastal Plastisphere composition was identified as incubation location, i.e., biogeography, while substrate type did not have a significant effect on bacterial community composition. The bacterial communities were consistently dominated by the classes Alphaproteobacteria, Gammaproteobacteria, and Bacteroidia, irrespective of sampling location or substrate type, however a core bacterial Plastisphere community was not observable at lower taxonomic levels. Overall, this study sheds light on the question of whether bacterial communities on plastic debris are shaped by the physicochemical properties of the substrate they grow on or by the marine environment in which the plastics are immersed. This study enhances the current understanding of biogeographic variability in the Plastisphere by including biofilms from plastics incubated in the previously uncharted Southern Hemisphere.

Seasonal biofilm formation on floating microplastics in coastal waters of intensified marinculture area

The environmental pollution caused by microplastics has received increasing attention recently. In this paper, we present the results of research into the bacterium attached to microplastics in four coastal mariculture zones in southeast China during winter and summer. Polyethene and polypropylene are the main microplastics in the surface water of mariculture area. The differences between the bacteria species composition found on the surface of microplastics in winter and summer were less than that found in the planktonic bacteria, indicating that biofilms protect the bacterium that live inside. Potentially pathogenic Vibrio and Pseudomonas spp. were more abundant in samples from ShanTou and QuanZhou during the summer. Bacteria related to the degradation of microplastics were found extensively on the surface of microplastics at all of the sampling sites. More attention should be paid to the risks resulting from the accumulation of harmful bacteria on microplastic surfaces during the summer.

Assessing the Risks of Potential Bacterial Pathogens Attaching to Different Microplastics during the Summer-Autumn Period in a Mariculture Cage

As microplastic pollution continues to increase, an emerging threat is the potential for microplastics to act as novel substrates and/or carriers for pathogens. This is of particular concern for aquatic product safety given the growing evidence of microplastic ingestion by aquaculture species. However, the potential risks of pathogens associated with microplastics in mariculture remain poorly understood. Here, an in situ incubation experiment involving three typical microplastics including polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP) was conducted during the summer–autumn period in a mariculture cage. The identification of potential pathogens based on the 16S rRNA gene amplicon sequencing and a custom-made database for pathogenic bacteria involved in aquatic environments, was performed to assess the risks of different microplastics attaching potential pathogens. The enrichment of pathogens was not observed in microplastic-associated communities when compared with free-living and particle-attached communities in surrounding seawater. Despite the lower relative abundance, pathogens showed different preferences for three microplastic substrates, of which PET was the most favored by pathogens, especially potentially pathogenic members of Vibrio, Tenacibaculum, and Escherichia. Moreover, the colonization of these pathogens on microplastics was strongly affected by environmental factors (e.g., temperature, nitrite). Our results provide insights into the ecological risks of microplastics in mariculture industry.

Distinct profile of bacterial community and antibiotic resistance genes on microplastics in Ganjiang River at the watershed level

Microplastics are of great public concern due to their wide distribution and the potential risk to humans and animals. In this study, the microplastic pollution associated with bacterial communities, human pathogenic bacteria, and antibiotic resistance genes (ARGs) were investigated compared to water, sediment, and natural wood particles. Microplastics were widely distributed in surface water of the Ganjiang River at a watershed level with an average value of 407 particles m^-3. The fragment was the main microplastic shape found in the basin. Microplastics had significantly higher observed species and Chao1 index of bacterial communities than those in water, but comparable to wood particles. However, there was no difference in the microplastics pollution and alpha diversity indices of bacterial between different reaches along the Ganjiang River. Flavobacterium, Rhodoferax, Pseudomonas, and Janthinobacterium on the microplastics were all found to be enriched compared with water and sediment. Principal component analysis of the composition and function profile of bacterial communities showed that microplastics provide a new microbial niche in the Ganjiang River, which was distinct from water, sediment, and natural wood. Pseudomonas genus dominated the composition of human pathogenic bacteria on the microplastics, which was significantly different from water and sediment. No difference was observed in the relative abundance of total ARGs among the four media. However, microplastic and wood particles showed similar composition patterns of ARGs compared with water and sediment.

Conditioning Film and Early Biofilm Succession on Plastic Surfaces

In the context of environmental plastic pollution, it is still under debate if and how the "plastisphere", a plastic-specific microbial community, emerges. In this study, we tested the hypothesis that the first conditioning film of dissolved organic matter (DOM) sorbs selectively to polymer substrates and that microbial attachment is governed in a substrate-dependent manner. We investigated the adsorption of stream water-derived DOM to polyethylene terephthalate (PET), polystyrene (PS), and glass (as control) including UV-weathered surfaces by Fourier-transform ion cyclotron mass spectrometry. Generally, the saturated, high-molecular mass and thus more hydrophobic fraction of the original stream water DOM preferentially adsorbed to the substrates. The UV-weathered polymers adsorbed more polar, hydrophilic OM as compared to the dark controls. The amplicon sequencing data of the initial microbial colonization process revealed a tendency of substrate specificity for biofilm attachment after 24 h and a clear convergence of the communities after 72 h of incubation. Conclusively, the adsorbed OM layer developed depending on the materials' surface properties and increased the water contact angles, indicating higher surface hydrophobicity as compared to pristine surfaces. This study improves our understanding of molecular and biological interactions at the polymer/water interface that are relevant to understand the ecological impact of plastic pollution on a community level.

Survival of human enteric and respiratory viruses on plastics in soil, freshwater, and marine environments

The public health significance of plastics and microplastics in different environmental matrices has mainly focused on the toxicological effects of human ingestion. But these pollutants can also harbour pathogenic bacteria as the surfaces of plastics in the environment quickly become colonised by microbial biofilm. This novel microbial habitat has been termed the 'plastisphere' and could facilitate the survival and dissemination of important bacterial and fungal pathogens. Importantly, however, the role of plastic pollution as a secondary pathway for the transmission of human pathogenic viruses has never been addressed. Due to the high prevalence of both enteric and respiratory viruses in the population and in the environment, there is significant potential for human viruses to become associated with the plastisphere. In this review we critically evaluate current knowledge on the interaction of human enteric and respiratory viruses with plastic surfaces and identify the main environmental conditions and plastic characteristics that could affect virus survival and persistence in the environment. Our hypothesis is that the plastisphere can enhance the adhesion, survival and dissemination of human pathogenic viruses and potentially lead to more effective transfer and transmission of viral diseases within the environment. We identify key research questions needed to more fully assess the potential human health risks associated with viruses on plastic surfaces. These include understanding, (1) the mechanisms of viral attachment to either naked or biofilm-colonised plastic (2) how the structural characteristics of viruses (e.g., enveloped, or non-enveloped), affect their persistence in the plastisphere, (3) whether the plastisphere offers protection and increases the persistence of infectious viruses in soil, freshwater, and marine environments.

Freshwater wild biota exposure to microplastics: A global perspective

Current understanding on the exposure of freshwater organisms to microplastics (plastics sized between 1 µm and 5 mm) has arisen mostly from laboratory experiments-often conducted under artificial circumstances and with unrealistic concentrations. In order to improve scientific links through real ecosystem exposure, we review field data on the exposure of free-living organisms to microplastics.We highlight that the main outputs provided by field research are an assessment of the occurrence and, at times, the quantification of microplastics in different animal taxa. Topics of investigation also include the causes of contamination and the development of biological monitoring tools. With regard to taxa, fish, mollusks, and arthropods are at the center of the research, but birds and amphibians are also investigated. The ingestion or occurrence of microplastics in organs and tissues, such as livers and muscles, are the main data obtained. Microorganisms are studied differently than other taxa, highlighting interesting aspects on the freshwater plastisphere, for example, related to the structure and functionality of communities. Many taxa, that is, mammals, reptiles, and plants, are still under-examined with regard to exposure to microplastics; this is surprising as they are generally endangered.As biota contamination is acknowledged, we contribute to an interdisciplinary scientific discussion aimed at a better assessment of knowledge gaps on methodology, impact assessment, and monitoring.

Microplastics accumulate fungal pathogens in terrestrial ecosystems

Microplastic (MP) is a pervasive pollutant in nature that is colonised by diverse groups of microbes, including potentially pathogenic species. Fungi have been largely neglected in this context, despite their affinity for plastics and their impact as pathogens. To unravel the role of MP as a carrier of fungal pathogens in terrestrial ecosystems and the immediate human environment, epiplastic mycobiomes from municipal plastic waste from Kenya were deciphered using ITS metabarcoding as well as a comprehensive meta-analysis, and visualised via scanning electron as well as confocal laser scanning microscopy. Metagenomic and microscopic findings provided complementary evidence that the terrestrial plastisphere is a suitable ecological niche for a variety of fungal organisms, including important animal and plant pathogens, which formed the plastisphere core mycobiome. We show that MPs serve as selective artificial microhabitats that not only attract distinct fungal communities, but also accumulate certain opportunistic human pathogens, such as cryptococcal and Phoma-like species. Therefore, MP must be regarded a persistent reservoir and potential vector for fungal pathogens in soil environments. Given the increasing amount of plastic waste in terrestrial ecosystems worldwide, this interrelation may have severe consequences for the trans-kingdom and multi-organismal epidemiology of fungal infections on a global scale.

Product Formulation Controls the Impact of Biofouling on Consumer Plastic Photochemical Fate in the Ocean

The photodegradation rates of floating marine plastics govern their environmental lifetimes, but the controls on this process remain poorly understood. Photodegradation of these materials has so far been studied under ideal conditions in the absence of environmental factors such as biofouling, which may slow photochemical transformation rates through light screening. To investigate this interaction, we incubated different plastics in continuous flow seawater mesocosms to follow (i) the extent of biofilm growth on the samples and (ii) decreases in light transmittance through the samples over time. We used consumer products with high relevance (e.g., shopping bags, water bottles, and packaging materials) and with different formulations, referring to primary polymers (polyethylene (PE) and polyethylene terephthalate (PET)) and inorganic additives (titanium dioxide (TiO₂)). The behavior of consumer-relevant formulations was compared to those of pure PE and PET films, revealing that the relative effects of UV- and, to a lesser extent, visible-light screening differ based on the formulation of the product. Pure PE showed greater relative UV-transmittance decreases (Δ = -34% through the entire sample, accounting for biofilm on both sides of the plastic film) than PET (Δ = -20%) and PE products with TiO₂ (Δ = < -10%). Our results demonstrate that even with biofouling, photodegradation remains a highly relevant process for the fate of marine plastics. However, we expect photodegradation rates of plastics in the ocean to be slower than those measured in laboratory studies, due to light screening by biofilms, and the specific formulation of plastic products is a key determinant of the extent of this effect.

Insight into the immune and microbial response of the white-leg shrimp Litopenaeus vannamei to microplastics

Microplastics (MPs) are a new type of environmental pollutant. To investigate the response of shrimp and their microflora to MPs, Litopenaeus vannamei (L. vannamei) was exposed to different concentrations of MPs (0, 50, 500, and 5000 μg/L, i.e., C, L, M and H groups) for 48 h. The survival rate, intake of MPs, immune-related gene expression and microbial response under MP exposure were detected. The results showed that the survival rate in the H group was significantly lower than those in the C, L and M groups, while the relative expression levels of proPO, TLR and ALF in the M and H groups were significantly higher than those in the C and L groups. For the microbial response, microbial community richness in the L group was significantly decreased, while community richness and diversity in the H group were significantly increased compared with those in the C group. The relative abundances of 3, 4 and 11 taxa were significantly changed after MP treatment at the phylum, class and genus levels, respectively. The results suggested that short-term exposure to low concentrations of MPs did not cause immune defense responses or death but affected the balance of bacterial composition in shrimp. Exposure to high concentrations of MPs can induce immune responses and microbial changes and can even cause death in shrimp. These findings increase our understanding of MP impacts on aquatic organisms.

A multi-OMIC characterisation of biodegradation and microbial community succession within the PET plastisphere

BACKGROUND

Plastics now pollute marine environments across the globe. On entering these environments, plastics are rapidly colonised by a diverse community of microorganisms termed the plastisphere. Members of the plastisphere have a myriad of diverse functions typically found in any biofilm but, additionally, a number of marine plastisphere studies have claimed the presence of plastic-biodegrading organisms, although with little mechanistic verification. Here, we obtained a microbial community from marine plastic debris and analysed the community succession across 6 weeks of incubation with different polyethylene terephthalate (PET) products as the sole carbon source, and further characterised the mechanisms involved in PET degradation by two bacterial isolates from the plastisphere.

RESULTS

We found that all communities differed significantly from the inoculum and were dominated by Gammaproteobacteria, i.e. Alteromonadaceae and Thalassospiraceae at early time points, Alcanivoraceae at later time points and Vibrionaceae throughout. The large number of encoded enzymes involved in PET degradation found in predicted metagenomes and the observation of polymer oxidation by FTIR analyses both suggested PET degradation was occurring. However, we were unable to detect intermediates of PET hydrolysis with metabolomic analyses, which may be attributed to their rapid depletion by the complex community. To further confirm the PET biodegrading potential within the plastisphere of marine plastic debris, we used a combined proteogenomic and metabolomic approach to characterise amorphous PET degradation by two novel marine isolates, Thioclava sp. BHET1 and Bacillus sp. BHET2. The identification of PET hydrolytic intermediates by metabolomics confirmed that both isolates were able to degrade PET. High-throughput proteomics revealed that whilst Thioclava sp. BHET1 used the degradation pathway identified in terrestrial environment counterparts, these were absent in Bacillus sp. BHET2, indicating that either the enzymes used by this bacterium share little homology with those characterised previously, or that this bacterium uses a novel pathway for PET degradation.

CONCLUSIONS

Overall, the results of our multi-OMIC characterisation of PET degradation provide a significant step forwards in our understanding of marine plastic degradation by bacterial isolates and communities and evidences the biodegrading potential extant in the plastisphere of marine plastic debris. Video abstract.

Microbial Communities on Plastic Polymers in the Mediterranean Sea

Plastic particles in the ocean are typically covered with microbial biofilms, but it remains unclear whether distinct microbial communities colonize different polymer types. In this study, we analyzed microbial communities forming biofilms on floating microplastics in a bay of the island of Elba in the Mediterranean Sea. Raman spectroscopy revealed that the plastic particles mainly comprised polyethylene (PE), polypropylene (PP), and polystyrene (PS) of which polyethylene and polypropylene particles were typically brittle and featured cracks. Fluorescence in situ hybridization and imaging by high-resolution microscopy revealed dense microbial biofilms on the polymer surfaces. Amplicon sequencing of the 16S rRNA gene showed that the bacterial communities on all plastic types consisted mainly of the orders Flavobacteriales, Rhodobacterales, Cytophagales, Rickettsiales, Alteromonadales, Chitinophagales, and Oceanospirillales. We found significant differences in the biofilm community composition on PE compared with PP and PS (on OTU and order level), which shows that different microbial communities colonize specific polymer types. Furthermore, the sequencing data also revealed a higher relative abundance of archaeal sequences on PS in comparison with PE or PP. We furthermore found a high occurrence, up to 17% of all sequences, of different hydrocarbon-degrading bacteria on all investigated plastic types. However, their functioning in the plastic-associated biofilm and potential role in plastic degradation needs further assessment.

The fate of plastic litter within estuarine compartments: An overview of current knowledge for the transboundary issue to guide future assessments

Plastics can enter biogeochemical cycles and thus be found in most ecosystems. Most studies emphasize plastic pollution in oceanic ecosystems even though rivers and estuaries are acknowledged as the main sources of plastics to the oceans. This review detected few studies approaching the transboundary issue, as well as patterns of estuarine gradients in predicting plastic distribution and accumulation in water, sediments, and organisms. Quantities of plastics in estuaries reach up to 45,500 items m^-3 in water, 567,000 items m^-3 in sediment, and 131 items per individual in the biota. The role of rivers and estuaries in the transport of plastics to the ocean is far from fully understood due to small sample sizes, short-term approaches, sampling techniques that underestimate small plastics, and the use of site-specific sampling rather than covering environmental gradients. Microfibres are the most commonly found plastic type in all environmental matrices but efforts to re-calculate pathways using novel sampling techniques and estimates are incipient. Microplastic availability to estuarine organisms and rising/sinking is determined by polymer characteristics and spatio-temporal fluctuations in physicochemical, biological, and mineralogical factors. Key processes governing plastic contamination along estuarine trophic webs remain unclear, as most studies used "species" as an ecological unit rather than trophic/functional guilds and ontogenetic shifts in feeding behaviour to understand communities and intraspecific relationships, respectively. Efforts to understand contamination at the tissue level and the contribution of biofouling organisms as vectors of contaminants onto plastic surfaces are increasing. In conclusion, rivers and estuaries still require attention with regards to accurate sampling and conclusions. Multivariate analysis and robust models are necessary to predict the fate of micro- and macroplastics in estuarine environments; and the inclusion of the socio-economic aspects in modelling techniques seems to be relevant regarding management approaches.

Impact of Microbial Colonization of Polystyrene Microbeads on the Toxicological Responses in the Sea Urchin Paracentrotus lividus

The sea urchin Paracentrotus lividus (P. lividus) was exposed to either virgin or biofilm-covered polystyrene microbeads (micro-PS, 45 μm) in order to test the effect of microbial colonization on the uptake, biodistribution, and immune response. The biofilm was dominated by bacteria, as detected by scanning electron microscopy and 16S rRNA sequencing. A higher internalization rate of colonized micro-PS inside sea urchins compared to virgin ones was detected, suggesting a role of the plastisphere in the interaction. Colonized and virgin micro-PS showed the same biodistribution pattern by accumulating mainly in the digestive system with higher levels and faster egestion rates for the colonized. However, a significant increase of catalase and total antioxidant activity was observed only in the digestive system of colonized micro-PS-exposed individuals. Colonized micro-PS also induced a significant decrease in the number of coelomocytes with a significant increase in vibratile cells, compared to control and virgin micro-PS-exposed animals. Moreover, a general time-dependent increase in the red/white amoebocytes ratio and reactive oxygen species and a decrease in nitrogen ones were observed upon exposure to both colonized and virgin micro-PS. Overall, micro-PS colonization clearly affected the uptake and toxicological responses of the Mediterranean sea urchin P. lividus in comparison to virgin micro-PS.

Microplastics are a hotspot for antibiotic resistance genes: Progress and perspective

Antibiotic resistance genes (ARGs) and microplastics in the environment are of great public concern due to their potential risk to human health. Microplastics can form distinct bacterial communities and absorb pollutants from the surrounding environment, which provide potential hosts and exert possible selection pressure of ARGs. We provide a practical evaluation of the scientific literature regarding this issue. The occurrence and transport of ARGs on microplastics in wastewater treatment plants, aquatic, terrestrial, and air environments were summarized. Selective enrichment of ARGs and antibiotic resistance bacteria on microplastics have been confirmed in different environments. Aggregates may be crucial to understand the behavior and transport of ARGs on microplastics, especially in the aquatic and terrestrial environment. Microplastics could be a carrier of ARGs between the environment and animals. Accumulation of pollutants and dense bacterial communities on microplastics provide favorable conditions for higher transfer rate and evolution of ARGs. More studies are still needed to understand the enrichment, transport, and transfer of ARGs on microplastics and provide a fundamental basis for evaluating their exposure health risk to humans.

Cross-Hemisphere Study Reveals Geographically Ubiquitous, Plastic-Specific Bacteria Emerging from the Rare and Unexplored Biosphere

While it is now appreciated that the millions of tons of plastic pollution travelling through marine systems carry complex communities of microorganisms, it is still unknown to what extent these biofilm communities are specific to the plastic or selected by the surrounding ecosystem. To address this, we characterized and compared the microbial communities of microplastic particles, nonplastic (natural and wax) particles, and the surrounding waters from three marine ecosystems (the Baltic, Sargasso and Mediterranean seas) using high-throughput 16S rRNA gene sequencing. We found that biofilm communities on microplastic and nonplastic particles were highly similar to one another across this broad geographical range. The similar temperature and salinity profiles of the Sargasso and Mediterranean seas, compared to the Baltic Sea, were reflected in the biofilm communities. We identified plastic-specific operational taxonomic units (OTUs) that were not detected on nonplastic particles or in the surrounding waters. Twenty-six of the plastic-specific OTUs were geographically ubiquitous across all sampled locations. These geographically ubiquitous plastic-specific OTUs were mostly low-abundance members of their biofilm communities and often represented uncultured members of marine ecosystems. These results demonstrate the potential for plastics to be a reservoir of rare and understudied microbes, thus warranting further investigations into the dynamics and role of these microbes in marine ecosystems.

IMPORTANCE This study represents one of the largest comparisons of biofilms from environmentally sampled plastic and nonplastic particles from aquatic environments. By including particles sampled through three separate campaigns in the Baltic, Sargasso, and Mediterranean seas, we were able to make cross-geographical comparisons and discovered common taxonomical signatures that define the plastic biofilm. For the first time, we identified plastic-specific bacteria that reoccur across marine regions. Our data reveal that plastics have selective properties that repeatedly enrich for similar bacteria regardless of location, potentially shifting aquatic microbial communities in areas with high levels of plastic pollution. Furthermore, we show that bacterial communities on plastic do not appear to be strongly influenced by polymer type, suggesting that other properties, such as the absorption and/or leaching of chemicals from the surface, are likely to be more important in the selection and enrichment of specific microorganisms.

Bacterial community profiling of floating plastics from South Mediterranean sites: First evidence of effects on mussels as possible vehicles of transmission

Plastic wastes accumulation in marine environments is becoming a crucial issue; while the toxicity to biota is quite well explored, a gap of knowledge still exists on the role that plastics play in shaping bacterial community structures in marine conditions and their possible transmission to humans. The present study intended first to profile bacterial community structure in floating plastic particles (FP) biofilms and seawater from four Tunisian coastal areas using high-throughput sequencing (HTS) of 16S rDNA. Subsequently, mussels (Mytilus galloprovincialis) as filter feeding organisms were exposed to the FP to broaden the knowledge on the potential role played by environmental plastic particles in shaping bacterial community structures and on their possibility to act as vehicles of bacteria through the food web. The mussels' microbiota was microbiologically analyzed through HTS, and the Histidine Rich Glycoprotein (HRG) gene expression level was investigated as the main immune response. Our results clearly showed a great variation in the composition of bacterial communities of FP and seawater from different geographical areas. Moreover, the gills of mussels exposed to sterilized seawater and native FP from each site exhibited a wider bacterial biodiversity. The gene expression level of HRG was found to be significantly higher in animals exposed to native FP when compared to sterilized FP. Our results should be carefully considered in view of the Trojan horse effects of FP toward bacteria and its potential toxicity.

Fingerprinting Plastic-Associated Inorganic and Organic Matter on Plastic Aged in the Marine Environment for a Decade

The long-term aging of plastic leads to weathering and biofouling that can influence the behavior and fate of plastic in the marine environment. This is the first study to fingerprint the contaminant profiles and bacterial communities present in plastic-associated inorganic and organic matter (PIOM) isolated from 10 year-aged plastic. Plastic sleeves were sampled from an oyster aquaculture farm and the PIOM was isolated from the intertidal, subtidal, and sediment-buried segments to investigate the levels of metal(loid)s, polyaromatic hydrocarbons (PAHs), per-fluoroalkyl substances (PFAS) and explore the microbial community composition. Results indicated that the PIOM present on long-term aged high-density polyethylene plastic harbored high concentrations of metal(loid)s, PAHs, and PFAS. Metagenomic analysis revealed that the bacterial composition in the PIOM differed by habitat type, which consisted of potentially pathogenic taxa including Vibrio, Shewanella, and Psychrobacter. This study provides new insights into PIOM as a potential sink for hazardous environmental contaminants and its role in enhancing the vector potential of plastic. Therefore, we recommend the inclusion of PIOM analysis in current biomonitoring regimes and that plastics be used with caution in aquaculture settings to safeguard valuable food resources, particularly in areas of point-source contamination.

Diversity and structure of microbial biofilms on microplastics in riverine waters of the Pearl River Delta, China

Riverine runoff is a significant transport pathway for microplastics (MPs) discharged from land-based sources to marine environments where MPs accumulate. Knowledge of riverine MP-associated biofilms will improve the understanding of the fate and potential effects of MPs in marine environments. This study aimed to characterize the microbial biofilms colonizing MPs in the riverine water of the Pearl River Delta, China, and identify the seasonal, geographical and environmental influences on MP-associated communities. We sampled MPs and the surrounding surface water from eight outlets in three seasons and analyzed their microbial communities by Illumina sequencing of the 16S rRNA gene libraries. Across all sampling seasons and locations, abundant MP-colonizing taxa belonged to the phylum Proteobacteria, which suggested initial biofilm development on those MPs. The structure and composition of MP-attached microbial communities varied with respect to season and location, and the microbial diversity of the MP-associated biofilm communities decreased in June compared with that in the April and November sampling events. Opportunistic pathogens of the genus Acinetobacter were significantly enriched on the MP surfaces for all sampling events. Among the 15 environmental variables examined, the main drivers of MP-associated biofilm community composition included IC, alkalinity, TOC, TDS, Cl^-, NO₃^-, NO₂^- and pH. This study provides an insight into the environmental factors that shape microbial biofilm colonization on MPs in estuary environments and a further understanding of the structure, diversity and ecological roles of MP-associated communities.

Effects of Plastic Debris on the Biofilm Bacterial Communities in Lake Water

Increasing discharge of plastic debris into aquatic ecosystems and the worsening ecological risks have received growing attention. Once released, plastic debris could serve as a new substrate for microbes in waters. The complex relationship between plastics and biofilms has aroused great interest. To confirm the hypothesis that the presence of plastic in water affects the composition of biofilm in natural state, in situ biofilm culture experiments were conducted in a lake for 40 days. The diversity of biofilm attached on natural (cobble stones (CS) and wood) and plastic substrates (Polyethylene terephthalate (PET) and Polymethyl methacrylate (PMMA)) were compared, and the community structure and composition were also analyzed. Results from high-throughput sequencing of 16S rRNA showed that the diversity and species richness of biofilm bacterial communities on natural substrate (observed species of 1353~1945, Simpson index of 0.977~0.989 and Shannon–Wiener diversity index of 7.42~8.60) were much higher than those on plastic substrates (observed species of 900~1146, Simpson index of 0.914~0.975 and Shannon–Wiener diversity index of 5.47~6.99). The NMDS analyses were used to confirm the taxonomic significance between different samples, and Anosim (p = 0.001, R = 0.892) and Adonis (p = 0.001, R = 808, F = 11.19) demonstrated that this classification was statistically rigorous. Different dominant bacterial communities were found on plastic and natural substrates. Alphaproteobacterial, Betaproteobacteria and Synechococcophycideae dominated on the plastic substrate, while Gammaproteobacteria, Phycisphaerae and Planctomycetia played the main role on the natural substrates. The bacterial community structure of the two substrates also showed significant difference which is consistent with previous studies using other polymer types. Our results shed light on the fact that plastic debris can serve as a new habitat for biofilm colonization, unlike natural substrates, pathogens and plastic-degrading microorganisms selectively attached to plastic substrates, which affected the bacterial community structure and composition in aquatic environment. This study provided a new insight into understanding the potential impacts of plastics serving as a new habitat for microbial communities in freshwater environments. Future research should focus on the potential impacts of plastic-attached biofilms in various aquatic environments and the whole life cycle of plastics (i.e., from plastic fragments to microplastics) and also microbial flock characteristics using microbial plastics in the natural environment should also be addressed.

Spatial and seasonal variations in biofilm formation on microplastics in coastal waters

At present, microplastics (MPs) have gradually become a hot issue in marine environmental pollution and may pose a potential threat to marine ecosystems. Since MPs are not easily biodegradable, they can provide the attachment substrates for various organisms, which will affect their floating and transport, and may also lead to the invasion of harmful microorganisms. In this study, polypropylene, polyethylene, polylactic acid pellets, and glass particles were exposed for 6 weeks in different seasons at three stations in the Yellow Sea, China. The results showed that the total amounts of biofilms significantly varied among seasons and functional zones and that the temperature of seawater was the main influencing factor. A variety of biological communities (especially diatoms and bacteria) and extracellular polymeric substances were observed on the MP surfaces using scanning electron microscopy and confocal laser scanning microscopy. Sequencing analysis indicated that the structure and composition of microbial communities on MPs mainly varied with seasons and locations. In addition, most of the microorganisms were generally attached to the surface and were not any specific selection of plastic by different chemical compositions. However, the bacteria inhabiting microplastics harbored distinct metabolisms. Our results suggest that low-density MPs may settle quickly in summer in some eutrophic areas.

Temperate and tropical coastal waters share relatively similar microbial biofilm communities while free-living or particle-attached communities are distinct

Free-living (FL) marine microbial communities differ from those attached to particles (PA). Likewise, biofilms (B) colonizing artificial surfaces, including plastics or ship hulls, hardly resemble their planktonic surroundings. However, few studies have examined the effect of the environment on these lifestyles and on the source of organisms colonizing marine surfaces. Using 16S rRNA gene metabarcoding, we identified specificities of marine prokaryotic community lifestyles (FL, PA or B) sampled in three coastal polluted locations with dissimilar environmental conditions: the North-Western Mediterranean Sea and the Atlantic and Indian Oceans. Biofilms developed over polyvinyl chloride (PVC) were found to be significantly different from FL or PA collected during the immersions. Alpha-diversity increased from FL to PA and to B, illustrating the integrative aspect of the latter, with little proportion of operational taxonomic units shared with the first two. Beta-diversity clustered first the lifestyles and then the sites. FL and PA were more affected by water quality, especially by trace metal contamination, whereas B were as sensitive to trace metals as to nutrients. Although biofilms should be supplied by the planktonic (ultra) rare biosphere, source tracking could only detect small contributions of FL or PA taxa to B communities.

Genomic and proteomic profiles of biofilms on microplastics are decoupled from artificial surface properties

Microplastics in marine ecosystems are colonized by diverse prokaryotic and eukaryotic communities. How these communities and their functional profiles are shaped by the artificial surfaces remains broadly unknown. In order to close this knowledge gap, we set up an in situ experiment with pellets of the polyolefin polymer polyethylene (PE), the aromatic hydrocarbon polymer polystyrene (PS), and wooden beads along a coastal to estuarine gradient in the Baltic Sea, Germany. We used an integrated metagenomics/metaproteomics approach to evaluate the genomic potential as well as protein expression levels of aquatic plastic biofilms. Our results suggest that material properties had a minor influence on the plastic-associated assemblages, as genomic and proteomic profiles of communities associated with the structurally different polymers PE and PS were highly similar, hence polymer-unspecific. Instead, it seemed that these communities were shaped by biogeographic factors. Wood, on the other hand, induced the formation of substrate-specific biofilms and served as nutrient source itself. Our study indicates that, while PE and PS microplastics may be relevant in the photic zone as opportunistic colonization grounds for phototrophic microorganisms, they appear not to be subject to biodegradation or serve as vectors for pathogenic microorganisms in marine habitats.

Temporal changes in water temperature and salinity drive the formation of a reversible plastic-specific microbial community

Plastic is a ubiquitous pollutant in the marine environment. Here, we investigated how temporal changes in environmental factors affect the microbial communities formed on plastic (polyethylene terephthalate; PET) versus a ceramic substrate. In situ mesocosms (N = 90 replicates) were deployed at the sediment-water interface of a coastal lagoon and sampled every 4 weeks for 424 days. Sequencing data (16S rRNA) was parsed based on variation in temperature with the exposure starting in fall 2016 and remaining in situ through the next four seasons (winter, spring, summer and fall 2017). PET biofilms were distinct during the summer when salinity and temperature were highest. In particular, a significant shift in the relative abundance of Ignavibacteriales and Cytophagales was observed during the summer, but PET and ceramic communities were again indistinguishable the following fall. Water temperature, salinity and pH were significant drivers of PET biofilm diversity as well as the relative abundance of plastic-discriminant taxa. This study illustrates the temporal and successional dynamics of PET biofilms and clearly demonstrates that increased water temperature, salinity, pH and exposure length play a role in the formation of a plastic-specific microbial community, but this specificity can be lost with a change in environmental conditions.

Exploring the Composition and Functions of Plastic Microbiome Using Whole-Genome Sequencing

Besides the ecotoxicological consequences of microplastics and associated chemicals, the association of microbes on plastics has greater environmental implications as microplastics may select for unique microbiome participating in environmentally significant functions. Despite this, the functional potential of the microbiome associated with different types of plastics is understudied. Here, we investigate the interaction between plastic and marine biofilm-forming microorganisms through a whole-genome sequencing approach on four types of microplastics incubated in the marine environment. Taxonomic analysis suggested that the microplastic surfaces exhibit unique microbial profiles and niche partitioning among the substrates. In particular, the abundance of Vibrio alginolyticus and Vibrio campbellii suggested that microplastic pollution may pose a potential risk to the marine food chain and negatively impact aquaculture industries. Microbial genera involved in xenobiotic compound degradation, carbon cycling, and genes associated with the type IV secretion system, conjugal transfer protein TraG, plant-pathogen interaction, CusA/CzcA family heavy metal efflux transfer proteins, and TolC family proteins were significantly enriched on all the substrates, indicating the variety of processes operated by the plastic-microbiome. The present study gives a detailed characterization of the rapidly altering microbial composition and gene pools on plastics and adds new knowledge surrounding the environmental ramifications of marine plastic pollution.

Techniques Used for Analyzing Microplastics, Antimicrobial Resistance and Microbial Community Composition: A Mini-Review

Antimicrobial resistance (AMR) is a global health threat. Antibiotics, heavy metals, and microplastics are environmental pollutants that together potentially have a positive synergetic effect on the development, persistence, transport, and ecology of antibiotic resistant bacteria in the environment. To evaluate this, a wide array of experimental methods would be needed to quantify the occurrence of antibiotics, heavy metals, and microplastics as well as associated microbial communities in the natural environment. In this mini-review, we outline the current technologies used to characterize microplastics based ecosystems termed "plastisphere" and their AMR promoting elements (antibiotics, heavy metals, and microbial inhabitants) and highlight emerging technologies that could be useful for systems-level investigations of AMR in the plastisphere.

Isolation and characterization of human pathogenic multidrug resistant bacteria associated with plastic litter collected in Zanzibar

Plastic pollution is a growing problem, not at least in areas where poor waste management results in direct pollution of coastal zones, such as South Asia and regions in Africa. In addition to the effect on ecosystems and their related services, plastic pollution may also affect human health indirectly as vectors for infectious disease. As plastic offers a suitable surface for the attachment of biofilm forming bacteria, it may contribute to disease outbreaks and antimicrobial resistance. To investigate the role of plastic litter as potential vectors for pathogenic bacteria, we collected plastic litter from four rural sites in Zanzibar, and isolated adhered bacteria. Isolates were short-read sequenced for further molecular analysis. This revealed that collected plastic litter was associated with diverse bacterial species, including human pathogens Citrobacter freundii, Klebsiella pneumoniae and Vibrio cholerae. Furthermore, most isolates were found to be multidrug resistant. Our findings confirm that plastic litter, serve as novel reservoir for human multidrug resistant pathogenic bacteria that combined with poor sanitation and waste handling, may lead to transmission of infectious diseases and antimicrobial resistance. These findings add a new level to the environmental challenges with plastic pollution; the potential health risk associated with exposure to plastic litter.

Effect of polymer type on the colonization of plastic pellets by marine bacteria

Plastic is omnipresent in the oceans and serves as a surface for biofilm-forming microorganisms. Plastic debris comprises different polymers, which may influence microbial colonization; here, we evaluated whether polymer type affects bacterial biofilm formation. Quantifying the biofilm on polyethylene (PE), polypropylene (PP) or polystyrene (PS) pellets by six marine bacterial strains (Vibrio,Pseudoalteromonas,Phaeobacter) demonstrated that each strain had a unique colonization behavior with either a preference for PS or PP over the other polymer types or no preference for a specific plastic type. PE, PP and PS pellets were exposed to natural seawater microbiota using free-living or total communities as inoculum. Microbial assembly as determined by 16S rRNA (V4) amplicon sequencing was affected by the composition of the initial inoculum and also by the plastic type. Known polymer and hydrocarbon degraders such as Paraglaciecola, Oleibacter and Hydrogenophaga were found in the plastic biofilms. Thus, on a community level, bacterial colonization on plastic is influenced by the microorganisms as well as the polymer type, and also individual strains can demonstrate polymer-specific colonization.

Early and differential bacterial colonization on microplastics deployed into the effluents of wastewater treatment plants

Microbial colonization of microplastics (MPs) in aquatic ecosystems is a well-known phenomenon; however, there is insufficient knowledge of the early colonization phase. Wastewater treatment plant (WWTP) effluents have been proposed as important pathways for MPs entry and transport in aquatic environments and are hotspots of bacterial pathogens and antibiotic resistance genes (ARGs). This study aimed at characterizing bacterial communities in the early stage of biofilm formation on seven different types of MPs deployed in two different WWTPs effluents as well as measuring the relative abundance of two ARGs (sulI and tetM) on the tested MPs. Illumina Miseq sequencing of the 16S rRNA showed significant higher diversity of bacteria on MPs in comparison with free-living bacteria in the WWTP effluents. β-diversity analysis showed that the in situ environment (sampling site) and hydrophobicity, to a lesser extent, had a role in the early bacterial colonization phase. An early colonization phase MPs-core microbiome could be identified. Furthermore, specific core microbiomes for each type of polymer suggested that each type might select early attachment of bacteria. Although the tested WWTP effluent waters contained antibiotic resistant bacteria (ARBs) harboring the sulI and tetM ARGs, MPs concentrated ARBs harboring the sulI gene but not tetM. These results highlight the relevance of the early attachment phase in the development of bacterial biofilms on different types of MP polymers and the role that different types of polymers might have facilitating the attachment of specific bacteria, some of which might carry ARGs.

Microplastics in the Marine Environment: Sources, Fates, Impacts and Microbial Degradation

The serious global microplastic pollution has attracted public concern in recent years. Microplastics are widely distributed in various environments and their pollution is already ubiquitous in the ocean system, which contributes to exponential concern in the past decade and different research areas. Due to their tiny size coupled with the various microbial communities in aquatic habitats capable of accumulating organic pollutants, abundant literature is available for assessing the negative impact of MPs on the physiology of marine organisms and eventually on the human health. This study summarizes the current literature on MPs in the marine environment to obtain a better knowledge about MP contamination. This review contains three sections: (1) sources and fates of MPs in the marine environment, (2) impacts of MPs on marine organisms, and (3) bacteria for the degradation of marine MPs. Some measures and efforts must be taken to solve the environmental problems caused by microplastics. The knowledge in this review will provide background information for marine microplastics studies and management strategies in future.

Trace Metal Contamination Impacts Predicted Functions More Than Structure of Marine Prokaryotic Biofilm Communities in an Anthropized Coastal Area

Trace metal (TM) contamination in marine coastal areas is a worldwide threat for aquatic communities. However, little is known about the influence of a multi-chemical contamination on both marine biofilm communities' structure and functioning. To determine how TM contamination potentially impacted microbial biofilms' structure and their functions, polycarbonate (PC) plates were immerged in both surface and bottom of the seawater column, at five sites, along strong TM contamination gradients, in Toulon Bay. The PC plates were incubated during 4 weeks to enable colonization by biofilm-forming microorganisms on artificial surfaces. Biofilms from the PC plates, as well as surrounding seawaters, were collected and analyzed by 16S rRNA amplicon gene sequencing to describe prokaryotic community diversity, structure and functions, and to determine the relationships between bacterioplankton and biofilm communities. Our results showed that prokaryotic biofilm structure was not significantly affected by the measured environmental variables, while the functional profiles of biofilms were significantly impacted by Cu, Mn, Zn, and salinity. Biofilms from the contaminated sites were dominated by tolerant taxa to contaminants and specialized hydrocarbon-degrading microorganisms. Functions related to major xenobiotics biodegradation and metabolism, such as methane metabolism, degradation of aromatic compounds, and benzoate degradation, as well as functions involved in quorum sensing signaling, extracellular polymeric substances (EPS) matrix, and biofilm formation were significantly over-represented in the contaminated site relative to the uncontaminated one. Taken together, our results suggest that biofilms may be able to survive to strong multi-chemical contamination because of the presence of tolerant taxa in biofilms, as well as the functional responses of biofilm communities. Moreover, biofilm communities exhibited significant variations of structure and functional profiles along the seawater column, potentially explained by the contribution of taxa from surrounding sediments. Finally, we found that both structure and functions were significantly distinct between the biofilm and bacterioplankton, highlighting major differences between the both lifestyles, and the divergence of their responses facing to a multi-chemical contamination.

Polycyclic aromatic hydrocarbon sorption and bacterial community composition of biodegradable and conventional plastics incubated in coastal sediments

Resistant to degradation, plastic litter poses a long-term threat to marine ecosystems. Biodegradable materials have been developed to replace conventional plastics, but little is known of their impacts and degradation in marine environments. A 14-week laboratory experiment was conducted to investigate the sorption of polycyclic aromatic hydrocarbons (PAHs) to conventional (polystyrene PS and polyamide PA) and bio-based, biodegradable plastic films (cellulose acetate CA and poly-L-lactic acid PLLA), and to examine the composition of bacterial communities colonizing these materials. Mesoplastics (1 cm²) of these materials were incubated in sediment and seawater collected from two sites in the Gulf of Finland, on the coast of the highly urbanized area of Helsinki, Finland. PS sorbed more PAHs than did the other plastic types at both sites, and the concentration of PAHs was consistently and considerably smaller in plastics than in the sediment. In general, the plastic bacterial biofilms resembled those in the surrounding media (water and/or sediment). However, in the sediment incubations, the community composition on CA diverged from that of the other three plastic types and was enriched with Bacteroidia and potentially cellulolytic Spirochaetia at both sites. The results indicate that certain biodegradable plastics, such as CA, may harbour potential bioplastic-degrading communities and that PAH sorption capacity varies between polymer types. Since biodegradable plastics are presented as replacements for conventional plastics in applications with risk of ending up in the marine environment, the results highlight the need to carefully examine the environmental behaviour of each biodegradable plastic type before they are extensively introduced to the market.

Distinct microbial metabolic activities of biofilms colonizing microplastics in three freshwater ecosystems

Concerns are growing about the increasing amounts of microplastics (MPs) and their ecological impacts, especially the influences of "plastisphere" in the freshwater ecosystems. Although the microbial structure and composition of biofilms are investigated, knowledge of their microbial functions remains limited. Herein, we investigated the functional diversity of carbon metabolism in biofilms colonizing one inert (glass) and two MPs as polyvinyl chloride (PVC) and polyethylene terephthalate (PET) substrates incubated for 44 days in situ in the Niushoushan River, the Qinhuai River, and Donghu Lake. 2D confocal laser scanning microscopy images visualized distinct micro-structures and biofilm compositions on three substrates. BIOLOG ECO microplates indicated variation on carbon utilization capacities of biofilms of inert and MPs in three freshwater ecosystems. Biofilms on PET showed lower capacities and carbon metabolism rates than those on glass and PVC, indicating the presence of substrate-specific functional diversity. The Shannon-Wiener diversity, Simpson diversity and Shannon evenness indices for the Niushoushan River and Donghu Lake were ordered as glass > PVC > PET. Besides to MPs-specific factors, environmental factors including nutrient (i.e., TN and TP) and turbidity largely shaped biofilm carbon metabolism. Overall findings demonstrated that as specific niches, MPs influenced microbial-mediated carbon cycling in the freshwater ecosystems and MPs-promoted microbial communities posed ecological significance.

Linking effects of microplastics to ecological impacts in marine environments

Recently, efforts to determine the ecological impacts of microplastic pollutants have increased because of plastic's accelerated contamination of the environment. The tiny size, variable surface topography, thermal properties, bioavailability and biological toxicity of microplastics all offer opportunities for these pollutants to negatively impact the environment. Additionally, various inorganic and organic chemicals sorbed on these particles may pose a greater threat to organisms than the microplastics themselves. However, there is still a big knowledge gap in the assessment of various toxicological effects of microplastics in the environment. Ecological risk assessment of microplastics has become more challenging with the current data gaps. Thus, a current literature review and identification of the areas where research on ecology of microplastics can be extended is necessary. We have provided an overview of various aspects of microplastics by which they interact negatively or positively with marine organisms. We hypothesize that biogeochemical interactions are critical to fully understand the ecological impacts, movement, and fate of microplastics in oceans. As microplastics are now ubiquitous in marine environments and impossible to remove, we recommend that it's not too late to converge research on plastic alternatives. In addition, strict actions should be taken promptly to prevent plastics from entering the environment.

Bibliometrics and visualization analysis regarding research on the development of microplastics

Microplastics have caused considerable harm to the environment and threatened human health due to their strong adsorption and hard biodegradation. Therefore, the research of microplastic received increasing attention recently, producing numbers of related achievements. To comprehensively grasp the quantitative information of published papers on "microplastics," we analyzed the research progress and hotspots of "microplastics" through visualization software "VOSviewer." The results show that the number of literature on microplastics published from 2009 to 2019 increased exponentially (R2 = 0.9873). The top 10 cited references are mainly in "zooplankton ingesting microplastics," "microplastics in artificially cultivated bivalve," "microplastics in surface waters such as lakes," etc. The cutting-edge microplastics research is adsorption, biodegradation, ingestion and accumulation model, and toxicity analysis. In addition, the results predict that the combination of constructed wetland, biotechnology, and photocatalysis to remove microplastics will become new hotspots. The study provides researchers in microplastics with an overview of existing research and directional guidance for future research.

Plastics and the microbiome: impacts and solutions

Global plastic production has increased exponentially since manufacturing commenced in the 1950's, including polymer types infused with diverse additives and fillers. While the negative impacts of plastics are widely reported, particularly on marine vertebrates, impacts on microbial life remain poorly understood. Plastics impact microbiomes directly, exerting toxic effects, providing supplemental carbon sources and acting as rafts for microbial colonisation and dispersal. Indirect consequences include increased environmental shading, altered compositions of host communities and disruption of host organism or community health, hormone balances and immune responses. The isolation and application of plastic-degrading microbes are of substantial interest yet little evidence supports the microbial biodegradation of most high molecular weight synthetic polymers. Over 400 microbial species have been presumptively identified as capable of plastic degradation, but evidence for the degradation of highly prevalent polymers including polypropylene, nylon, polystyrene and polyvinyl chloride must be treated with caution; most studies fail to differentiate losses caused by the leaching or degradation of polymer monomers, additives or fillers. Even where polymer degradation is demonstrated, such as for polyethylene terephthalate, the ability of microorganisms to degrade more highly crystalline forms of the polymer used in commercial plastics appears limited. Microbiomes frequently work in conjunction with abiotic factors such as heat and light to impact the structural integrity of polymers and accessibility to enzymatic attack. Consequently, there remains much scope for extremophile microbiomes to be explored as a source of plastic-degrading enzymes and microorganisms. We propose a best-practice workflow for isolating and reporting plastic-degrading taxa from diverse environmental microbiomes, which should include multiple lines of evidence supporting changes in polymer structure, mass loss, and detection of presumed degradation products, along with confirmation of microbial strains and enzymes (and their associated genes) responsible for high molecular weight plastic polymer degradation. Such approaches are necessary for enzymatic degraders of high molecular weight plastic polymers to be differentiated from organisms only capable of degrading the more labile carbon within predominantly amorphous plastics, plastic monomers, additives or fillers.

Relative Influence of Plastic Debris Size and Shape, Chemical Composition and Phytoplankton-Bacteria Interactions in Driving Seawater Plastisphere Abundance, Diversity and Activity

The thin film of life that inhabits all plastics in the oceans, so-called "plastisphere," has multiple effects on the fate and impacts of plastic in the marine environment. Here, we aimed to evaluate the relative influence of the plastic size, shape, chemical composition, and environmental changes such as a phytoplankton bloom in shaping the plastisphere abundance, diversity and activity. Polyethylene (PE) and polylactide acid (PLA) together with glass controls in the forms of meso-debris (18 mm diameter) and large-microplastics (LMP; 3 mm diameter), as well as small-microplastics (SMP) of 100 μm diameter with spherical or irregular shapes were immerged in seawater during 2 months. Results of bacterial abundance (confocal microscopy) and diversity (16S rRNA Illumina sequencing) indicated that the three classical biofilm colonization phases (primo-colonization after 3 days; growing phase after 10 days; maturation phase after 30 days) were not influenced by the size and the shape of the materials, even when a diatom bloom (Pseudo-nitzschia sp.) occurred after the first month of incubation. However, plastic size and shape had an effect on bacterial activity (3H leucine incorporation). Bacterial communities associated with the material of 100 μm size fraction showed the highest activity compared to all other material sizes. A mature biofilm developed within 30 days on all material types, with higher bacterial abundance on the plastics compared to glass, and distinct bacterial assemblages were detected on each material type. The diatom bloom event had a great impact on the plastisphere of all materials, resulting in a drastic change in diversity and activity. Our results showed that the plastic size and shape had relatively low influence on the plastisphere abundance, diversity, and activity, as compared to the plastic composition or the presence of a phytoplankton bloom.

Biosecurity implications of drifting marine plastic debris: Current knowledge and future research

The introduction and spread of marine non-indigenous species (NIS) and pathogens into new habitats are a major threat to biodiversity, ecosystem services, human health, and can have substantial economic consequences. Shipping is considered the main vector for marine biological invasions; less well understood is the increased spread of marine NIS and pathogens rafting on marine plastic debris (MPD). Despite an increasing research interest and recent progress in characterizing the plastisphere, this manuscript highlights critical knowledge gaps and research priorities towards a better understanding of the biosecurity implications of MPD. We advocate for future research to (i) investigate plastisphere community succession and the factors influencing NIS propagules and pathogens recruitment through robust experimental investigations; (ii) combine microscopy and molecular approaches to effectively assess the presence of specific taxa; (iii) include additional genetic markers to thoroughly characterize the biodiversity associated with MPD and explore the presence of specific marine pests.

Prokaryotic community succession and assembly on different types of microplastics in a mariculture cage

Microplastics have emerged as a new anthropogenic substrate that can readily be colonized by microorganisms. Nevertheless, microbial community succession and assembly among different microplastics in nearshore mariculture cages remains poorly understood. Using an in situ incubation experiment, 16S rRNA gene amplicon sequencing, and the neutral model, we investigated the prokaryotic communities attached to polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP) in a mariculture cage in Xiangshan Harbor, China. The α-diversities and compositions of microplastic-attached prokaryotic communities were significantly distinct from free-living and small particle-attached communities in the surrounding water but relatively similar to the large particle-attached communities. Although a distinct prokaryotic community was developed on each type of microplastic, the communities on PE and PP more closely resembled each other. Furthermore, the prokaryotic community dissimilarity among all media (microplastics and water fractions) tended to decrease over time. Hydrocarbon-degrading bacteria Alcanivorax preferentially colonized PE, and the genus Vibrio with opportunistically pathogenic members has the potential to colonize PET. Additionally, neutral processes dominated the prokaryotic community assembly on PE and PP, while selection was more responsible for the prokaryotic assembly on PET. The assembly of Planctomycetaceae and Thaumarchaeota Marine Group I taxa on three microplastics were mainly governed by selection and neutral processes, respectively. Our study provides further understanding of microplastic-associated microbial ecology in mariculture environments.

Metal resistance genes enrichment in marine biofilm communities selected by biocide-containing surfaces in temperate and tropical coastal environments

Microorganisms able to form biofilms in marine ecosystems are selected depending on immersed surfaces and environmental conditions. Cell attachment directly on toxic surfaces like antifouling coatings suggests a selection of tolerant (or resistant) organisms with characteristics conferring adaptive advantages. We investigated if environment would drive metal resistance gene abundance in biofilms on artificial surfaces. Biofilms were sampled from three surfaces (a PVC reference and two antifouling coatings) deployed in three coastal waters with dissimilar characteristics: The Mediterranean Sea (Toulon) and Atlantic (Lorient) and Indian (Reunion) Oceans. The two coatings differed in metals composition, either Cu thiocyanate and Zn pyrithione (A3) or Cu2O (Hy). Metal resistance genes (MRG) specific to copper (cusA, copA, cueO) or other metals (czcA and pbrT) were monitored with qPCR in parallel to the microbial community using 16S rRNA gene metabarcoding. A lower α-diversity on A3 or Hy than on PVC was observed independent on the site. Weighted Unifrac suggested segregation of communities primarily by surface, with lower site effect. Metacoder log2 fold change ratio and LeFSe discrimination suggested Marinobacter to be specific of Hy and Altererythrobacter, Erythrobacter and Sphingorhabdus of A3. Likewise, the relative abundance of MRG (MRG/bacterial 16S rRNA) varied between surfaces and sites. A3 presented the greatest relative abundances for cusA, cueO and czcA. The latter could only be amplified from A3 communities, except at Toulon. Hy surface presented the highest relative abundance for copA, specifically at Lorient. These relative abundances were correlated with LeFSe discriminant taxa. Dasania correlated positively with all MRG except cueO. Marinobacter found in greater abundance in Hy biofilm communities correlated with the highest abundances of copA and Roseovarius with czcA. These results prove the selection of specific communities with abilities to tolerate metallic biocides forming biofilms over antifouling surfaces, and the secondary but significant influence of local environmental factors.

A critical review of interactions between microplastics, microalgae and aquatic ecosystem function

With the widespread occurrence of microplastics in aquatic ecosystems having been firmly established, the focus of research has shifted towards the assessments of their influence on ecosystem functions and food webs. This includes interactions between microplastics and microalgae, as fundamental components at the base of aquatic food webs and pivotal organisms in a wide range of ecosystem functions. In this review, we present the current state of knowledge on microalgae-microplastic interactions and summarize the potential effect on their respective fate. Microplastics can and do interact with microalgae and the available literature has suggested that the epiplastic community of microalgae differs consistently from the surrounding aquatic communities; however, it is still not clear whether this different colonization is linked to the composition of the surface or more to the availability of a "hard" substrate on which organisms can attach and grow. Further studies are needed to understand to what extent the properties of different plastic materials and different environmental factors may affect the growth of microalgae on plastic debris. Biofouling may alter microplastic properties, especially increasing their density, consequently affecting the vertical fluxes of plastics. Moreover, microplastics may have toxic effects on microalgae, which could be physical or related to chemical interactions with plasticizers or other chemicals associated with plastics, with consequences for algal growth, photosynthetic activity, and morphology. Microplastics seems to have the potential to affect not only the quality (e.g., fatty acids and lipids composition, food dilution effect) but also the quantity of algal production, both positively and negatively. This may have consequences for energy fluxes, which may propagate throughout the whole food web and alter aquatic productivity. Even though experimental results have indicated reciprocal impacts between plastics and microalgae, it is currently difficult to predict how these impacts may manifest themselves at the ecosystem level. Therefore, further studies are needed to address this important topic.

Vibrio Colonization Is Highly Dynamic in Early Microplastic-Associated Biofilms as Well as on Field-Collected Microplastics

Microplastics are ubiquitous in aquatic ecosystems and provide a habitat for biofilm-forming bacteria. The genus Vibrio, which includes potential pathogens, was detected irregularly on microplastics. Since then, the potential of microplastics to enrich (and serve as a vector for) Vibrio has been widely discussed. We investigated Vibrio abundance and operational taxonomic unit (OTU) composition on polyethylene and polystyrene within the first 10 h of colonization during an in situ incubation experiment, along with those found on particles collected from the Baltic Sea. We used 16S rRNA gene amplicon sequencing and co-occurrence networks to elaborate the role of Vibrio within biofilms. Colonization of plastics with Vibrio was detectable after one hour of incubation; however, Vibrio numbers and composition were very dynamic, with a more stable population at the site with highest nutrients and lowest salinity. Likewise, Vibrio abundances on field-collected particles were variable but correlated with proximity to major cities. Vibrio was poorly connected within biofilm networks. Taken together, this indicates that Vibrio is an early colonizer of plastics, but that the process is undirected and independent of the specific surface. Still, higher nutrients could enhance a faster establishment of Vibrio populations. These parameters should be considered when planning studies investigating Vibrio on microplastics.

Marine hydrocarbon-degrading bacteria breakdown poly(ethylene terephthalate) (PET)

Pollution of aquatic ecosystems by plastic wastes poses severe environmental and health problems and has prompted scientific investigations on the fate and factors contributing to the modification of plastics in the marine environment. Here, we investigated, by means of microcosm studies, the role of hydrocarbon-degrading bacteria in the degradation of poly(ethylene terephthalate) (PET), the main constituents of plastic bottles, in the marine environment. To this aim, different bacterial consortia, previously acclimated to representative hydrocarbons fractions namely, tetradecane (aliphatic fraction), diesel (mixture of hydrocarbons), and naphthalene/phenantrene (aromatic fraction), were used as inocula of microcosm experiments, in order to identify peculiar specialization in poly(ethylene terephthalate) degradation. Upon formation of a mature biofilm on the surface of poly(ethylene terephthalate) films, the bacterial biodiversity and degradation efficiency of each selected consortium was analyzed. Notably, significant differences on biofilm biodiversity were observed with distinctive hydrocarbons-degraders being enriched on poly(ethylene terephthalate) surface, such as Alcanivorax, Hyphomonas, and Cycloclasticus species. Interestingly, ATR-FTIR analyses, supported by SEM and water contact angle measurements, revealed major alterations of the surface chemistry and morphology of PET films, mainly driven by the bacterial consortia enriched on tetradecane and diesel. Distinctive signatures of microbial activity were the alteration of the FTIR spectra as a consequence of PET chain scission through the hydrolysis of the ester bond, the increased sample hydrophobicity as well as the formation of small cracks and cavities on the surface of the film. In conclusion, our study demonstrates for the first time that hydrocarbons-degrading marine bacteria have the potential to degrade poly(ethylene terephthalate), although their degradative activity could potentially trigger the formation of harmful microplastics in the marine environment.

Interactions between microplastics and organic pollutants: Effects on toxicity, bioaccumulation, degradation, and transport

Microplastics (MPs), defined as particles with diameters <5 mm and including nanoplastics (NPs), with diameters <1 μm, are characterized by large specific surface areas and hydrophobicity. In aquatic and terrestrial environments, MPs interact with co-occurring organic pollutants through sorption and desorption, which alters the environmental behavior of the pollutants, such as their toxicity, bioaccumulation, degradation, and transport. In this review, we summarize the results of current studies of the interactions between MPs and organic contaminants, and focus on the different mechanisms and subsequent ecological risks of contaminant transfer among environmental media, MPs and organisms. The sorption/desorption of organic pollutants on/from MPs is discussed with respect to solution conditions and the properties of both the MPs and the pollutants. More importantly, the ability of MPs to alter the toxicity, bioaccumulation, degradation, and transport of organic pollutants through these interactions is considered as well. We then examine the interrelationships of the different environmental behaviors of MPs and organic pollutants and the roles played by environmental processes. Finally, we identify the remaining knowledge gaps that must be filled in further studies in order to accurately evaluate the environmental risks of MPs and their associated organic pollutants.

Ocean acidification alters bacterial communities on marine plastic debris

The increasing quantity of plastic waste in the ocean is providing a growing and more widespread novel habitat for microbes. Plastics have taxonomically distinct microbial communities (termed the 'Plastisphere') and can raft these unique communities over great distances. In order to understand the Plastisphere properly it will be important to work out how major ocean changes (such as warming, acidification and deoxygenation) are shaping microbial communities on waste plastics in marine environments. Here, we show that common plastic drinking bottles rapidly become colonised by novel biofilm-forming bacterial communities, and that ocean acidification greatly influences the composition of plastic biofilm assemblages. We highlight the potential implications of this community shift in a coastal community exposed to enriched CO₂ conditions.