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

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.

Selection for antimicrobial resistance in the plastisphere

Microplastics and antimicrobials are widespread contaminants that threaten global systems and frequently co-exist in the presence of human or animal pathogens. Whilst the impact of each of these contaminants has been studied in isolation, the influence of this co-occurrence in driving antimicrobial resistance (AMR)1 in microplastic-adhered microbial communities, known as 'the Plastisphere', is not well understood. This review proposes the mechanisms by which interactions between antimicrobials and microplastics may drive selection for AMR in the Plastisphere. These include: 1) increased rates of horizontal gene transfer in the Plastisphere compared with free-living counterparts and natural substrate controls due to the proximity of cells, co-occurrence of environmental microplastics with AMR selective compounds and the sequestering of extracellular antibiotic resistance genes in the biofilm matrix. 2) An elevated AMR selection pressure in the Plastisphere due to the adsorbing of AMR selective or co-selective compounds to microplastics at concentrations greater than those found in surrounding mediums and potentially those adsorbed to comparator particles. 3) AMR selection pressure may be further elevated in the Plastisphere due to the incorporation of antimicrobial or AMR co-selective chemicals in the plastic matrix during manufacture. Implications for both ecological functioning and environmental risk assessments are discussed, alongside recommendations for further research.

Microbes and microplastics: Community shifts along an urban coastal contaminant gradient

Plastic substrates introduced to the environment during the Anthropocene have introduced new pathways for microbial selection and dispersal. Some plastic-colonising microorganisms have adapted phenotypes for plastic degradation (selection), while the spatial transport (dispersal) potential of plastic colonisers remains controlled by polymer-specific density, hydrography and currents. Plastic-degrading enzyme abundances have recently been correlated with concentrations of plastic debris in open ocean environments, making it critical to better understand colonisation of hydrocarbon degraders with plastic degradation potential in urbanised watersheds where plastic pollution often originates. We found that microbial colonisation by reputed hydrocarbon degraders on microplastics (MPs) correlated with a spatial contaminant gradient (New York City/Long Island waterways), polymer types, temporal scales, microbial domains and putative cell activity (DNA vs. RNA). Hydrocarbon-degrading taxa enriched on polyethylene and polyvinyl chloride substrates relative to other polymers and were more commonly recovered in samples proximal to New York City. These differences in MP colonisation could indicate phenotypic adaptation processes resulting from increased exposure to urban plastic runoff as well as differences in carbon bioavailability across polymer types. Shifts in MP community potential across urban coastal contaminant gradients and polymer types improve our understanding of environmental plastic discharge impacts toward biogeochemical cycling across the global ocean.

Microplastic polymer properties as deterministic factors driving terrestrial plastisphere microbiome assembly and succession in the field

Environmental microplastic (MP) is ubiquitous in aquatic and terrestrial ecosystems providing artificial habitats for microbes. Mechanisms of MP colonization, MP polymer impacts, and effects on soil microbiomes are largely unknown in terrestrial systems. Therefore, we experimentally tested the hypothesis that MP polymer type is an important deterministic factor affecting MP community assembly by incubating common MP polymer types in situ in landfill soil for 14 months. 16S rRNA gene amplicon sequencing indicated that MP polymers have specific impacts on plastisphere microbiomes, which are subsets of the soil microbiome. Chloroflexota, Gammaproteobacteria, certain Nitrososphaerota, and Nanoarchaeota explained differences among MP polymers and time points. Plastisphere microbial community composition derived from different MP diverged over time and was enriched in potential pathogens. PICRUSt predictions of pathway abundances and quantitative PCR of functional marker genes indicated that MP polymers exerted an ambivalent effect on genetic potentials of biogeochemical cycles. Overall, the data indicate that (i) polymer type as deterministic factor rather than stochastic factors drives plastisphere community assembly, (ii) MP impacts greenhouse gas metabolism, xenobiotic degradation and pathogen distribution, and (iii) MP serves as an ideal model system for studying fundamental questions in microbial ecology such as community assembly mechanisms in terrestrial environments.

Extreme weather events as an important factor for the evolution of plastisphere but not for the degradation process

Marine plastics, with their negative effects on marine life and the human health, have been recently recognized as a new niche for the colonization and development of marine biofilms. Members of the colonizing communities could possess the potential for plastic biodegradation. Thus, there is an urgent need to characterize these complex and geographically variable communities and elucidate the functionalities. In this work, we characterize the fungal and bacterial colonizers of 5 types of plastic films (High Density Polyethylene, Low Density Polyethylene, Polypropylene, Polystyrene and Polyethylene Terepthalate) over the course of a 242-day incubation in the south-eastern Mediterranean and relate them to the chemical changes observed on the surface of the samples via ATR-FTIR. The 16s rRNA and ITS2 ribosomal regions of the plastisphere communities were sequenced on four time points (35, 152, 202 and 242 days). The selection of the time points was dictated by the occurrence of a severe storm which removed biological fouling from the surface of the samples and initiated a second colonization period. The bacterial communities, dominated by Proteobacteria and Bacteroidetes, were the most variable and diverse. Fungal communities, characterized mainly by the presence of Ascomycota, were not significantly affected by the storm. Neither bacterial nor fungal community structure were related to the polymer type acting as substrate, while the surface of the plastic samples underwent weathering of oscillating degrees with time. This work examines the long-term development of Mediterranean epiplastic biofilms and is the first to examine how primary colonization influences the microbial community re-attachment and succession as a response to extreme weather events. Finally, it is one of the few studies to examine fungal communities, despite them containing putative plastic degraders.

Characteristics of microplastic pollution in golden pompano (Trachinotus ovatus) aquaculture areas and the relationship between colonized-microbiota on microplastics and intestinal microflora

Microplastic (MPs) pollution is a global marine environmental problem. The effects of MPs on the gut microbiota of aquatic organisms have received considerable attention. For example, microbes colonizing MPs in pond cultures alter the structure and function of the intestinal microbes of shrimp and fish. It was hypothesized that bacteria on MPs in natural mariculture areas also interact with the intestinal flora of golden pompano (Trachinotus ovatus) because biofilms can form on the surface of MPs during long-term floating in seawater. To our knowledge, this study is the first to investigate MPs pollution in T. ovatus aquaculture. DNA sequencing and bioinformatics analysis confirmed the effect of microbial colonization of MPs on the intestinal flora of T. ovatus. The MPs detected in the gut wet weight (w.w.) of golden pompano (546 ± 52 items/g) were mainly pellets and fragments of blue or green, whereas the sediment MPs dry weight (d.w.) (4765 ± 116 items/kg) were mainly black fibers. The MPs richness in the sediment gradually increased from the open-sea aquaculture area to the estuarine aquaculture area and was positively correlated with the MPs richness in the intestinal tract of golden pompano. MPs 20-200 μm were the most common in the gut and sediment. The intake of MPs increased the abundance of Proteobacteria and decreased that of Firmicutes in the intestinal flora. The functional compositions of MP-colonizing microbes and gut microbiota were similar, suggesting that the two communities influence each other. Network analysis further confirmed this and revealed that Vibrio plays a key role in the intestinal flora and surface microorganisms of MPs. Overall, the intake of MPs by aquatic animals not only affects the intestinal flora and intestinal microbial function, but also poses potential risks to aquaculture.

Microbial colonization and degradation of marine microplastics in the plastisphere: A review

Marine microplastic pollution is a growing problem for ecotoxicology that needs to be resolved. In particular, microplastics may be carriers of "dangerous hitchhikers," pathogenic microorganisms, i.e., Vibrio. Microplastics are colonized by bacteria, fungi, viruses, archaea, algae and protozoans, resulting in the biofilm referred to as the "plastisphere." The microbial community composition of the plastisphere differs significantly from those of surrounding environments. Early dominant pioneer communities of the plastisphere belong to primary producers, including diatoms, cyanobacteria, green algae and bacterial members of the Gammaproteobacteria and Alphaproteobacteria. With time, the plastisphere mature, and the diversity of microbial communities increases quickly to include more abundant Bacteroidetes and Alphaproteobacteria than natural biofilms. Factors driving the plastisphere composition include environmental conditions and polymers, with the former having a much larger influence on the microbial community composition than polymers. Microorganisms of the plastisphere may play key roles in degradation of plastic in the oceans. Up to now, many bacterial species, especially Bacillus and Pseudomonas as well as some polyethylene degrading biocatalysts, have been shown to be capable of degrading microplastics. However, more relevant enzymes and metabolisms need to be identified. Here, we elucidate the potential roles of quorum sensing on the plastic research for the first time. Quorum sensing may well become a new research area to understand the plastisphere and promote microplastics degradation in the ocean.

Plastic-microbe interaction in the marine environment: Research methods and opportunities

Approximately 9 million metric tons of plastics enters the ocean annually, and once in the marine environment, plastic surfaces can be quickly colonised by marine microorganisms, forming a biofilm. Studies on plastic debris-biofilm associations, known as plastisphere, have increased exponentially within the last few years. In this review, we first briefly summarise methods and techniques used in exploring plastic-microbe interactions. Then we highlight research gaps and provide future research opportunities for marine plastisphere studies, especially, on plastic characterisation and standardised biodegradation tests, the fate of "environmentally friendly" plastics, and plastisphere of coastal habitats. Located in the tropics, Southeast Asian (SEA) countries are significant contributors to marine plastic debris. However, plastisphere studies in this region are lacking and therefore, we discuss how the unique environmental conditions in the SEA seas may affect plastic-microbe interaction and why there is an imperative need to conduct plastisphere studies in SEA marine environments. Finally, we also highlight the lack of understanding of the pathogenicity and ecotoxicological effects of plastisphere on marine ecosystems.

Genome-based taxonomic rearrangement of Oceanobacter-related bacteria including the description of Thalassolituus hydrocarbonoclasticus sp. nov. and Thalassolituus pacificus sp. nov. and emended description of the genus Thalassolituus

Oceanobacter-related bacteria (ORB) are a group of oligotrophic marine bacteria play an underappreciated role in carbon cycling. They have been frequently described as one of the dominant bacterial groups with a wide distribution in coastal and deep seawater of global oceans. To clarify their taxonomic affiliation in relation to alkane utilization, phylogenomic and comparative genomics analyses were performed based on currently available genomes from GenBank and four newly isolated strains, in addition to phenotypic and chemotaxonomic characteristics. Consistently, phylogenomic analysis robustly separated them into two groups, which are accordingly hydrocarbon-degrading (HD, Thalassolituus and Oleibacter) and non-HD (NHD, Oceanobacter). In addition, the two groups can also be readily distinguished by several polyphasic taxonomic characteristics. Furthermore, both AAI and POCP genomic indices within the HD group support the conclusion that the members of the genus Oleibacter should be transferred into the genus Thalassolituus. Moreover, HD and NHD bacteria differed significantly in terms of genome size, G + C content and genes involved in alkane utilization. All HD bacteria contain the key gene alkB encoding an alkane monooxygenase, which can be used as a marker gene to distinguish the members of closely related genera Oceanobacter and Thalassolituus. Pangenome analysis revealed that the larger accessory genome may endow Thalassolituus with the flexibility to cope with the dynamics of marine environments and thrive therein, although they possess smaller pan, core- and unique-genomes than Oceanobacter. Within the HD group, twelve species were clearly distinguished from each other by both dDDH and ANI genomic indices, including two novel species represented by the newly isolated strains alknpb1M-1 ^T and 59MF3M-4 ^T , for which the names Thalassolituus hydrocarbonoclasticus sp. nov. and Thalassolituus pacificus sp. nov. are proposed. Collectively, these findings build a phylogenetic framework for the ORB and contribute to understanding of their role in marine carbon cycling.

Bacterial colonization dynamics of different microplastic types in an anoxic salt marsh sediment and impact of adsorbed polychlorinated biphenyls on the plastisphere

Plastic debris dispersed into the environment provide a substrate for microbial colonization, constituting a new human-made ecosystem called "plastisphere", and altering the microbial species distribution in aquatic, coastal and benthic ecosystems. The study aims at exploring the interaction among microplastics (MPs) made of different polymers, a persistent organic contaminant (polychlorinated biphenyls, PCBs), and the environmental microbial communities, in an anoxic marine sediment. Plastic pellets were incubated in the field in a salt marsh anoxic sediment, to observe the stages of plastisphere formation, by quantitative PCR and 16S rRNA gene sequencing, and PCB dechlorination activity on the MPs surface. Microbes from the sediment rapidly colonized the different microplastics types, with PVC recruiting a peculiar community enriched in sulfate-reducing bacteria. The composition of the plastisphere varied along the 1-year incubation possibly in response either to warmer temperatures in spring-summer or to microhabitat's changes due to the progressive plastic surface weathering. Even if PCB contaminated MPs were able to recruit potentially dehalogenating taxa, actual dechlorination was not detectable after 1 year. This suggests that the concentration of potentially dehalorespiring bacteria in the natural environment could be too low for the onset of the dechlorination process on MP-sorbed contaminants. Our study, which is among very few available longitudinally exploring the plastisphere composition in an anoxic sediment context, is the first exploring the fate and possible biodegradation of persistent organic pollutants sorbed on MPs reaching the seafloor.

Pathogens transported by plastic debris: does this vector pose a risk to aquatic organisms?

Microplastics are small (<5 mm) plastic particles of varying shapes and polymer types that are now widespread global contaminants of marine and freshwater ecosystems. Various estimates suggest that several trillions of microplastic particles are present in our global oceanic system, and that these are readily ingested by a wide range of marine and freshwater species across feeding modes and ecological niches. Here, we present some of the key and pressing issues associated with these globally important contaminants from a microbiological perspective. We discuss the potential mechanisms of pathogen attachment to plastic surfaces. We then describe the ability of pathogens (both human and animal) to form biofilms on microplastics, as well as dispersal of these bacteria, which might lead to their uptake into aquatic species ingesting microplastic particles. Finally, we discuss the role of a changing oceanic system on the potential of microplastic-associated pathogens to cause various disease outcomes using numerous case studies. We set out some key and imperative research questions regarding this globally important issue and present a methodological framework to study how and why plastic-associated pathogens should be addressed.

Plastic properties affect the composition of prokaryotic and eukaryotic communities and further regulate the ARGs in their surface biofilms

Plastic wastes are ubiquitous in the offshore and oceans with an increasing quantity, and inevitably, microbial communities colonized the plastics to form biofilms, which have become dispersal vectors for antibiotic resistance genes (ARGs). This study focused on the impact of plastic properties including hardness, wettability, and zeta-potential on the biomass, prokaryotic and eukaryotic communities and ARGs in biofilms formed on specific plastics (polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET)) in an estuarine environment. The results showed that, in comparison to PP, more biomass characterized by more dry weight, chlorophyll a (Chl a) and total organic carbon (TOC) was found in biofilms formed on PE and PET, which may be related to their lower surface wettability. Proteobacteria were the dominant prokaryotic phyla, and they accounted for 53.06%, 81.90%, 37.06%, 76.25%, and 54.27% of the total sequences in biofilms on PE, PP, PET, water and sediment, respectively. Ascomycota were the predominant eukaryotic phyla in biofilms, water, and sediment, and their abundances were elevated in biofilms on PP, which accounted for 34.73%. The biofilms on PP had a higher relative abundance of ARGs (3.13) compared to those on PE (2.59) and PET (0.23). Furthermore, both the plastic-biofilm properties (e.g. dry weight, Chl a, and TOC) and microbial communities (e.g., Fungi and Proteobacteria) may be involved in regulating the abundance of ARGs. Moreover, mobile genetic elements (MGEs) were significantly correlated to both the absolute and relative abundance of ARGs, indicating that MGEs may regulate the migration of ARGs in biofilms. Taken together, this investigation provides the significance of the plastic type, surface properties, and surrounding environments in shaping microbial communities and ARGs in biofilms formed on plastics.

Bacterial colonisation dynamics of household plastics in a coastal environment

Accumulation of plastics in the marine environment has widespread detrimental consequences for ecosystems and wildlife. Marine plastics are rapidly colonised by a wide diversity of bacteria, including human pathogens, posing potential risks to health. Here, we investigate the effect of polymer type, residence time and estuarine location on bacterial colonisation of common household plastics, including pathogenic bacteria. We submerged five main household plastic types: low-density PE (LDPE), high-density PE (HDPE), polypropylene (PP), polyvinyl chloride (PVC) and polyethylene terephthalate (PET) at an estuarine site in Cornwall (U.K.) and tracked bacterial colonisation dynamics. Using both culture-dependent and culture-independent approaches, we found that bacteria rapidly colonised plastics irrespective of polymer type, reaching culturable densities of up to 1000 cells cm³ after 7 weeks. Community composition of the biofilms changed over time, but not among polymer types. The presence of pathogenic bacteria, quantified using the insect model Galleria mellonella, increased dramatically over a five-week period, with Galleria mortality increasing from 4% in week one to 65% in week five. No consistent differences in virulence were observed between polymer types. Pathogens isolated from plastic biofilms using Galleria enrichment included Serratia and Enterococcus species and they harboured a wide range of antimicrobial resistance genes. Our findings show that plastics in coastal waters are rapidly colonised by a wide diversity of bacteria independent of polymer type. Further, our results show that marine plastic biofilms become increasingly associated with virulent bacteria over time.

Bacterial colonisation of plastic in the Rockall Trough, North-East Atlantic: An improved understanding of the deep-sea plastisphere

Plastic pollution has now been found within multiple ecosystems across the globe. Characterisation of microbial assemblages associated with marine plastic, or the so-called 'plastisphere', has focused predominantly on plastic in the epipelagic zone. Whether this community includes taxa that are consistently enriched on plastic compared to surrounding non plastic surfaces is unresolved, as are the ecological implications. The deep sea is likely a final sink for most of the plastic entering the ocean, yet there is limited information on microbial colonisation of plastic at depth. The aim of this study was to investigate deep-sea microbial communities associated with polystyrene (PS) and polyurethane (PU) with Bath stone used as a control. The substrates (n = 15) were deployed in the Rockall Trough (Atlantic), and recovered 420 days later from a depth of 1796 m. To characterise the bacterial communities, 16S rRNA genes were sequenced using the Illumina MiSeq platform. A dominant core microbiome (taxa shared across all substrates) comprised 8% of total ASVs (amplicon sequence variant) and accounted for 92% of the total community reads. This suggests that many commonly reported members of the plastisphere are simply opportunistic which freely colonise any hard surface. Transiently associated species consisted of approximately 7% of the total community. Thirty genera were enriched on plastic (P < 0.05), representing 1% of the total community. The discovery of novel deep-sea enriched taxa included Aurantivirga, Algivirga, IheB3-7, Spirosoma, HTCC5015, Ekhidna and Calorithrix on PS and Candidatus Obscuribacter, Haloferula, Marine Methylotrophic Group 3, Aliivibrio, Tibeticola and Dethiosulfatarculus on PU. This small fraction of the microbiome include taxa with unique metabolic abilities and show how bacterial communities can be shaped by plastic pollution at depth. This study outlines a novel approach in categorising the plastisphere to elucidate the ecological implications of enriched taxa that show an affinity for colonising plastic.

Microbial pioneers of plastic colonisation in coastal seawaters

Plastics, when entering the environment, are immediately colonised by microorganisms. This modifies their physico-chemical properties as well as their transport and fate in natural ecosystems, but whom pioneers this colonisation in marine ecosystems? Previous studies have focused on microbial communities that develop on plastics after relatively long incubation periods (i.e., days to months), but very little data is available regarding the earliest stages of colonisation on buoyant plastics in marine waters (i.e., minutes or hours). We conducted a preliminary study where the earliest hours of microbial colonisation on buoyant plastics in marine coastal waters were investigated by field incubations and amplicon sequencing of the prokaryotic and eukaryotic communities. Our results show that members of the Bacteroidetes group pioneer microbial attachment to plastics but, over time, their presence is masked by other groups - Gammaproteobacteria at first and later by Alphaproteobacteria. Interestingly, the eukaryotic community on plastics exposed to sunlight became dominated by phototrophic organisms from the phylum Ochrophyta, diatoms at the start and brown algae towards the end of the three-day incubations. This study defines the pioneering microbial community that colonises plastics immediately when entering coastal marine environments and that may set the seeding Plastisphere of plastics in the oceans.

Effect of particle size on the colonization of biofilms and the potential of biofilm-covered microplastics as metal carriers

Upon release into the aquatic environment, the surface of microplastics (MPs) can be readily colonized by biofilms, which may enhance the adsorption of contaminants. In this study, industrial-grade polystyrene (PS) of about 4 mm in size (MP4000-1), food-grade PS of about 4 mm in size (MP4000-2), and Powder PS of about 75 μm in size (MP75) were co-cultured with a model freshwater fungus, namely Acremonium strictum strain KR21-2, for seven days to form biofilms on their surface. We also determined the changes in surface physicochemical properties of the biofilm-covered MPs (BMPs) and the heavy metal adsorption capacity of the original MPs and BMPs. The results revealed that the biofilms improve the adsorption of heavy metals on MPs, and the particle size of MPs plays a crucial role in biofilm colonization and adsorption of heavy metals by BMPs. MP75 can carry more biofilm on its surface than that of the two MP4000s and form heteroaggregates with biofilms. In addition, there were more functional groups on the surface of BMP75 than on the surface of the two BMP4000s, which could promote the electrostatic interaction and chemical association of heavy metals. Moreover, BMP75 exhibited a higher capacity to adsorb Cu and reduce Cr (VI), which may be related to the functional groups in its biofilm. Overall, this study showed that after biofilms colonization, BMPs of smaller size have more significant potential as a metal vector, and the particle size deserves more scientific attention during the risk assessment.

Floating plastics and their associated biota in the Western South Atlantic

The lack of information about plastic pollution in many marine regions hinders firm actions to manage human activities and mitigate their impacts. This study conducted for the first time a quali-quantitative evaluation of floating plastics and their associated biota from coastal and oceanic waters in South Brazil. Plastics were collected using a manta net, and were categorized according to their shape, size, malleability and polymer composition. Multi-marker DNA metabarcoding (16S, and 18S V4 and V9 rRNA regions) was performed to identify prokaryotes and eukaryotes associated to plastics. We found 371 likely plastic particles of several sizes, shapes and polymers, and the average concentration of plastics at the region was 4461 items.km^-2 (SD ± 3914). Microplastics (0.5 - 5 mm) were dominant in most sampling stations, with fragments and lines representing the most common shapes. Diverse groups of prokaryotes (20 bacteria phyla) and eukaryotes (41 groups) were associated with plastics. Both the community composition and richness of epiplastic organisms were highly variable between individual plastics but, in general, were not influenced by plastic categories. Organisms with potential pathogenicity (e.g. Vibrio species. and Alexandrium tamarense), as well as potential plastic degraders (e.g. Ralstonia, Pseudomonas, and Alcanivorax species), were found. The information generated here is pivotal to support strategies to prevent the input and mitigate the impacts of plastics and their associated organisms on marine environments.