Fouling Microbial Communities on Plastics Compared with Wood and Steel: Are They Substrate- or Location-Specific?

Biodegradation of polyethylene by the marine fungus Parengyodontium album

Plastic pollution in the marine realm is a severe environmental problem. Nevertheless, plastic may also serve as a potential carbon and energy source for microbes, yet the contribution of marine microbes, especially marine fungi to plastic degradation is not well constrained. We isolated the fungus Parengyodontium album from floating plastic debris in the North Pacific Subtropical Gyre and measured fungal-mediated mineralization rates (conversion to CO2) of polyethylene (PE) by applying stable isotope probing assays with 13C-PE over 9 days of incubation. When the PE was pretreated with UV light, the biodegradation rate of the initially added PE was 0.044 %/day. Furthermore, we traced the incorporation of PE-derived 13C carbon into P. album biomass using nanoSIMS and fatty acid analysis. Despite the high mineralization rate of the UV-treated 13C-PE, incorporation of PE-derived 13C into fungal cells was minor, and 13C incorporation was not detectable for the non-treated PE. Together, our results reveal the potential of P. album to degrade PE in the marine environment and to mineralize it to CO2. However, the initial photodegradation of PE is crucial for P. album to metabolize the PE-derived carbon.

Biofilms on plastic litter in an urban river: Community composition and activity vary by substrate type

In aquatic ecosystems, plastic litter is a substrate for biofilms. Biofilms on plastic and natural surfaces share similar composition and activity, with some differences due to factors such as porosity. In freshwaters, most studies have examined biofilms on benthic substrates, while little research has compared the activity and composition of biofilms on buoyant plastic and natural surfaces. Additionally, the influence of substrate size and successional stage on biofilm composition has not been commonly assessed. We incubated three plastics of distinct textures that are buoyant in rivers, low-density polyethylene (rigid; 1.7 mm thick), low-density polyethylene film (flexible; 0.0254 mm thick), and foamed polystyrene (brittle; 6.5 mm thick), as well as wood substrates (untreated oak veneer; 0.6 mm thick) in the Chicago River. Each material was incubated at three sizes (1, 7.5, and 15 cm2 ). Substrates were incubated at 2-10 cm depths and removed weekly for 6 weeks. On each substrate we measured chlorophyll concentration, biofilm biomass, respiration, and flux of nitrogen gas. We sequenced 16S and 23S rRNA genes at Weeks 1, 3, and 6 to capture biofilm community composition across successional stages. Chlorophyll, biomass, and N2 flux were similar across substrates, but respiration was greater on wood than plastics. Bacterial and algal richness and diversity were highest on foam and wood compared to polyethylene substrates. Bacterial biofilm community composition was distinct between wood and plastic substrates, while the algal community was distinct on wood and foam, which were different from each other and polyethylene substrates. These results indicate that polymer properties influence biofilm alpha and beta diversity, which may affect transport and distribution of plastic pollution and associated microbes, as well as biogeochemical processes in urban rivers. This study provides valuable insights into the effects of substrate on biofilm characteristics, and the ecological impacts of plastic pollution on urban rivers. PRACTITIONER POINTS: Plastic physical and chemical properties act as forces of selection for biofilm. Biofilm activity was similar among three different types of plastic. Community composition between plastic and wood was different.

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.

Microbial colonization and chemically influenced selective enrichment of bacterial pathogens on polycarbonate plastic

Plastic pollution in aquatic environments poses significant concerns due to its potential to serve as a refuge for aquatic pathogens. However, the role of plastic surfaces and microbial biofilm interfaces in facilitating pathogen development remains poorly understood. In this study, a microcosm setup was employed to investigate the interactions between plastics and the microbial community and examine the differences in bacterial community composition and potential pathogen occurrences between the plastisphere-biofilm and surrounding seawater. Community composition analysis combined with SEM observations over time indicated that biofilm extracellular polymeric substance formation over 14 days had a link with the relative abundance and succession patterns of pathogen taxa. Colony clusters were observed on biofilms from day 7 and coincided with higher bacterial pathogen dominance. On day 14, pathogen abundance overall decreased with a potentially degrading biofilm. Pseudomonas and Pseudoalteromonas were the dominant potential pathogen groups observed in the microcosm. When further subjected to chemical treatment as an imposed environmental stress over time, biofilm-associated Psuedoalteromonas sharply increased in abundance after three days of exposure, but quickly diminished by 14 days in favor of genera such as Acinetobacter, Pseudomonas, and Staphylococcus. These results suggest that environmental plastisphere-biofilms can promote the early selection, enrichment, and spread of pathogenic bacteria in the aquatic environment and could be later worsened under chemical and long-term pressure. This study provided new insights into the succession of pathogens in plastisphere biofilms, contributing to the understanding of pathogen risks involved in emerging plastisphere biofilms in light of global plastic pollution.

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.

Distinct microbial communities degrade cellulose diacetate bioplastics in the coastal ocean

IMPORTANCE

Cellulose diacetate (CDA) is a promising alternative to conventional plastics due to its versatility in manufacturing and low environmental persistence. Previously, our group demonstrated that CDA is susceptible to biodegradation in the ocean on timescales of months. In this study, we report the composition of microorganisms driving CDA degradation in the coastal ocean. We found that the coastal ocean harbors distinct bacterial taxa implicated in CDA degradation and these taxa have not been previously identified in prior CDA degradation studies, indicating an unexplored diversity of CDA-degrading bacteria in the ocean. Moreover, the shape of the plastic article (e.g., a fabric, film, or foam) and plasticizer in the plastic matrix selected for different microbial communities. Our findings pave the way for future studies to identify the specific species and enzymes that drive CDA degradation in the marine environment, ultimately yielding a more predictive understanding of CDA biodegradation across space and time.

Plastic substrate and residual time of microplastics in the urban river shape the composition and structure of bacterial communities in plastisphere

The widespread secondary microplastics (MPs) in urban freshwater, originating from plastic wastes, have created a new habitat called plastisphere for microorganisms. The factors influencing the structure and ecological risks of the microbial community within the plastisphere are not yet fully understood. We conducted an in-site incubation experiment in an urban river, using MPs from garbage bags (GB), shopping bags (SB), and plastic bottles (PB). Bacterial communities in water and plastisphere incubated for 2 and 4 weeks were analyzed by 16S high-throughput sequencing. The results showed the bacterial composition of the plastisphere, especially the PB, exhibited enrichment of plastic-degrading and photoautotrophic taxa. Diversity declined in GB and PB but increased in SB plastisphere. Abundance analysis revealed distinct bacterial species that were enriched or depleted in each type of plastisphere. As the succession progressed, the differences in community structure was more pronounced, and the decline in the complexity of bacterial community within each plastisphere suggested increasing specialization. All the plastisphere exhibited elevated pathogenicity at the second or forth week, compared to bacterial communities related to natural particles. These findings highlighted the continually evolving plastisphere in urban rivers was influenced by the plastic substrates, and attention should be paid to fragile plastic wastes due to the rapidly increasing pathogenicity of the bacterial community attached to them.

Degradation of starch-based bioplastic bags in the pelagic and benthic zones of the Gulf of Oman

The Gulf of Oman is becoming increasingly polluted with plastics, hence bioplastics have been considered 'a substitute', although their biodegradability in marine environments has not been well investigated. Most research has been performed on cellulose-based bioplastics, whereas starch-based bioplastics have proven to be a suitable, but less researched, alternative. This study is the first of its kind designed to investigate the degradability of two different types of starch-based bioplastic bags, available in the market and labeled as "biodegradable", in the pelagic and benthic zones of one of the warmest marine environment in the world. Fourier-Transform Infrared Spectroscopy (FTIR) showed a clear reduction in the presence of OH, CH, and CO in the bioplastic bags after 5 weeks of immersion. Thermo-Gravimetric Analysis (TGA) indicated degradation of glycerol, starch, and polyethylene. The biofouling bacterial communities on bioplastic surfaces showed distinct grouping based on the immersion zone. Candidaatus saccharibacteria, Verrucomicrobiae, Acidimicrobiia and Planctomycetia sequences were only detectable on bioplastics in the pelagic zone, whereas Actinomyces, Pseudomonas, Sphingobium and Acinetobacter related sequences were only found on bioplastics in the benthic layer. We conclude that starch-based bioplastics are more readily degradable in the Gulf of Oman than conventional plastics, hence could serve as a better environmentally friendly alternative.

Substrate Specificity of Biofilms Proximate to Historic Shipwrecks

The number of built structures on the seabed, such as shipwrecks, energy platforms, and pipelines, is increasing in coastal and offshore regions. These structures, typically composed of steel or wood, are substrates for microbial attachment and biofilm formation. The success of biofilm growth depends on substrate characteristics and local environmental conditions, though it is unclear which feature is dominant in shaping biofilm microbiomes. The goal of this study was to understand the substrate- and site-specific impacts of built structures on short-term biofilm composition and functional potential. Seafloor experiments were conducted wherein steel and wood surfaces were deployed for four months at distances extending up to 115 m away from three historic (>50 years old) shipwrecks in the Gulf of Mexico. DNA from biofilms on the steel and wood was extracted, and metagenomes were sequenced on an Illumina NextSeq. A bioinformatics analysis revealed that the taxonomic composition was significantly different between substrates and sites, with substrate being the primary determining factor. Regardless of site, the steel biofilms had a higher abundance of genes related to biofilm formation, and sulfur, iron, and nitrogen cycling, while the wood biofilms showed a higher abundance of manganese cycling and methanol oxidation genes. This study demonstrates how substrate composition shapes biofilm microbiomes and suggests that marine biofilms may contribute to nutrient cycling at depth. Analyzing the marine biofilm microbiome provides insight into the ecological impact of anthropogenic structures on the seabed.

Aquatic plastisphere: Interactions between plastics and biofilms

Because of the high production rates, low recycling rates, and poor waste management of plastics, an increasing amount of plastic is entering the aquatic environment, where it can provide new ecological niches for microbial communities and form a so-called plastisphere. Recent studies have focused on the one-way impact of plastic substrata or biofilm communities. However, our understanding of the two-way interactions between plastics and biofilms is still limited. This review first summarizes the formation process and the co-occurrence network analysis of the aquatic plastisphere to comprehensively illustrate the succession pattern of biofilm communities and the potential consistency between keystone taxa and specific environmental behavior of the plastisphere. Furthermore, this review sheds light on mutual interactions between plastics and biofilms. Plastic properties, environmental conditions, and colonization time affect biofilm development. Meanwhile, the biofilm communities, in turn, influence the environmental behaviors of plastics, including transport, contaminant accumulation, and especially the fragmentation and degradation of plastics. Based on a systematic literature review and cross-referencing from these disciplines, the current research focus, and future challenges in exploring aquatic plastisphere development and biofilm-plastic interactions are proposed.

Microbial community shift on artificial biological reef structures (ABRs) deployed in the South China Sea

Many Artificial Reefs (ARs) have been used worldwide for marine habitat and coral reef restoration. However, the microbial community structure that colonize the ARs and their progressive development have been seldom investigated. In this study, the successive development of the microbial communities on environmentally friendly Artificial Biological Reef structures (ABRs)^R made of special concrete supported with bioactive materials collected from marine algal sources were studied. Three seasons (spring, summer and autumn), three coral reef localities and control models (SCE) without bioactive material and (NCE) made of normal cement were compared. The structure of the microbial pattern exhibited successive shifts from the natural environment to the ABRs supported with bioactive materials (ABAM). Cyanobacteria, Proteobacteria, and Planctomycetota were shown to be the most three dominant phyla. Their relative abundances pointedly increased on ABAM and SCE models compared to the environment. Amplicon Sequence Variant (ASV) Richness and Shannon index were obviously higher on ABAM models and showed significant positive relationship with that of macrobenthos than those on the controls and the natural reef (XR). Our results offer successful establishment of healthy microbial films on the ABR surfaces enhanced the restoration of macrobenthic community in the damaged coral reefs which better understands the ecological role of the ABRs.

Biotechnological methods to remove microplastics: a review

Microplastics pollution is major threat to ecosystems and is impacting abiotic and biotic components. Microplastics are diverse and highly complex contaminants that transport other contaminants and microbes. Current methods to remove microplastics include biodegradation, incineration, landfilling, and recycling. Here we review microplastics with focus on sources, toxicity, and biodegradation. We discuss the role of algae, fungi, bacteria in the biodegradation, and we present biotechnological methods to enhance degradation, e.g., gene editing tools and bioinformatics.

Influence of microplastics on microbial anaerobic detoxification of chlorophenols

Microplastics (MPs) can absorb halogenated organic compounds and transport them into marine anaerobic zones. Microbial reductive dehalogenation is a major process that naturally attenuates organohalide pollutants in anaerobic environments. Here, we aimed to determine the mechanisms through which MPs affect the microbe-mediated marine halogen cycle by incubating 2,4,6-trichlorophenol (TCP) dechlorinating cultures with various types of MPs. We found that TCP was dechlorinated to 4-chlorophenol in biotic control and polypropylene (PP) cultures, but essentially terminated at 2,4-dichlorophenol in polyethylene (PE) and polyethylene terephthalate (PET) cultures after incubation for 20 days. Oxygen-containing functional groups such as peroxide and aldehyde were enriched on PE and PET after incubation and corresponded to elevated levels of intracellular reactive oxygen species (ROS) in the microorganisms. Adding PE or PET to the cultures exerted limited effects on hydrogenase and ATPase activities, but delayed the expression of the gene encoding reductive dehalogenase (RDase). Considering the limited changes in the microbial composition of the enriched cultures, these findings suggested that microbial dechlorination is probably affected by MPs through the ROS-induced inhibition of RDase synthesis and/or activity. Overall, our findings showed that extensive MP pollution is unfavorable to environmental xenobiotic detoxification.

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.

Time-series incubations in a coastal environment illuminates the importance of early colonizers and the complexity of bacterial biofilm dynamics on marine plastics

The problematic of microplastics pollution in the marine environment is tightly linked to their colonization by a wide diversity of microorganisms, the so-called plastisphere. The composition of the plastisphere relies on a complex combination of multiple factors including the surrounding environment, the time of incubation along with the polymer type, making it difficult to understand how the biofilm evolves during the microplastic lifetime over the oceans. To better define bacterial community assembly processes on plastics, we performed a 5 months spatio-temporal survey of the plastisphere in an oyster farming area in the Bay of Brest (France). We deployed three types of plastic pellets in two positions in the foreshore and in the water column. Plastic-associated biofilm composition in all these conditions was monitored using 16 S rRNA metabarcoding and compared to free-living and attached bacterial members of seawater. We observed that bacterial families associated to plastic pellets were significantly distinct from the ones found in seawater, with a significant prevalence of filamentous Cyanobacteria on plastics. No convergence towards a unique plastisphere was detected between polymers exposed in the intertidal and subtidal area, emphasizing the central role of the surrounding environment on constantly shaping the plastisphere community diversity. However, we could define a bulk of early-colonizers of marine biofilms such as Alteromonas, Pseudoalteromonas or Vibrio. These early-colonizers could reach high abundances in floating microplastics collected in field-sampling studies, suggesting the plastic-associated biofilms could remain at early development stages across large oceanic scales. Our study raises the hypothesis that most members of the plastisphere, including putative pathogens, could result of opportunistic colonization processes and unlikely long-term transport.

Influence of Sharklet-Inspired Micropatterned Polymers on Spatio-Temporal Variations of Marine Biofouling

This article aims to show the influence of surface characteristics (microtopography, chemistry, mechanical properties) and seawater parameters on the settlement of marine micro- and macroorganisms. Polymers with nine microtopographies, three distinct mechanical properties, and wetting characteristics are immersed for one month into two contrasting coastal sites (Toulon and Kristineberg Center) and seasons (Winter and Summer). Influence of microtopography and chemistry on wetting is assessed through static contact angle and captive air bubble measurements over 3-weeks immersion in artificial seawater. Microscopic analysis, quantitative flow cytometry, metabarcoding based on the ribulose biphosphate carboxylase (rbcL) gene amplification, and sequencing are performed to characterize the settled microorganisms. Quantification of macrofoulers is done by evaluating the surface coverage and the type of organism. It is found that for long static in situ immersion, mechanical properties and non-evolutive wettability have no major influence on both abundance and diversity of biofouling assemblages, regardless of the type of organisms. The apparent contradiction with previous results, based on model organisms, may be due to the huge diversity of marine environments, both in terms of taxa and their size. Evolutive wetting properties with wetting switching back and forth over time have shown to strongly reduce the colonization by macrofoulers.

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.

Micro(nano)plastic size and concentration co-differentiate nitrogen transformation, microbiota dynamics, and assembly patterns in constructed wetlands

Micro/nano-sized plastics (MPs/NPs) existing in wastewater system are the potential threats to nitrogen (N) biotransformation. Constructed wetlands (CWs) as wastewater treatment systems are considered the important barriers preventing MPs/NPs from entering the open water. However, little is known about how the accumulation of MPs/NPs affects microbial N transformation, dynamics, assembly, and metabolism of wetland microbiota. Herein, we constructed 12 wetland systems to address the above knowledge gaps over 300-day exposure to different sizes (3 mm - 60 nm) and concentrations (10 - 1000 μg/L) of MPs/NPs. The results showed that MPs/NPs accumulation caused decrease in NH₄⁺-N removal (by 7.6% - 71.2%) and microbial diversity and intriguingly altered microbiota composition (especially in the high-concentration groups) without damage on the high removal efficiency of NO₃^--N and NO₂^--N (66.2% - 99.8%) in all except for the nano-sized plastic-exposed wetlands. Moreover, MPs/NPs exposure induced shift in the strengths of non-random species aggregation and segregation patterns co-differentiated by the size and concentration of MPs/NPs, and MPs/NPs accumulation created size-differentiated alternative niches for nitrogen-transforming bacteria, e.g., canonical nitrifiers (Nitrospira and Nitrosomonas) and denitrifiers (Thauera, Comamonas, and Aquabacterium), which were enriched in MPs groups where denitrifying enzyme-coding genes were also enriched, suggesting potential positive impact of larger plastics on denitrification. Our study highlights MPs/NPs-induced divergence in microbiota dynamics and nitrogen transformation in CWs, and provides important insights into how microbiota structurally and functionally respond to long-term MPs/NPs disturbance.

Plastisphere community assemblage of aquatic environment: plastic-microbe interaction, role in degradation and characterization technologies

It is undeniable that plastics are ubiquitous and a threat to global ecosystems. Plastic waste is transformed into microplastics (MPs) through physical and chemical disruption processes within the aquatic environment. MPs are detected in almost every environment due to their worldwide transportability through ocean currents or wind, which allows them to reach even the most remote regions of our planet. MPs colonized by biofilm-forming microbial communities are known as the ''plastisphere". The revelation that this unique substrate can aid microbial dispersal has piqued interest in the ground of microbial ecology. MPs have synergetic effects on the development, transportation, persistence, and ecology of microorganisms. This review summarizes the studies of plastisphere in recent years and the microbial community assemblage (viz. autotrophs, heterotrophs, predators, and pathogens). We also discussed plastic-microbe interactions and the potential sources of plastic degrading microorganisms. Finally, it also focuses on current technologies used to characterize those microbial inhabitants and recommendations for further research.

Quantifying the importance of plastic pollution for the dissemination of human pathogens: The challenges of choosing an appropriate 'control' material

Discarded plastic wastes in the environment are serious challenges for sustainable waste management and for the delivery of environmental and public health. Plastics in the environment become rapidly colonised by microbial biofilm, and importantly this so-called 'plastisphere' can also support, or even enrich human pathogens. The plastisphere provides a protective environment and could facilitate the increased survival, transport and dissemination of human pathogens and thus increase the likelihood of pathogens coming into contact with humans, e.g., through direct exposure at beaches or bathing waters. However, much of our understanding about the relative risks associated with human pathogens colonising environmental plastic pollution has been inferred from taxonomic identification of pathogens in the plastisphere, or laboratory experiments on the relative behaviour of plastics colonised by human pathogens. There is, therefore, a pressing need to understand whether plastics play a greater role in promoting the survival and dispersal of human pathogens within the environment compared to other substrates (either natural materials or other pollutants). In this paper, we consider all published studies that have detected human pathogenic bacteria on the surfaces of environmental plastic pollution and critically discuss the challenges of selecting an appropriate control material for plastisphere experiments. Whilst it is clear there is no 'perfect' control material for all plastisphere studies, understanding the context-specific role plastics play compared to other substrates for transferring human pathogens through the environment is important for quantifying the potential risk that colonised plastic pollution may have for environmental and public health.

A review on marine plastisphere: biodiversity, formation, and role in degradation

The pollution of plastic waste has become an increasingly serious environmental crisis. Recently, plastic has been detected in various kinds of environments, even in human tissues, which is an increasing threat to the ecosystems and humans. In the ocean, the plastic waste is eventually fragmentized into microplastics (MPs) under the disruption of physical and chemical processes. MPs are colonized by microbial communities such as fungi, diatoms, and bacteria, which form biofilms on the surface of the plastic called “plastisphere”. In this review, we summarize the studies related to microorganisms in the plastisphere in recent years and describe the microbial species in the plastisphere, mainly including bacteria, fungi, and autotrophs. Secondly, we explore the interactions between MPs and the plastisphere. The depth of MPs in the ocean and the nutrients in the surrounding seawater can have a great impact on the community structure of microorganisms in the plastisphere. Finally, we discuss the types of MP-degrading bacteria in the ocean, and use the “seed bank” theory to speculate on the potential sources of MP-degrading microorganisms. Challenges and future research prospects are also discussed.

Bioplastic accumulates antibiotic and metal resistance genes in coastal marine sediments

The oceans are increasingly polluted with plastic debris, and several studies have implicated plastic as a reservoir for antibiotic resistance genes and a potential vector for antibiotic-resistant bacteria. Bioplastic is widely regarded as an environmentally friendly replacement to conventional petroleum-based plastic, but the effects of bioplastic pollution on marine environments remain largely unknown. Here, we present the first evidence that bioplastic accumulates antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) in marine sediments. Biofilms fouling ceramic, polyethylene terephthalate (PET), and polyhydroxyalkanoate (PHA) were investigated by shotgun metagenomic sequencing. Four ARG groups were more abundant in PHA: trimethoprim resistance (TMP), multidrug resistance (MDR), macrolide-lincosamide-streptogramin resistance (MLS), and polymyxin resistance (PMR). One MRG group was more abundant in PHA: multimetal resistance (MMR). The relative abundance of ARGs and MRGs were strongly correlated based on a Mantel test between the Bray-Curtis dissimilarity matrices (R = 0.97, p < 0.05) and a Pearson's analysis (R = 0.96, p < 0.05). ARGs were detected in more than 40% of the 57 metagenome-assembled genomes (MAGs) while MRGs were detected in more than 90% of the MAGs. Further investigation (e.g., culturing, genome sequencing, antibiotic susceptibility testing) revealed that PHA biofilms were colonized by hemolytic Bacillus cereus group bacteria that were resistant to beta-lactams, vancomycin, and bacitracin. Taken together, our findings indicate that bioplastic, like conventional petroleum-based plastic, is a reservoir for resistance genes and a potential vector for antibiotic-resistant bacteria in coastal marine sediments.

New approaches for the characterization of plastic-associated microbial communities and the discovery of plastic-degrading microorganisms and enzymes

Plastics in the environment represent new substrates for microbial colonization, and recent methodological advances allow for in-depth characterization of plastic-associated microbial communities (PAMCs). Over the past several decades, discovery of plastic degrading enzymes (PDEs) and plastic degrading microorganisms (PDMs) has been driven by efforts to understand microbially-mediated plastic degradation in the environment and to discover biocatalysts for plastic processing. In this review, we discuss the evolution of methodology in plastic microbiology and highlight major advancements in the field stemming from computational microbiology. Initial research relied largely on culture-based approaches like clear-zone assays to screen for PDMs and microscopy to characterize PAMCs. New computational tools and sequencing technologies are accelerating discoveries in the field through culture-independent and multi-omic approaches, rapidly generating targets for protein engineering and improving the potential for plastic-waste management.

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.

Bacterial community structure of early-stage biofilms is dictated by temporal succession rather than substrate types in the southern coastal seawater of India

Bacterial communities colonized on submerged substrata are recognized as a key factor in the formation of complex biofouling phenomenon in the marine environment. Despite massive maritime activities and a large industrial sector in the nearshore of the Laccadive Sea, studies describing pioneer bacterial colonizers and community succession during the early-stage biofilm are scarce. We investigated the biofilm-forming bacterial community succession on three substrata viz. stainless steel, high-density polyethylene, and titanium over 15 days of immersion in the seawater intake area of a power plant, located in the southern coastal region of India. The bacterial community composition of biofilms and peripheral seawater were analyzed by Illumina MiSeq sequenced 16S rRNA gene amplicons. The obtained metataxonomic results indicated a profound influence of temporal succession over substrate type on the early-stage biofilm-forming microbiota. Bacterial communities showed vivid temporal dynamics that involved variations in abundant bacterial groups. The proportion of dominant phyla viz. Proteobacteria decreased over biofilm succession days, while Bacteroidetes increased, suggesting their role as initial and late colonizers, respectively. A rapid fluctuation in the proportion of two bacterial orders viz. Alteromonadales and Vibrionales were observed throughout the successional stages. LEfSe analysis identified specific bacterial groups at all stages of biofilm development, whereas no substrata type-specific groups were observed. Furthermore, the results of PCoA and UPGMA hierarchical clustering demonstrated that the biofilm-forming community varied considerably from the planktonic community. Phylum Proteobacteria preponderated the biofilm-forming community, while the Bacteroidetes, Cyanobacteria, and Actinobacteria dominated the planktonic community. Overall, our results refute the common assumption that substrate material has a decisive impact on biofilm formation; rather, it portrayed that the temporal succession overshadowed the influence of the substrate material. Our findings provide a scientific understanding of the factors shaping initial biofilm development in the marine environment and will help in designing efficient site-specific anti-biofouling strategies.

Diatom and cyanobacteria communities on artificial polymer substrates in the Crimean coastal waters of the Black Sea

This research on the species diversity of fouling diatoms and cyanobacteria on different polymer materials and carried out from August to November 2020 in Karantinnaya Bay of the Black Sea. There were 75 taxa of diatoms and 24 of cyanobacteria. The maximum diatoms (31 species) were on the biodegradable bag and cyanobacteria (16) on the plastic bottle. A little known for the Black Sea species of diatoms and cyanobacteria were recorded. The diatoms Cylindrotheca closterium, Nitzschia sigma, and cyanobacteria Spirulina subsalsa were found on all samples. A tendency to increase diversity and species similarity was revealed during long-term exposition of substrates. To the end of exposition, the periphyton communities became indifferent to the type of substrate and acquired signs of natural fouling, which was observed especially for cyanobacteria. The occurrence and species similarity of diatoms and cyanobacteria communities on different substrates are discussed.

Microbial Diversity and Activity During the Biodegradation in Seawater of Various Substitutes to Conventional Plastic Cotton Swab Sticks

The European Parliament recently approved a new law banning single-use plastic items for 2021 such as plastic plates, cutlery, straws, cotton swabs, and balloon sticks. Transition to a bioeconomy involves the substitution of these banned products with biodegradable materials. Several materials such as polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), poly(butylene succinate) (PBS), polyhydroxybutyrate-valerate (PHBV), Bioplast, and Mater-Bi could be good candidates to substitute cotton swabs, but their biodegradability needs to be tested under marine conditions. In this study, we described the microbial life growing on these materials, and we evaluated their biodegradability in seawater, compared with controls made of non-biodegradable polypropylene (PP) or biodegradable cellulose. During the first 40 days in seawater, we detected clear changes in bacterial diversity (Illumina sequencing of 16S rRNA gene) and heterotrophic activity (incorporation of ³H-leucine) that coincided with the classic succession of initial colonization, growth, and maturation phases of a biofilm. Biodegradability of the cotton swab sticks was then tested during another 94 days under strict diet conditions with the different plastics as sole carbon source. The drastic decrease of the bacterial activity on PP, PLA, and PBS suggested no bacterial attack of these materials, whereas the bacterial activity in PBAT, Bioplast, Mater-Bi, and PHBV presented similar responses to the cellulose positive control. Interestingly, the different bacterial diversity trends observed for biodegradable vs. non-biodegradable plastics allowed to describe potential new candidates involved in the degradation of these materials under marine conditions. This better understanding of the bacterial diversity and activity dynamics during the colonization and biodegradation processes contributes to an expanding baseline to understand plastic biodegradation in marine conditions and provide a foundation for further decisions on the replacement of the banned single-used plastics.

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.

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.

Hydrodynamics and surface properties influence biofilm proliferation

A biofilm is an interface-associated colloidal dispersion of bacterial cells and excreted polymers in which microorganisms find protection from their environment. Successful colonization of a surface by a bacterial community is typically a detriment to human health and property. Insight into the biofilm life-cycle provides clues on how their proliferation can be suppressed. In this review, we follow a cell through the cycle of attachment, growth, and departure from a colony. Among the abundance of factors that guide the three phases, we focus on hydrodynamics and stratum properties due to the synergistic effect such properties have on bacteria rejection and removal. Cell motion, whether facilitated by the environment via medium flow or self-actuated by use of an appendage, drastically improves the survivability of a bacterium. Once in the vicinity of a stratum, a single cell is exposed to near-surface interactions, such as van der Waals, electrostatic and specific interactions, similarly to any other colloidal particle. The success of the attachment and the potential for detachment is heavily influenced by surface properties such as material type and topography. The growth of the colony is similarly guided by mainstream flow and the convective transport throughout the biofilm. Beyond the growth phase, hydrodynamic traction forces on a biofilm can elicit strongly non-linear viscoelastic responses from the biofilm soft matter. As the colony exhausts the means of survival at a particular location, a set of trigger signals activates mechanisms of bacterial release, a life-cycle phase also facilitated by fluid flow. A review of biofilm-relevant hydrodynamics and startum properties provides insight into future research avenues.

Comparative Analysis of the Ecological Succession of Microbial Communities on Two Artificial Reef Materials

Concrete and wood are commonly used to manufacture artificial reefs (ARs) worldwide for marine resource enhancement and habitat restoration. Although microbial biofilms play an important role in marine ecosystems, the microbial communities that colonize concrete and wooden ARs and their temporal succession have rarely been studied. In this study, the temporal succession of the microbial communities on concrete and wooden AR blocks and the driving factors were investigated. The composition of the microbial communities underwent successive shifts over time: among the six dominant phyla, the relative abundances of Proteobacteria, Cyanobacteria and Gracilibacteria significantly decreased in wood, as did that of Cyanobacteria in concrete. Operational taxonomic units (OTU) richness and Shannon index were significantly higher in concrete than in wood. Non-metric multidimensional scaling ordination placed the microbial communities in two distinct clusters corresponding to the two substrate materials. The macrobenthic compositions of concrete and wood were broadly similar and shifted over time, especially in the first five weeks. The Shannon index of the microbial communities in concrete and wood increased significantly with the organism coverage. The results provide fundamental data on microbial community succession during the initial deployment of ARs and contribute to understanding the ecological effects of ARs.

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.

Food or just a free ride? A meta-analysis reveals the global diversity of the Plastisphere

It is now indisputable that plastics are ubiquitous and problematic in ecosystems globally. Many suggestions have been made about the role that biofilms colonizing plastics in the environment—termed the “Plastisphere”—may play in the transportation and ecological impact of these plastics. By collecting and re-analyzing all raw 16S rRNA gene sequencing and metadata from 2,229 samples within 35 studies, we have performed the first meta-analysis of the Plastisphere in marine, freshwater, other aquatic (e.g., brackish or aquaculture) and terrestrial environments. We show that random forest models can be trained to differentiate between groupings of environmental factors as well as aspects of study design, but—crucially—also between plastics when compared with control biofilms and between different plastic types and community successional stages. Our meta-analysis confirms that potentially biodegrading Plastisphere members, the hydrocarbonoclastic Oceanospirillales and Alteromonadales are consistently more abundant in plastic than control biofilm samples across multiple studies and environments. This indicates the predilection of these organisms for plastics and confirms the urgent need for their ability to biodegrade plastics to be comprehensively tested. We also identified key knowledge gaps that should be addressed by future studies.

Marine Plastic Debris: A New Surface for Microbial Colonization

Plastics become rapidly colonized by microbes when released into marine environments. This microbial community-the Plastisphere-has recently sparked a multitude of scientific inquiries and generated a breadth of knowledge, which we bring together in this review. Besides providing a better understanding of community composition and biofilm development in marine ecosystems, we critically discuss current research on plastic biodegradation and the identification of potentially pathogenic "hitchhikers" in the Plastisphere. The Plastisphere is at the interface between the plastic and its surrounding milieu, and thus drives every interaction that this synthetic material has with its environment, from ecotoxicity and new links in marine food webs to the fate of the plastics in the water column. We conclude that research so far has not shown Plastisphere communities to starkly differ from microbial communities on other inert surfaces, which is particularly true for mature biofilm assemblages. Furthermore, despite progress that has been made in this field, we recognize that it is time to take research on plastic-Plastisphere-environment interactions a step further by identifying present gaps in our knowledge and offering our perspective on key aspects to be addressed by future studies: (I) better physical characterization of marine biofilms, (II) inclusion of relevant controls, (III) study of different successional stages, (IV) use of environmentally relevant concentrations of biofouled microplastics, and (V) prioritization of gaining a mechanistic and functional understanding of Plastisphere communities.

The influence of plastic pollution and ocean change on detrital decomposition

Plastic pollution and ocean change have mostly been assessed separately, missing potential interactions that either enhance or reduce future impacts on ecosystem processes. Here, we used manipulative experiments with outdoor mesocosms to test hypotheses about the interactive effects of plastic pollution, ocean warming and acidification on macrophyte detrital decomposition. These experiments focused on detritus from kelp, Ecklonia radiata, and eelgrass, Zostera muelleri, and included crossed treatments of (i) no, low and high plastic pollution, (ii) current/future ocean temperatures, and (iii) ambient/future ocean partial pressure of carbon dioxide (pCO₂). High levels of plastic pollution significantly reduced the decomposition rate of kelp and eelgrass by approximately 27% and 36% in comparison to controls respectively. Plastic pollution also significantly slowed the nitrogen liberation from seagrass and kelp detritus. Higher seawater temperatures significantly increased the decomposition rate of kelp and eelgrass by 12% and 5% over current conditions, respectively. Higher seawater temperatures were also found to reduce the nitrogen liberation in eelgrass. In contrast, ocean acidification did not significantly influence the rate of macrophyte decomposition or nutrient liberation. Overall, our results show how detrital processes might respond to increasing plastic pollution and ocean temperatures, which has implications for detrital-driven secondary productivity, nutrient dynamics and carbon cycling.

Cultivation substrata differentiate the properties of river biofilm EPS and their binding of heavy metals: A spectroscopic insight

River biofilms inevitably serve as recipients of heavy metals including copper (Cu) and cadmium (Cd) following their introduction in fluvial systems. Nevertheless, the effects of cultivation substrata on the characteristics of river biofilm extracellular polymeric substances (EPS) and the binding behaviors of heavy metals on biofilms remain unclear. Integrating spectroscopic methods with chemometric analyses, we explored the binding behaviors of Cu(II) and Cd(II) onto biofilm EPS cultivated from two representative substrata at the molecular level. Chemical analysis revealed that biofilm cultivated on polyethylene (PE) pieces contained more non-fluorescent protein fractions, whereas EPS from periphyton grown on mineral, i.e., cobblestones was richer in aromatic fractions and polysaccharides. Excitation-emmision matrix combined with parallel factor analysis suggested a stronger interaction between fluorophores in periphytic EPS with Cu(II) compared to fluorophores in plastic biofilm EPS. Integrated use of infrared spectroscopy and two-dimensional correlation analyses revealed that, during the heavy metal binding processes, the amines and phenolics in plastic biofilm EPS gave the fastest responses to metal binding. While the amides and the aliphatic fractions in periphytic EPS showed a preferential binding to heavy metals. This study differentiates the effects of cultivation substrata on structuring the biofilm EPS characteristics and offers new insights into the environmental behaviors of heavy metal discharge into fluvial systems in river biofilm matrix.

Microbial Colonization in Marine Environments: Overview of Current Knowledge and Emerging Research Topics

Microbial biofilms are biological structures composed of surface-attached microbial communities embedded in an extracellular polymeric matrix. In aquatic environments, the microbial colonization of submerged surfaces is a complex process involving several factors, related to both environmental conditions and to the physical-chemical nature of the substrates. Several studies have addressed this issue; however, more research is still needed on microbial biofilms in marine ecosystems. After a brief report on environmental drivers of biofilm formation, this study reviews current knowledge of microbial community attached to artificial substrates, as obtained by experiments performed on several material types deployed in temperate and extreme polar marine ecosystems. Depending on the substrate, different microbial communities were found, sometimes highlighting the occurrence of species-specificity. Future research challenges and concluding remarks are also considered. Emphasis is given to future perspectives in biofilm studies and their potential applications, related to biofouling prevention (such as cell-to-cell communication by quorum sensing or improved knowledge of drivers/signals affecting biological settlement) as well as to the potential use of microbial biofilms as sentinels of environmental changes and new candidates for bioremediation purposes.

Ecology of the plastisphere

The plastisphere, which comprises the microbial community on plastic debris, rivals that of the built environment in spanning multiple biomes on Earth. Although human-derived debris has been entering the ocean for thousands of years, microplastics now numerically dominate marine debris and are primarily colonized by microbial and other microscopic life. The realization that this novel substrate in the marine environment can facilitate microbial dispersal and affect all aquatic ecosystems has intensified interest in the microbial ecology and evolution of this biotope. Whether a 'core' plastisphere community exists that is specific to plastic is currently a topic of intense investigation. This Review provides an overview of the microbial ecology of the plastisphere in the context of its diversity and function, as well as suggesting areas for further research.

Microbial Ecotoxicology of Marine Plastic Debris: A Review on Colonization and Biodegradation by the "Plastisphere"

Over the last decades, it has become clear that plastic pollution presents a global societal and environmental challenge given its increasing presence in the oceans. A growing literature has focused on the microbial life growing on the surfaces of these pollutants called the "plastisphere," but the general concepts of microbial ecotoxicology have only rarely been integrated. Microbial ecotoxicology deals with (i) the impact of pollutants on microbial communities and inversely (ii) how much microbes can influence their biodegradation. The goal of this review is to enlighten the growing literature of the last 15 years on microbial ecotoxicology related to plastic pollution in the oceans. First, we focus on the impact of plastic on marine microbial life and on the various functions it ensures in the ecosystems. In this part, we also discuss the driving factors influencing biofilm development on plastic surfaces and the potential role of plastic debris as vector for dispersal of harmful pathogen species. Second, we give a critical view of the extent to which marine microorganisms can participate in the decomposition of plastic in the oceans and of the relevance of current standard tests for plastic biodegradability at sea. We highlight some examples of metabolic pathways of polymer biodegradation. We conclude with several questions regarding gaps in current knowledge of plastic biodegradation by marine microorganisms and the identification of possible directions for future research.