MIASMAS - MIcroplastic Associated Spread of Microbial Assemblages in Aquatic (eco)Systems

As millions of tonnes of plastic end up in aquatic ecosystems globally every year, there is mounting concern about microplastics, i.e. small plastic pieces created when larger pieces break apart, or manufactured for industrial products, including cosmetics and packaging materials. Microplastics are long-lived and accumulate in food chains, potentially harming lifeforms, including humans. Besides toxic effects of plastic chemicals, microplastics in waters provide ideal substrates for microbial colonization (biofilms). Microbial communities in these biofilms can host human pathogens and enable gene exchange among microorganisms, including virulence and antimicrobial resistance genes. As plastic longevity, hydrophobicity and biofilm-enhanced buoyancy favour long-distance dispersal of microplastics, they provide novel vector substrates for spread of potentially hazardous microorganisms. Microplastics may also select for unique microbial assemblages due to hard attachment surfaces, particle-specific properties (including novel organic polymers, additives and sorbed contaminants) providing carbon sources for microbial metabolism, and secondary microbial biofilm members attaching to biofilm polysaccharides or primary colonizers. Moreover, biofilms increase the likelihood of microplastic ingestion, deposition and decomposition. While most microplastic research focuses on marine environments, microplastic dynamics in freshwater are under-researched. Freshwater accumulates microplastics from several sources, including land run-off and wastewater treatment plants, and rivers may transport microplastics to seas/oceans. Co-emission with wastewater exposes microplastics to pathogens, antimicrobials and antimicrobial-resistant microorganisms in wastewater streams, generally near densely populated areas, enabling their transport to other (downstream) areas. Few studies examined the capacity of microplastic-associated biofilms in freshwater to develop distinctive microbial consortia. Field data on microplastic abundance, sources and biofilms in freshwater are needed to assess health risks and to include lotic ecosystems in global budgets of plastic. In this project, we will determine microplastic (20µm-5mm) concentrations, their chemical properties and microbial assemblages (including human pathogens, virulence and antimicrobial resistance genes), considering also local environmental factors, in one of the longest European rivers: the Rhine, specifically at the river entry into the Netherlands and at its main estuary in the North Sea, as to monitor what is coming from upstream, what is reaching the North Sea, and what would be the Netherlands’ own contribution to Rhine’s microplastic pollution. Using established mathematical models, we will then quantify human exposure to microplastic-associated microorganisms. With a consortium of 3 leading Dutch research institutes in water research, public and environmental health (National Institute for Public Health and the Environment; Watercycle Research institute; Utrecht University’s Institute for Risk Assessment Sciences) we will determine whether/how: 1) microplastic concentrations, their chemical properties and microbial assemblages differ seasonally and over the course of the river; 2) microplastic-associated microbial assemblages differ from those on natural substrates (seston); 3) these assemblages include potentially harmful microorganisms and depend, to some extent, on local environmental factors and microplastic chemical properties. Microplastics will be collected, quantified and chemically characterized, and the total bacterial, viral (DNA viruses) and parasitic population (including virulome and resistome) in their biofilms and in seston will be determined with shotgun metagenomic sequencing. Differences in microbial composition on microplastic vs. seston samples, and differences over sites and seasons in microplastic- and seston-associated microbial consortia, microplastic concentrations and polymer properties, as well as their interrelations and effects of environmental factors, will be assessed. Detailed bioinformatics analyses will uncover biofilm-associated taxonomic, functional and metabolic profiles. This project will thus provide fundamental knowledge on the biohazards of microplastic dispersal via freshwater, including the risk of introduction of existing diseases through new transmission routes into areas/niches where they are new and can stimulate the global spread of waterborne diseases and antimicrobial resistance. This data will provide a solid and necessary anchor point for future developments in risk assessment and management of microplastics. Applicants contribute since many years to several national and international scientific advisory boards, so through these forums, knowledge gained in this project may be directly discussed with the relevant stakeholders.