Seite - 183 - in Freshwater Microplastics - Emerging Environmental Contaminants?

A growing body of research has investigated the impacts of microplastics on biota, which may involve direct and indirect processes (e.g., physical blockage caused by ingested particles, as well as their ability to transport harmful com- pounds, pathogens, and algae) [2, 8–10]. Even so, little is known about the ecological effects of microplastics within freshwaters [10]. For example, while microplastic-associatedmicrobial (bacterial, archaeal, and picoeukaryotic) assem- blagesare likely toprofoundly influence thedistribution, impacts, and fateof these pollutants, research into this topichas focusedonmarineenvironments [11–13]. In streams and other habitats, biofilms1 are primary sites for carbon and nutrient transformations and form the base of foodwebs, contributing to local and global ecosystem functioning [14].As they are also essential to pollutant biodegradation, an improved knowledge ofmicrobial-microplastic interactions is required to pre- dict theenvironmental impactsofplasticdebris [15]. Investigating this topic could inform the development of solutions to manage plastic pollution by determining how it affects processes includingmicrobially mediated primary production and interactions between plastic-associated (“plastisphere”) taxa and other organisms [11, 12, 16, 17]. It could also lead to insights concerning the biodegradability of plastic litter and facilitate the development of new approaches to plastic disposal and/or recycling [18]. Freshwater andmarine habitats share a number of features, but there are also differences between them that may affect the development and activities of plastisphere consortia. To facilitate investigation of this topic, findings based on marine plastisphere research are compared with those available for freshwaters. Following an assessment of recent discoveries concerning the formation and dis- tributionofplastic-associatedbiofilms, our knowledge concerning their ecological rolesandability todriveprocesses includingpolymerbiodegradation isconsidered. Finally, some of themain knowledge gaps in plastisphere research are discussed andused to highlightmethodological advances inmicrobial ecology that could be used to improveour understandingofmicrobial-microplastic interactions. 2 FreshwaterPlastisphereAssemblages: State of theScience 2.1 FactorsContributing toBiofilmFormation andComposition Fundamental processes involved in biofilm formation are well established, with initial attachment followed by maturation and the eventual detachment of cells [19]. There are also further factors thatmay influence the formation, composition, 1Surface-associated aggregates ofmicrobial cells encased in amatrix of extracellular polymeric substances. Microplastic-AssociatedBiofilms:AComparisonofFreshwater andMarine. . . 183