| Summary: | While the sources and fates of plastic pollution are receiving growing attention, major knowledge gaps exist. Among these, microbial degradation (aka biodegradation) of plastics remains poorly investigated. The process of biodegradation begins with the formation of biofilm on the polymer surface; our study aimed to investigate microbial colonization of polymer surfaces in the Arctic marine environment around Tromsø, Norway. An immersion experiment was designed to assess microbiome community composition on four different types of pre-production microplastic (<5mm in diameter) pellets (Low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS) and polyethylene-terephthalate (PET)) and rubber (a non-synthetic polymer used as a control) over a period of 6 months at two different locations around Tromsø. Surface states of pre and post-immersion polymer samples were examined using Scanning Electron Microscopy. Samples were taken at 6 months post-immersion, and surface biofilm was subject to chemical and enzymatic digestion and DNA extraction by phenol-chloroform separation. Genotyping using 16S, 18S and ITS 2 rRNA gene amplification and next-generation sequencing on the Illumina platform was employed to identify bacterial, eukaryotic and fungal microbial life on the polymer surfaces. Investigation of the species richness and diversity within and among polymer types (alpha and beta-diversity, respectively) contribute key insights to the body of knowledge relating to the plastic microbiome and its potential role in polymer degradation. Taxonomic profiles were compared against a database of known polymer-degrading microbes to determine if any microbial degradation was likely under Arctic conditions. Several notable operational taxonomical units were identified including members belonging to obligate hydrocarbon-degrading bacterial species, marine fish pathogens, and members of families containing polymer-degrading bacterial species. Significant differences in community structure were noted between polymer-associated and both rubber and free-floating bacterial communities, as well as differences in select eukaryotic and fungal communities.
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