Abstract
BackgroundSynthetic microplastics (≤5-mm fragments) are emerging environmental contaminants that have been found to accumulate within coastal marine sediments worldwide. The ecological impacts and fate of microplastic debris are only beginning to be revealed, with previous research into these topics having primarily focused on higher organisms and/or pelagic environments. Despite recent research into plastic-associated microorganisms in seawater, the microbial colonization of microplastics in benthic habitats has not been studied. Therefore, we employed a 14-day microcosm experiment to investigate bacterial colonization of low-density polyethylene (LDPE) microplastics within three types of coastal marine sediment from Spurn Point, Humber Estuary, U.K.ResultsBacterial attachment onto LDPE within sediments was demonstrated by scanning electron microscopy and catalyzed reporter deposition fluorescence in situ hybridisation (CARD-FISH). Log-fold increases in the abundance of 16S rRNA genes from LDPE-associated bacteria occurred within 7 days with 16S rRNA gene numbers on LDPE surfaces differing significantly across sediment types, as shown by quantitative PCR. Terminal-restriction fragment length polymorphism (T-RFLP) analysis demonstrated rapid selection of LDPE-associated bacterial assemblages whose structure and composition differed significantly from those in surrounding sediments. Additionally, T-RFLP analysis revealed successional convergence of the LDPE-associated communities from the different sediments over the 14-day experiment. Sequencing of cloned 16S rRNA genes demonstrated that these communities were dominated after 14 days by the genera Arcobacter and Colwellia (totalling 84–93% of sequences). Attachment by Colwellia spp. onto LDPE within sediments was confirmed by CARD-FISH.ConclusionsThese results demonstrate that bacteria within coastal marine sediments can rapidly colonize LDPE microplastics, with evidence for the successional formation of plastisphere-specific bacterial assemblages. Although the taxonomic compositions of these assemblages are likely to differ between marine sediments and the water column, both Arcobacter and Colwellia spp. have previously been affiliated with the degradation of hydrocarbon contaminants within low-temperature marine environments. Since hydrocarbon-degrading bacteria have also been discovered on plastic fragments in seawater, our data suggest that recruitment of hydrocarbonoclastic bacteria on microplastics is likely to represent a shared feature between both benthic and pelagic marine habitats.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-014-0232-4) contains supplementary material, which is available to authorized users.
Highlights
Synthetic microplastics (≤5-mm fragments) are emerging environmental contaminants that have been found to accumulate within coastal marine sediments worldwide
Bacterial cells were found to be attached onto low-density polyethylene (LDPE) surfaces exposed to sediment from site SP2 for 14 days, as shown by 4′,6-diamidino-2-phenylindole (DAPI) staining and catalyzed reporter deposition in situ fluorescence hybridization (CARD-FISH) analysis performed with the oligonucleotide probes EUB338 I-III (Figure 2a-d)
Bacterial 16S rRNA gene numbers on LDPE fragments exposed to the three sediment types during the 14-day experiment were quantified (Figure 3) as a proxy of the relative abundance of plastic-colonizing bacteria using quantitative real-time PCR (Q-PCR)
Summary
Synthetic microplastics (≤5-mm fragments) are emerging environmental contaminants that have been found to accumulate within coastal marine sediments worldwide. Whilst the physical impacts caused by plastic debris (for example, entanglement and suffocation of wildlife) are well-recognized [11], the rapid proliferation of microplastics (≤5 mm fragments) in marine habitats [2,8,12] is leading to a reevaluation of the potential detrimental effects of plastic litter [13] Microplastics represent both a physical and chemical threat to the ecological integrity of our seas and oceans [9] due to their high potential to become ingested by wildlife, and their capacity to transport persistent organic pollutants (for example, polynuclear aromatic hydrocarbons) and plastic additives into marine food webs [14,15]. This is true for coastal and intertidal sediments that represent sinks for the accumulation of plastic litter [7,9,12,16,17,18], where microplastic concentrations may reach up to 81 parts per million by mass [16] and constitute as much as 80% of plastic debris within the seafloor [19]
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