COS 194-6 - Plastic colonizers of the Bermuda platform: An in-situ longitudinal microbial community assessment

Abstract: Plastic waste accumulation in marine environments has complex, unintended impacts which can drive changes in community dynamics across ecological levels. Polyolefin polymers: Polyethylene (PE) and polypropylene (PP) are two of the most globally abundant plastics found in the surface seawater. To measure succession in communities of marine bacterial colonizers of polyolefins, a long-term in-situ incubation time-series experiment was conducted in the oligotrophic coastal waters of the Bermuda platform. Our goals were to identify microbial taxa that colonize polyolefins and isolate microbial cultures for future studies of the biochemistry of microbe-plastic interactions. HDPE, LDPE, PP and glass coupons were incubated in surface seawater for 11 weeks and sampled at two-week intervals. Seawater and biofilms from the coupons were collected for 16S rDNA sequencing, seawater chemical properties were measured, and plastic coupons were collected to measure changes in the surface chemistry of plastics by FTIR/HIM. The most abundant colonizing taxa ( >5% relative abundance) were cosmopolitan colonizers that previously have been reported. The composition of dominant members of biofilm communities was highly similar across treatments, but showed strong evidence of community succession (p< 0.01). Significant differences between treatments in rare community composition were observed, potentially indicating specific microbial interactions based on surface chemistry. A stark transition in community composition in all treatments occurred between days 42 and 56. Prior to the transition, the Alteromonadaceae, Marinomonadaceae, Saccharospirillaceae, Vibrionaceae, Thalassospiraceae, and Flavobacteriaceaefamilies were the dominant colonizers.

Following the transition, the relative abundance of these taxa declined, while Hyphomonadaceae, Rhodobacteraceae and Saprospiraceae increased. Over the course of the incubation, 16 significant polyolefin-enriched taxa were observed: two from lineages known to include hydrocarbon degraders (Pseudooceanicola and an unclassified Rhodobacteraceae) and a close relative of a voracious hydrocarbon degrader and potential LDPE degrader (Alcanivorax sp), Ketobacter spp. As a result of these findings, evidence of multiple microbial taxa enriched from long-term marine incubations of plastics were found. Some of the taxa were not previously known to be associated with plastics, their significant enrichment suggests they might be involved in marine plastic degradation. In conclusion, the described organisms should be viewed as potential targets for future investigations in understanding and simulating plastic degradation in the marine environment.