Plastic Debris in the Marine Environment: Fate, Fragmentation, and Niche Opportunities of the Plastisphere

The goal of this dissertation was to examine the fate and fragmentation of plastic debris in the marine environment and characterize the microbial communities colonizing naturally occurring substrates and geologically recent plastic inputs in the ocean using analytical chemistry and genomic techniques. Altogether, the data presented herein reveal the presence of heretofore undescribed plastic accumulation zones in the ocean and depict a stark contrast in microbial traits between early and mature plastic biofilm stages. These data further suggest that emergent plastic biofilm properties can be forecasted across environmental gradients, with the largescale genomic characteristics of early colonizers varying little across conditions. Chapter I of this thesis is an introduction to the current body of work regarding the plastisphere. Chapter II explores the ‘cradle to grave’ fragmentation, transformation, and transport of model microplastic particles and single-use plastic items in an artificial beach setting. Chapter III presents the first metagenomic insights into early biofilm formation on virgin microplastic surfaces in the marine environment and how early colonizers self-assemble, compared to mature, taxonomically, and metabolically diverse biofilms residing on free-drifting plastic pollution. Chapter IV further investigates microbial adaptations for initial colonization of virgin control and plastic surfaces and examines biofilm assemblage dynamics by employing metagenomics on a 16-day time series in a wastewater treatment facility. Chapter V synthesizes observations from the previous core chapters and discusses what these findings mean in a broader ecological and evolutionary perspective. Appendix 1 is a reprint of the manuscript describing the distribution of microplastics beneath the inner and outer plastic accumulation zones of the South Atlantic Subtropical Gyre. Appendix 2 is a submitted manuscript detailing the isolation, characterization, and selective adaptations of Vibrio bacteria colonizing eel leptocephali, free-drifting plastic pollution, Sargassum, and seawater in the North Atlantic Ocean.