marine metagenome Metagenome

Marine plastic debris has become a significant concern in ocean ecosystems worldwide. Little is known however, about its influence on microbial community structure and function. In 2008, we surveyed microbial communities and metabolic activities in seawater and on plastic on an oceanographic expedition through the 'Great Pacific garbage patch'. The concentration of plastic particles in surface seawater within different size classes (2-5 mm and > 5 mm) ranged from 0.35-3.7 particles m-3 across sampling stations. These densities and the particle size distribution were consistent with previous values reported in the North Pacific Ocean. Net community oxygen production (NCP = gross primary production – community respiration) on plastic debris was positive and so net autotrophic, whereas NCP in bulk seawater was close to zero. Scanning electron microscopy and metagenomic sequencing of plastic-attached communities revealed the dominance of a few metazoan taxa, and a diverse assemblage of photoautotrophic and heterotrophic protists and bacteria. Bryozoa, Cyanobacteria, Alphaproteobacteria and Bacteroidetes dominated all plastic particles, regardless of particle size. Bacteria inhabiting plastic were taxonomically distinct from surrounding picoplankton, and appeared well adapted to a surface-associated lifestyle. Genes with significantly higher abundances among plastic-attached bacteria included che genes, secretion system genes and nifH genes, suggesting enrichment for chemotaxis, frequent cell-to-cell interactions and nitrogen fixation. In aggregate, our findings suggest that plastic debris forms a habitat for complex microbial assemblages that have lifestyles, metabolic pathways and biogeochemical activities that are distinct from free-living planktonic microbial communities.