Metagenomics of the open ocean Plastisphere: a novel microbial niche with unique functional potential

Introduction

Plastic pollution in the oceans has become a major concern and focus of research in the last decades. Research so far has focused on the distribution of plastics and the taxonomic composition of the microbes living on plastic particles (termed Plastisphere). However, a functional understanding of the Plastisphere is lacking and thus its impact on global ecosystem functioning is unknown.

Goals

The aim of this study was to examine the functional potential and genetic adaptation of the open ocean Plastisphere based on a comparative metagenomics study with the surrounding seawater microbiome.

Materials & Methods

Plastic particles were collected from the North Atlantic and North Pacific Garbage patch on research cruises in summer 2019. Metagenomic DNA samples were extracted and sequenced. The resulting sequencing data was differentially binned into bacterial metagenome-assembled genomes (MAGs). The MAGs were used for Hidden Markov Model profiling utilizing public KEGG profiles of metabolic pathways, nitrogen cycling and others relevant for a surface-attached lifestyle in the oligotrophic open ocean.

Results

More than 1700 Plastisphere MAGs were reconstructed and compared to >450 corresponding seawater MAGs from the Tara Oceans project. The Plastisphere displayed a distinct microbiome that is similar across ocean basins and different to the surrounding seawater on the taxonomic class level. The Plastisphere further contains a higher genomic potential for coping with UV induced stress, as well as for diverse carbon utilization pathways, nitrogen fixation and uptake of essential elements (Ni, Po).

Summary

The open ocean Plastisphere is a complex assemblage of auto- and heterotrophic bacteria which appears to select for bacteria capable to cope with different stressors as well as having high metabolic flexibility. Our metagenomic study highlights that the open ocean Plastisphere displays a distinct functional profile, enabling microbes to thrive in an oligotrophic ocean.