Diversity of marine microeukaryotes in the global deep ocean

Abstract

The aim of this work was to study the diversity of bathypelagic microeukaryotes. Seawater samples were taken at around 4000 m depth in 27 stations distributed in the main oceans. Pyrosequencing was used to obtain about half a million tags from the 18S rDNA V4 region, then clustered into 2482 OTUs at 97% similarity. The relative pyrotag abundance of the 20 most abundant OTUs matched well with the results of a parallel metagenomic analysis of 18S rDNA genes, suggesting little PCR bias in the tag-approach. There was a weak trend of genetic similarity among geographically close stations and among samples from the same water-mass, but we did not find a typical global community. Instead, there were four phylogenetic groups (Collodaria, Chrysophytes, Basidiomycota and MALV-II) mixed in different proportions. The amount of phylogenetic novelty was concentrated in three hotspots accounting for 6% of pyrotags globally. Rarefaction curves suggested that there were OTUs still waiting to be discovered. Our study is an essential step for a more detailed investigation of the deep ocean microbiota and suggests idiosyncratic microeukaryotic assemblages in distinct regions