Picoeukaryotes are convincingly integral members of marine ecosystems in terms of cell abundance, biomass, activity, and diversity and they play crucial roles in food webs and biogeochemical cycles. Their diversity can hardly be investigated by regular microscopy, and instead a variety of molecular tools have been applied, unveiling a large phylogenetic diversity and the presence of novel lineages within the assemblage. In this talk I will first present a general overview of the taxonomic groups forming the marine picoeukaryotes using sequencing surveys from community DNA and single cell genomics. Then I will take advantage of the circumglobal Malaspina expedition to analyze patterns of their distribution in the global ocean. Metabarcoding of the V4 region of the rDNA in the surface and bathypelagic samples (about 4000 m) will be combined with the analysis of vertical profiles of metagenomes to analyze the taxonomic transitions between the surface lit waters and the dark ocean. Particular taxonomic cases will be presented, such as the finding of planktonic fungi in deep waters or the distribution and abundance through automatic microscopy of uncultured MAST cells. Our study adds the vertical dimension to other concomitant global studies of protist diversity

European Molecular Biology Organization (EMBO) Symposia, A New Age of Discovery for Aquatic Microeukaryotes, 26-29 January 2016, Heidelberg, Germany

Peer Reviewed