Global comparative analysis of prokaryotic and eukaryotic diversity contributing to oceanic photosynthesis using data from Tara Oceans and Malaspina expeditions

Abstract

Motivation: Phototrophic picoeukaryotes or PPEs (organisms measuring ¿ 3¿m) contrib- ute to half of the oxygenic photosynthesis activity in open oceans and play key trophic roles for the functioning of these ecosystems. Despite their ecological value, the dynam- ics and taxonomic composition of these communities are poorly known at global scales, whereas the distribution of cyanobacteria (the only prokaryotes known to be capable of oxygenic photosynthesis) has been widely studied. Nowadays, molecular methods based on high-throughput technology allow us to do new valuable steps towards the compre- hension PPEs communities structure. In this study, we analyze 160 samples from surface waters (3m to 5m) collected along Tara Oceans and Malaspina circumglobal expeditions with PRC-based amplicons and metagenomic sequencing approaches for characterizing the global relative abundance and richness of PPEs and cyanobacteria. Results: We identify Chrysophyceae, Dictyochophyceae, Pelagophyceae, Prasinophyceae and Prymnesiophyceae as dominant PPE groups in the photosynthetic communities of global open ocean surface waters. Prymnesiophyceae, Prasinophyceae and Dictyocho- phyceae emerge as the classes with the highest diversity and abundance of plastidial se- quences. When comparing PPEs and cyanobacteria distribution, we observe that cyano- bacteria are more widely distributed and abundant. The evolutionary diversification of both communities has been described at class and genus level based on ribosomal DNA sequencing data obtained through two molecular approaches, (PCR-based amplicons and metagenomes), for which we report contradictory results and limitations in the quantification of cyanobacteria and PPE groups