Revealing and analyzing networks of marine microbial ecosystems

International audienceUnderstanding interactions between microbial communities and their environment well enough to be able to predict diversity or biotic response on the basis of physicochemical parameters is a fundamental pursuit of microbial ecology that still eludes us. Networks have become a key approach to understanding systems of interacting objects, and network based analysis recently shown great promises to decipher microbial interactions. However, modeling microbial communities is a complicated task, because (i) communities are complex, (ii) most are described qualitatively, and (iii) quantitative understanding of the way communities interacts with their surroundings remains incomplete.We propose herein a network analysis that aims to overcome these points while focusing on one open biological question: revealing and analyzing plankton networks driving carbon export in the global ocean.The biological carbon pump is the process by which photosynthesis transforms CO2 to organic carbon sinking to the deep-ocean as particles where it is sequestered. While the intensity of the pump correlate to plankton community composition, the underlying ecosystem structure and interactions driving this process remain largely uncharacterized Here we use environmental and metagenomic data gathered during the Tara Oceans expedition to improve understanding of these drivers. We show that specific plankton communities correlate with carbon export and highlight unexpected and overlooked taxa such as Radiolaria, alveolate parasites and bacterial pathogens, as well as Synechococcus and their phages, as key players in the biological pump. Additionally, we show that the abundances of just a few bacterial and viral genes predict most of the global ocean carbon export’s variability. Together these findings help elucidate ecosystem drivers of the biological carbon pump and present a case study for scaling from genes-to-ecosystems