BYGENEX

Oceanic bacterivory is the process through which marine bacteria are grazed by microbial eukaryotes. It consumes a large fraction of bacterial production, transfers bacterial biomass to upper trophic levels, and completes the inorganic nutrient recycling needed for regenerated primary production. Global estimates indicate that ~15% of the Earth’s primary production circulates through this process. Despite its central role in marine food webs, the identity of the dominant grazers is not well known, and in situ bacterivory rates are seldom measured as they require laborious techniques. Consequently, it is impossible to predict how oceanic bacterivory will react in light of the dramatic anthropogenic change we are facing. The aim of BYGENEX is to fill this gap and develop a quantitative approach to study oceanic bacterivory by using emerging omics-based tools that target marker genes for phagocytosis, the cellular mechanism behind bacterivory. We will first prepare an exhaustive collection of genomes from the main bacterivores in the global ocean. Then, we will identify highly expressed genes involved in phagocytosis in cultured and uncultured species across taxonomic lineages. We will perform in situ expression analysis of phagocytosis marker genes to quantify bacterivory rates of the community and of the dominant species, after calibration with direct activity measures. Finally, data from cruises will benchmark the present state of bacterivory in a range of oceanic regimes, and we will simulate bacterivory using a global ecosystem model to analyse ecosystem-wide effects of this process. BYGENEX will provide new tools to quantify oceanic bacterivory at unprecedented large scales and open the way to improve our current understanding of the structure and function of the microbial component and its role in the global marine system.