Metabolic interactions in oceanic photosymbioses

Symbiosis between heterotrophic hosts and microalgae (photosymbiosis) is a widespread and ecologically important phenomenon in the oceanic plankton. Symbiotic organisms like radiolarians (unicellular eukaryotes) are key players in marine biogeochemical cycles by contributing to predation and primary production. While knowledge of the diversity of symbiotic partners has improved in recent years, metabolic interactions remain poorly understood. This project will explore the metabolic basis of planktonic photosymbiosis, with radiolarians as an ecologically relevant model, to understand the functioning of the partnership and its contribution to elemental cycling in the pelagic ecosystem. An original and cutting-edge single-cell approach involving stable isotopes and high-resolution chemical imaging techniques (e.g. ToF-SIMS and nanoSIMS) will be used to visualize the elemental and isotopic composition of intact radiolarian symbioses at the subcellular level, and to quantify the assimilation and transfer of nutrients between partners in different experimental conditions. The same approach will be applied on cultured free-living symbionts to determine the degree of host control over symbiont metabolism.

The following aims of the IP Chemical’s fate is supported by the planned work: i) Unravel molecular characteristics governing (bio-)transformation of chemicals, in this particular case the transfer of chemicals e.g. nutrients, metabolites from one species to another and their assimilation into the cell biomass. ii) Provide options to control input and fate of environmental chemicals, in our propose work the construction of a reference metabolic framework as a tool to compare nutritional strategies between various symbioses in order to provide a global ecological context of the importance of symbiosis in bio-transformation of elements and chemicals in the context of ocean acidification and climate change.