Periodic Reporting for period 3 - PhotoPHYTOMICS (Photosynthesis in PHYTOplankton Mixtures to Investigate Community Structuration.)
Período documentado: 2020-01-01 hasta 2021-06-30
We use this method to analyze the effects of three major parameters that contribute to shaping the ecological patterns at sea: competition for nutrients; direct inhibition of the metabolism of competitors through the use of secondary metabolites (allelopathy), and the responses of phytoplankton species to the rapid and intense light changes they experience. These studies will be conducted both in laboratory conditions and in the field for validation. The overall goal is to provide a new tool allowing the study in situ and in real time of the cellular mechanisms giving rise to the ecological patterns observed in the Ocean. This is crucial for fundamental research but also to better understand and anticipate climate changes (eutrophication, changes of phytoplankton communities with the arrival of new toxic species, …).
In WP1, we focused on the allelopathic interactions between "red tide" dinoflagellates and co-occuring diatoms. In all cases, the dinoflagellates release allelochemicals which target the diatom and inhibit photosynthesis. Using the « photosynthesis in mixture » method, and thanks to new collaboration with ecological biochemistry, we first decipghered the allelopathic interaction between the toxic dinoflagellate Amphidinium carterae and diatoms. We discovered the nature of the secondary metabolite secreted by the dinoflagellate, its target and the mechanism of photosynthesis inhibition. Using dinoflagellate/diatom co-cultures, we could show that the presence of the dinoflagellate immediately arrests photosynthesis and growth. Finally, a screening revealed that this dinoflagellate was toxic to more diatoms, some prasinophytes or natural diatom populations in the field. The two other projects are focusing on the inhibition of the photosynthesis of the diatom Chaetoceros muelleri and Licmophora by the dinoflagellates Alexandrium minutum and Ostreopsis ovata, respectively.
WP2 was supposed to start on the second half of the ERC project but we could already achieve a proof of methods: the use of ECS signals to study photosynthetic responses in experiments of competition for nitrogen.
Regarding WP3, we could establish for the first time the light-dependencies of the two enzymes involved in the regulation of photoprotection in diatoms : the diatoxanthin epoxidase and the diadinoxanthin deepoxidase. The light dependencies of those two enzymes are modified depending on the light conditions the diatoms experience, revealing an additional a level of light acclimation. The very peculiar regulation of the epoxidase was confirmed in the field. In collaboration with University of Liège, we observed a similar behavior in another photosynthetic clade, sister to diatoms.
WP4 is a transversal task which corresponds to the testing in the field of results and hypothesis coming from the laboratory. Thanks to several missions in Roscoff (France) and in Bergen (Norway), we could test our models for WP1 and WP3. At that occasion, new allelopathic interactions were identified in the field and strains were isolated in collaboration with the biological station of Roscoff (Fance), the Weizmann Institute (Israel) and the university of Bergen (Norway). Those allelopathic interactions are now being studied in the laboratory (WP1). We also managed to extract the light dependencies of photosynthesis of diatoms and dinoflagellates from natural assemblages in the field, paving the path to the use of our methodology in situ.
In WP2, we aim at applying the same procedure used for allelopathy to competition for nutrients. The goal is to provide the community of researchers interested in nutrient competition in the marine environment with a robust method allowing to add physiological information to the growth phenotypes classically obtained in nutrient stressed co-cultures experiments.
In WP3, we aim at understanding the molecular determinants of the epoxidase and deepoxidase peculiar light regulation. Then, we will extend the work to another group of photosynthetic microalgae : dinoflagellates.
In WP4, we will continue studying allelopathic interactions in the field, trying to isolate new couples of strains showing allelopathic interactions targeting photosynthesis in connection with WP1. And we will work more on the light responses of diatoms and dinoflagellates in the field in connection with WP3. Also, unexpected results obtained during a mesocosm in Bergen prompt us to investigate the importance of photosynthesis in the mechanism of viral infection of the coccolithophore Emiliania huxleyi, another biotic interaction which was initially not formally explicited in the project.