In WP1, we focused on the allelopathic interactions between "red tide" dinoflagellates (Amphidinium carterae, Alexandrium minutum and Ostreopsis ovata) and co-occuring diatoms involving the release of allelochemicals targeting photosynthesis. Using the « photosynthesis in mixture » method, we especially focused on deciphering the allelopathy between the toxic dinoflagellate Amphidinium carterae and diatoms, including the nature of the secondary metabolite, its target, the inhibition mechanism. We performed a screening of the species sensitive to the secondary metabolite secreted by this dinoflagellate and started screening for other allelopathic interactions than the ones involving diatoms and dinoflagellates. One PhD thesis and four papers have been published, another one will be submitted at the end of 2023. This WP gave rise to 7 talks in national and international conferences and to collaboration with the startup Immunrise Biocontrol.
WP2, aiming at studying competition for nutrients, was modified during the course of the project. New ECS-based methods were developed to assess the PSII/PSI stoichiometry, the Cyclic Electron Flow and the regulation of the plastid ATPase, all rapidly identified as main signatures of nitrogen deficiency . We could achieve a proof of methods of the use of ECS deconvolution to study competition for nitrogen or phosphorous. Investigating the interplay between allelopathy and nutrient deficiencies revealed the important role of phosphorous for the production of the secondary metabolite by A. carterae. Three papers and two PhD thesis have been published and 5 manuscripts are in preparation. This WP gave rise to 8 talks in national and international conferences.
In WP3, we investigated the photosynthetic response of diatoms to light stress. We could establish for the first time the light-dependencies of the two enzymes involved in the regulation of photoprotection in diatoms, which revealed an additional level of light response that we also observed in another photosynthetic clade sister to diatoms. We developed a new method to probe lumenal pH in vivo and investigated the role of ion channels in the regulation of the lumenal pH and qE. We used a series of LHCX1 mutants in Phaeodactylum tricornutum to investigate the importance of qE in the overall regulation of the photosynthetic process, including photo-inhibition, cyclic electron flow and photosynthesis-modulated gene expression. Studies on other species were also performed, including the polar species Fragilariopsis cylindrus and the facultative phototroph Cyclotella cryptica. In this WP3, 4 reviews about photophysiology in diatoms and their green counterparts and 4 experimental papers have been published; 5 more are in preparation. This WP gave rise to 7 talks in national or international conferences.
WP4 is a transversal task which corresponds to the testing in the field of results and hypothesis coming from the laboratory. A library of ECS spectra has been reinforced and we could characterize ECS signals in cyanobacteria, extending the spectrum of application of the ECS deconvolution method. Thanks to several missions in Roscoff (France), in Bergen (Norway) and in the canadian Arctic (Dark Edge mission, Canada) we could test models developed in the laboratory for WP1 and WP3. We also managed to extract the light dependencies of photosynthesis of diatoms and dinoflagellates from natural assemblages in the field. One paper is published in this WP and a method paper about the ECS deconvolution method is in preparation which includes the library of ECS spectra, the proof of method of the ECS deconvolution and the screening of allelopathic interactions in the Roscoff Culture Collection. As forecasted at the beginning of the project, the transition from laboratory studies to in situ studies will take time but we developed a new high-sensitivity instrument allowing to work at low microalgal densities, paving the path to the use of our methodology in situ.
