Sulphur is an essential element for life that cycles rapidly in the pelagic ocean in the form of biogenic dimethylated compounds. Over three decades, dimethylated sulphur has been intensively investigated for its emission to the atmosphere and its suggested roles in returning sulphur to continents and in climate regulation. While the climate connection still awaits definitive confirmation or denial, these research efforts have provided important advances in plankton physiology and ecology, since these forms of sulphur arise from organism adaptation to saline and sunlit waters and are integral to the food web machinery. Previous studies have disclosed biochemical and trophic cycling pathways and their taxonomic affiliations. Also, evidence for their behaviour as infochemicals in organism-organism communication has been obtained. However, their contribution to the functioning of marine ecosystems remains largely unexplored, particularly with respect to the emerging renewed picture of food webs, where classical functional roles blur and concepts like multifunctional organisms and interdependence become the rule rather than the exception. I propose to bridge microbial physiology, ecology and biogeochemistry to explore new roles of dimethylated sulphur in microbial food-web interactions. I will build upon a combination of molecular tools, isotopes, single-cell analyses, physiological dyes, chemotaxis experiments, modelling, sea-going opportunities and an existing collection of samples from diverse oceanic biomes. Hypothesis-driven research is expected to yield paradigm shifts in (i) phytoplankton-bacteria interactions through nitrogen fixation and vitamin exchange; (ii) phytoplankton-phytoplankton interactions to overcome energy limitation to growth; (iii) phytoplankton-herbivore interactions for selective grazing on weakened prey. Overall, I intend to assess if interactions through dimethylated sulphur make microbial food-webs more robust and efficient.

ERC-2018-ADG