Close encounters in the phycosphere: Microscale syntrophic interactions between diatom and diazotroph populations

2026-07-22

Bacterial interactions with eukaryotic phytoplankton are ubiquitous in marine ecosystems. The basis of many of these interactions is a reciprocal exchange of metabolites that mutually benefits the organisms involved. Under diffusion limitation, such relationships typically require close spatial coupling between the two partners. How long these intimate interactions must endure for a sustained exchange to occur is unclear and challenges our judgement of what truly constitutes a symbiosis. Understanding the dynamics of syntrophic interactions is essential to understand the impact of bacterial communities in marine biogeochemical cycles. With this proposal, I intend to evaluate the potential role of diazotrophic bacteria in alleviating the nutrient demands of algae in nitrogen-limited environments. To achieve this, I plan to establish a model microbial system with a marine heterotrophic diazotroph, which has an obligate dependency on photosynthetically fixed carbon, and a diatom, which relies on nitrogen fixed by the diazotroph. I will construct a microfluidic bioreactor to enable detailed monitoring of the spatiotemporal distribution of bacteria and diatom cells during long-term culturing. Integrating this microenvironment with stable-isotope probing and Raman microscopy will allow me to quantify carbon and nitrogen uptake and transfer rates between partners. By relating microbial behaviour to single-cell activity rates, this project will offer invaluable information connecting the structure, dynamics and function of microbial consortia, and thereby provide robust insights into the basal ecological functioning that supports aquatic ecosystems.

Switzerland

2026-02-15