Pedro Junger, jeune chercheur à l’Institut de Biologie de l’École Normale Supérieure de Paris, donnera un séminaire à l’Amphithéâtre OCEANOMED, Bâtiment Méditerranée, Campus de Luminy, le mardi 16 juin 2026 à 11h00 sur le thème : Linking genomics and remote sensing to diagnose phytoplankton iron stress in the global ocean.
Abstract
Marine ecosystems rely almost entirely on primary production provided by phytoplankton, which globally perform 50% of the photosynthesis on our planet, fixing atmospheric carbon dioxide and driving the biological carbon pump, a key process in climate regulation. Their ability to capture carbon, however, depends on the availability of scarce nutrients like iron. Climate change and human activities are shifting the oceanic distribution and bioavailability of iron, yet the responses of different phytoplankton groups to these changes remain poorly understood.
In this talk, I will describe how we combined omics data and satellite observations to map phytoplankton iron nutritional status at the global scale. We analyzed the abundance and expression of iron-responsive genes in metagenomes (n=2,155) and metatranscriptomes (n=1,466) from 655 stations across three global ocean expeditions.
Our approach exploits a well-known physiological response: under iron limitation, phytoplankton swap iron-containing proteins in the photosynthetic electron transport chain (ferredoxin, cytochrome c6) for iron-free alternatives (flavodoxin, plastocyanin). The ratio between these protein pairs serves as a proxy for iron stress. These genomic proxies correlated strongly with satellite-derived estimates of phytoplankton physiological status and modeled iron concentrations. Using a Random Forest model trained on satellite products, biogeochemical model outputs, and nutrient data, we predicted global distributions of iron stress that accurately captured well-known iron-limited regions, including the Southern Ocean, equatorial Pacific, and subarctic Pacific. Validation against independent bottle bioassays confirmed metatranscriptomics as particularly well-suited for diagnosing iron stress in situ. This work provides a scalable framework for linking genomics and remote sensing to monitor global phytoplankton iron stress.