Deep Proteomic Profiles of the Antarctic Diatom <i>Fragilariopsis Cylindrus</i> Under Varying Iron and Manganese Conditions

Fragilariopsis cylindrus is a key diatom in the Southern Ocean, where low iron and manganese availability constrain primary production and biogeochemical activity. The molecular mechanisms used by polar diatoms, including F. cylindrus, to cope with trace metal limitations remain largely unexplored. Here we present phenotypic characterizations and proteomic profiles of F. cylindrus grown under controlled iron (low, medium, high) and manganese (low, high) conditions that reflect those observed in the Southern Ocean. Using data-independent acquisition mass spectrometry, we measured over 8000 unique proteins capturing diverse metabolic responses, including those related to photosynthesis, elemental transport, and intracellular trafficking. We confirm consistent expression of canonical iron stress proteins (e.g., phytotransferrin) under low iron, and identify additional candidate biomarkers for iron and manganese stress that could be explored in future laboratory and field experiments. Our data also support the notion that one flavodoxin isoform in F. cylindrus is iron responsive and one is not, and show that PsaE, a protein associated with the iron-rich photosystem-I, is upregulated under low iron. Altogether, this dataset is among the most comprehensive proteomic characterizations of trace metal physiology in polar diatoms to date, providing a foundation for connecting molecular responses to trace metal availability and ocean biogeochemistry.