CBIOMES researchers take a deep dive into Fragilariopsis cylindrus metal stress responses.
Reporting by Helen Hill for CBIOMES
The recent CBIOMES‑affiliated study by Loay J. Jabre, Elden Rowland, J. Scott P. McCain, and Erin M. Bertrand offers an unusually deep look into the molecular strategies that allow the Antarctic diatom Fragilariopsis cylindrus to survive in one of the most trace‑metal‑limited regions on Earth. Their 2026 Proteomics paper, Deep Proteomic Profiles of the Antarctic Diatom Fragilariopsis cylindrus Under Varying Iron and Manganese Conditions, brings together controlled laboratory experiments and expansive proteomic measurements to illuminate how this ecologically dominant species responds to fluctuations in iron and manganese—two metals that shape the productivity of the Southern Ocean and, by extension, global biogeochemical cycles.
At the heart of the work is a simple but powerful question: how does F. cylindrus maintain its metabolic balance in waters where iron and manganese are chronically scarce. These metals are essential cofactors for photosynthesis, respiration, and antioxidant defense, yet the Southern Ocean receives only limited inputs from dust and continental sources. The authors approached this challenge by growing F. cylindrus under a matrix of iron and manganese concentrations—low, medium, and high iron crossed with low and high manganese—and then applying data‑independent acquisition mass spectrometry to quantify more than eight thousand proteins. This scale of coverage is rare for any marine microbe and unprecedented for a polar diatom, giving the research community a resource that will anchor future physiological and modeling studies.
The proteomic patterns reveal a diatom that is both sensitive to metal availability and remarkably adept at compensating for it. Under low‑iron conditions, the cells expressed well‑known iron‑stress proteins, including phytotransferrin, which facilitates iron uptake when dissolved iron is scarce. Alongside these canonical markers, the authors identified new candidate biomarkers for both iron and manganese stress—proteins whose functions are not yet fully understood but whose expression patterns strongly track metal availability. These candidates open the door to future work on how diatoms sense and respond to their chemical environment.
One of the most intriguing findings concerns flavodoxin isoforms. Flavodoxins are iron‑free substitutes for ferredoxin, a key electron carrier in photosynthesis. The study provides evidence that F. cylindrus possesses two distinct flavodoxins, but only one responds to iron limitation. This divergence suggests a functional specialization that may help the species maintain redox balance even when iron is severely limiting—a clever evolutionary strategy in a region where iron scarcity is the norm rather than the exception.
The researchers also observed unexpected behavior in PsaE, a protein associated with photosystem I. Instead of decreasing under low iron, as might be expected for an iron‑rich complex, PsaE increased in abundance. This pattern hints at a restructuring of the photosynthetic apparatus that allows the diatom to maintain energy production despite metal stress. Beyond photosynthesis, the proteomic shifts extended into pathways related to intracellular trafficking, elemental transport, and broader metabolic reorganization, underscoring how deeply metal availability influences cellular physiology.
The significance of this work extends far beyond the laboratory. Diatoms like F. cylindrus are major contributors to Southern Ocean primary production and carbon export. Their ability to thrive under metal limitation affects not only local ecosystem dynamics but also global carbon cycling. By mapping protein‑level responses across realistic gradients of iron and manganese, the study provides molecular constraints that can be incorporated into biogeochemical models, improving predictions of how polar ecosystems will respond to climate‑driven changes in nutrient supply. The newly identified biomarkers also offer tools for interpreting field samples, enabling researchers to infer metal stress in natural diatom populations with greater precision.
Publication:
Jabre, Loay J., Elden Rowland, J. Scott P. McCain, Erin M. Bertrand (2026), Deep Proteomic Profiles of the Antarctic Diatom Fragilariopsis Cylindrus Under Varying Iron and Manganese Conditions, Proteomics, doi: 10.1002/pmic.70109