In cyanobacteria, metal ions have central roles in important metabolic processes, including respiration, nitrogen fixation, light harvesting, and photosynthesis. However, the modes of accumulation and subcellular storage locations of many of these components are poorly understood. There is a current need to understand these processes at the cell population level, and to map subcellular localization at high resolution. We are working with collaborators in the WUSTL Department of Earth and Planetary Sciences to use secondary ion mass spectrometry (SIMS) to probe the uptake and localization of important elements in cyanobacterial cells. In particular, in cyanobacteria, as in other photosynthetic organisms, large amounts of iron are needed to maintain functional photosystem I (PSI) complexes, and therefore photosynthetic organisms require efficient mechanisms to accumulate and store available iron. Our studies probe the uptake and subcellular distribution of iron, with the goal of identifying the localization of pools of intracellular iron.