Although the role of iron in marine productivity has received a great deal of attention, no iron storage protein has been isolated from a marine microorganism previously. We describe an Fe-binding protein belonging to the Dps family (DNA binding protein from starved cells) in the N 2 -fixing marine cyanobacterium Trichodesmium erythraeum . A dps gene encoding a protein with significant levels of identity to members of the Dps family was identified in the genome of T. erythraeum . This gene codes for a putative Dps T. erythraeurm protein (Dps tery ) with 69% primary amino acid sequence similarity to Synechococcus DpsA. We expressed and purified Dps tery , and we found that Dps tery , like other Dps proteins, is able to bind Fe and DNA and protect DNA from degradation by DNase. We also found that Dps tery binds phosphate, like other ferritin family proteins. Fe K near-edge X-ray absorption of Dps tery indicated that it has an iron core that resembles that of horse spleen ferritin.