Iron Storage Capacity and its Ecological Role within Phylogenetically Distinct Marine Diatoms

Natalie Cohen1, Jeremy E Jacquot2, Brooke Stemple1, William G Sunda3, Benjamin S Twining2 and Adrian Marchetti4, (1)University of North Carolina at Chapel Hill, Department of Marine Science, Chapel Hill, NC, United States, (2)Bigelow Lab for Ocean Sciences, East Boothbay, ME, United States, (3)Retired, Washington, DC, United States, (4)University of North Carolina at Chapel Hill, Marine Sciences, Chapel Hill, NC, United States
Abstract:
Natural and artificial iron fertilization occurring in iron-limited regions of the ocean often results in large blooms of pennate diatoms. The ability of these pennate diatoms to quickly respond to bioavailable iron and proliferate has been attributed in part to their use of the iron storage protein ferritin. Recent concerted efforts to sequence the transcriptomes of eukaryotic protists have made it apparent that some, but not all, centric diatoms also possess a ferritin gene homolog. Using a combination of physiological and molecular biological techniques, we determined the cellular iron quotas and associated ferritin gene expression within both ferritin-containing and non-containing centric and pennate diatoms grown under a range of iron concentrations. Our results show that under steady-state conditions there are no clear differences between the maximum iron cellular quotas of ferritin-containing versus non-ferritin containing centric and pennate diatoms. However, based on differences in gene expression patterns, ferritin appears to play fundamentally different functional roles between centric and pennate diatoms. We propose the success of oceanic pennate diatoms such as Pseudo-nitzschia following iron addition is not only a function of achieving a high iron storage capacity, but also due to their unique ability to drastically reduce intracellular iron requirements while still maintaining rapid growth rates, and depends on iron bioavailability in the environment.