Iron enrichment of High Nitrate, Low Chlorophyll (HNLC) waters of the subarctic Pacific lead seed populations of Pseudo-nitzschia (pennate) diatoms to rapidly bloom. Recent findings from laboratory and field experiments show that Pseudo-nitzschia species posses the ability to grow on strongly complexed Fe (III), and that this ability is directly dependent on Cu availability. This Fe uptake system is induced under Fe-stress, and its efficiency contrasts what is known about other coastal diatoms. Genes homologous to high affinity Fe uptake proteins are found in T. pseudonana, and should be present in Pseudo-nitzschia species. Because T. pseudonana possesses putative genes for high-affinity Fe uptake proteins and can still be readily starved for Fe under normal laboratory culture conditions, it is implied that the Fe uptake system in T. pseudonana is incomplete, or that some environmental factor prevents induction or limits the functionality of the high affinity Fe uptake system in contrast to the highly efficient system in Pseudo-nitzschia. As a result, more molecular and physiological studies are needed to better ascertain the mechanism and functionality of the high affinity Fe uptake systems in eukaryotic diatoms such as T. pseudonana and Pseudo-nitzschia species.
In this study, researchers at the University of California at Santa-Cruz and the University of Rhode Island will focus on understanding the relationship between Fe redox chemistry in seawater and the molecular, biologically mediated reactions that render Fe availability for uptake by eukaryotic phytoplankton. The team of scientists will establish whether or not the structural components of the high affinity Fe uptake system indicated by sequence homology can function in T. pseudonana and if the same components are present and can function in Pseudo-nitzschia spp. The researchers will also examine how the gene expression patterns of the high affinity iron uptake homologues are induced by Fe stress, and how the presence of these proteins correlates with the rates of Fe and Cu uptake in Pseudo-nitzschia spp. and T. pseudonana. In addition, the work will determine which cell fraction harbors this additional Cu quota and whether or not the increased Cu requirement of Pseudo-nitzschia under Fe stress occurs with other phytoplankton species in offshore waters. This work will be important to understanding the mechanistic controls that effect the Fe uptake of large diatoms, as well as provide insight into how the natural or anthropogenic fluxes of iron to HNLC waters influence the export of carbon to the deep ocean and effect the global climate. In terms of broader impacts, the project will provide the training, education, and research to a beginning female investigator, a Ph.D. student, and a graduate student. A high school teacher who will bring the field results to the science classroom will also participate in the project.
