Investigating mechanisms of trace metal metabolism and subcellular protein localization in marine phytoplankton

Marine phytoplankton are responsible for half of global net primary production, serve as the base of the marine food web, and factor into numerous biogeochemical processes. In the open ocean, trace metal nutrients are depleted to concentrations that can regulate phytoplankton growth and community structure. Iron (Fe) limits primary production in large regions of the ocean, while metals such as zinc (Zn) and copper (Cu) have more subtle effects. Selective pressures imposed by trace metal nutrient scarcity in the ocean have driven phytoplankton to develop characteristics and strategies that mitigate trace metal limitation, including decreased cellular requirements and high-affinity uptake pathways for Fe and Zn. Aspects of intracellular metal homeostasis in these organisms have also been shaped to enable strategies such as Fe storage in excess of quotas required for optimal growth and the flexible use of different metals to fulfill the same demands. Characterizing these strategies is essential for understanding interactions between trace metals, marine primary production, and other environmental conditions, and to predict how these interactions will be affected by projected climate scenarios. This dissertation contains three studies with the common goal of investigating mechanisms of trace metal metabolism in marine phytoplankton that allow their survival in metal-poor marine environments. The first explores luxury Fe storage in the cyanobacterium Prochlorococcus marinus. It presents Fe quotas and abundances of the Fe-storage protein ferritin under a range of Fe concentrations, and changes in ferritin abundance following shifts in Fe availability. The next study investigates mechanisms that enable the coccolithophore Emiliania huxleyi to use cobalt or cadmium to fulfill its Zn requirement. Comparing the proteomes of cultures grown under different trace metal treatments revealed proteins that were sensitive to individual metals and potentially facilitate Zn substitution or counteract stresses it imposes. The final study presents a spatially resolved proteome of the diatom T. pseudonana with a focus on its endomembrane system. The predicted subcellular locations of metal transporters and proteins that may facilitate Fe uptake and storage are discussed. The dissertation concludes with a review of the main findings of each section and a discussion of avenues for future research.Ph.D.Includes bibliographical reference