Iron-related molecular physiology of marine diatoms: Individual genes to community metatranscriptomes Public Deposited

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  • March 19, 2019
Creator
  • Cohen, Natalie
    • Affiliation: College of Arts and Sciences, Department of Marine Sciences
Abstract
  • This dissertation aims to elucidate the molecular and physiological adaptations that determine the survival of diatoms under iron stress – an outcome with pronounced biogeochemical implications for nutrient cycling and carbon transfer between the atmosphere and the ocean. The following research has demonstrated that Pseudo-nitzschia, a genus of marine pennate diatoms, is unique among studied diatoms in its strategies for coping with iron stress and quickly responding to bioavailable iron, and highlights the mechanisms by which its competitive tendencies are achieved. Community-wide bioinformatic analyses of natural diatom communities within the Northeast (NE) Pacific Ocean indicate changes in iron bioavailability may influence vitamin, nitrate and iron metabolism, with responses varying by algal taxa and geographical region. In particular, laboratory analyses support a direct iron effect on diatom B7 synthesis, but show no iron influence on B12-sensitive protein machinery. Therefore, molecular indications of B12-stress in the NE Pacific Ocean following iron enrichment are likely a result of B12 consumption by blooming taxa offsetting B12 production. Furthermore, chronically iron-limited NE Pacific Ocean diatoms demonstrate a distinct transcriptomic response following iron enrichment as compared to coastal diatoms of the California Upwelling Zone receiving sporadic iron supplies. Genes highly expressed following iron addition in oceanic diatoms correspond to processes including iron storage and vitamin B7 synthesis, with these expression patterns not shared by diatoms from coastal locations. In addition, genes of interest involved in iron and nitrogen metabolism exhibit divergent expression patterns as a function of iron status between the two diatom genera investigated, Pseudo-nitzschia and Thalassiosira. Although some strategies appear universal, we report here distinct mechanisms among regions and taxa for dealing with iron stress and responding to iron enrichment events. Using targeted physiological and gene expression approaches on the oceanic diatom Pseudo-nitzschia granii, the molecular bases underlying this organism’s exceptional ability to cope in low-iron environments are explored. Iron storage abilities and associated ferritin gene expression in this oceanic diatom and several other coastal diatoms were investigated within laboratory studies. Pseudo-nitzschia granii was unique in its broad iron quota range and ferritin transcript response, consistent with long-term luxury iron storage. Several of the other diatoms examined contain two distinct putative ferritin genes that differ in their expression patterns as a function of iron status, with some ferritins increasing in expression under iron limiting conditions. Our results suggest that diatom ferritins may serve multiple functional roles among marine diatoms. Finally, a combination of transcriptomic sequencing and proteomic approaches was performed on P. granii under iron-replete and iron-limited conditions. Findings suggest the success of this species during periods of iron enrichment and its persistence under iron limitation stems from its competitive physiological and genetic characteristics, including constitutive use of iron-independent proteins, coordinated use of iron-dependent and –independent proteins depending on iron status, and enhanced vitamin biosynthesis under iron-replete conditions. Collectively, this research increases our understanding of how diatoms, with an emphasis on Pseudo-nitzschia, restructure their iron metabolism, respond to iron scarcity, and in turn alter their environment.
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  • In Copyright
Advisor
  • Alperin, Marc
  • Paerl, Hans W.
  • Marchetti, Adrian
  • Sunda, William
  • MacGregor, Barbara
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2017
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