Characterization of ferredoxin and flavodoxin as molecular indicators of iron limitation in marine eukaryotic phytoplankton
Citable URI
https://hdl.handle.net/1912/5706Location
Equatorial Pacific OceanDOI
10.1575/1912/5706Abstract
Expression and regulation of the ferredoxin and flavodoxin proteins in
marine phytoplankton were investigated to assess their utility as biomarkers
of iron limitation. A phylogenetic survey of seventeen microalgal species
showed flavodoxin induction, with accompanying ferredoxin repression, to
be a common response to iron stress. A minority of organisms examined
never expressed flavodoxin, a condition associated with, but not characteristic
of, neritic habitats. Antibodies raised against ferredoxin and flavodoxin from
Thalassiosira weissflogii proved to be mono- and diatom-specific,
respectively.
Flavodoxin induction responded specifically to iron limitation and not to
nitrogen, phosphorus, silicate, zinc or light deficiency. In iron-limited T.
weissflogii, relative cellular ferredoxin and flavodoxin content (Fd index)
varied with growth rates above ~50%μmax and was not affected by growth on
either nitrate or ammonium as a sole nitrogen source. Below ~50%μmax,
ferredoxin was absent. This variation with severity of stress and specificity to
iron limitation make the Fd index an excellent choice as an indicator of iron
limitation.
HPLC measurement of ferredoxin and flavodoxin during the IronExII
mesoscale enrichment experiment detected a strong flavodoxin signal but no
significant ferredoxin synthesis, despite increases in chlorophyll and
photosynthetic efficiency (Fv/Fm) observed by others. The absence of
ferredoxin and the persistence of flavodoxin suggested that iron addition
released the phytoplankton from iron starvation but was insufficient to
completely relieve physiological iron limitation. Laboratory experiments
demonstrated that a pennate diatom clone isolated from the IronExII bloom
expressed both flavodoxin and ferredoxin and could alter its protein
expression in about one day, further supporting the conclusion of continued
iron limitation during IronExII. During IronExII, Fd index was uniformly zero while Fv/Fm increased from
0.26 to 0.56. In contrast, a laboratory iron addition experiment showed little
change in Fv/Fm when the Fd index increased from 0.5-0.9. A conceptual
model of the covariation of Fv/Fm and Fd index describes a complementary
relationship between the two measures. Model results suggest that
photochemical systems are affected by iron limitation only after cellular
adaptive capacity, in the form of ferredoxin, is exhausted.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1997
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Suggested Citation
Thesis: Erdner, Deana L., "Characterization of ferredoxin and flavodoxin as molecular indicators of iron limitation in marine eukaryotic phytoplankton", 1997-09, DOI:10.1575/1912/5706, https://hdl.handle.net/1912/5706Related items
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