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Nitrate regulation of Fe reduction and transport by Fe‐limited Thalassiosira oceanica
Author(s) -
Maldonado Maria T.,
Price Neil M.
Publication year - 2000
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2000.45.4.0814
Subject(s) - nitrate , phytoplankton , ammonium , nitrate reductase , limiting , chemistry , thalassiosira pseudonana , environmental chemistry , steady state (chemistry) , nuclear chemistry , nutrient , mechanical engineering , organic chemistry , engineering
Under Fe‐limiting conditions, nitrate (NO 3 − )‐grown marine diatoms have higher intracellular Fe requirements, but divide as fast or faster than ammonium (NH 4 + )‐grown cells by maintaining faster steady‐state Fe uptake rates. Here we report that Thalassiosira oceanica , clone 1003, possesses an Fe reductase that reduces Fe(III) bound to a variety of organic ligands, including the siderophore desferrioxamine B (DFB), a high affinity, Fe(III)‐specific ligand. Reduction is mediated extracellularly and is induced by Fe deficiency. Cellular rates of Fe(III) reduction are significantly faster in NO 3 − ‐ than in NH 4 + ‐grown cultures suggesting a link with N metabolism. At subsaturating Fe concentrations, short‐ and long‐term Fe uptake rates are also significantly faster in NO 3 − ‐ than in NH 4 + ‐grown cells. The results suggest that when Fe is limiting, faster rates of reduction of organically bound Fe(III) by phyto‐plankton promote faster rates of Fe transport and growth. The implications of these findings could be significant for understanding phytoplankton Fe nutrition in oceanic waters where organic complexation dominates the speciation of Fe. We hypothesize that the reductive Fe transport pathway may enable phytoplankton to directly utilize Fe bound to strong organic ligands in the sea.