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Zinc isotope fractionation during high‐affinity and low‐affinity zinc transport by the marine diatom Thalassiosira oceanica
Author(s) -
John Seth G.,
Geis Robert W.,
Saito Mak A.,
Boyle Edward A.
Publication year - 2007
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.2007.52.6.2710
Subject(s) - isotopes of zinc , diatom , fractionation , zinc , isotope fractionation , environmental chemistry , isotope , seawater , chemistry , adsorption , stable isotope ratio , phytoplankton , algae , botany , biology , ecology , chromatography , nutrient , physics , organic chemistry , quantum mechanics
We have measured the isotopic fractionation of zinc (Zn) during uptake by the marine diatom Thalassiosira oceanica cultured at a range of free Zn 2+ concentrations representative of the natural range from coastal and oligotrophic regions of the ocean. Harvested cells were rinsed with either plain seawater or a wash designed to remove adsorbed extracellular metals. Unwashed cells had much higher levels of Zn and were isotopically heavier than the media, indicating a positive isotope effect for extracellular Zn adsorption. Internalized Zn, measured in washed cells, was isotopically lighter than the media. The magnitude of Zn isotope fractionation changed with free Zn2+ concentration, corresponding to a switch on the part of T. oceanica between the predominance of high‐ and low‐affinity Zn transport pathways. The total isotope effect for uptake (δ 66 Zn) was ‐0.2% for high‐affinity uptake at low Zn concentrations and ‐0.8% at the highest Zn concentrations, where low‐affinity uptake is dominant. To our knowledge, this is the first study to describe a physiological basis for biological metal isotope fractionation during transport across the cell membrane. Similar high‐ and low‐affinity Zn transport pathways are common among marine phytoplankton, suggesting that the processes described here are an important factor in natural marine Zn isotope variations.