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Extracellular production of superoxide by marine diatoms: Contrasting effects on iron redox chemistry and bioavailability
Author(s) -
Kustka Adam B.,
Shaked Yeala,
Milligan Allen J.,
King D. Whitney,
Morel François M. M.
Publication year - 2005
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.2005.50.4.1172
Subject(s) - chemistry , superoxide , extracellular , redox , thalassiosira weissflogii , superoxide dismutase , xanthine oxidase , nuclear chemistry , xanthine , bioavailability , extracellular polymeric substance , biochemistry , inorganic chemistry , biophysics , antioxidant , organic chemistry , enzyme , biology , bioinformatics , genetics , phytoplankton , biofilm , nutrient , bacteria
We report the extracellular production of superoxide in cultures of the marine diatoms Thalassiosira weissflogii and Thalassiosira pseudonana . In EDTA‐buffered media with ~45 pmol L −1 iron (Fe)(III)', over half the Fe(III) reduction is mediated by extracellular O 2 − production. Surprisingly, even though we saw a consistent inhibition of Fe reduction by the addition of superoxide dismutase (SOD) and enhancement of Fe reduction due to superoxide production using the xanthine‐xanthine oxidase system (X‐XO), we observed no effect of SOD or X‐XO on Fe uptake in these cultures. We also observed no effect of SOD on the uptake of Fe from either ferrihydrite, an Fe‐labeled porphyrin, or as regenerated by metazoan grazers. Our data reveal that Fe(II)' is formed by O 2 − via the reduction of Fe(III)' rather than by the reduction and dissociation of FeEDTA complexes in EDTA‐buffered media. This bulk‐phase reduction of Fe(III)' by O 2 − is a “futile” reductive step, as the Fe(II)' formed is rapidly reoxidized to Fe(III)' in pH 8 oxygenated seawater.