Extracellular production of superoxide by marine diatoms: Contrasting effects on iron redox chemistry and bioavailability
Extracellular production of superoxide by marine diatoms: Contrasting effects on iron redox chemistry and bioavailability
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DOI：
10.4319/lo.2005.50.4.1172
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发表时间：
2005-07-01
影响因子：
4.5
通讯作者：
Morel, FMM
中科院分区：
文献类型：
--
作者：
Kustka, AB;Shaked, Y;Morel, FMM
我们报道了在海水硅藻藻和假硅藻藻的培养中超氧化物的胞外生产。在edta缓冲培养基中，铁（Fe）（III）'的浓度为45 pmol L-1，超过一半的Fe（III）还原是通过细胞外生成介导的。令人惊讶的是，尽管我们发现添加超氧化物歧化酶（SOD）对铁还原有一致的抑制作用，并且使用黄嘌呤-黄嘌呤氧化酶系统（X-XO）产生超氧化物可以增强铁还原，但我们没有观察到SOD或X-XO对这些培养物中铁摄取的影响。我们还观察到SOD对铁水合铁（铁标记的卟啉）或后生动物食草动物再生的铁的吸收没有影响。我们的数据显示，Fe(II)‘是由O-2通过Fe(III)’的还原形成的，而不是由edta缓冲介质中FeEDTA络合物的还原和解离形成的。O-2（-）对Fe(III)‘的体相还原是一个“无用的”还原步骤，因为形成的Fe(II)’在pH为8的含氧海水中迅速再氧化为Fe(III)'。
We report the extracellular production of superoxide in cultures of the marine diatoms Thalassiosira weissflogii and Thalassiosira pseudonana. In EDTA-buffered media with similar to 45 pmol L-1 iron (Fe)(III)', over half the Fe(III) reduction is mediated by extracellular 0, 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.