The role of reduction in iron uptake processes in a unicellular, planktonic cyanobacterium

Authors

  • Chana Kranzler,

    1. Department of Plant and Environmental Sciences, The Alexander Silberman Institute of Life Sciences, Edmond J. Safra Campus, Givat Ram, Hebrew University of Jerusalem, Jerusalem, Israel.
    2. Interuniversity Institute for Marine Sciences in Eilat, POB 469, Eilat 88103, Israel.
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  • Hagar Lis,

    1. Interuniversity Institute for Marine Sciences in Eilat, POB 469, Eilat 88103, Israel.
    2. The Freddy and Nadine Herrmann Institute of Earth Sciences, Edmond J. Safra Campus, Givat Ram, Hebrew University of Jerusalem, Jerusalem, Israel.
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  • Yeala Shaked,

    1. Interuniversity Institute for Marine Sciences in Eilat, POB 469, Eilat 88103, Israel.
    2. The Freddy and Nadine Herrmann Institute of Earth Sciences, Edmond J. Safra Campus, Givat Ram, Hebrew University of Jerusalem, Jerusalem, Israel.
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  • Nir Keren

    Corresponding author
    1. Department of Plant and Environmental Sciences, The Alexander Silberman Institute of Life Sciences, Edmond J. Safra Campus, Givat Ram, Hebrew University of Jerusalem, Jerusalem, Israel.
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E-mail nirkeren@vms.huji.ac.il; Tel. (+972) 2 6585233; Fax (+972) 2 6584425.

Summary

In many aquatic environments the essential micronutrient iron is predominantly complexed by a heterogeneous pool of strong organic chelators. Research on iron uptake mechanisms of cyanobacteria inhabiting these environments has focused on endogenous siderophore production and internalization. However, as many cyanobacterial species do not produce siderophores, alternative Fe acquisition mechanisms must exist. Here we present a study of the iron uptake pathways in the unicellular, planktonic, non-siderophore producing strain Synechocystis sp. PCC 6803. By applying trace metal clean techniques and a chemically controlled growth medium we obtained reliable and reproducible short-term (radioactive assays) and long-term (growth experiments) iron uptake rates. We found that Synechocystis 6803 is capable of acquiring iron from exogenous ferrisiderophores (Ferrioxamine-B, FeAerobactin) and that unchelated, inorganic Fe is a highly available source of iron. Inhibition of iron uptake by the Fe(II)-specific ligand, ferrozine, indicated that reduction of both inorganic iron and ferrisiderophore complexes occurs before transport through the plasma membrane. Measurements of iron reduction rates and the inhibitory effect of ferrozine on growth supported this conclusion. The reduction-based uptake strategy is well suited for acquiring iron from multiple complexes in dilute aquatic environments and may play an important role in other cyanobacterial strains.

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