Iron in Cyanobacteria

Kranzler, Chana; Rudolf, Mareike; Keren, Nir; Schleiff, Enrico

doi:10.1016/b978-0-12-394313-2.00003-2

Cited by 72 publications

(73 citation statements)

References 203 publications

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“…Thermal dissolution and photochemical reduction of siderophore-bound iron may provide a source of free Fe 0 for uptake. Although both siderophoremediated and reductive iron uptake pathway have been reported in cyanobacteria (Kranzler et al, 2012;Stevanovic et al, 2012), the latter seems to be the dominant pathway. OM transport of both siderophore-Fe (despite its low rate) and Fe 0 are under the control of the TonB-ExbB-ExbD-dependent transport system (Figures 4a and b).…”

Section: Discussionmentioning

confidence: 92%

New insights into iron acquisition by cyanobacteria: an essential role for ExbB-ExbD complex in inorganic iron uptake

Jiang

Lou

et al. 2014

The ISME Journal

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Cyanobacteria are globally important primary producers that have an exceptionally large iron requirement for photosynthesis. In many aquatic ecosystems, the levels of dissolved iron are so low and some of the chemical species so unreactive that growth of cyanobacteria is impaired. Pathways of iron uptake through cyanobacterial membranes are now being elucidated, but the molecular details are still largely unknown. Here we report that the non-siderophore-producing cyanobacterium Synechocystis sp. PCC 6803 contains three exbB-exbD gene clusters that are obligatorily required for growth and are involved in iron acquisition. The three exbB-exbDs are redundant, but single and double mutants have reduced rates of iron uptake compared with wild-type cells, and the triple mutant appeared to be lethal. Short-term measurements in chemically well-defined medium show that iron uptake by Synechocystis depends on inorganic iron (Fe 0 ) concentration and ExbB-ExbD complexes are essentially required for the Fe 0 transport process. Although transport of iron bound to a model siderophore, ferrioxamine B, is also reduced in the exbB-exbD mutants, the rate of uptake at similar total [Fe] is about 800-fold slower than Fe 0 , suggesting that hydroxamate siderophore iron uptake may be less ecologically relevant than free iron. These results provide the first evidence that ExbB-ExbD is involved in inorganic iron uptake and is an essential part of the iron acquisition pathway in cyanobacteria. The involvement of an ExbB-ExbD system for inorganic iron uptake may allow cyanobacteria to more tightly maintain iron homeostasis, particularly in variable environments where iron concentrations range from limiting to sufficient.

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Section: Discussionmentioning

confidence: 92%

New insights into iron acquisition by cyanobacteria: an essential role for ExbB-ExbD complex in inorganic iron uptake

Jiang

Lou

et al. 2014

The ISME Journal

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“…Reduction plays a central role in iron uptake of the non‐siderophore producer Synechocystis sp. (Kranzler et al ., 2011; 2013a; 2013b). Encouraged by the observed Fe′ uptake observed in Anabaena sp., inhibition of uptake by the Fe(II) chelator, Ferrozine (Fz), was examined.…”

Section: Resultsmentioning

confidence: 99%

Multiple modes of iron uptake by the filamentous, siderophore‐producing cyanobacterium, Anabaena sp. PCC 7120

Rudolf

Kranzler

Lis

et al. 2015

Molecular Microbiology

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SummaryIron is a member of a small group of nutrients that limits aquatic primary production. Mechanisms for utilizing iron have to be efficient and adapted according to the ecological niche. In respect to iron acquisition cyanobacteria, prokaryotic oxygen evolving photosynthetic organisms can be divided into siderophore-and non-siderophore-producing strains. The results presented in this paper suggest that the situation is far more complex. To understand the bioavailability of different iron substrates and the advantages of various uptake strategies, we examined iron uptake mechanisms in the siderophore-producing cyanobacterium Anabaena sp. PCC 7120. Comparison of the uptake of iron complexed with exogenous (desferrioxamine B, DFB) or to self-secreted (schizokinen) siderophores by Anabaena sp. revealed that uptake of the endogenous produced siderophore complexed to iron is more efficient. In addition, Anabaena sp. is able to take up dissolved, ferric iron hydroxide species (Fe′) via a reductive mechanism. Thus, Anabaena sp. exhibits both, siderophore-and non-siderophore-mediated iron uptake. While assimilation of Fe′ and FeDFB are not induced by iron starvation, FeSchizokinen uptake rates increase with increasing iron starvation. Consequently, we suggest that Fe′ reduction and uptake is advantageous for low-density cultures, while at higher densities siderophore uptake is preferred.

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“…Siderophores are low molecular weight, high‐affinity Fe 3+ chelators produced by some fungi and bacteria, including cyanobacteria (Neilands, ; Hopkinson & Morel, ). Picocyanobacteria do not appear to produce siderophores, although some Synechococcus can (Kranzler et al ., ), but may have the ability to access siderophore‐bound Fe 3+ (Hopkinson & Morel, ). A reduction step to free the bound Fe 3+ and transport it into the cell as Fe 2+ is probably necessary (Boukhalfa & Crumbliss, ; Harrington & Crumbliss, ; Kranzler et al ., ).…”

Section: The Critical Role Of Ferrous Ironmentioning

confidence: 99%

A novel model for cyanobacteria bloom formation: the critical role of anoxia and ferrous iron

et al. 2014

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SUMMARY1. A novel conceptual model linking anoxia, phosphorus (P), nitrogen (N), iron (Fe) and sulphate to the formation of noxious filamentous and colonial cyanobacteria blooms is presented that reconciles seemingly contradictory ideas about the roles of P, N and Fe in bloom formation. 2. The model has several critical concepts: (i) P regulates biomass and productivity in fresh waters until excessive loading renders a system N-limited or light-limited, but it is the availability of ferrous ions (Fe 2+ ) that regulates the ability of cyanobacteria to compete with its eukaryotic competitors; (ii) Fe 2+ diffusing from anoxic sediments is a major Fe source for cyanobacteria, which acquire it by migrating downwards into Fe 2+-rich anoxic waters from oxygenated waters; and (iii) subsequent cyanobacterial siderophore production provides a supply of Fe 3+ for reduction at cyanobacteria cell membranes that leads to very low Fe 3+ concentrations in the mixing zone.3. When light and temperature are physiologically suitable for cyanobacteria growth, bloom onset is regulated by the onset of internal Fe 2+ loading which in turn is controlled by anoxia, reducible Fe content of surface sediments and sulphate reduction rate.4. This conceptual model provides the basis for improving the success of approaches to eutrophication management because of its far-reaching explanatory power over the wide range of conditions where noxious cyanobacteria blooms have been observed.

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Iron in Cyanobacteria

Cited by 72 publications

References 203 publications

New insights into iron acquisition by cyanobacteria: an essential role for ExbB-ExbD complex in inorganic iron uptake

New insights into iron acquisition by cyanobacteria: an essential role for ExbB-ExbD complex in inorganic iron uptake

Multiple modes of iron uptake by the filamentous, siderophore‐producing cyanobacterium, Anabaena sp. PCC 7120

A novel model for cyanobacteria bloom formation: the critical role of anoxia and ferrous iron

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