Iron Speciation and Physiological Analysis Indicate that Synechococcus sp. PCC 7002 Reduces Amorphous and Crystalline Iron Forms in Synthetic Seawater Medium

Annie Vera Hunnestad,Murat Van Ardelan,Martin Frank Hohmann-Marriott,Anne Ilse Maria Vogel,Maria Guadalupe Digernes

doi:10.3390/jmse8120996

Annie Vera Hunnestad, Murat Van Ardelan + Show 3 more

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https://doi.org/10.3390/jmse8120996

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Abstract

Cyanobacteria have high iron requirements due to iron-rich photosynthetic machineries. Despite the high concentrations of iron in the Earth’s crust, iron is limiting in many marine environments due to iron’s low solubility. Oxic conditions leave a large portion of the ocean’s iron pool unavailable for biotic uptake, and so the physiochemical properties of iron are hugely important for iron’s bioavailability. Our study is the first to investigate the effect of iron source on iron internalization and extracellular reduction by Synechococcus sp. PCC 7002. The results indicated that the amorphous iron hydrolysis species produced by FeCl3 better support growth in Synechococcus through more efficient iron internalization and a larger degree of extracellular reduction of iron than the crystalline FeO(OH). An analysis of dissolved iron (II) indicated that biogenic reduction took place in cultures of Synechococcus grown on both FeCl3 and FeO(OH).

Highlights

Iron is one of the most abundant elements in the Earth’s crust, but limits primary production in 25–50% of marine environments due to its solubility and consequent bioavailability [1,2]
This high iron requirement is mostly due to the photosynthetic complex: a total of 12 iron atoms are needed per Photosystem I (PSI) protein complex [9], and two-to-three iron atoms are required per Photosystem Iron and Iron (II) (PSII) [10]
While a high relative PSII/PSI ratio was seen in both cultures, the Synechococcus grown on FeO(OH) had a significantly higher relative PSII/PSI ratio compared to that grown on FeCl3 (p-value:

Summary

Introduction

Iron is one of the most abundant elements in the Earth’s crust, but limits primary production in 25–50% of marine environments due to its solubility and consequent bioavailability [1,2]. Cyanobacteria have as much as ten times higher iron requirements than non-photosynthetic bacteria of a similar cell-size [8]. This high iron requirement is mostly due to the photosynthetic complex: a total of 12 iron atoms are needed per Photosystem I (PSI) protein complex [9], and two-to-three iron atoms are required per Photosystem II (PSII) [10]. Iron-rich proteins such as ferredoxin and cytochromes, as well as several enzymes involved in photosynthetic electron transport, account for approximately 80% of the organism’s iron demand [11]

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