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Oxygenic photosynthesis as a protection mechanism for cyanobacteria against iron-encrustation in environments with high Fe2+ concentrations

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Ionescu,  D.
Permanent Research Group Microsensor, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Buchmann,  B.
Permanent Research Group Microsensor, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Häusler,  S.
Permanent Research Group Microsensor, Max Planck Institute for Marine Microbiology, Max Planck Society;

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de Beer,  D.
Permanent Research Group Microsensor, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Polerecky,  L.
Permanent Research Group Microsensor, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Citation

Ionescu, D., Buchmann, B., Heim, C., Häusler, S., de Beer, D., & Polerecky, L. (2014). Oxygenic photosynthesis as a protection mechanism for cyanobacteria against iron-encrustation in environments with high Fe2+ concentrations. Frontiers in Microbiology, 5: 459, pp. 1-10.


Cite as: https://hdl.handle.net/21.11116/0000-0001-C51B-3
Abstract
If O-2 is available at circumneutral pH, Fe2+ is rapidly oxidized to Fe3+, which precipitates as FeO(OH). Neutrophilic iron oxidizing bacteria have evolved mechanisms to prevent self-encrustation in iron. Hitherto, no mechanism has been proposed for cyanobacteria from Fe2+-rich environments; these produce O-2 but are seldom found encrusted in iron. We used two sets of illuminated reactors connected to two groundwater aquifers with different Fe2+ concentrations (0.9 mu M vs. 26 mu M) in the Aspo Hard Rock Laboratory (HRL), Sweden. Cyanobacterial biofilms developed in all reactors and were phylogenetically different between the reactors. Unexpectedly, cyanobacteria growing in the Fe2+-poor reactors were encrusted in iron, whereas those in the Fe2+-rich reactors were not. In-situ microsensor measurements showed that O-2 concentrations and pH near the surface of the cyanobacterial biofilms from the Fe2+-rich reactors were much higher than in the overlying water. This was not the case for the biofilms growing at low Fe2+ concentrations. Measurements with enrichment cultures showed that cyanobacteria from the Fe2+-rich environment increased their photosynthesis with increasing Fe2+ concentrations, whereas those from the low Fe2+ environment were inhibited at Fe2+ > 5 mu M. Modeling based on in-situ O-2 and pH profiles showed that cyanobacteria from the Fe2+-rich reactor were not exposed to significant Fe2+ concentrations. We propose that, due to limited mass transfer, high photosynthetic activity in Fe2+-rich environments forms a protective zone where Fe2+ precipitates abiotically at a non-lethal distance from the cyanobacteria. This mechanism sheds new light on the possible role of cyanobacteria in precipitation of banded iron formations.