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Oxygenic photosynthesis as a protection mechanism for cyanobacteria against iron-encrustation in environments with high Fe(2+) concentrations.

Ionescu D, Buchmann B, Heim C, Häusler S, de Beer D, Polerecky L - Front Microbiol (2014)

Bottom Line: Hitherto, no mechanism has been proposed for cyanobacteria from Fe(2+)-rich environments; these produce O2 but are seldom found encrusted in iron.Modeling based on in-situ O2 and pH profiles showed that cyanobacteria from the Fe(2+)-rich reactor were not exposed to significant Fe(2+) concentrations.This mechanism sheds new light on the possible role of cyanobacteria in precipitation of banded iron formations.

View Article: PubMed Central - PubMed

Affiliation: Microsensor Group, Max-Planck Institute for Marine Microbiology Bremen, Germany ; Department of Stratified Lakes, Leibniz Institute for Freshwater Ecology and Inland Fisheries Stechlin, Germany.

ABSTRACT
If O2 is available at circumneutral pH, Fe(2+) is rapidly oxidized to Fe(3+), 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 Fe(2+)-rich environments; these produce O2 but are seldom found encrusted in iron. We used two sets of illuminated reactors connected to two groundwater aquifers with different Fe(2+) concentrations (0.9 μM vs. 26 μM) in the Äspö Hard Rock Laboratory (HRL), Sweden. Cyanobacterial biofilms developed in all reactors and were phylogenetically different between the reactors. Unexpectedly, cyanobacteria growing in the Fe(2+)-poor reactors were encrusted in iron, whereas those in the Fe(2+)-rich reactors were not. In-situ microsensor measurements showed that O2 concentrations and pH near the surface of the cyanobacterial biofilms from the Fe(2+)-rich reactors were much higher than in the overlying water. This was not the case for the biofilms growing at low Fe(2+) concentrations. Measurements with enrichment cultures showed that cyanobacteria from the Fe(2+)-rich environment increased their photosynthesis with increasing Fe(2+) concentrations, whereas those from the low Fe(2+) environment were inhibited at Fe(2+) > 5 μM. Modeling based on in-situ O2 and pH profiles showed that cyanobacteria from the Fe(2+)-rich reactor were not exposed to significant Fe(2+) concentrations. We propose that, due to limited mass transfer, high photosynthetic activity in Fe(2+)-rich environments forms a protective zone where Fe(2+) 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.

No MeSH data available.


Fe2+ model results of the non-aerated Fe2+-rich (A) and aerated Fe2+-poor (B) reactors. Steady state Fe2+ profiles above cyanobacteria biofilms (graph 1) were calculated using microprofiles of O2 and pH measured in-situ (graph 2). Steady state was achieved once Fe2+ consumption by abiotic oxidation (Ox) was equal to Fe2+ supplied by diffusion (Diff) (graph 3). The change in Fe2+ concentration at the biofilm surface is shown as a function of time (graph 4).
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Figure 4: Fe2+ model results of the non-aerated Fe2+-rich (A) and aerated Fe2+-poor (B) reactors. Steady state Fe2+ profiles above cyanobacteria biofilms (graph 1) were calculated using microprofiles of O2 and pH measured in-situ (graph 2). Steady state was achieved once Fe2+ consumption by abiotic oxidation (Ox) was equal to Fe2+ supplied by diffusion (Diff) (graph 3). The change in Fe2+ concentration at the biofilm surface is shown as a function of time (graph 4).

Mentions: Modeling in the non-aerated Fe2+-rich reactor revealed that the steady state Fe2+ concentration profile was reached in ~10 min. Fe2+ concentration at the biofilm surface decreased from the initial value of 30 μM to below 0.001 μM in about 20 s, and in the steady state the Fe2+ concentration was below 0.001 μM already at a distance of ~400 μm from the biofilm surface (Figure 4A). In contrast, in the aerated Fe2+-poor reactor the steady state was reached after a much longer time (~2 h) and the concentration at the biofilm surface did not decrease below 0.3 μM (Figure 4B).


Oxygenic photosynthesis as a protection mechanism for cyanobacteria against iron-encrustation in environments with high Fe(2+) concentrations.

Ionescu D, Buchmann B, Heim C, Häusler S, de Beer D, Polerecky L - Front Microbiol (2014)

Fe2+ model results of the non-aerated Fe2+-rich (A) and aerated Fe2+-poor (B) reactors. Steady state Fe2+ profiles above cyanobacteria biofilms (graph 1) were calculated using microprofiles of O2 and pH measured in-situ (graph 2). Steady state was achieved once Fe2+ consumption by abiotic oxidation (Ox) was equal to Fe2+ supplied by diffusion (Diff) (graph 3). The change in Fe2+ concentration at the biofilm surface is shown as a function of time (graph 4).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4151041&req=5

Figure 4: Fe2+ model results of the non-aerated Fe2+-rich (A) and aerated Fe2+-poor (B) reactors. Steady state Fe2+ profiles above cyanobacteria biofilms (graph 1) were calculated using microprofiles of O2 and pH measured in-situ (graph 2). Steady state was achieved once Fe2+ consumption by abiotic oxidation (Ox) was equal to Fe2+ supplied by diffusion (Diff) (graph 3). The change in Fe2+ concentration at the biofilm surface is shown as a function of time (graph 4).
Mentions: Modeling in the non-aerated Fe2+-rich reactor revealed that the steady state Fe2+ concentration profile was reached in ~10 min. Fe2+ concentration at the biofilm surface decreased from the initial value of 30 μM to below 0.001 μM in about 20 s, and in the steady state the Fe2+ concentration was below 0.001 μM already at a distance of ~400 μm from the biofilm surface (Figure 4A). In contrast, in the aerated Fe2+-poor reactor the steady state was reached after a much longer time (~2 h) and the concentration at the biofilm surface did not decrease below 0.3 μM (Figure 4B).

Bottom Line: Hitherto, no mechanism has been proposed for cyanobacteria from Fe(2+)-rich environments; these produce O2 but are seldom found encrusted in iron.Modeling based on in-situ O2 and pH profiles showed that cyanobacteria from the Fe(2+)-rich reactor were not exposed to significant Fe(2+) concentrations.This mechanism sheds new light on the possible role of cyanobacteria in precipitation of banded iron formations.

View Article: PubMed Central - PubMed

Affiliation: Microsensor Group, Max-Planck Institute for Marine Microbiology Bremen, Germany ; Department of Stratified Lakes, Leibniz Institute for Freshwater Ecology and Inland Fisheries Stechlin, Germany.

ABSTRACT
If O2 is available at circumneutral pH, Fe(2+) is rapidly oxidized to Fe(3+), 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 Fe(2+)-rich environments; these produce O2 but are seldom found encrusted in iron. We used two sets of illuminated reactors connected to two groundwater aquifers with different Fe(2+) concentrations (0.9 μM vs. 26 μM) in the Äspö Hard Rock Laboratory (HRL), Sweden. Cyanobacterial biofilms developed in all reactors and were phylogenetically different between the reactors. Unexpectedly, cyanobacteria growing in the Fe(2+)-poor reactors were encrusted in iron, whereas those in the Fe(2+)-rich reactors were not. In-situ microsensor measurements showed that O2 concentrations and pH near the surface of the cyanobacterial biofilms from the Fe(2+)-rich reactors were much higher than in the overlying water. This was not the case for the biofilms growing at low Fe(2+) concentrations. Measurements with enrichment cultures showed that cyanobacteria from the Fe(2+)-rich environment increased their photosynthesis with increasing Fe(2+) concentrations, whereas those from the low Fe(2+) environment were inhibited at Fe(2+) > 5 μM. Modeling based on in-situ O2 and pH profiles showed that cyanobacteria from the Fe(2+)-rich reactor were not exposed to significant Fe(2+) concentrations. We propose that, due to limited mass transfer, high photosynthetic activity in Fe(2+)-rich environments forms a protective zone where Fe(2+) 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.

No MeSH data available.