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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.


Related in: MedlinePlus

In-situ O2 and pH microprofiles in cyanobacterial biofilms from aerated and non-aerated Fe2+-rich and aerated Fe2+-poor reactors. All profiles were measured under similar irradiance as that used during long-term incubations of the reactors. Measurements in the biofilm from the aerated Fe2+-poor reactor were conducted outside of the reactor using the natural water purged with N2 gas to maintain anoxic conditions.
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Figure 2: In-situ O2 and pH microprofiles in cyanobacterial biofilms from aerated and non-aerated Fe2+-rich and aerated Fe2+-poor reactors. All profiles were measured under similar irradiance as that used during long-term incubations of the reactors. Measurements in the biofilm from the aerated Fe2+-poor reactor were conducted outside of the reactor using the natural water purged with N2 gas to maintain anoxic conditions.

Mentions: In-situ microsensor measurements revealed high volumetric rates of oxygenic photosynthesis in the biofilms forming in the Fe2+-rich reactors. This was demonstrated by the steep gradients in O2 and pH around the biofilm-water interface (Figure 2) as well as by direct rate measurements using the light-dark-shift method of Revsbech and Jorgensen (1981) (Figure S4). In contrast, O2 and pH profiles had only minute peaks in the biofilms in the Fe2+-poor reactor (Figure 2), indicating very low rates of photosynthesis. Based on the measured O2 profiles, the estimated net areal rates of photosynthesis were 21–23 and 1.5–5 μmol m−2 s−1 in the biofilms from the Fe2+-rich and Fe2+-poor reactors, respectively. This pattern was consistent with the approximately 10-fold difference in the cyanobacterial biomass (see above).


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)

In-situ O2 and pH microprofiles in cyanobacterial biofilms from aerated and non-aerated Fe2+-rich and aerated Fe2+-poor reactors. All profiles were measured under similar irradiance as that used during long-term incubations of the reactors. Measurements in the biofilm from the aerated Fe2+-poor reactor were conducted outside of the reactor using the natural water purged with N2 gas to maintain anoxic conditions.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: In-situ O2 and pH microprofiles in cyanobacterial biofilms from aerated and non-aerated Fe2+-rich and aerated Fe2+-poor reactors. All profiles were measured under similar irradiance as that used during long-term incubations of the reactors. Measurements in the biofilm from the aerated Fe2+-poor reactor were conducted outside of the reactor using the natural water purged with N2 gas to maintain anoxic conditions.
Mentions: In-situ microsensor measurements revealed high volumetric rates of oxygenic photosynthesis in the biofilms forming in the Fe2+-rich reactors. This was demonstrated by the steep gradients in O2 and pH around the biofilm-water interface (Figure 2) as well as by direct rate measurements using the light-dark-shift method of Revsbech and Jorgensen (1981) (Figure S4). In contrast, O2 and pH profiles had only minute peaks in the biofilms in the Fe2+-poor reactor (Figure 2), indicating very low rates of photosynthesis. Based on the measured O2 profiles, the estimated net areal rates of photosynthesis were 21–23 and 1.5–5 μmol m−2 s−1 in the biofilms from the Fe2+-rich and Fe2+-poor reactors, respectively. This pattern was consistent with the approximately 10-fold difference in the cyanobacterial biomass (see above).

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.


Related in: MedlinePlus