Heim, Christine N.

[["dc.bibliographiccitation.artnumber","459"],["dc.bibliographiccitation.journal","Frontiers in Microbiology"],["dc.bibliographiccitation.volume","5"],["dc.contributor.author","Ionescu, Danny"],["dc.contributor.author","Buchmann, Bettina"],["dc.contributor.author","Heim, Christine"],["dc.contributor.author","de Beer, Dirk"],["dc.contributor.author","Polerecky, Lubos"],["dc.contributor.author","Häusler, Stefan"],["dc.date.accessioned","2018-11-07T09:35:23Z"],["dc.date.available","2018-11-07T09:35:23Z"],["dc.date.issued","2014"],["dc.description.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."],["dc.description.sponsorship","DFG (German Research Foundation) research unit FOR 571"],["dc.identifier.doi","10.3389/fmicb.2014.00459"],["dc.identifier.isi","000341683600001"],["dc.identifier.pmid","25228899"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/11793"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/32374"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Frontiers Media S.A."],["dc.relation.eissn","1664-302X"],["dc.relation.issn","1664-302X"],["dc.rights","CC BY 3.0"],["dc.rights.uri","https://creativecommons.org/licenses/by/3.0/"],["dc.title","Oxygenic photosynthesis as a protection mechanism for cyanobacteria against iron-encrustation in environments with high Fe2+ concentrations"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","6"],["dc.bibliographiccitation.journal","Frontiers in Earth Science"],["dc.bibliographiccitation.volume","3"],["dc.contributor.author","Heim, Christine N."],["dc.contributor.author","Simon, Klaus"],["dc.contributor.author","Ionescu, Danny"],["dc.contributor.author","Reimer, Andreas"],["dc.contributor.author","de Beer, Dirk"],["dc.contributor.author","Quéric, Nadia Valérie"],["dc.contributor.author","Reitner, Joachim"],["dc.contributor.author","Thiel, Volker"],["dc.date.accessioned","2019-07-09T11:41:14Z"],["dc.date.available","2019-07-09T11:41:14Z"],["dc.date.issued","2015"],["dc.description.abstract","Microbial iron oxyhydroxides are common deposits in natural waters, recent sediments, and mine drainage systems. Along with these minerals, trace and rare earth elements (TREE) are being accumulated within the mineralizing microbial mats. TREE patterns are widely used to characterize minerals and rocks, and to elucidate their evolution and origin. However, whether and which characteristic TREE signatures distinguish between a biological and an abiological origin of iron minerals is still not well-understood. Here we report on long-term flow reactor studies performed in the Tunnel of Äspö (Äspö Hard Rock Laboratory, Sweden). The development of microbial mats dominated by iron-oxidizing bacteria (FeOB), namely Mariprofundus sp. and Gallionella sp were investigated. The feeder fluids of the flow reactors were tapped at 183 and 290 m below sea-level from two brackish, but chemically different aquifers within the surrounding, ~1.8 Ga old, granodioritic rocks. The experiments investigated the accumulation and fractionation of TREE under controlled conditions of the subsurface continental biosphere, and enabled us to assess potential biosignatures evolving within the microbial iron oxyhydroxides. After 2 and 9 months, concentrations of Be, Y, Zn, Zr, Hf, W, Th, Pb, and U in the microbial mats were 103- to 105-fold higher than in the feeder fluids whereas the rare earth elements and Y (REE+Y) contents were 104- and 106-fold enriched. Except for a hydrothermally induced Eu anomaly, the normalized REE+Y patterns of the microbial iron oxyhydroxides were very similar to published REE+Y distributions of Archaean Banded Iron Formations (BIFs). The microbial iron oxyhydroxides from the flow reactors were compared to iron oxyhydroxides that were artificially precipitated from the same feeder fluid. Remarkably, these abiotic and inorganic iron oxyhydroxides show the same REE+Y distribution patterns. Our results indicate that the REE+Y mirror closely the water chemistry, but they do not allow to distinguish microbially mediated from inorganic iron precipitates. Likewise, all TREE studied showed an overall similar fractionation behavior in biogenic, abiotic, and inorganic iron oxyhydroxides. Exceptions are Ni and Tl, which were only accumulated in the microbial iron oxyhydroxides and may point to a potential utility of these elements as microbial biosignatures."],["dc.identifier.doi","10.3389/feart.2015.00006"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/11851"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/58377"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.publisher","Frontiers Media S.A."],["dc.relation.eissn","2296-6463"],["dc.relation.issn","2296-6463"],["dc.rights","CC BY 4.0"],["dc.rights.uri","https://creativecommons.org/licenses/by/4.0/"],["dc.title","Assessing the utility of trace and rare earth elements as biosignatures in microbial iron oxyhydroxides"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]