Project

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The origin and legacy of microbially-derived magnetism in marine sediments

Applicant Gehring Andreas
Number 165851
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.10.2016 - 30.09.2020
Approved amount 243'054.00
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All Disciplines (3)

Discipline
Geophysics
Geology
Mineralogy

Keywords (7)

diagenesis; magnetofossil; microbial biogeochemistry; quantiative FMR spectroscopy; Magnetotactic bacteria ; rock magnetism; Benguela upwelling system

Lay Summary (German)

Lead
Bakterien sind wichtig für das Verständnis der Entwicklungsgeschichte des Lebens auf der Erde. Über deren Auftreten ist jedoch wenig bekannt, da Bakterien nicht erhalten bleiben in Sedimenten. Magnetotaktische Bakterien (MTB) enthalten Nanopartikel, generell aus Magnetit (Fe3O4), in Ketten angeordnet, in ihren Zellen. Diese Ketten erzeugen einen starken Dipol, der den MTB als Kompass dient, um ihr bevorzugtes Habitat zu finden. Die relativ stabilen Nanopartikel bleiben als Magnetofossile generell erhalten und können als mikrobiologische Indikatoren in geologischen Systemen verwendet werden. Um dieses Potenzial auszuschöpfen, müssen die magnetischen Eigenschaften von intakten Bakterien und deren Veränderung durch organischen Zerfall während der Diagenese im Detail bekannt sein.
Lay summary

Das primäre Ziel ist ein besseres Verständnis des Auftretens von MTB in einem marinen System und deren Erhaltung als Magnetofossile in Sedimenten als Schlüssel für die Identifikation von Bakterien in Ablagerungen in einem geologischen Zeitraum. Im Detail werden wir (i) Sedimentkerne ziehen im Schelfbereich vor Namibia, das eines der klassischen „Upwellig-Gebiete“ der Erde ist, und (ii) in den Sedimentproben mit Hilfe der Ferromagnetischen Resonanzspektroskopie (FMR) nach magnetischen Mustern suchen, die entweder für intakte MTB oder für deren magnetischen Überreste charakteristisch sind. Hierfür wird ein neues Simulationsmodell für die FMR-Spektren entwickelt, das eine routinemässige Auswertung der Sedimentproben ermöglicht. (iii) werden wir die FMR-Untersuchungen durch sedimentologische, chemische und mikrobiologische Analysen zur Beschreibung von diagenetischen Prozessen ergänzen, so dass ein möglichst vollständiges Bild der Magnetofossilisierung entsteht.

Unsere Arbeit ist ein neuer Ansatz zur Identifikation von MTB und deren Relikte in geologischen Systemen. Wenn es gelingt, sowohl intakte MTB als auch Magnetofossile in marinen Sedimenten zu finden, ist dies ein wichtiger Beitrag für die Suche nach bakteriellem Leben in der Erdgeschichte.

 

Direct link to Lay Summary Last update: 14.11.2016

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Polycrystalline texture causes magnetic instability in greigite
Lesniak Barbara, Koulialias Dimitrios, Charilaou Michalis, Weidler Peter G., Rhodes Jordan M., Macdonald Janet E., Gehring Andreas U. (2021), Polycrystalline texture causes magnetic instability in greigite, in Scientific Reports, 11(1), 3024-3024.
Ferromagnetic resonance of magnetite biominerals traces redox changes
BlattmannThomas, LesniakBarbara, García-RubioInés, CharilaouMichalis, WesselsMartin, EglintonTimothy, GehringAndreas (2020), Ferromagnetic resonance of magnetite biominerals traces redox changes, in Earth and Planetary Science Letters, 545, 116.

Collaboration

Group / person Country
Types of collaboration
Biogeochemistry group at ETH Zurich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
ESR group at ETH Zurich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure

Abstract

SummaryOur knowledge on the microbial evolution on the Earth is fragmentary and this mainly because soft-bodied microorganisms do not preserve well in sedimentary environments. Among the microbes, magnetotactic bacteria (MTB) represent a special class of organisms, because they precipitate biominerals, which can be preserved while the cellular matter is decomposed. The MTB form magnetosomes, which are intracellular ferrimagnetic nano-particles, mainly comprising of magnetite (Fe3O4), encapsulated in membranes. These magnetosomes generated by genetically-driven processes, have narrow size and shape distributions and in mature MTB they are aligned in chains. This configuration causes an interaction-induced shape anisotropy, i.e., pronounced magnetic uniaxiality that is the characteristic trait to magnetically identify MTB. In geological systems magnetic remains of MTB, denoted as magnetofossils, are valuable recorders of environmental conditions and of microbial ecology. However, the detection of magnetofossils can be complicated because diagenetic processes can lead to the decomposition of the cellular matter, which destabilizes the chain configuration of the magnetosomes. Such decay, resulting in chain fragments or in extreme case in clumps, can in turn change the interaction-induced shape anisotropy of the magnetite configurations. Consequently, the unequivocal detection of MTB in geological records, and establishing the biogeochemical conditions under which their magnetic signals are produced and preserved, becomes critical. In the proposed project we will investigate the habitats of MTB and the preservation of magnetofossils in marine sediments. For the sediment sampling we choose the continental margin of SW Africa. In this area, the northward flowing Benguela Current creates upwelling along the coast, which leads to one of the world’s most productive marine ecosystems, and an equally pronounced and widespread oxygen deficient zone. Such conditions are favorable habitats for MTB, which are mainly found in the anoxic-oxic transition zones. Sediment cores selected to span a range of redox conditions, water depths, carbon contents, mineralogy, and physical properties will be subjected to a suite of measurements that will provide a crucial framework for correlation with and interpretation of magnetic signals. We will analyse both surface sediments (0-1 cm) as well as deeper sediment layers in order to investigate early diagenetic transformations in organic matter and corresponding magnetic properties. The magnetic analysis includes classical rock-magnetic experiments in order to determine the concentration and grain size properties of the sediment samples and advanced multi-frequency ferromagnetic resonance (FMR) spectroscopy. We apply X-band (9 GHz) FMR spectroscopy in concert with S-band (4 GHz) and Q-band (36 GHz) at room and low temperature for the decipherment of the anisotropy properties of the magnetic content of the sediments and to numerically isolate spectral traits that are characteristic of MTB and magnetofossils, respectively. All the FMR spectra will be used for the numerical simulation in order to quantify different contributions to the total anisotropy properties of different magnetic components and their assemblies. This will be done by the advancement of our algorithm for intact MTB to magnetofossils with multiple magnetosome configurations. The combination of biochemical and FMR spectroscopic information from different depositional settings along a continental margin will provide an insight into the origin and legacy of microbially-derived magnetism in marine sediments, and this in turn will enable critical advances in our knowledge of past life and the microbial evolution on Earth and even other extra-terrestrial bodies.
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