Unravelling the magnetic signatures of magnetofossils from mutant magnetotactic bacteria
Abstract
Magnetite (Fe3O4) is a ubiquitous iron oxide found in sediments and sedimentary rocks. It is a major carrier of sediment and rock magnetization, and is used for numerous applications in Earth sciences. Nanoparticles of magnetite can be produced through abiotic processes or by microbial organisms. Among the latter, magnetotactic bacteria (MTB) are the only microorganisms producing single- or multi-stranded chains of single-domain magnetite nanoparticles in a genetically-controlled manner. They generate specific magnetic structures with high magnetic anisotropy that can be identified from FORC (First Order Reversal Curves) measurements. When MTB cells die, their magnetite chains can be trapped into sediments and subsequently fossilized. MTB fossils (hereafter referred to as magnetofossils) can be preserved over geological times, and contribute to sedimentary paleomagnetic and environmental records. The unambiguous identification of magnetofossils and their discrimination from abiotic magnetite would thus provide strong constraints on the evolution of life and environmental conditions over geological times. However, some fossilized assemblages bear contradictory signatures pointing to magnetic components that have distinct abiotic or biological origin(s). Using mutant MTB producing looped magnetite chains, we propose that the unresolved magnetic fingerprints are produced by a mixture of single-stranded and multi-stranded chains of biological magnetite which points to the importance of MTB for the magnetization of rocks and sediments. This work resolves longstanding and ongoing controversies about the interpretation of sedimentary sources of single-domain magnetite, establishing a theoretical and experimental framework that explains the magnetofossil signature and provides insights into the diversity of ancient MTB populations, and into mechanisms affecting the paleomagnetic recording efficiency of magnetofossil-rich sediments.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMGP45A..01A