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Published January 2008 | Accepted Version
Journal Article Open

The identification and biogeochemical interpretation of fossil magnetotactic bacteria


Magnetotactic bacteria, which most commonly live within the oxic-anoxic transition zone (OATZ) of aquatic environments, produce intracellular crystals of magnetic minerals, specifically magnetite or greigite. The crystals cause the bacteria to orient themselves passively with respect to the geomagnetic field and thereby facilitate the bacteria's search for optimal conditions within the sharp chemical gradients of the OATZ. The bacteria may also gain energy from the redox cycling of their crystals. Because magnetotactic bacteria benefit from their magnetic moments, natural selection has promoted the development of traits that increase the efficiency with which the intracellular crystals impart magnetic moments to cells. These traits also allow crystals produced by magnetotactic bacteria (called magnetofossils when preserved in sediments) to be distinguished from abiogenic particles and particles produced as extracellular byproducts of bacterial metabolism. Magnetofossils are recognizable based on their narrow size and shape distributions, distinctive morphologies with blunt crystal edges, chain arrangement, chemical purity, and crystallographic perfection. This article presents a scheme for rating magnetofossil robustness based on these traits. The magnetofossil record extends robustly to the Cretaceous and with lesser certainty to the late Archean. Because magnetotactic bacteria predominantly live in the OATZ, the abundance and character of their fossils can reflect environmental changes that alter the chemical stratification of sediments and the water column. The magnetofossil record therefore provides an underutilized archive of paleoenvironmental information. Several studies have demonstrated a relationship between magnetofossil abundance and glacial/interglacial cycles, likely mediated by changes in pore water oxygen levels. More speculatively, a better-developed magnetofossil record might provide constraints on the long-term evolution of marine redox stratification. More work in modern and ancient settings is necessary to explicate the mechanisms linking the abundance and character of magnetofossils to ancient biogeochemistry.

Additional Information

Author postprint. Published version, © 2007 Elsevier B.V. Received 16 April 2007; accepted 6 August 2007. Available online 14 August 2007. This work was funded by grants from the Agouron Institute and the NASA Astrobiology Instrument Development program (to JLK) and from the Moore Foundation and NSF Graduate Research Fellowships (to REK). Mark Hounslow, Hojatollah Vali, and Atsuko Kobayashi graciously provided TEM images. We thank Jared Leadbetter, Adam Maloof, Cody Nash, Dianne Newman, and Lael Vetter for helpful discussion.

Attached Files

Accepted Version - Kopp2008_Postprint_The_identification_and_interpretation_of_fossil_magnetotactic_bacteria.pdf



Additional details

August 22, 2023
October 16, 2023