Open Access

Formation of magnetite in Magnetospirillum gryphiswaldense studied with FORC diagrams

Earth, Planets and Space200961:BF03352894

Received: 19 November 2007

Accepted: 20 March 2008

Published: 23 January 2009


In order to study the formation of magnetite in magnetotactic bacteria, FORC diagrams were measured on a set of cultured Magnetospirillum gryphiswaldense, following an assay in which the iron uptake is used only for magnetite formation and not for cell growth. This enabled us to follow the magnetite formation independently of growth. The FORC diagrams showed a clear evolution from a size-distribution with a majority of superparamagnetic grains, to a distribution dominated by stable, single-domain grains, but still containing some superparamagnetic particles. TEM observations confirm this evolution. According to the saturation isothermal remanent magnetization cooling and warming curves, the Verwey transition can only be seen in the most mature samples, and slightly below 120 K. This suggests that the samples may have suffered from some partial oxidation.

Key words

Magnetotactic bacteria FORC diagrams magnetite