Formation of tabular single-domain magnetite induced by Geobacter metallireducens GS-15
Distinct morphological characteristics of magnetite formed intracellularly
by magnetic bacteria (magnetosome) are invoked as compelling evidence
for biological activity on Earth and possibly on Mars. Crystals of magnetite
produced extracellularly by a variety of bacteria including Geobacter
metallireducens GS-15, thermophilic bacteria, and psychrotolerant
bacteria are, however, traditionally not thought to have nearly as distinct
morphologies. The size and shape of extracellular magnetite depend on
the culture conditions and type of bacteria. Under typical CO2-rich
culture conditions, GS-15 is known to produce superparamagnetic magnetite
(crystal diameters of approximately <30 nm). ln the current study,
we were able to produce a unique form of tabular, single-domain magnetite
under nontraditional (low-CO2) culture conditions. This magnetite
has a distinct crystal habit and magnetic properties. This magnetite could
be used as a biosignature to recognize ancient biological activities in
terrestrial and extraterrestrial environments and also may be a major
carrier of the magnetization in natural sediments.
SREL Reprint #2796
Vali, H., B. Weiss, Y. Li, S. K. Sears, S. S. Kim, J. L. Kirschvink and C. L. Zhang. 2004. Formation of tabular single-domain magnetite induced by geobacter metallireducens GS-15. Proceedings of the National Academy of Sciences 101:16121-16126.
