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Published November 16, 2004 | Published
Journal Article Open

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). In 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.

Additional Information

Copyright © 2004 by the National Academy of Sciences. Edited by Russell J. Hemley, Carnegie Institution of Washington, Washington, DC, and approved October 4, 2004 (received for review June 7, 2004). Published online before print November 3, 2004, 10.1073/pnas.0404040101 This paper was submitted directly (Track II) to the PNAS office. We thank John D. Coates for providing the GS-15 culture; Jeannie Mui of the McGill University Facility for Electron Microscopy Research for assistance with sample preparation for TEM; and two anonymous reviewers for their constructive comments. This work was supported by the Natural Sciences and Engineering Research Council of Canada and the Fonds Quebecois de la Recherche sur la Nature et les Technologies to the Centre for Biorecognition and Biosensors (H.V.) and the American Chemical Society Petroleum Research Fund and U.S. Department of Energy Financial Assistance Award DE-FC09-96SR18546 to the University of Georgia Research Foundation (C.L.Z.).

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