Magnetofossils, the Magnetization of Sediments, and the Evolution of Magnetite Biomineralization

103

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-CO 2) 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.

Section: Biological-induced Nucleation and Growth Of Magnetitementioning

confidence: 99%

Formation of tabular single-domain magnetite induced by Geobacter metallireducens GS-15

Vali

Weiss

et al. 2004

103

Section: Characteristics Of Biogenic Magnetitementioning

confidence: 99%

“…However, Darwinian evolution in biological systems that use magnetotaxis would favor the evolution of magnetites optimized for magnetic field interactions. Field studies of the swimming behavior of terrestrial magnetotactic bacteria argue strongly that magnetotaxis is likely the main driving force in their production of magnetite (4,5,7). Although results from the Mars Global Surveyor (MGS) indicate that Mars had a significant global magnetic field until Ϸ4 Ga ago (16), remnant crustal magnetism is nevertheless today both widespread and sufficiently strong (Ͼ5 T) to support magnetotaxis (16,18).…”

Section: Sources Of Carbonmentioning

confidence: 99%

“…These characteristics are the result of biochemical and genetic control by the organism and are consistent with natural (Darwinian) selection to maximize the magnetic dipole moment of the individual magnetite crystals as well as that of the entire cell (2). These characteristics can be used to define a terrestrial biosignature (2,7,18).A biosignature is useful only if it is not produced by natural inorganic processes; that is, one that does not happen through random, stochastic interactions or is not a product of directed human intervention, which is better described as a synthetic inorganic process. No published reports of inorganic ''MV-1-like'' truncated hexa-octahedral magnetites are known.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Truncated hexa-octahedral magnetite crystals in ALH84001: Presumptive biosignatures

Thomas‐Keprta

Clemett

Bazylinski

et al. 2001

168

McKay et al. [(1996)Science 273, 924 -930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe3O4) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexaoctahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexaoctahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found. W e report here the presence of single-domain, chemically pure, truncated hexa-octahedral magnetite crystals in terrestrial samples and Martian meteorite ALH84001. We suggest that the truncated hexa-octahedral magnetite crystals in the Martian meteorite ALH84001 were likely formed by a biogenic process. These magnetite crystals are embedded in Ϸ3.91 (Ϯ0.05)-Ga-old carbonate globules (1) that fill cracks and pore space in the 4.5-Ga-old Martian meteorite ALH84001. These truncated hexa-octahedral magnetite crystals are identical to those produced intracellularly by the marine magnetotactic bacterium strain MV-1 (2-7); natural selection has optimized the magnetic moment of MV-1 magnetite particles (2,(8)(9)(10)(11)(12). There is no known natural terrestrial inorganic mechanism that can explain the observation of truncated hexa-octahedral magnetite crystals associated with MV-1. Therefore, unless there is an unknown inorganic process on Mars, which seems to be absent on the Earth, we suggest that ALH84001 truncated hexaoctahedral magnetites formed by a similar mechanism to their terrestrial biogenic counterparts. As such, these crystals are interpreted as Martian magnetofossils and they constitute evidence of the oldest life yet found. In support of this, we note that early Mars likely had free-standing bodies of liquid water (13,14), and both organic (15) and inorganic carbon and energy (e.g., atmospheric CO 2 13 ) sources. Furthermore, early Mars also likely possessed a substantial planetary magnetic field (16), which would have been sufficient to support the evolution and growth of magnetotactic bacteria. Characteristics of Biogenic MagnetiteMagnetotactic bacteria produce well ordered membranebounded intracellular crystals of magnetite (Fe 3 O 4 ) and͞or greigi...

“…Despite this, extensive research over the past 30 years has demonstrated that many organisms have the biochemical ability to precipitate the ferrimagnetic minerals magnetite (Fe3O4) (10)(11)(12)(13)(14)(15)(16) and greigite (Fe3S4) (17). In terms of its phyletic distribution, magnetite biomineralization is particularly widespread, having been documented in monerans (10), protists (11), and animals (12)(13)(14)(15)(16), with a fossil record extending back into Precambrian time (18). Within Kingdom Animalia, it is known within the mollusks (12), arthropods (13), and chordates (14,15) and is suspected in many more groups (16).…”

mentioning

confidence: 99%

Magnetite biomineralization in the human brain.

Kirschvink

Kobayashi-Kirschvink

Woodford

1992

Self Cite

532

357

Although the mineral magnetite (Fe3O4) is precipitated biochemically by bacteria, protists, and a variety of animals, it has not been documented previously in human tissue. Using an ultrasensitive superconducting magnetometer in a clean-lab environment, we have detected the presence of ferromagnetic material in a variety of tissues from the human brain. Magnetic particle extracts from solubilized brain tissues examined with high-resolution transmission electron microscopy, electron diffraction, and elemental analyses identify minerals in the magnetitemaghemite family, with many of the crystal morphologies and structures resembling strongly those precipitated by magnetotactic bacteria and fish. These magnetic and high-resolution transmission electron microscopy measurements imply the presence of a minimum of 5 million single-domain crystals per gram for most tissues in the brain and >100 million crystals per gram for pia and dura. Magnetic property data indicate the crystals are in clumps of between 50 and 100 particles. Biogenic magnetite in the human brain may account for high-field saturation effects observed in the Ti and T2 values of magnetic resonance imaging and, perhaps, for a variety of biological effects of low-frequency magnetic fields.