SREL Reprint #2332

Formation of single-domain magnetite by a thermophilic bacterium

Chuanlun Zhang1, Hojatollah Vali2, Christopher S. Romanek3, Tommy J. Phelps1, and Shi V. Liu4

1Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
2Electron Microscopy Center, McGill University, Montreal, Quebec H3A 2B2, Canada
3Department of Geology and Savannah River Ecology Laboratory, University of Georgia,
Aiken, South Carolina 29802, USA
4Department of Microbiology and Immunology, Allegheny University of the Health Sciences,
Philadelphia, Pennsylvania 19129, USA

Abstract: Magnetite is a common product of bacterial iron reduction and may serve as a potential physical indicator of biological activity in geological settings. Here we report the formation of single-domain magnetite under laboratory conditions by a thermophilic fermentative bacterial strain TOR-39 that was isolated from the deep subsurface. Time-course analyses were performed at 65ºC to study the effect of bacterial activity on solution chemistry and magnetite formation during the growth of TOR-39. Run products were examined by transmission electron microscopy. Magnetite particles formed exclusively outside of bacterial cells and exhibited octahedral shapes having relatively equal length and width (<15% difference). Tiny magnetite particles (<12 nm) nucleated between 10 and 11 h of incubation and increased to average lengths of 55.4 ± 26.8 nm after 24 h of incubation. Between 24 h and 22 d of incubation, magnetite particles maintained average lengths of 56.2 ± 24.8 nm. Based on size constraints, greater than 85% of the particles observed fell within the magnetic single domain. Little to no magnetite was detected in abiotic controls at 65 or 95ºC, or in TOR-39 cultures whose activity was suppressed. Unlike mesophilic iron-reducing bacteria (e.g., GS-15), TOR-39 produced crystals having shapes and sizes similar to some particles produced intracellularly by magnetotactic bacteria. Thus the single-domain magnetite produced by thermopiles such as TOR-39 may represent a heretofore unrecognized biological contribution to natural remanent magnetization in sedimentary basins and other geothermal environments.

SREL Reprint #2332

Zhang, C., H. Vali, C.S. Romanek, T.J. Phelps, and S.V. Liu. 1998. Formation of single-domain magnetite by a thermophilic bacterium. American Mineralogist 83:1409-1418.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).