ZHANG, CHUANLUN¹, HOJATOLLAH VALI², CHRISTOPHER S. ROMANEK³, TOMMY J. PHELPS⁴, and SHI V. LIU^5
1Univ. Missouri, Columbia, MO
²McGill University, Montreal, Canada
³SREL, Univ. Georgia, Aiken, GA
⁴ORNL, Oak Ridge, TN
⁵Allegheny Univ., Philadelphia, PA

Abstract: Formation of Single-Domain Magnetite by a Thermophilic Bacterium

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 65°C to study the effect of bacterial activity on solution chemistry and magnetite formation during the growth of TOR-39. Run products were examined by high-resolution transmission electron microscopy. Magnetite particles formed exclusively outside of bacterial cells and exhibited diamond shapes having relatively equal length and width (<15% difference). Tiny magnetite particles (<12 nm) nucleated between 10 h 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. Over this time period greater than 85% of the particles observed fell within the magnetic single domain. No magnetite was detected in abiotic controls 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 thermophiles such as TOR-39 may have heretofore unrecognized significance in the biological contribution to natural remanent magnetization in sedimentary basins and other geothermal environments.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas