Other
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993e%26psl.120..283m&link_type=abstract
Earth and Planetary Science Letters (ISSN 0012-821X), vol. 120, no. 3-4, p. 283-300
Other
99
Bacteria, Magnetic Properties, Magnetite, Magnetization, Rocks, Room Temperature, Temperature Effects
Scientific paper
We report results on the magnetic properties of magnetites produced by magnetotactic and dissimilatory iron-reducing bacteria. Magnetotactic bacterial (MTB) strains MS1, MV1 and MV2 and dissimilatory iron-reducing bacterium strain GS-15, grown in pure cultures, were used in this study. Our results suggest that a combination of room temperature coercivity analysis and low temperature remanence measurements provides a characteristic magnetic signature for intact chains of single domain (SD) particles of magnetite from MTBs. The most useful magnetic property measurements include: (1) acquisition and demagnetization of isothermal remanent magnetization (IRM) using static, pulse and alternating fields; (2) acquisition of anhysteretic remanent magnetization (ARM); and (3) thermal dependence of low temperature (20 K) saturation IRM after cooling in zero field (ZFC) of in a 2.5 T field (FC) from 300 K. However, potentially the most diagnostic magnetic parameter for magnetosome chain identification in bulk sediment samples is related to the difference between low temperature zero-field and field cooled SIRMs on warming through the Verwey transition (T approximately = 100 K). Intact chains of unoxidized magnetite magnetosomes have ratios of delta(sub FC)/delta(sub ZFC) greater than 2, where the parameter delta is a measure of the amount of remanence lost by warming through the Verwey transition. Disruption of the chain structure or conversion of the magnetosomes to maghemite reduces the delta(sub FC)/delta(sub ZFC) ratio to around 1, similar to values observed for some inorganic magnetite, maghemite, greigite and GS-15 particles. Numerical simulations of delta(sub FC)/delta(sub ZFC) ratios for simple binary mixtures of magnetosome chains and inorganic magnetic fractions suggest that the delta(sub FC)/delta(sub ZFC) parameter can be a sensitive indicator of biogenic magnetite in the form of intact chains of magnetite magnetosomes and can be a useful magnetic technique for identifying them in whole-sediment samples. The strength of our approach lies in the comparative ease and rapidity with which magnetic measurements can be made, compared to techniques such as electron microscopy.
Bazylinski Dennis A.
Frankel Richard B.
Moskowitz Bruce M.
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