ASGSB 1998 Annual Meeting Abstracts

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MAGNETOTACTIC BACTERIA AND GRAVITY. J.F. Doyle, H. Wachtel and P. Todd, University of Colorado at Boulder

The magnetotactic bacterium Magnetospirillum magnetotacticum, strain MS-1, is thought to respond to magnetic fields to guide tactic movement. Owing to its internal magnetite particles ("magnetosomes"), cells can also be moved and guided by externally applied magnetic fields, which can be combined in various ways with the gravity vector. This organism therefore provides an opportunity to test our previously demonstrated hypothesis that suspended bacteria prevented from sedimenting (Escherichia coli and Bacillus subtilis), as in microgravity, grow to higher final cell concentrations than when allowed to sediment at 1 x g. M. magnetotacticum cultures were grown in defined medium ATCC-1643 at 30^oC and were found to have a doubling time of about 4-5 h and a final cell concentration of about 9 x 10⁸ cells/ml. Current-carrying wire coils were designed and constructed to form magnetic fields capable of imposing forces comparable in magnitude to that of gravity on suspended bacteria in vertical 9 ml tube cultures. Field mapping showed a vertical trapping region having maximum field strength of 20 mT (milliTesla) and horizontal variance of + 5%. The objective of this design was to oppose, to the extent possible, the gravitational force on bacteria. Such a design is used as a basis for space flight experiments in which, rather than being quiescently suspended, bacteria would be subject to a gravity-like force, so that complementary experiments can be performed in which a magnetic field can be used, on one hand, to establish functional weightlessness and on the other, magnetopseudogravity.

This research was supported by NASA Grant NAGW-1197, and by SHOT, Inc., Floyd Knobs, IN.

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