Physics – Medical Physics
Scientific paper
Jan 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aipc..420..761u&link_type=abstract
Space technology and applications international forum - 1998. AIP Conference Proceedings, Volume 420, pp. 761-764 (1998).
Physics
Medical Physics
Aerospace Bio- And Medical Physics
Scientific paper
An unusual group of iron bacteria has recently been discovered which form inclusion bodies containing a form of iron oxide known as magnetite (ferrosoferric oxide, Fe3O4.) The inclusions are of a nano-particle size, are encased within a protein envelope, and are called magnetosomes. Magnetosomes are arranged adjacent to one another and parallel to the long axis of the cell such that cells appear to contain an electron-dense string of beads. The bacteria containing magnetosomes exhibit metal reductase activity, an activity critical to element recycling in nature, and the inclusions are a means for the organism to sequester reduced iron atoms and thereby keep iron reduction stoichiometry favorable. The magnetosomes also allow the bacteria to display magnetotaxis, which is movement in response to a magnetic field, such as the north or south magnetic poles. It is presumed that the bacteria use the alignment to the earth's magnetic field to orient themselves downward towards sediments where the habitat is favorable to their growth and metabolism. The comparatively few species of these bacteria isolated in the northern and southern hemispheres respond to magnetic north and south respectively, or alternatively respond only to the magnetic pole of the hemisphere from which they were isolated. This apparent dichotomy in response to magnetism could mean that the organisms are not responding to magnetism, per se, but instead are using the magnetosomes to respond to gravity. To resolve if magnetosomes respond to gravity in addition to magnetism we have used Magnetospirillum magnetotacticum, a well-studied magnetotactic bacterium isolated in the northern hemisphere, to examine magnetotactic behavior in the absence of gravity. Experiments to compare the orientation of Magnetospirillum magnetotacticum to north- or south-pole magnets were conducted in normal gravity and in the microgravity environments aboard the Space Shuttle and Space Station MIR. In each of the microgravity situations studied, bacteria were impaired in their ability to orient to magnets, suggesting that on earth the bacteria use magnetosomes to respond to gravity. These experiments could have significant commercial utility and could lead to the use of magnetosomes to direct biodegrading bacteria to contaminated aquifers or soils and likewise could be used to direct and localize bacteria used in element leaching and microbial mining.
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