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Why Some Bacteria Are Magnetic? They seem to use Earth's magnetic field in orientation	By Stefan Anitei, Science Editor 23rd of October 2006, 12:49 GMT Adjust text size:


Researchers at the Naval Research Laboratory (NRL) and Purdue University have tried to decode the cause of the natural magnetism found in some bacteria. The magnetic bacteria live in ponds and lakes bellow the surface, in environments with low supply of oxygen. In fact, they are inhibited by high amounts of oxygen. The study was made on Magnetospirillum magneticum (pohoto) species. The magnetic bacteria possess some microscopic magnetic particles named magnetosomes. The magnetic bacteria expose magnetotaxis: in a magnetic field, the bacteria align like tiny compass needles. The team would like to create through genetic engineering a bacterium strain that become magnetic only when exposed to specific contaminants, in order to be used as living chemical sensors. First, they produced a non magnetic strain, without magnetosomes. "Genetic modification allowed us to directly observe differences in behavior between magnetic and non-magnetic versions of the same bacterium," said Professor Bruce Applegate. Scientists suspected that the bacteria use the Earth's magnetic field to orientate themselves while searching the proper oxygen concentrations rather than randomly swimming in all directions. "By observing how the bacteria moved away from oxygen that we added to their environment," reports Dr. McRae Smith, from NRL, "we directly measured how much magnetotaxis helps." NRL's Dr. Paul Sheehan adds, "by mathematically modeling their motion, we determined that being magnetic actually makes the bacteria much more sensitive to oxygen when in a magnetic field, so that they swim away from oxygen at much lower concentrations." And the bacteria were more affected if the power of the magnetic field was growing. But the accurate mechanism behind this behavior is still unknown. Scientists are intrigued because the Earth's magnetic field is too weak to affect in such a dimension the bacterial evolution. "Therefore," concludes Dr. Whitman of NRL, "the advantage to these bacteria in nature must be very small." "But over millions of years, this very subtle advantage has somehow produced bacterial magnetism."

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