A weak magnetic field could speed the growth of crippled bacteria.© PunchstockCan magnetic fields affect living creatures? Scientists have spent decades trying to understand how migrating birds might sense the Earth's magnetic field, but have never isolated the biochemical reactions responsible.
Others believe that the magnetic fields produced by electrical power lines might be harmful, yet no one has found convincing proof of how magnets could have a biological effect.
Until now. Scientists have demonstrated that a weak magnetic field can affects production of a certain molecule found in a photosynthetic bacterium.
This is the first time a magnetic effect of this kind has been seen, says Peter Hore, a physical chemist at the University of Oxford, UK, who led the research effort.
Chemists already knew that magnetic fields can affect certain chemical reactions involving radicals, molecules that contain unpaired electrons. But these reactions rely on molecules not found in living creatures. The question remained whether such magnetic-field effects occur in real biological systems, says Thorsten Ritz, a biophysicist at the University of California, Irvine.
Radical approach
Hore's team used a mutant strain of the bacterium Rhodobacter sphaeroides called R-26. The strain lacks a protective chemical known as a carotenoid that normally soaks up damaging radicals: "This bacterium was deliberately modified to be sensitive to magnetic fields," explains Hore. "We wanted to maximize the field's effect."
The bacterium contains a pair of chlorophyll molecules, which allow it to harvest energy from light. But the process relies on a cascade of chemical reactions that can also turn oxygen from the air into a highly reactive form called singlet oxygen, which can damage DNA or proteins in a cell. A magnetic field slightly changes this sequence of reactions by stabilizing a radical molecule formed from chlorophyll that would otherwise generate singlet oxygen.
The scientists removed the photosynthetic molecules from R-26 to study them, and found that a magnetic field of 20 millitesla, just 400 times the Earth's magnetic field, was enough to cut singlet oxygen production by up to 50%. The team also saw that under this magnetic field, roughly 50 times weaker than that generated by the lifting electromagnets found in junkyards, the photosynthetic molecules were protected against singlet oxygen damage.
This suggests that the R-26 bacteria should grow better in a magnetic field, so the researchers are now watching laboratory cultures for the effect. They have published their research online in the journal Chemical Communications1.
Flying high
Some scientists have proposed that similar chemistry gives birds their amazing navigational skills. There is growing evidence that microscopic magnetic particles in their beaks may help them find their way (see ""Homing pigeons reveal true magnetism":http://www.nature.com/news/2004/041122/full/041122-7.html"), but Hore explains that this may only give the birds a 'map sense'.
In other words, the birds build a mental contour map of the ground by simply remembering variations in the strength of the Earth's magnetic field as they fly overhead. Hore says that a 'compass sense' (the ability to identify magnetic north) is more likely to rely on a chemical reaction involving radicals.
"I think the study makes it more plausible that a real biological reaction can exist [in these birds] that is sensitive to weak magnetic field effects," agrees Ritz.
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