The motion of a magnetotactic bacterium submitted to an oscillating magneti
c field was studied. The nature of the U-turn process, which occurred when
the magnetic field was reversed, was investigated. It is analytically shown
that this process presents a chaotic behavior. When the magnetic field is
reversed the bacterium may decide if the turning will be to the right side
or to the left side. Such choice is highly sensitive to the initial conditi
ons, making it impossible to predict which side will be taken in the U-turn
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