Quantifying the Magnetic Advantage in Magnetotaxis
M. J. Smith 1, P. E. Sheehan 1, L. L. Perry 2, K. O. O'Connor 2, L. N. Csonka 2, B. M. Applegate 2 and Lloyd Whitman 1*
1 Naval Research Laboratory
2 Purdue University
* To whom correspondence should be addressed. E-mail: whitman{at}nrl.navy.mil.
Submitted on March 15, 2006
Revised on April 20, 2006
Accepted on 8 May 2006
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Abstract |
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Magnetotactic bacteria are characterized by the production of magnetosomes, nanoscale particles of lipid bilayer encapsulated magnetite, that act to orient the bacteria in magnetic fields. These magnetosomes allow magneto-aerotaxis, which is the motion of the bacteria along a magnetic field and toward preferred concentrations of oxygen. Magneto-aerotaxis has been shown to direct the motion of these bacteria downward towards sediments and microaerobic environments favorable for growth. Herein, we compare the magneto-aerotaxis of wild-type, magnetic Magnetospirillum magneticum AMB 1 with a non magnetic mutant we have engineered. Using an applied magnetic field and an advancing oxygen gradient, we have quantified the magnetic advantage in magneto-aerotaxis as a more rapid migration to preferred oxygen levels. Magnetic, wild-type cells swimming in an applied magnetic field more quickly migrate away from the advancing oxygen than either wild-type cells in a zero field or the non-magnetic cells in any field. We find that the responses of the magnetic and mutant strains are well described by a relatively simple analytical model, an analysis of which indicates that the key benefit of magnetotaxis is an enhancement of a bacterium's ability to detect oxygen, not an increase in its average speed moving away from high oxygen concentrations.
Key Words:
Magnetospirillum, aerotaxis, magnetosome, migration
