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Published online: 23 September 2009 | doi:10.1038/nchina.2009.187

Biophysics: Slightly inclined

Felix Cheung

Introduction

© (2009) Elsevier

Magnetotactic bacteria possess an ability known as magnetotaxis, which allows them to use the Earth's magnetic field to navigate during migration. The classical model of magnetotaxis predicts that the migration velocity of magnetotactic bacteria increases monotonically with the strength of the magnetic field, but a team led by Yongxin Pan at the Chinese Academy of Sciences in Beijing, China, and Michael Winklhofer at Ludwig-Maximilians-Universität in Munich, Germany¹, has found otherwise.

The researchers tested the classical model experimentally using MYC-1, a type of magnetotactic bacteria extracted from the sediments of Lake Miyun near Beijing. Each MYC-1 bacterium possesses a magnetosome chain that serves as the compass needle for navigation, and two bundles of flagella that serve as propellers for locomotion.

Normally, MYC-1 bacteria move along the magnetic field lines on a helical trajectory, but in a rotating magnetic field, they swim on a circular path (see image). The researchers studied the migration velocity of MYC-1 bacteria under an applied rotating magnetic field. They found that the migration velocity decreased as the magnetic field strength increased from 0.1 mT, equivalent to the Earth's magnetic field, up to 1.5 mT.

One explanation for this unexpected observation is that the magnetosome chain of MYC-1 is inclined with respect to the flagellar propulsion axis. The effect, however, is apparent only in magnetic fields greater than 0.1 mT, suggesting that magnetotaxis is optimized for the Earth's magnetic field.

The authors of this work are from:
Biogeomagnetism Group, Key Laboratory of the Earth's Deep Interior, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China; State Key Laboratory of Lithospheric Evolution, Beijing, China; Department of Earth and Environmental Science, Ludwig-Maximilians-Universität, Munich, Germany.

Reference

1. Pan, Y. et al. Reduced efficiency of magnetotaxis in magnetotactic coccoid bacteria in higher than geomagnetic fields. Biophys. J. 97, 986–991 (2009).
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