Switching of swimming modes in Magnetospirillium gryphiswaldense

TL;DR

This study reveals that Magnetospirillum gryphiswaldense can rapidly switch between fast and slow swimming modes in magnetic fields, with implications for understanding magnetotactic navigation and bacterial motility mechanisms.

Contribution

It introduces a new model explaining swimming mode switching based on flagellum rotation and provides a novel method to measure the bacterium's magnetic moment.

Findings

Cells switch swimming modes in less than 0.2 seconds.

A model explains trajectory variations based on flagellum rotation.

Magnetic moment measured as (2.0 ± 0.6) × 10^{-16} Am^2.

Abstract

The microaerophilic magnetotactic bacterium Magnetospirillum gryphiswaldense swims along magnetic field lines using a single flagellum at each cell pole. It is believed that this magnetotactic behavior enables cells to seek optimal oxygen concentration with maximal efficiency. We analyse the trajectories of swimming M. gryphiswaldense cells in external magnetic fields larger than the earth's field, and show that each cell can switch very rapidly (in < 0.2 s) between a fast and a slow swimming mode. Close to a glass surface, a variety of trajectories was observed, from straight swimming that systematically deviates from field lines to various helices. A model in which fast (slow) swimming is solely due to the rotation of the trailing (leading) flagellum can account for these observations. We determined the magnetic moment of this bacterium using a new method, and obtained a value of (2.0 $\pm$ 0.6) $\times$ $10^{-16}$ Am$^2$. This value is found to be consistent with parameters emerging from quantitative fitting of trajectories to our model.