Abstract
There is a good deal of published evidence that indicates that all magnetosomes within a single cell of a magnetotactic bacterium are magnetically oriented in the same direction so that they form a single magnetic dipole believed to assist navigation of the cell to optimal environments for their growth and survival. Some cells of the cultured magnetotactic bacterium Magnetovibrio blakemorei strain MV-1 are known to have relatively wide gaps between groups of magnetosomes that do not seem to interfere with the larger, overall linear arrangement of the magnetosomes along the long axis of the cell. We determined the magnetic orientation of the magnetosomes in individual cells of this bacterium using Fe 2p X-ray magnetic circular dichroism (XMCD) spectra measured with scanning transmission X-ray microscopy (STXM). We observed a significant number of cases in which there are sub-chains in a single cell, with spatial gaps between them, in which one or more sub-chains are magnetically polarized opposite to other sub-chains in the same cell. These occur with an estimated frequency of 4.0±0.2%, based on a sample size of 150 cells. We propose possible explanations for these anomalous cases which shed insight into the mechanisms of chain formation and magnetic alignment.
Highlights
Magnetotactic bacteria (MTB) are ubiquitous in marine and freshwater environments [1,2,3]
The image was recorded in transmission using a photon energy of 709.8 eV and converted to optical density (OD) using the intensity in areas without cells in this image
In addition to the cells with clearly visible chains of magnetosomes, this field of view contains a number of unstructured features of amorphous material, of unknown character but likely either extracellular material from the MV-1 cells or residual material from the culturing medium
Summary
Magnetotactic bacteria (MTB) are ubiquitous in marine and freshwater environments [1,2,3]. They are a diverse group phylogenetically and morphologically which are linked by the ability to biomineralize membrane-bounded magnetic nanoparticles termed magnetosomes. By reducing a threedimensional search problem to one of a single dimension, magnetotaxis allows for motile bacteria to more efficiently locate and maintain position at an optimal chemical environment, generally the oxic-anoxic interface, in aquatic habitats characterized by vertical chemical (e.g., oxygen) concentration gradients [5]. In chemically-stratified habitats, MTB appear to have a significant advantage over non-magnetotactic bacteria in locating their preferred environment [6]
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