Magnetic Bacteria

Magnetic or “magnetotactic” bacteria were first discovered in the 1960s, and naturally organize themselves in the direction of Earth’s magnetic field, as shown in this video:

Video by Melbynfm

Inside these bacteria there is a row of iron-containing crystals aligned with the long axis of the cell, giving them the equivalent of an internal magnetic compass needle (Molecular mechanisms of magnetosome formation. Ann Rev Biochem 2007 76: 351-66). Such bacteria can sense and align themselves relative to the earth’s magnetic field. Magnetotactic bacteria are major constituents of many natural microbial communities, especially in aquatic habitats. There is a broad range of shapes and groups of magnetic bacteria. However, cultivation of these organisms in the laboratory is often difficult and only few strains of magnetotactic bacteria have been isolated in pure culture, a tiny minority of the vast diversity of naturally occurring populations from largely unexplored natural habitats such as the marine environment.

So why would bacteria want to be magnetic? Leaving aside the possibility that they are magnetic by accident, e.g. as a consequence of some metabolic byproduct, the truth is that we really don’t know the reason. However, the most likely explanation lies not in north-south alignment, but in up and down. The magnetotactic bacteria we know about require low but very precise levels of oxygen to survive, and must live in sediments where the oxygen concentration is just right for their needs. Over much of the globe, the Earth’s magnetic field actually points down towards the centre of the planet, so by following these lines of magnetic flux, they are able to ensure that they bury themselves in the sediment, which is exactly where they want to be. Thus the majority of magnetotactic in the Northern Hemisphere are north seeking, and those in the Southern Hemisphere are south seeking.

So, just one of nature’s curiosities then? Possibly not. One of the hottest areas of scientific research at present is nanotechnology, the fabrication of devices with dimensions on an atomic or molecular scale. By understanding how these bacteria construct the internal magnetosomes which give them their unique properties, we may be able to learn how to use this knowledge in a range of engineering and biotechnological applications (Molecular analysis of magnetotactic bacteria and development of functional bacterial magnetic particles for nano-biotechnology. Trends Biotechnol 2007 25: 182-8).