Magnetism & navigation – in bacteria

Last week I was doing a session with some local Schol Bio students & we were talking about navigation & migration. One of the cues animals use to navigate round their world is magnetism – more specifically, sensitivity to the Earth's magnetic field. We agreed that we'd heard about some birds (e.g. pigeons) using magnetic cues, but then I asked, what about bacteria?

A while now I read an article by Stephen Jay Gould (one of my heroes who, sadly, died in 2002) about some species of bacteria being able to use magnetic fields to navigate. No, really. And today I found a blog with reference to a recent paper that looked at how this might work. The blog also mentioned other researchers (this link is to some good stuff on migration & navigation in general).

Magnetotactic bacteria live in water and contain tiny strings of magnetite crystals (there are some nice images here). And apparently they use these to orient themselves by the Earth's magnetic field and swim downwards – that's where all the rotting plant material is, and also tends to be the part of the water column where oxygen levels are lower. What a neat adaptation. What's just as interesting is that in magnetotactic bacteria from the southern hemisphere, the polarity of the magnetite crystals is the opposite of that in northern hemisphere bacteria!

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