More on Magnetic Bacteria

Those of my readers who followed me from my old blog may remember this post on magnetic bacteria. In it I discuss how a new technique called cyroelectron tomography has allowed researchers to gain new insights into how magnetosomes are arranged in some bacteria.
magnetosomes_xl.jpg
Above is a picture of magnetosome chains.


Magnetotactic bacteria display two different behaviors. In the first, called polar, the bacteria swim either north or south depending on what hemisphere they reside in or at least that has been the case up till now. In the second, called axial, the bacteria swims back and forth. Most magnetotactic bacteria in the northern hemishpere have north polarity, when exposed to higher oxygen levels they swim towards geomagnetic north which directs them downwards towards more anoxic environments (works the same way in the southern hemisphere as well). In July of 2004, however, an unusual species with southern polarity was found living in a pond in Massachusetts. They occur in mixed colonies (i.e. of north and south polarity bacteria) with occasional blooms of bacteria of one or the other polarity. Researchers found a significant relationship between oxidation reduction potential (that is the ability to accept or donate electrons, more negative values indicate a reducing environment and less negative values indicate an oxidizing environment). In the northern hemisphere a bacteria with southern polarity would end up moving towards an oxidizing atmosphere rather than away which leads researchers to question the current model of the adaptive significance of polarity in these bacteria.
With one caveat:

There are reasons to believe the behavior of magneotactic bacteria in situ could differ from behavior in the laboratory. Magnetotactic bacteria at the chemocline of a stratified water column rarely, if ever, experience atmospheric oxygen levels like those in the standard laboratory assay for polarity. They also experience chemical gradients (particularly of iron and sulfur species) not present in a drop of water exposed to air in the laboratory assay.

The article, published in the January 20th edition of Science can be found here

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9 Responses

  1. Ah, you know this is the topic close to my heart….as I commented profusely on your old blog post about it. I will check out the paper for the new stuff. Cool!

  2. Yup! What I found particularly interesting was how difficult they are to study in lab conditions.

  3. But, would you call this a sensory system? No nerves involved, after all. No possibility of centrifugal modulation, either.

  4. I happened across your blog and just wanted to say I am the lead author on the magnetotactic paper you describe. MB are always surprising us and every time we look at a sample, we see something new. It’s definitely a challenge to apply their behavior in the lab to conditions in the environment. Feel free to email me with any questions.

  5. Coturnix – That is a good question, that I must confess I do not know the answer to.
    Greigite – Thanks for stopping by. I hope I did justice to your paper (it is a long way from anthropology)…

  6. It’s so cool when you comment on someone’s work and the author of the work comments on your blog.

  7. It has only happened to me a couple of times and it always shocks me a little when it does happen. Definately cool!

  8. hi again, just wanted to reply and say that you did a great job describing the paper. I find it cool that other people get interested in the same things I do.

  9. This post and the last one (linked to above)pretty much sum up my knowledge of the subject, so it’s really not a subject I know much about…Like Coturnix, though, I find magnetic bacteria really fascinating.

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