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.
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
Filed under: Bacteria