Monday, November 21, 2005

Magnetic Bacteria

The above is a picture of Magnetospirillum gryphiswaldense a unique type of bacteriathat is magnetotactic. That is it uses the earth's magnetic field to find suitable environmental conditions. How does it work? Well, Magnetospirillum absorb large amounts of iron to produce an oxide called magnetite. The magnetite is formed into magnetosomes which are strung out in a chain.

This raises two interesting questions. First, what are the genetics behind it? Second, how does the bacteria accomplish this? The two questions are related. Researchers, at the Max Planck Institute, first focused on identifying the part of the DNA that carried the code for magnetosome formation. They found a fragment containing about 25-30 different magnetosome genes. One gene had a product (MamJ) that was similar to proteins that control crystallization processes in bones, teeth and mussel shells among others. Once this gene was removed they discovered something interesting.

The picture on the left shows normal bacteria, the one on the right shows mutant bacteria with the Mamj gene disabled. Notice the magnetosomes form a straight chain in the normal but are clumped in the mutant. What was going on here? Researchers then used a relatively new technique called cyroelectron tomography to examine the magnetosome chain in more detail. This is what they saw:

The blue is cell membrane, the red are the magnetosomes, the green is a previously unknown filamentous structure (resembling a cytoskeleton)and the yellow is the MamJ product. Apparently, the MamJ product develops on the magnetosome and the filament and this is what allows them to form a chain. In the mutant bacteria, which lacks the MamJ, the magnetosomes clump toghether one they reach a certain size. This is fascinating, but there is an interesting evolutionary wrinkle. Some organisms, such as salmon and homing pidgeons, also orient themselves to magnetic fields. Interestingly, they also have magnetite chains in some of their tissue and may develop through similar mechanisms. I eagerly await further developments.

For more info:

Science Daily

The Press Release (where some of the pics and info for this post came from)

Magneto-Lab: Research(where some of the pics and info for this post came from)

The Research is also being published in Nature, Advanced Online Publication, November 20, 2005