( c field sensor function was disrupted; ...)Bacteria which sense the Earth's magnetic field

c field sensor function was disrupted; the cells could only orient themselves weakly in the magnetic field. Inspection by an electron microscope showed that the mutants' magnetosome crystals did not build a perfectly organised linear chain -- as the wild type's did -- but rather clumped together into irregularly arranged clusters. (see image 1)

The scientists genetically marked the MamJ protein with the fluorescent reporter protein GFP ("green fluorescent protein") and could thus track the fusion protein in the living bacteria cells. As they suspected, the protein was associated with the magnetosome chain. But microscopy made it apparent that MamJ arranges itself along a filamentous structure which trails like a string through the entire cell. In looking for this structure, the researchers used a new electron microscopic method which was developed in the Department of Molecular Structural Biology at the Max Planck Institute of Biochemistry, and which has already helped shed light on many cellular structures and functions.

Cyroelectron tomography makes it possible to analyse structures in detail inside an intact, shock-frozen cell (minus 196 degrees celsius), and to display them in three dimensions, at a resolution of just a few nanometres. In Dr Jürgen Plitzko's research group in Martinsried, Manuela Gruska's doctoral work involved investigating magnetic bacteria cells using this technology, and comparing the wild type with the MamJ mutants. She was able to make visible not only the magnetite crystal, but also the surrounding membrane vesicle, in a resolution never achieved before.

Amazingly, the scientists saw a previously unknown filamentous structure along the magnetosome chain of the wild type cells. It resembled a similar structure which structural biologists from Martinsried had already imaged in three dimensions in other cells. This shed light on the crux of the problem with the magnetosome chain: although in the wild type, the magneto
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Source:Max-Planck-Gesellschaft

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