( hereby summing their magnetic moments. ...)Bacteria which sense the Earth's magnetic field

hereby summing their magnetic moments. Only such a chain structure allows the magnetosomes to behave together like a compass needle which orients the bacteria inside the relatively weak magnetic field of the Earth. But until now, scientists did not know how magnetosome chains are formed.

The research group of Dr Dirk Schüler at the Max Planck Institute for Marine Microbiology has been investigating magnetosome formation in the magnetotactic bacterium Magnetospirillum gryphiswaldense, which the scientists found in the mud of a creek at Greifswald, in the northeast corner of Germany. Recently, the researchers were able to identify the part of the DNA that seemed to carry the entire genetic information required for formation and organisation of magnetosome particles. In this genomic fragment, known as a "magnetosome island", there are at least 25-30 different magnetosome genes, whose exact role had not been known in detail.

The researchers more closely investigated the magnetosome island and its function. They came across a gene, one of whose products (among other magnetosome proteins) is a component of the membrane that encloses every indivudual magnetite crystal. This protein, called MamJ, exhibits an unusually high portion of amino acids, aligned in repeats. MamJ has a remote similarity to proteins which control crystallisation processes in other biominerals, like bones, teeth, otoliths, and mussel shells. Thus, the scientists initially suspected MamJ is responsible for the development of magnetite crystals.

Although it is difficult to cultivate and manipulate Magnetospirillum gryphiswaldense in the laboratory, as part of his doctoral work André Scheffel succeeded in removing the relevant gene from the genome. In this way, mutant bacteria were created which were lacking the MamJ protein. The mutants, surprisingly, still developed magnetosome crystals, which resembled the wild type in shape, size, and number. But the sensitivity of the magneti
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Source:Max-Planck-Gesellschaft

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