Magnetospirillum magnetotacticum MS-1

Magnetospirillum magnetotacticum, strain MS-1, is a Gram-negative, motile, microaerophilic spirillum, 0.5 x 5 microns, belonging to the alpha-subdivision of the proteobacteria. It was first isolated from pond water by R. P. Blakemore in 1975. Its most interesting property is that it forms single-domain crystals of the iron mineral magnetite (Fe3O4). Each crystal is enclosed in a membrane and is called a magnetosome. The crystals are arranged in long chains keeping the north/south orientation so that the whole structure functions as a bar magnet and causes the organism to exhibit magnetotaxis. Specifically, it is thought to follow the magnetic field lines of the earth downward to regions favorable to growth. Since Blakemore's discovery many other magnetotactic bacteria, with different morphologies and producing different magnetic minerals, have been observed in both fresh and salt water environments, although relative few have been cultured.

There is considerable interest in understanding both the mechanism by which the organism synthesizes magnetite and the crystalline structure of the magnetite product. Biologically it is studied as a possible model for the process of biomineralization and for its role in the evolution of the magnetotactic response in higher organisms. It is of geological interest for its contribution to the magnetization of sediments and for its potential as a geobiological tracer, since it leaves a detectable fossil remain. Finally, because of the exceptionally fine quality of its single-domain magnetic crystals, the product, magnetite, has many practical uses. Commercial uses include magnetic tapes, magnetic targeting of pharmaceuticals, cell separation, and applications in magnetic resonance imaging.

According to recent genetic studies, the genome of MS-1 is a 4.3 Mb circle and three of the genes that might be involved in magnetite synthesis have been mapped so far. Information from a total genome sequence would greatly accelerate the identification of additional genes that might be involved and suggest other candidates for further investigation. In addition, knowledge of the over-all arrangement of the genes would allow us to determine if, for example, they are organized into a cassette that could be transferred to other organisms. Finally, a complete sequence will permit comparisons with the total genomes of other magnetotactic organisms, as they become available, and further aid in defining the regions and genes essential for magnetite biomineralization.