Identification of iron transporters expressed in the magnetotactic bacterium Magnetospirillum magnetotacticum.

The magnetotactic bacterium Magnetospirillum magnetotacticum MS-1 mineralizes the magnetite (Fe(3)O(4)) crystal and organizes a highly ordered intracellular structure, called the magnetosome. However, the iron transport system, which supports the biogenesis of magnetite, is not fully understood. In this study, we first identified the expressions of both the ferric and the ferrous iron transporter proteins in M. magnetotacticum. The cellular protein compositions of ferric and ferrous iron-rich cultures were examined using two-dimensional electrophoresis. According to the gel patterns, two outer-membrane ferric-siderophore receptor homologues were identified as proteins strongly induced in the ferrous iron-rich condition. Also, we identified for the first time that the ferrous iron transport protein, FeoB, is expressed in the M. magnetotacticum cytoplasmic membrane using immunoblotting.