Iron-regulated expression and membrane localization of the magA protein in Magnetospirillum sp. strain AMB-1.

The magA gene from Magnetospirillum sp. strain AMB-1 is required for the synthesis of bacterial magnetic particles (BMPs). This gene has been cloned, sequenced and found to encode a protein which is homologous to the Escherichia coli potassium efflux membrane-binding protein, KefC. By using the firefly luciferase gene (luc) cloned downstream of the magA promoter, the effect of iron on regulation of magA expression was investigated, and transcription of magA was found to be enhanced by low concentrations of iron. Intracellular localization of the MagA protein was studied using magA-luc fusion proteins. The luc gene was cloned downstream of the magA hydrophilic C-terminal domain. Detection of luciferase activity in the cytoplasm, cell membrane, and magnetic particle membrane subcellular fractions confirmed that the MagA fusion protein was localized in the cell membrane. The fusion protein was also detected on the surface of the lipid bilayer covering the magnetic particles. These results suggest that MagA is a membrane-bound protein, the expression of which is enhanced at low iron concentrations.