AN IRON-REGULATED GENE, MAGA, ENCODING AN IRON TRANSPORT PROTEIN OF MAGNETOSPIRILLUM SP STRAIN AMB-1

Magnetospirillum sp. AMB-1 is a freshwater magnetic bacterium which sy nthesizes intracellular particles of magnetite (Fe3O4). A genomic DNA fragment required for synthesis of magnetic particles was previously i solated from a nonmagnetic transposon Tn5 mutant, We have determined t he complete nucleotide sequence of this fragment. The 2975-base pair r egion contains two putative open reading frames. One open reading fram e, designated magA, encodes a polypeptide which is ho homologous to th e cation efflux proteins, the Escherichia coli potassium ion-transloca ting protein, KefC, and the putative Na+/H+-antiporter, NapA, from Ent erococcus hirae. Northern hybridization demonstrated that the magA mRN A transcript is 1.3 kilobases in size, corresponding to the size of th e magA gene, A functional promoter was located upstream from the magA gene, and the transcription in AMB-I was regulated by environmental ir on concentration, Vesicles isolated from E. coli in which the MagA pro tein was expressed exhibited iron accumulation ability. We consider th at the MagA protein is an iron transport involved in the synthesis of magnetic particles in AMB-1.