Genetic analysis of magnetic bacteria

Magnetospirillum sp. AMB-1 is a freshwater magnetic bacterium which synthesizes intracellular particles of magnetite (Fe₃O₄). Agenomic DNA fragment required for synthesis of magnetic particles was previously isolated from a nonmagnetic mutant. We have determined the complete nucleotide sequence of this fragment. The 2975 bp region contains two putative open reading frames. One ORF, designated magA, encodes a polypeptide which is homologous to the cation efflux proteins, the Escherichia coli potassium ion translocating protein, KefC. Inverted vesicles prepared from Escherichia coli cell membrane, in which the MagA protein was expressed, exhibited iron accumulation ability. We consider that the MagA protein is an iron transport protein involved in the synthesis of magnetic particles in AMB-1. Intracellular localization of the MagA protein was studied using magA-luc fusion proteins. 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.