Recombinant host cells are provided. The cell genome contains heterologous gene expression cassettes capable of being expressed in the host cell, where the gene expression cassettes encode a nucleic acid sequence encompassing at least 80% of the full-length sequence of the mamAB operon, the mamGDFC operon, and the tmms6 operon of a magnetotactic alphaproteobacterium, respectively. The cells may further comprise gene expression cassettes capable of being expressed in the host cell, where the gene expression cassettes encode a nucleic acid sequence encompassing at least 80% of the full-length sequence of the mamXY operon and/or the feoABI operon of a magnetotactic alphaproteobacterium; where the recombinant host cell, upon expression of the gene expression cassettes in their entirety, is capable of producing magnetic nanoparticles. Preferably, the recombinant host cell is derived from Rhodospirillum rubrum. Methods of producing these recombinant host cells by genetic transposition are provided.