Proteomic analysis of irregular, bullet-shaped magnetosomes in the sulphate-reducing magnetotactic bacterium Desulfovibrio magneticus RS-1

Recent molecular studies on magnetotactic bacteria have identified a number of proteins associated with bacterial magnetites (magnetosomes) and elucidated their importance in magnetite biomineralisation. However, these analyses were limited to magnetotactic bacterial strains belonging to the α-subclass of Proteobacteria. We performed a proteomic analysis of magnetosome membrane proteins in Desulfovibrio magneticus strain RS-1, which is phylogenetically classified as a member of the δ-Proteobacteria. In the analysis, the identified proteins were classified based on their putative functions and compared with the proteins from the other magnetotactic bacteria, Magnetospirillum magneticum AMB-1 and M. gryphiswaldense MSR-1. Three magnetosome-specific proteins, MamA (Mms24), MamK, and MamM, were identified in strains RS-1, AMB-1, and MSR-1. Furthermore, genes encoding ten magnetosome membrane proteins, including novel proteins, were assigned to a putative magnetosome island that contains subsets of genes essential for magnetosome formation. The collagen-like protein and putative iron-binding proteins, which are considered to play key roles in magnetite crystal formation, were identified as specific proteins in strain RS-1. Furthermore, genes encoding two homologous proteins of Magnetococcus MC-1 were assigned to a cryptic plasmid of strain RS-1. The newly identified magnetosome membrane proteins might contribute to the formation of the unique irregular, bullet-shaped crystals in this microorganism.