Size, domain structure and phylogenetic tree of SPFH subfamilies. This figure shows the upper half, for the full image please see Additional file 3. (a) Schematic representation of sizes and domain structure of all identified SPFH subfamilies, as well as the accompanying NfeD proteins. (b) Phylogenetic tree of prokaryotic SPFH proteins. The tree was created using the most diverse members of each subfamily, after alignment with ClustalW. Tree creation was performed with MEGA 4 (BLOSUM matrix and Neighbor joining algorithm, 1000 bootstrap replications).