TABLE 1.

Synopsis of genes known to control magnetosome biosynthesis in magnetotactic spirilla^a

Genes	Affected function upon deletion
mamA (“mms24”), mamB, mamQ/mamQ-like	Vesicle formation
mamC (“mms13”), mamD (“mms7”)/mamD-like, mamE/limE/mamE-like, mamF/mamF-like, mamG, mamH, mamI, mamL/mamL-like, mamM, mamN, mamO/limO, mamP, mamR, mamS, mamT, mamX, mamZ, mms5, mms6, mms36, mms48, mmsF, mmxF, feoB1, feoB2, ftsZm, feR5, feR6, amb411	Iron transport/magnetite biomineralization and crystal size control
mamJ/limJ/mamJ-like, mamK/mamK-like, mamY	Magnetosome chain formation, localization and dynamics
mamU, mamV, mamW, mms5	Uncertain
nap, nirS, nirN, norC, norB, fnr, cbb3, fur (not magnetosome island encoded)	Redox balance or iron homeostasis

^aAll essential and most of the accessory genes cluster in a genomic island (“magnetosome island”). A few genes have been identified and named twice, such as mamA/mms24. The “-like” genes are restricted to M. magneticum and have been identified as paralogs of the respective mam genes in a genomic “islet” of this organism. This redundancy is partially responsible for some differences in deletion mutant phenotypes of M. gryphiswaldense and M. magneticum. In other MTB, homologs for most of the mam and mms genes have been detected as well. However, with increasing phylogenetic distance to magnetospirilla, distinctive genes occur such as mad genes in greigite mineralizing Deltaproteobacteria or man genes in Nitrospirae. Moreover, some gene functions are redundant and some deletion phenotypes are pleiotropic so that unique functions cannot yet be assigned to all of the listed genes (for example, MamB plays a crucial role in vesicle formation but also in iron transport [47]). Biomineralization phenotypes owing to nap, nir, nor, fnr, cbb3, and fur deletion are likely an indirect effect of perturbed cellular redox balance or iron homeostasis. Products of further genes (not listed) have been found associated with magnetosomes (43), but their significance is not yet clear.