Essential for magnetosome formation (PubMed:13129949). Not essential for formation of magnetosome membrane vesicles. One of 7 genes (mamLQBIEMO) able to induce magnetosome membrane biogenesis; coexpression of mamLQRBIEMO in a deletion of the 17 gene mamAB operon restores magnetosome vesicle formation but not magnetite biosynthesis (PubMed:27286560). Tagged protein is more abundant in cell inner membrane, is visible as puncate spots all throughout inner and magnetosome membranes. Part of the probable 17 gene mamAB operon. No magnetic response, no magnetosomes, no iron crystals of any sort. MamC is mislocalized in punctate spots throughout the cell (PubMed:24816605). Magnetosome vesicles are fewer and smaller, sometimes align in a chain with the filament, only a few have very small crystals. Many other, possibly precursor magnetosome vesicles, are visible, some are attached to the cell inner membrane. MamI mislocalized to 1 to a few patches in most cells (PubMed:27286560). Deletion of approximately 80 kb of DNA, including this operon, leads to cells that are non-magnetic, lack internal membrane systems, grow poorly, have reduced mobility and take-up and accumulate iron poorly (PubMed:13129949). This bacteria makes up to 60 cubo-octahedral magnetosomes of about 45 nm in diameter which contain membrane-bound crystals of magnetite (Fe(3)O(4)). Expression of just the minimal mamAB gene cluster (MGMSRv2__2365 to MGMSRv2__2381), including this gene, is sufficient to form a minimal magnetosome chain with small magnetite particles. Belongs to the LemA family.