Plays a role in regulating magnetite crystal size; partially redundant function with MamF. Part of the probable mms6 operon. Intermediate magnetic response, slightly smaller magnetosomes. Double mamF-mmsF and double mms6-mmsF deletions have a normal magnetic response, slightly smaller, fewer magnetosomes (PubMed:24816605). Deletion of the 4 gene operon (mms6, mmsF, mms36 and mms48) gives an intermediate magnetic response with fewer, smaller magnetosomes in irregular pseudo-chains (PubMed:22043287, PubMed:24816605). 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)). Belongs to the magnetosome MamF/MmsF protein family. Extended N-terminus.