A network of coiled-coil and actin-like proteins controls the cellular organization of magnetosome organelles in deep-branching magnetotactic bacteria

Abstract

Magnetotactic Bacteria (MTB) are a diverse group of microorganisms that use magnetosomes, organelles composed of magnetite or greigite, to navigate along geomagnetic fields. While MTB span several phyla and exhibit diverse phenotypes, magnetosome formation has been mechanistically studied in only two species of Alphaproteobacteria. Here, we use Desulfovibrio magneticus RS-1 to uncover the mechanisms behind tooth-shaped magnetosome assembly in deep-branching MTB. Our findings show that magnetic particles in RS-1 initially form randomly within the cell before localizing to the positive cell curvature. Genetic and proteomic analyses indicate that early biomineralization involves membrane-associated proteins found in all MTB, while later stages depend on coiled-coil (Mad20, 23, 25, and 26) and actin-like (MamK and Mad28) proteins, most of which are unique to deep-branching MTB. These findings suggest that while biomineralization originates from a common ancestor, magnetosome chain organization has distinct evolutionarily origins among different MTB lineages.