Mad28, a conserved actin-like protein in deep-branching magnetotactic bacteria, exhibits cell curvature-dependent localization.

Magnetotactic bacteria (MTB) synthesize magnetic bacterial organelles called magnetosomes, which enable them to navigate along the geomagnetic field in aquatic environments. The actin-like cytoskeletal protein MamK forms filaments that associate with magnetosomes and mediate their positioning. Interestingly, in seven phyla, including IMPORTANCE: Bacteria are capable of precisely positioning nanosized, membrane-enclosed organelles within their limited cellular spaces. This study shows that two distinct actin-like proteins contribute to magnetosome positioning through separate mechanisms in deep-branching magnetotactic bacteria. This contrasts with the evolutionary strategy observed in eukaryotic cells, where a single actin protein performs multiple functions. Furthermore, the findings suggest that the protein Mad28 is involved in sensing membrane curvature, introducing a novel functional property for bacterial actin-like proteins. These findings offer new insights into the role of the cytoskeleton in organelle positioning within micron-scale bacterial cells.