Fig. 4

Two models for the evolution of magnetotaxis in the domain Bacteria. a The last universal common ancestor of magnetotactic bacteria (LUCA MTB) was a magnetite (Fe₃O₄)-producing MTB present as the ancestor of each of the Proteobacteria, Nitrospirae, and Omnitrophica phyla. Multiple independent instances of MGC loss then ensued in each phylum or class. The Fe₃O₄-type MGC was duplicated and one diversified to a greigite (Fe₃S₄)-type MGC in the Deltaproteobacteria. The Fe₃S₄-type MGC is hypothesized to have been transferred to Latescibacteria and Planctomycetes. These transfer events must have occurred early because of the large phylogenetic distance between Fe₃S₄ magnetosome proteins of Deltaproteobacteria and the Latescibacteria and Planctomycetes phyla (Fig. 3b). b In the second hypothesis the LUCA MTB contained an unknown type of ancient MGC, which was duplicated and diverged to generate both Fe₃O₄- and Fe₃S₄-type MGCs in the last common ancestor of the Proteobacteria, Nitrospirae, Omnitrophica, Latescibacteria, and Planctomycetes phyla. Multiple instances of MGC loss then occurred during evolution, with some lineages losing both clusters while others retained one or two types. For both hypothetical scenarios, vertical inheritance followed by multiple independent MGC losses is considered to be the major force that drove evolution of magnetotaxis, although recent horizontal transfers of MGCs might have occurred within some classes, genera (e.g., Magnetospirillum), or species