Regardless of their morphology, all MTB studied so far are motile by means of flagella and are gram-negative bacteria of various phyla. Despite the majority of known species' being proteobacteria, e.g. Magnetospirillum magneticum an alphaproteobacterium, members of various phyla possess the magnetosome gene cluster, such as Candidatus Magnetobacterium bavaricum a Nitrospira.[24] The arrangement of flagella differs and can be polar, bipolar, or in tufts.