Practice question

Magnetosomes function as magnetoreceptor enabling magnetotaxis, not oxygen sensing or nutrient storage. Each magnetosome contains single domain crystal magnetite Fe3O4 35-120 nm with stable magnetic moment. Chain arrangement gives permanent magnetic dipole moment causing whole bacterium to behave as compass needle aligning with Earth's magnetic field inclination. This alignment simplifies navigation in stratified aquatic habitats where oxygen and sulfide gradients vertical. By swimming aligned with field lines, bacteria efficiently reach oxic anoxic interface where metabolism optimal microaerophilic respiration using oxygen as terminal acceptor while avoiding higher toxic oxygen tension and still accessing reduced sulfur compounds. Behavior termed magneto-aerotaxis combines magnetotactic alignment passive, chemotactic active sensing via Aer receptors. Mutants lacking magnetosome chain show random swimming impaired in gradient tubes. Magnetosome production energetically costly requiring iron uptake FeoB ferrous transporter, controlled precipitation via MamM MamB cation diffusion facilitators, Mms6 template. Hence function allow orientation along Earth's magnetic field facilitating vertical migration to preferred redox zone.