How light affect the magnetotactic behavior and reproduction of ellipsoidal multicellular magnetoglobules?

Magnetotactic bacteria(MTB)synthesize intracellular magnetic organelles,magnetosomes,which consist of magnetic crystals that are enveloped in a membrane.Magnetosomes are organized into a chain(s)and confer on cells a magnetic dipolar moment.This magnetic property allows MTB cells to align and swim along geomagnetic field lines,a movement referred to as magnetotaxis.Some MTB species change their swim direction in response to illumination by UV,violet and blue light.Here we analyzed the polarity of morphology,magnetism,and motion in Mediterranean multicellular magnetotactic prokaryotes,also called,magnetoglobules or MMP.The magnetoglobules were assembled from 60-80 cells into an asymmetric ellipsoidal morphology with a relative narrow and large end.They swam dominantly northward,parallel to the direction of the magnetic field,with the narrow-end as the leading side.In response to a reversal in the direction of the magnetic field,they aligned quickly along the magnetic field lines and kept swimming northward.Interestingly,under constant illumination,385-nm UV light,magnetoglobules changed their swimming direction southward anti-parallel to the direction of the magnetic field,with the large-end as the leading side.The change from a northward to southward direction occurred along with an increase of swimming speed.A minimum of 35-mW/cm^(2) irradiance of UV light was sufficient to trigger the swimming re-orientation.UV radiation also triggered the unidirectional division of magnetoglobules.Together these results revealed a coordination of the polarity of magnetoglobule morphology,magnetic moment,and swimming orientation,in response to magnetic and optical stimuli.The UV triggered the reversal of magnetotaxis and magnetoglobule division indicating the ecological significance of light for multicellular magnetotactic prokaryotes.