Magnetoreception has only been described in magnetotactic bacteria. Monteil et al. now report a mutualistic symbiosis between excavate protists and ectosymbiotic Deltaproteobacteria, revealing an example of eukaryotic magnetoreception acquired by symbiosis. The researchers used a magnetic enrichment protocol on anoxic marine sediments and water in a dyked area sheltered from major currents and found that north-seeking magnetotactic bacteria were the dominant magnetically responsive organisms. They observed populations of atypical south-seeking organisms that were identified to be protists. Electron microscopy of the protists revealed that they were attached to rod-shaped bacteria containing magnetite particles (magnetic ectosymbiotic bacteria). The researchers propose a number of possible mutual benefits for the bacteria and protist, and state that elaborated syntrophy, in which metabolic exchange is enabled by the positioning of the consortium in optimal redox conditions, seems to be the ultimate basis of the symbiosis.
Monteil, C. L. et al. Ectosymbiotic bacteria at the origin of magnetoreception in a marine protist. Nat. Microbiol. https://doi.org/10.1038/s41564-019-0432-7 (2019)
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Kelsey, R. Magnetotactic symbiosis in marine sediments. Nat Rev Microbiol 17, 398 (2019). https://doi.org/10.1038/s41579-019-0210-9