Magnetotaxis in an anaerobic ciliate via tripartite syntrophy.

Authors

Mitali Chitnis, Leon Kaub, Peter Vďačný, Lisa M Beiers, Sebastian Sturm, Ömer K Coskun, Daniel B Mills, Gonzalo V Gomez-Saez, Larissa Mengue, Klaus-Dirk Gottschaldt, Stuart A Gilder, Tomáš Obert, Ivan Rurik, Elena V Sturm, William D Orsi

Published in

Proceedings of the National Academy of Sciences of the United States of America. Volume 123. Issue 30. Pages e2609513123. Jul 28, 2026. Epub Jul 20, 2026.

Abstract

Magnetotaxis has evolved independently numerous times in bacteria, whereby genetically controlled biomineralization of nano-crystalline magnets results in swimming along Earth's magnetic field lines. Compared to magnetotactic bacteria (MTB), evolutionary mechanisms of magnetotaxis as a trait in eukaryotes remain poorly understood. Here, we report a magnetotactic ciliate, Tropidoatractus magnetotacticus sp. nov., that acquires magnetotaxis via syntrophy. T. magnetotacticus exhibits magnetotaxis due to the magnetic moment of internal ferrimagnetic magnetite (Fe₃O₄) nanoparticles forming ellipsoidal "necklace-shaped" parallel chains. Electron microscopy revealed T. magnetotacticus hosts numerous internal rod-shaped bacteria containing these magnetosome chains. Consistent with this, a genomic population of MTB (Thermodesulfobacteriota) in magnetically sorted T. magnetotacticus cells was found that encoded and expressed a magnetosome gene cluster responsible for magnetosome Fe₃O₄ biomineralization closely related to that of the ectosymbiont "Candidatus Desulfarcum epimagneticum." T. magnetotacticus also housed a second genomic population affiliated with the endosymbiotic methanogen Methanoregula. Metatranscriptomes of sorted T. magnetotacticus cells show eukaryotic hydrogenosomal Fe-hydrogenase gene expression, and expression of genes encoding proteins in an electron transport chain indicative of H₂-producing mitochondria-related organelles. Active gene expression of energy metabolism pathways indicates a tripartite syntrophic network whereby anaerobic fermentation products from T. magnetotacticus are consumed by two syntrophic partners: MTB producing the magnetosome chains and hydrogenotrophic methanogens. Our findings show how magnetotaxis can emerge as a trait in eukaryotes via syntrophic cooperation.

PMID:
42475569
Bibliographic data and abstract were imported from PubMed on 21 Jul 2026.

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