Abstract
Magnetoreception is a remarkable ability found across a diverse range of organisms, including bacteria, birds, fish, insects, and mammals, enabling them to detect and harness the Earth’s geomagnetic field. Recently, the recruitment of biomineralizing ectosymbionts by euglenozoans was evidenced as an ecological strategy for microeukaryotes to acquire this sense. Here, we report a case of magnetosymbiosis involving a ciliate and four populations of endosymbiotic bacteria experiencing genome reduction. Among these bacteria, one group of sulphate-reducing Desulfovibrionales was found to biomineralize bundles of bullet-shaped magnetite crystals. The ciliate’s magnetotaxis mirrors that of free-living magnetotactic bacteria and euglenozoans, enabling efficient navigation in chemically stratified aquatic environments. However, in this case, magnetotaxis arises from an endosymbiotic interaction. Using a combination of optical-, confocal-, electron- and X-ray-based microscopy techniques, together with genomic analyses, these findings demonstrate that magnetosymbiosis can emerge in unicellular eukaryotic lineages through endosymbiotic integration, expanding our understanding of such interactions in aquatic ecosystems. More broadly, this work contributes to the ongoing debate on the origins of magnetoreception in eukaryotes.
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Data availability
Data generated or analyzed during this study are included in this published article and its Supplementary Information and Description of Additional Supplementary Files. The sequencing data were deposited on public databases. The 16S rRNA gene amplicon sequences have been deposited in the NCBI Genbank database under the accession numbers OR342250-OR342267, OR294250-OR294271, OR250250-OR250289, OR294289-OR294298, and OR294333-OR294370. The genome assemblies were deposited in the NCBI BioProject database under the accession number PRJEB65892.
Code availability
Scripts are available at: https://github.com/labgem/metacoco124.
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Acknowledgements
This work was supported by the French National Research Agency (SymbioMagnet ANR-21-CE02-0034-01 and ANCESMAG ANR-20-CE92-0050) and the CNRS—mission pour les initiatives transverses et interdisciplinaires (MITI), adaptation du vivant à son environnement (SymbioAdapt project). R. Bolzoni's PhD contract was supported by the CNRS—MITI. This work benefited from access to ALBA and has been supported by iNEXT-Discovery, project number 2022025566, funded by the Horizon 2020 program of the European Commission. Synchrotron beamtime at ID16B of the European Synchrotron Radiation Facility (ESRF) is also acknowledged under proposal LS2983. We acknowledge the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) at CEA Cadarache for the access to the transmission electron microscope Tecnai G2 BioTWIN. This work received support from the French government under the France 2030 investment plan, as part of the Initiative d’Excellence d’Aix-Marseille Université—A*MIDEX, and is part of the Institute of Microbiology, Bioenergies and Biotechnology - IM2B (AMX-19-IET-006). We are grateful to the INRA MIGALE bioinformatics platform (http://migale.jouy.inrae.fr) for providing computational resources. The LABGeM (CEA/Genoscope & CNRS UMR8030), the France Génomique and French Bioinformatics Institute national infrastructures (funded as part of Investissement d’Avenir program managed by Agence Nationale pour la Recherche, contracts ANR-10-INBS-09, ANR-11-INBS-0013 and ANR-21-ESRE-0048) are acknowledged for support within the MicroScope annotation platform. F. Abreu acknowledges the Brazilian agencies CNPq, FAPERJ, CAPES, the microscopy facility CENABIO, and Dr. Jefferson Cypriano for their support in TEM observation. We thank Zoé Rouy for data submission to public databases. We thank Matthieu Amor, Tanguy Le Borgne, and Camille Bouchez for their help in sampling the aquatic environments in Britany.
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C.L.M., D.V., K.B., and C.T.L. designed the project, analyzed and interpreted the data. C.L.M., R.B., B.A., D.M.C., C.G., N.M., M.B., S.F., V.dC., F.S-P., E.P., A.D., D.V., C.C., F.A., K.B., and C.T.L. performed the experiments and interpreted the data. C.L.M. and C.T.L. prepared the manuscript.
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Bolzoni, R., Monteil, C.L., Alonso, B. et al. Magnetoreception in a freshwater ciliate arises from endosymbiosis. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70462-8
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DOI: https://doi.org/10.1038/s41467-026-70462-8
