Backseat drivers: A symbiosis between magnetotactic bacteria and protists

Currently, no study has yet shown that microbial eukaryotes possess magnetotactic mechanisms. However, Monteil et al. (2019) revealed that, through a fascinating symbiosis, some protists are capable of indirectly utilising this ability.

Anoxic marine sediment samples taken from the Mediterranean, San Francisco Bay and New Zealand underwent magnetic enrichment. This resulted in the attraction of a group of flagellated protozoans, identified as Symbiontida. Upon closer inspection, their surfaces were found to be covered with magnetosome-containing Deltaproteobacteria – known as magnetotactic bacteria. Whilst magnetotactic bacteria are often classified as being motile, genomic analysis revealed that these lack genes coding for flagellar proteins or chemotaxis. A further phylogenetic tree analysis indicates that these two species have a congruent evolution and diversification. Through this coevolution and resulting mutualistic symbiosis, it seems that the bacteria have lost their own motility, with this instead being provided by the flagellated host protist. In turn, the protist ‘gains’ magnetotaxis from the ectosymbiotic bacteria, potentially improving their navigational abilities. Furthermore, they may benefit from syntrophy, transferring hydrogen-based products amongst themselves. This is an exceptional case of symbiosis allowing for eukaryotic magnetoreception, however, the mechanisms through which this occurs, and its potential benefits, remains to be explored in depth.

Monteil, C., Vallenet, D., Menguy, N., Benzerara, K., Barbe, V., Fouteau, S., & Cruaud, C., & Floriani, M., Viollier, E., Adryanczyk, G., Leonhardt, N., Faivre, D., Pignol, D., Lopez-Garcia, P., Weld, R., & Lefèvre, C. (2019). Ectosymbiotic bacteria at the origin of magnetoreception in a marine protist. Nature Microbiology, 4, 1088–1095.