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Submarine symbiosis: microorganisms that never get lost

A team of CEA-Biam has uncovered a symbiotic behavior between magnetism-using bacteria and eukaryotic microorganisms.

Published on 14 May 2019
Magnetoreception allows organisms to orient themselves and navigate along the lines of Earth’s magnetic field. We understand relatively well the cellular and biophysical processes involved in this function in some prokaryotic microorganisms, but much less in eukaryotic microorganisms. Magnetoreception in magnetotactic bacteria is due to ferromagnetic crystals bio-mineralized in micro-chambers called magnetosomes. Magnetoreception paired together with a chemotaxis system form the basis of magnetotaxis, which helps bacteria travel towards ideal zones for their growth. 

The CEA-Biam researchers found eukaryotic microorganisms with the same magnetotactic behavior as BMT in marine sediments. Using microscopy and genomic approaches, they showed that those organisms live in symbiosis with magnetic bacteria lacking a flagellum. Those bacteria completely cover the host and form an assembly called a holobiont. The micro-holobiont can orient itself thanks to the alignment of the bacteria, and their line of magnetosomes, on the eukaryotic cell’s axis of motion. The partners’ mutual and sustainable interaction relies on a double-edged cooperation, involving not only joint magnetotaxis, but also metabolic exchanges. Those notably depend on the exchange of molecular hydrogen produced by the protist’s organelles (hydrogenosomes), which could serve as an energy source for ectosymbiotic bacteria. 

This research on magnetotactic symbiosis has not only improved our view on the diversity of organisms sensible to Earth’s magnetic field, it also has deepened our knowledge of the ecologic strategies involved in microorganisms’ adaptation to their environment. Now the researchers wish to develop this research field to better understand the functional and evolutionary mechanisms involved in sensory cooperation between interacting species, and its role in their adaption to anoxic environments. 

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