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Changing microbial activities during low salinity acclimation in the brown alga Ectocarpus subulatus

Hetty Kleinjan
  • Function : Author
Gianmaria Caliafano
  • Function : Author
Méziane Aite
  • Function : Author
Enora Fremy
  • Function : Author
Clémence Frioux
  • Function : Author
Elham Karimi
  • Function : Author
Thomas Wichard
Anne Siegel
Catherine Boyen
  • Function : Author


Summary Ectocarpus subulatus is one of the few brown algae found in river habitats. Its ability to tolerate freshwater is due, in part, to its uncultivated microbiome. We investigated this phenomenon by modifying the microbiome of laboratory-grown E. subulatus using mild antibiotic treatments, which affected its ability to grow in low salinity. The acclimation to low salinity of fresh water-tolerant and intolerant holobionts was then compared. Salinity had a significant impact on bacterial gene expression as well as the expression of algae- and bacteria-associated viruses in all holobionts, albeit in different ways for each holobiont. On the other hand, gene expression of the algal host and metabolite profiles were affected almost exclusively in the fresh water intolerant holobiont. We found no evidence of bacterial protein production that would directly improve algal stress tolerance. However, we identified vitamin K synthesis as one possible bacterial service missing specifically in the fresh water-intolerant holobiont in low salinity. We also noticed an increase in bacterial transcriptomic activity and the induction of microbial genes involved in the biosynthesis of the autoinducer AI-1, a compound that regulates quorum sensing. This could have caused a shift in bacterial behavior in the intolerant holobiont, resulting in virulence or dysbiosis. Originality-Significance Statement The importance of symbiotic microbes for the health and stress resistance of multicellular eukaryotes is widely acknowledged, but understanding the mechanisms underlying these interactions is challenging. They are especially difficult to separate in systems with one or more uncultivable components. We bridge the gap between fully controlled, cultivable model systems and purely environmental studies through the use of a multi-omics approach and metabolic models on experimentally modified “holobiont” systems. This allows us to generate two promising working hypotheses on the mechanisms by which uncultivated bacteria influence their brown algal host’s fresh water tolerance.
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hal-03429533 , version 1 (15-11-2021)



Hetty Kleinjan, Gianmaria Caliafano, Méziane Aite, Enora Fremy, Clémence Frioux, et al.. Changing microbial activities during low salinity acclimation in the brown alga Ectocarpus subulatus. 2021. ⟨hal-03429533⟩
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