Every eukaryotic organism has its own microbiota which exerts major physiological and developmental influences on the host. The microbial-algal associations are recognized as meta-organisms or holobionts: a functional unit of eukaryotic cells and microorganisms. Better understanding into the microbiota associated with macroalgae has been obtained recently; however, these studies are focused mainly in green macroalgae. In this thesis, the symbiotic relationship between the brown algal model Ectocarpus sp. and its associated microbiota was studied.
This work highlights the critical role of bacteria on reproduction, growth and development of Ectocarpus sp. Although the mechanisms involved in these interactions were not deciphered, the results suggest that some kind of communication seems required to display the effects recorded during the experiments. Bacterial effect on the algal physiology was also remarkable since one single bacterial isolate triggered major change in the algal exometabolomic profile.
The second part of the thesis shows that cytokinins produce the same effect on algal development than bacterial isolates.
Finally, the thesis describes bacterial communities associated to cultured and wild Ectocarpus. It was established that culture conditions of Ectocarpus impose pressures that shape bacterial communities more than other variables, such as algal geographic location. The predicted functional similarity between bacterial communities points out to ecological redundancy among microbial taxa.
Altogether, this thesis presents a general view of the interaction between Ectocarpus sp. and its associated microbiota. The results from this study highlight the relevance of bacteria to their macroalgal partners, extending the current knowledge on eukaryote-bacteria interactions.