The invasive success of the green macroalga Caulerpa cylindracea has repeatedly been linked to an association with bacterial communities, emphasizing the need to consider the alga together with its bacterial symbionts as a dynamic entity or ‘holobiont’. To this end, we characterized the bacterial communities in the rhizosphere of C. cylindracea and assessed their stability under different environmental conditions. Although the rhizoid-associated communities were distinct from the ones found in the sediment, they harboured several bacterial groups that are commonly found in this habitat, including Desulfobacterales and Actinomycetales. Furthermore, results showed that the application of different abiotic stressors did not have a profound effect on bacterial diversity or community composition. Nonetheless, several bacteria were exclusively found on stressed algae, while others were consistently present under all conditions. These core bacteria mainly belonged to the order Desulfobacterales, which may provide a competitive advantage to this alga by inducing changes in sediment biogeochemistry. Moreover, our results provided the first indication that C. cylindracea may be able to partly shape the structure of its associated communities by using chemical metabolites. These findings raise the hypothesis that C. cylindracea increases its invasive potential by assembling bacterial communities providing ecologically relevant functions.
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