Large-Scale Microbiome Profiling of Brown Algae Identifies a Specific Vibrio aphrogenes Clade Strain That Promotes...

Marine macroalgae are foundation species of coastal ecosystems, maintaining close interactions with their microbiome for development and environmental adaptation. Although secure attachment to substrates is essential for both morphological development and survival, the potential causal link between microbial symbionts and this fundamental attachment process remains poorly understood. To address this gap, we integrated large-scale field sampling with functional validation to identify bacteria that influence the attachment of brown algae, specifically comparing attached and drifted individuals of Undaria pinnatifida and Ecklonia cava. Notably, Vibrio was consistently enriched in attached algae, whereas Marinomonas dominated drifted individuals. Translating these field observations into lab-scale validation, we isolated and evaluated their biofilm-formation capacity and impact on gametophyte settlement. A specific isolate belonging to the Vibrio aphrogenes clade exhibited superior biofilm formation and significantly enhanced algal abundance 2.57-fold in co-culture with U. pinnatifida gametophytes. These findings provide a scientific basis for developing bacterial inocula for seaweed seedling production and support broader macroalgae restoration strategies under changing environmental conditions.