Prof. Dr. Sebastian Fraune, Heinrich Heine University Düsseldorf

From Immunity to Adaptation: Microbiome Control in a Sea Anemone

Marine invertebrates are continuously exposed to highly diverse microbial communities, making them powerful models for studying host–microbe interactions. In my talk, I will present our work on the sea anemone Nematostella vectensis to uncover mechanisms that govern bacterial recognition, microbiome establishment, and host adaptation. We show that host colonization is not a passive process but is controlled by selective innate immune responses mediated by specialized phagocytic cell clusters, the nematosomes. These immune structures preferentially eliminate foreign bacteria while permitting colonization by native strains, thereby shaping microbiome composition. Using genetic and functional approaches, we identify the transcription factor cJUN as a key regulator of this selective phagocytosis and microbiome homeostasis. Beyond host control of bacterial membership, we explore how microbial colonizers contribute to host acclimation and adaptation to environmental stress. Given the rapid pace of climate change, genetic adaptation alone may be insufficient for long-lived organisms. Our results support the concept that the microbiota provides a mechanism for rapid, flexible adaptation, highlighting the holobiont as a critical unit of resilience in changing marine environments.