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Marine biology: Publication in Nature Communications
Researchers from Heinrich Heine University Düsseldorf (HHU) and Kiel University (CAU) have examined immune system function in an early branching animal – a sea anemone. They discovered that the immune system of these animals is capable of selectively distinguishing between different microorganisms and thus protecting beneficial over harmful bacteria – an ability, which has only been attributed to vertebrates to date. So-called “nematosomes” play an important role in this, as the researchers now describe in the scientific journal Nature Communications. The findings emerged from work in the Collaborative Research Centre CRC 1182.
The innate immune system is seen as the first line of defence against pathogens. According to conventional wisdom, it reacts immediately, but largely non-specifically to infecting microorganisms. By contrast, the adaptive immune system of vertebrates is able to discriminate between beneficial and harmful bacteria. This is because only the adaptive immune system has antibodies and memory cells, which are trained by contact with pathogens over the lifetime of the animal.
In the study that has now been published in Nature Communications, a research team headed by Professor Dr Sebastian Fraune from the HHU Institute of Zoology and Organismic Interactions has now established in collaboration with colleagues from Kiel University (CAU) that this view needs to be updated. The researchers proved that even the sea anemone Nematostella vectensis – an animal that represents an early branch of animal evolution – can selectively distinguish between microorganisms although it only possesses an innate immune system.
The study focused on motile multicellular bodies inside the sea anemone – so-called nematosomes. The researchers showed that these structures preferentially engulf and break down non-native bacteria, while they largely spare bacteria, which naturally belong to the sea anemone and are beneficial for it – its “microbiome”. In this way, the nematosomes contribute to maintaining a stable and healthy microbial community.
The cJun gene plays a key role in controlling nematosome function. Using the genetic scissor CRISPR/Cas, the researchers explicitly switched off this gene. The modified sea anemones produced significantly fewer nematosomes and lost the ability to distinguish reliably between non-native and their body’s own bacteria. This resulted in a microbiome imbalance and the animals became more susceptible to bacterial infections.
Dr Nida Kaya is the lead author of the study and the research formed the focus of her doctoral studies: “Our findings show that the targeted identification of microorganisms is not a privilege restricted to the adaptive immune system. Rather, even invertebrates already possess sophisticated mechanisms for supporting beneficial microorganisms and selectively controlling potentially harmful bacteria.”
Professor Fraune adds: “The ability to identify microorganisms on a selective basis is thus likely to be significantly older than assumed to date and already developed early on in the evolution of these animals. This study thus supplies important new findings about the evolutionary origins of the immune system. It shows how animals have maintained a balance between beneficial microorganisms and pathogens for hundreds of millions of years.”
The study offers new perspectives for research into the innate immune system and its evolutionary development. At the same time, it raises the question as to the extent of the innate immune system’s capabilities. The sea anemone represents a good model system for decoding fundamental principles of immunobiology, which may have been preserved in many animal groups up to the present day.
Professor Fraune: “The so-called immunological memory of invertebrates is particularly interesting in this context. Once they have encountered certain pathogens, they seem to be able to respond more quickly or effectively to repeated contact, even without an adaptive immune system. This phenomenon is referred to as ‘trained immunity’ or innate immune memory.”
The nematosomes described in the study represent a promising model system for examining the cellular and molecular mechanisms of such memory effects. As the cells can differentiate between closely related bacterial strains and their activity is controlled by cJun, future research can focus explicitly on the signalling pathways, which form the basis for improved recognition of microorganisms.
CRC 1182 “Origin and Function of Metaorganisms”
The Collaborative Research Centre “Origin and Function of Metaorganisms” is an interdisciplinary network involving around 80 researchers that investigates the interactions of specific microbial communities with multicellular host organisms. It is supported by the German Research Foundation (DFG) and deals with the question of how plants and animals, including humans, form functional units (metaorganisms) together with highly specific communities of microbes.
The aim is to understand why and how microbial communities enter into these long-term connections with their host organisms and what functional consequences these interactions have. CRC 1182 brings together scientists from Kiel University (CAU), the GEOMAR Helmholtz Centre for Ocean Research Kiel, the Max Planck Institute for Evolutionary Biology in Plön, Heinrich Heine University Düsseldorf, the Leibniz Institute for Science and Mathematics Education, and the Muthesius University of Fine Arts and Design in Kiel.
N. H. Kaya, M. Abukhalaf, G. Fuentes, J. Taubenheim, U. Hentschel, A. Tholey & S. Fraune; c-JUN controls microbial colonization via selective phagocytosis in the sea anemone Nematostella; Nat Commun 17, 6087 (2026)
DOI: 10.1038/s41467-026-75511-w
The sea anemone Nematostella vectensis. In the enlarged section, the nematosomes – which are key to ...
Copyright: HHU/Nida Kaya
Images of a nematosome taken using a scanning electron microscope (left) and a confocal microscope ( ...
Copyright: HHU/Nida Kaya
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