Invertebrates can distinguish good from bad bacteria
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 systems of these animals can selectively distinguish between different microorganisms, protecting beneficial bacteria from harmful bacteria—an ability that has been attributed only to vertebrates to date. So-called "nematosomes" play an important role in this process.
The innate immune system is considered the first line of defense against pathogens. According to conventional wisdom, it reacts immediately but largely nonspecifically to infecting microorganisms. By contrast, the adaptive immune system of vertebrates can discriminate between beneficial and harmful bacteria. This is because only the adaptive immune system has antibodies and memory cells trained through contact with pathogens over an animal's lifetime.
In the study published in Nature Communications, a research team led by Dr. Sebastian Fraune of the HHU Institute of Zoology and Organismic Interactions, in collaboration with colleagues from Kiel University (CAU), established that this view needs to be updated. The researchers proved that even the sea anemone Nematostella vectensis—an animal that represents an early branch in animal evolution—can selectively distinguish between microorganisms, although it possesses only 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 largely sparing bacteria that naturally belong to and benefit the sea anemone—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 scissors CRISPR/Cas, the researchers switched off this gene. The modified sea anemones produced significantly fewer nematosomes and lost the ability to reliably distinguish between non-native bacteria and their 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 was 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."
Fraune said, "The ability to identify microorganisms on a selective basis is thus likely to be significantly older than assumed to date and developed early in the evolution of these animals. This study provides 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 of the extent of the innate immune system's capabilities. The sea anemone is a good model system for decoding fundamental principles of immunobiology that may have been preserved in many animal groups up to the present day.
Fraune said, "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. Because the cells can differentiate between closely related bacterial strains and their activity is controlled by cJun, future research can focus on the signaling pathways that underlie improved recognition of microorganisms.
Publication details
N. H. Kaya et al, c-JUN controls microbial colonization via selective phagocytosis in the sea anemone Nematostella, Nature Communications (2026). DOI: 10.1038/s41467-026-75511-w
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Citation: Invertebrates can distinguish good from bad bacteria (2026, July 16) retrieved 16 July 2026 from https://phys.org/news/2026-07-invertebrates-distinguish-good-bad-bacteria.html
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