Humans, animals, plants and single-celled organisms use small biomolecules as signaling substances to send messages or trigger reactions. "Microorganisms produce a variety of such substances, and we are just beginning to understand this language," says Axel Brakhage, director of the Leibniz Institute for Natural Product Research and Infection Biology and professor at Friedrich Schiller University Jena. He and his research group have found that representatives of the bacterial genus Streptomyces are particularly capable of communication.

Triggers of symbiosis, shape change and biofilm formation

The widespread soil bacterium produces a variety of different arginoketides. On the one hand, these natural substances are often potential antibiotics or effective against cancer cells. On the other hand, it has been shown that these substances produced by many organisms often trigger reactions in other organisms that are not otherwise observed there: A fungus suddenly enters into a symbiosis with a green alga, another fungus changes its shape, or a bacterium suddenly forms a biofilm.

"In previous studies, we have already seen that the fungus Aspergillus nidulans produces some substances only in the presence of streptomycetes," reports Maria Stroe, first author of a study on this topic in the journal Nature Micobiology. Behind this was the arginoketide azalomycin F. In further experiments, other arginoketides of the bacterium also led to unusual reactions of the fungus. "We therefore suspected that we may have found a general mechanism of microbial communication," concludes Lukas Zehner, who was also involved in the study.

Approach to biological plant protection

The observed effect is not limited to A. nigulans. In the presence of Streptomyces iranensis, a variety of fungi form biomolecules that they do not otherwise produce. When the researchers genetically prevented the bacterium from producing arginoketides, the fungal responses failed to materialize.

"We are now trying to understand what effects the production of arginoketides itself and also the substances then produced in a second wave by fungi have on the composition of microbial communities, the microbiomes," explains study leader Brakhage. In addition to theoretical understanding of microbial communities and evolution, this could also have practical benefits: Among other things, A. nigulans inhibits a fungus that is the causative agent of a plant disease. Perhaps this is an approach for biological plant protection.

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