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Fairytale intestines

In both ancient fairy tales and modern science fiction movies, nature is often portrayed as a mystical entity and as a sum of highly complicated, interacting, and interdependent organisms. Surprisingly much of this could be science as well as fairy tale and fiction:

For example, more and more evidence shows that plants in forests may be connected by a giant underground network of fungi, through which they interact and exchange nutrients or signals throughout. Molecules essential for survival can thus not only be taken up from the soil by the so-called "mycorrhizal fungi" and made available to the plant, but can also be transported from plant to plant via the fungus. Data also indicate that injured or weaker trees receive nutrients from other trees, or mother trees specifically send nutrients to their seedlings via the underground network of fungi. Similarly, it has been shown that after a pest infestation of one tree, a distant second tree begins to produce defensive substances against those exact pests. Here, therefore, a warning substance must have emanated from the first tree, which could be transported via the underground network of fungi. Furthermore, the interactions in a forest are not limited to the transport of substances via fungal networks. Plants and fungi could not survive if there were not other microorganisms in the soil that convert nutrients into available forms or keep pests away. The microorganisms, in turn, would find it difficult to survive without other small animals that crush falling leaves and thus produce the food base for the microorganisms.

Another fascinating example of an interaction between organisms was observed in a Hawaiian dwarf squid. The squid appears to glow at night on its underside to camouflage itself in the light of the stars. However, this phenomenon could only be detected in the presence of certain bacteria. The glow is only possible after bacteria of a certain species are ingested after the fish is born. They initiate a morphological modification of the luminescent organ, without which no luminescence could occur. The same species of bacteria is also able to luminesce by itself. However, the bacteria begin to luminesce only when they are present in large numbers. Before that, they ensure themselves by the so-called "quorum sensing" via an exchange of signal substances among themselves about when their number is sufficient to produce a sufficiently visible luminosity.

Similar scientific phenomena apply to humans: In the human intestine alone live 100 trillion bacteria of 500 different strains, which interact with each other and with the human body in amazing ways throughout. It could be shown that the bacteria in the intestine could influence not only the physical well-being but also the mental one, i.e. have a direct influence on the human being's feelings, thoughts, sensations, and ability to live. We need microorganisms in our bodies to protect us from pathogens, boost digestion, and get vital vitamins. However, this influence of microorganisms could go much further. Experiments on mice show that a certain composition of microorganisms in the gut can cause depression-like symptoms and alter the need for social interactions.

These examples show that interactions between different organisms not only influence life on earth, but make it possible in the first place. Symbiotic coexistence probably arose early in evolution. An association between fungi and plants, for example, predates the ability to form roots and formed the basis for plant land colonization. Symbioses underwent millennia of co-adaptation to optimize their interaction. These strict interdependencies of different organisms are often summarized in science as "holobiont" and are an important component of current research. Human actions, however, can have a major impact on holobionts in nature. Artificial management of soils destroys the natural diversity of organisms and can destroy fungal networks. Likewise, the human intake of antibiotics, which is mostly non-specific to bacterial infections, has a negative impact on the helpful and necessary bacteria in the intestines. On the other hand, the effect of holobionts can also be used profitably in the future. In agriculture, for example, helpful organisms could be added to the soil to prevent the addition of mineral fertilizer. Likewise, the medical administration of an intact gut bacteria culture could help prevent or cure diseases.

In its degree of fascination, the holobiont phenomenon can easily be lumped into fictional tales of the Tree of Souls in Avatar or Grandmother Willow from Pocahontas. So there is far more fabulousness in the nature of the Earth - and in our intestines.

signed: Valentin Kurbel

Bayreuth, July 2023

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