In a laboratory belonging to the Swiss Federal Institute of Technology Zurich, a team of researchers has just achieved the unthinkable: reconstructing and observing live one of the most enigmatic processes of the evolution of life on Earth.
For the first time ever, the formation of an endosymbiotic relationship (an intimate association between two organisms where one lives inside the other, forming a functional unit) between two unicellular organisms was provoked and studied closely. A microscopic alliance that allowed life to emerge on our planet. For more information about this work, you can consult the team’s publication, published in the journal Nature on October 2, 2024.
A bicycle pump, a microscope and a revolutionary discovery
The story of this discovery begins with a seemingly insurmountable challenge: how to introduce a bacteria into a fungal cell protected by an almost impenetrable wall? Faced with this obstacle, Gabriel Giger, doctoral student at the Swiss Federal Institute of Technology in Zurich, has developed a methodology that is, to say the least, original.
His team first developed a specific enzyme cocktail to soften the cell wallthen used an atomic force microscope equipped with FluidFM technology; a high-precision tool that allows samples to be manipulated and analyzed at the nanoscale; transformed into a microscopic syringe.
Faced with the intracellular pressure which systematically expelled the cytoplasm (liquid contents of the fungal cell) during injection attempts, Giger had the idea of using… a bicycle pump. Yes, you read that right. This clever solution made it possible to generate a pressure three times greater than that of automobile tires, sufficient to force the passage of bacteria through the cell wall.
Thomas Richards, an evolutionary biologist at the University of Oxford, although not involved in this study, could not help but comment this clever diversion of an everyday object. « Adapting such technology to inject bacteria into a fungus is frankly impressive ».
The pact between a fungus and a bacteria
The team chose as a study model a natural association between the fungus Rhizopus microsporus and the bacteria Mycetohabitans rhizoxinicaa duo responsible for the wilt disease of rice plants. This choice was not a coincidence : in nature, these two organisms have developed such a close relationship that the fungus can no longer reproduce without its bacterial partner.
The first tests with the infamous bacteria Escherichia coli (which caused a false scandal during the 2024 Olympics) revealed the complexity of the business. These bacteria, once introduced, multiplied too quickly, triggering a fatal immune response from the fungus.
On the other hand, M. rhizoxinica demonstrated a remarkable ability to find the right balance. It reproduced at a rate compatible with its host, avoiding the activation of immune defenses while maintaining a viable population. The “good” bacteria (Mycetohabitans rhizoxinica in this case) therefore knows how to live with the fungus without killing itunlike E. coli.
The researchers even managed to observe how bacteria gradually colonized the fungal spores, ensuring their transmission to subsequent generations. This ability to integrate into the host’s reproductive cycle constitutes a fundamental step in establishing a lasting endosymbiotic relationship.
This type of relationship has played an absolutely indispensable role in the development of life on Earth, at several levels. Eukaryotic cells, which constitute all multicellular organisms (animals, plants and fungi), are thought to arise from endosymbiosis. Bacteria were encompassed by other cells, establishing a symbiotic relationship. Over time, these bacteria transformed into essential cellular organelles: mitochondria (for cellular respiration) and chloroplasts (for photosynthesis).
The acquisition of these organelles has opened new metabolic pathways, allowing organisms to exploit new ecological niches and diversify. For example, the appearance of photosynthesis thanks to chloroplasts radically transformed the composition of the Earth’s atmosphere by enriching the air with oxygen, which allowed the appearance of more complex life forms. Endosymbiosis later allowed organisms to acquire new functions, to specialize and to form even more complex multicellular organisms.
Cellular symbiosis, a driver of innovation?
Over ten successive generations, researchers have documented an eexcellent mutual adaptation between the two organisms. The fungus genome quickly acquired mutations facilitating coexistence with its bacterial partner, while the bacteria optimized their integration into the fungal spores.
Julia Vorholt, a microbiologist at the Swiss Federal Institute of Technology Zurich explains that partners literally become “ dependent on each other “. This interdependence manifests itself at both the metabolic and genetic levels, ultimately creating a new, fully functional unit.
Researchers are now considering developing synthetic cells with endosymbionts, organisms living inside another cell with specific capabilities, which could help develop new methodological approaches in biotechnology. Potential applications could range from the design of new drugs for the targeted depollution of ecosystems. Although it has flown a little under the radar, this study represents a giant step in our understanding of the living world, and especially in our skills in cellular engineering.
- Swiss researchers have recreated an endosymbiotic relationship between a bacteria and a fungus, essential for the evolution of complex organisms.
- An innovative method, combining a precision microscope and a bicycle pump, made it possible to introduce the bacteria into the fungus despite a resistant cellular barrier.
- This discovery could lead to the creation of synthetic cells capable of new functions.
???? To not miss any news from Presse-citron, follow us on Google News and WhatsApp.
Related News :