08 October 2024, In a groundbreaking experiment, scientists have successfully implanted bacteria into larger fungal cells, mimicking a type of symbiotic relationship believed to have sparked the evolution of complex life forms over a billion years ago. The discovery offers new clues into how cell features like mitochondria and chloroplasts essential components of modern eukaryotic cells might have emerged.
The study, led by microbiologist Julia Vorholt from the Swiss Federal Institute of Technology in Zurich (ETH Zurich), was published in the journal Nature on 2 October 2024. Using a minute, hollow needle and an air pump, the team created a symbiotic system that mirrors natural endosymbiosis—where one organism lives inside another in a mutually beneficial relationship. This feat could help researchers better understand the formation of the complex cellular machinery that powers life today.
Recreating Ancient Relationships
Endosymbiotic relationships, in which a microbial partner resides within the cells of a host organism, are found across numerous species, including insects and fungi. Scientists believe that modern mitochondria and chloroplasts, the energy-producing and photosynthetic organelles in plant and animal cells, evolved from bacteria that entered a similar relationship with early eukaryotic cells.
However, uncovering the precise mechanisms that allowed these early partnerships to form and thrive has been challenging, largely due to the ancient nature of the events. To tackle this, Vorholt’s team spent years engineering endosymbiosis in the lab, delivering bacterial cells directly into fungal cells.
The Technical Challenge
One of the main hurdles was physically inserting bacteria into the fungi, which have thick, high-pressure cell walls. The team used a needle with a diameter of just 500-1,000 nanometres to pierce the fungal walls and inject the bacteria. They then employed a bicycle pump, and later an air compressor, to push the bacteria through the needle and into the host cells.
After this complex process, the fungal cell despite initially undergoing a period of “surgical shock”—survived and reproduced. Importantly, some of the resulting fungal spores contained bacteria, demonstrating that the newly created endosymbiosis could be passed to future generations.
Success and Adaptation
Although the experiment succeeded in creating symbiotic organisms, only a small percentage of spores that contained bacteria were able to germinate effectively. Over several generations, however, the team was able to improve the symbiosis by selectively breeding the spores that showed better survival rates. After ten generations, the bacteria-containing spores germinated almost as efficiently as those without bacteria.
The exact reasons behind this rapid adaptation are still unclear, but the study identified a few genetic mutations in the fungal cells that seemed to enhance germination success. Surprisingly, the bacteria themselves did not undergo any notable genetic changes.
Implications for Evolution and Beyond
The findings of this study could offer valuable insight into how the first symbiotic relationships between bacteria and early eukaryotes evolved, eventually leading to the formation of the mitochondria and chloroplasts that are critical to complex life. Thomas Richards, an evolutionary biologist at the University of Oxford, speculated that the fungi’s immune system might initially resist symbiosis, with mutations possibly playing a role in overcoming this resistance.
Looking ahead, this kind of research could lead to the creation of novel organisms with practical applications, such as developing fungi or other life forms that can consume carbon dioxide or atmospheric nitrogen. According to Vorholt, the goal is to introduce new traits into organisms in ways that would be difficult to achieve through traditional genetic engineering.
This research not only opens new doors to understanding the origins of life on Earth but also raises exciting possibilities for biotechnology and environmental innovation.
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