An international team of scientists has discovered the first nitrogen-fixing organelle inside a eukaryotic cell, which can replace fertilizers. The discovery, described in an article published in the journal Science, refutes the long-held idea that only bacteria are capable of taking nitrogen from the atmosphere and converting it into a form suitable for life.
The nitrogen-fixing organelle is the fourth example in the history of primary endosymbiosis, the process by which a prokaryotic cell is absorbed by a eukaryotic cell and develops into an organelle. In the same way, cells acquired mitochondria and plastids, such as chloroplasts. The new organelle was named nitroplast.
In 1998, scientists discovered a short DNA sequence from an unknown nitrogen-fixing cyanobacterium, designated UCYN-A, in Pacific seawater. It turned out that UCYN-A is located inside seaweed, which 10 years later was successfully cultivated in the laboratory.
UCYN-A was originally thought to be an endosymbiotic bacterium closely related to algae. However, in a separate paper in the journal Cell, the scientists presented evidence that the bacterium has co-evolved with its host and now meets the criteria for an organelle. Thus, the growth of the host cell and UCYN-A is not only controlled by general nutrient metabolism, but organelle-like bacteria import proteins from the cells.
The host cell produces proteins and marks them with a specific amino acid sequence that carries a signal that you need to send these proteins to the nitroplast. These compounds are then incorporated into UCYN-A metabolism. In addition, UCYN-A replicates synchronously with the algae cell and is inherited like other organelles.
Mitochondria and chloroplasts arose billions of years ago, and nitroplasts, according to the authors, appeared about 100 million years ago, which gives a more modern view of organellogenesis. Scientists suggest that the nitrogen-fixing organelle could be introduced into crop plants in the future, which would reduce the use of fertilizers.