In a groundbreaking development, scientists have uncovered a significant departure from the conventional understanding of nitrogen fixation in living organisms. Traditionally, it has been taught that only bacteria can convert atmospheric nitrogen into a form usable for life. Furthermore, it was believed that plants, such as legumes, achieved nitrogen fixation by hosting symbiotic bacteria in their root nodules. However, recent research has upended this long-held belief.

Two recent papers by an international team of scientists, published in Science and Cell, have unveiled the existence of the first known nitrogen-fixing organelle within a eukaryotic cell. This organelle represents the fourth example of primary endosymbiosis, a process in which a prokaryotic cell is engulfed by a eukaryotic cell and evolves beyond symbiosis into an organelle.

The discovery of this nitrogen-fixing organelle, termed a “nitroplast” by the researchers, results from decades of meticulous work and a stroke of luck. The journey began in 1998 when a short DNA sequence from an unknown nitrogen-fixing cyanobacterium was found in Pacific Ocean seawater. This mysterious organism, named UCYN-A, was later discovered to be closely associated with a marine alga after years of dedicated study.

The researchers’ findings suggest that UCYN-A has evolved beyond a mere endosymbiont and now exhibits characteristics of an organelle. This revelation challenges the traditional understanding of organelle origins and provides a new perspective on the evolution of cellular structures.

The implications of this discovery extend beyond the realm of scientific curiosity. The newfound organelle sheds light on the evolution of cellular structures and has the potential to impact agriculture and our understanding of ocean ecosystems. UCYN-A’s ability to fix nitrogen from the atmosphere is globally significant, and its discovery may offer insights into incorporating natural nitrogen fixation into agricultural practices.

While this discovery marks a significant leap in our understanding of cellular biology, many questions remain unanswered. Researchers are eager to delve deeper into the functioning of UCYN-A and its algal host, paving the way for further discoveries in this fascinating field.

References

• Coale, T. H., Loconte, V., Turk-Kubo, K. A., Vanslembrouck, B., Mak, W. K. E., Cheung, S., Ekman, A., Chen, J.-H., Hagino, K., Takano, Y., Nishimura, T., Adachi, M., Le Gros, M., Larabell, C., & Zehr, J. P. (2024). Nitrogen-fixing organelle in a marine alga. Science, 384(6692), 217–222. https://doi.org/10.1126/science.adk1075
• Cornejo-Castillo, F. M., Inomura, K., Zehr, J. P., & Follows, M. J. (2024). Metabolic trade-offs constrain the cell size ratio in a nitrogen-fixing symbiosis. Cell, 187(7), 1762-1768.e9. https://doi.org/10.1016/j.cell.2024.02.016
• Malsbury, E. & University of California-Santa Cruz. (2024, April 11). Scientists discover first nitrogen-fixing organelle. Phys.org. https://phys.org/news/2024-04-scientists-nitrogen-organelle-1.html
• Martínez-Pérez, C., Mohr, W., Löscher, C. R., Dekaezemacker, J., Littmann, S., Yilmaz, P., Lehnen, N., Fuchs, B. M., Lavik, G., Schmitz, R. A., LaRoche, J., & Kuypers, M. M. M. (2016). V. Nature Microbiology, 1(11), 1–7. https://doi.org/10.1038/nmicrobiol.2016.163