The first known nitroplasts

When Tyler Coale finished analyzing the proteomes of Braarudosphaera bigelowii and the spherical body nestled inside the cytoplasm of the algal cells, he realized he may have solved a mystery his adviser had uncovered decades before. Proteins translated from nuclear DNA were being transported into the spheroid; the structure was clearly more than a nitrogen-fixing symbiote to the host cell. "It is behaving as an organelle," Coale says. That makes it the first nitrogen-fixing organelle, or nitroplast, ever identified ( Science 2024, DOI: 10.1126/science .adk1075 ). "He got the data back, he presented it, and it was fantastic," says Jonathan Zehr , Coale's postdoctoral adviser at the University of California, Santa Cruz, whose study of nitrogen-fixing organisms spans decades. In 1998, while hunting for nitrogenase -coding genes in seawater, Zehr discovered that organisms within the unicellular cyanobacteria group A, or UCYN-A, were capable of nitrogen fixation. He was shocked when,