Nitrogen-fixing organelle in a marine alga - Tyler H. Coale, et al. https://pubmed.ncbi.nlm.nih.gov/38603509/

but wait, there’s more:

The nitroplast: A nitrogen-fixing organelle A bacterial endosymbiont of marine algae evolved to an organelle https://www.science.org/doi/10.1126/science.ado8571

Wow, this sounds really nifty!!! Anyone got full paper accesss? $30 a pop is a bit pricey, for this humble one.