Nitrogen fixing organelle in a marine alga

Symbiotic interactions were key to evolution of chloroplast and mitochondria organelles which mediate carbon and energy metabolism in eukaryotes. Biological nitrogen fixation, the reduction of abundant atmospheric nitrogen gas (N2) to biologically available ammonia is a key metabolic process performed exclusively by prokaryotes. UCYN-A is a metabolically streamlined N2-fixing cyanobacterium previously reported to be an endosymbiont of a marine unicellular alga. Here we show that UCYN-A has been tightly integrated into algal cell architecture and organellar division, and that it imports proteins encoded by the algal genome. These are characteristics of organelles and show that UCYN-A has evolved beyond endosymbiosis and functions as an early evolutionary stage N2-fixing organelle, or “nitroplast”., , , # Data from: Nitrogen fixing organelle in a marine alga

[https://doi.org/10.5061/dryad.2z34tmptf](https://doi.org/10.5061/dryad.2z34tmptf)

## Description of the data and file structure:

### SXT:

3-dimensional soft X-ray tomographic data generated by the National Center for X-ray Tomography (ncxt.org). Each file represents one or more cells of *B. bigelowii*-UCYN-A complex. Files are in the MRC file format. File details below.

Cell identification:

* Zehr_UCYNA_FR12_fission_xxx_xxx:= data showing two UCYN-A with relative alteration of host cell's structural features (mitochondrial network, nucleus, plastids)
* Zehr_UCYNA_FR12_cytokinesis_xxx_xxx:= data showing the process of the cytokinesis of doubling cells
* Zehr_UCYNA_FR12_growth_xxx_xxx:= data showing the process of cell's growth and reorganization after cytokinesis
* Zehr_UCYNA_FR12_L0_xxx_xxx:= data showing cell's architecture at L0 (cells harvested at 9 am)
* Zehr_UCYNA_FR12_L6_xxx_xxx:= data showing cell's architecture at L6...