Azotobacter vinelandii

Azotobacter vinelandii is Gram-negative diazotroph that can fix nitrogen while grown aerobically. It is a genetically tractable system that is used to study nitrogen fixation. These bacteria are easily cultured and grown.
"A. vinelandii" is a free-living N2 fixer known to produce many phytohormones and vitamins in soils. It produces fluorescent pyoverdine pigments.
The nitrogenase holoenzyme of "A. vinelandii" has been characterised by X-ray crystallography in both ADP tetrafluoroaluminate-bound and MgATP-bound states. The enzyme possesses molybdenum iron-sulfido cluster cofactors (FeMoco) as active sites, each bearing two pseudocubic iron-sulfido structures.
Variable ploidy.
"A. vinelandii" can contain up to 80 chromosome copies per cell. However this is only seen in fast growing culture, whereas cultures grown in synthetic minimal media are not polyploid.