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Which free-living bacteria can fix atmospheric nitrogen?

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A labeled diagram of a periodic table entry for nitrogen shows its atomic number 7, symbol N, electron configuration, atomic weight, and name. Symbols indicate nitrogen is a nonmetal gas at room temperature, has a hexagonal crystal structure, and strongly acidic higher-valence oxides. A key explains the diagram's icons and color coding.
nitrogen

Free-living (nonsymbiotic) bacteria are microorganisms that can transform atmospheric nitrogen into fixed nitrogen without relying on a host plant. These organisms are essential to the nitrogen cycle and include the following genera and types:

  • Cyanobacteria: Including the genera Anabaena and Nostoc.12
  • Azotobacter: Large, rod-shaped or spherical bacteria commonly found in soil and sewage.132
  • Beijerinckia: A genus of free-living nitrogen-fixing bacteria.12
  • Clostridium: A genus that also functions as a free-living nitrogen fixer.12

These bacteria operate independently in their environments, unlike symbiotic bacteria such as Rhizobium, which require a host plant to perform nitrogen fixation.12