Microbes play a prominent role in the global nitrogen cycle. One link in that cycle, the reduction of atmospheric dinitrogen (N₂) to ammonia, is accomplished only by prokaryotes. Ammonia is assimilated by cells and is incorporated into numerous biomolecules. In addition to aliphatic amines and amino acids, there are thousands of naturally occurring nitrogenous ring compounds. For one class alone, the alkaloids, over 10,000 different structures have been elucidated. Nitrogenous industrial compounds include NH₃, nitrate, and nitric acid.

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