Azospirillum

Azospirillum is a Gram-negative, microaerophilic, non-fermentative and nitrogen-fixing bacterial genus from the family of Rhodospirillaceae. Azospirillum bacteria can promote plant growth.

== Characteristics == The genus Azospirillum belongs in the Alphaproteobacteria class of bacteria. Azospirillum are gram-negative, do not form spores, and have a slightly twisted oblong-rod shape. Azospirillum have at least one flagellum and sometimes multiple flagella, which they use to move rapidly. Azospirillum are aerobic, but many can also function as microaerobic diazotrophs, meaning, under low oxygen conditions, they can change inert nitrogen from the air into biologically usable forms. At least three species, A. melinis, A. thiophilum, and A. humicireducens are facultative anaerobes, and can live, if necessary, without oxygen. Growth of Azospirillum is possible between 5 °C and 42 °C and in substrates with a pH of 5 to 9, with optimal growth occurring around 30 °C and 7 pH. Microbiologists use nitrogen-free semi-solid media to isolate Azospirillum from samples. The most commonly used media is called "NFb".