Diazotrophs

Diazotrophs are microorganisms that 'fix' atmospheric nitrogen gas in to a more usable form such as ammonia. Examples of organisms that do this are rhizobia and Frankia (in symbiosis) and Azospirillum . A diazotroph is an organism that is able to grow without external souces of fixed nitrogen. All diazotrophs contain iron-molybdenum nitrogenase systems. Two of the most studied systems are those of Klebsiella pneumoniae and Azotobacter vinlandii. These systems are used because of their genetic tractability and their fast growth . Dixon R and Kahn D. 2004. Genetic regulation of biological nitrogen fixation. Nat Rev Microbiol. 2(8):621-31.