Relative levels of guanosine 5'-diphosphate 3'-diphosphate (ppGpp) in some N2 fixing bacteria during derepression and repression of nitrogenase.

Addition of ammonium to N2 fixing cultures of Azotobacter vinelandii, Klebsiella pneumoniae and Clostridium pasteurianum rapidly reduced the intracellular levels of guanosine 5'-diphosphate 3'-diphosphate (ppGpp) by 70-90%. This change might reflect a regulatory role of ppGpp in nitrogen metabolism.