FACTORS AFFECTING NITROGEN-FIXATION AND NIF GENE-TRANSCRIPTION IN AZOSPIRILLUM-BRASILENSE

The effect of environmental factors on nitrogenase activity and on tra nscription of nif genes in Azospirillum brasilense was investigated. A ddition of ammonium, glutamine, oxygen, nitrate or nitrite together wi th either iron limitation or shift of temperature caused different lev els of inhibition of nitrogenase activity. The nif mRNA was completely absent after addition of either ammonium or glutamine and after iron deprivation, while oxygen, nitrate or nitrite partially decreased the presence of nif mRNA. It is concluded that in A. brasilense the contro l of the nitrogenase switch-off is independent of the transcription of nif genes.