STUDIES ON THE REGULATION OF GENES RELATED TO NITROGEN FIXATION AND N-ASSIMILATION IN Azoarcus sp. strain BH72:THE ROLE OF NtrBC

The aim of this work is to study the regulation of genes related to nitrogen fixation and N-assimilation in Azoarcus sp. strain BH72 and elucidate the role of NtrBC in this regulatory process. Characterization of the transcripts for nitrogenase and its transcription activator, revealed unusual as well as common features in strain BH72. Success has been made to clone and characterize ntrBC of strain BH72, which act as an important two-component system in sensing and initialising the N-regulatory cascade. An ntrBC deletion mutant although nif in phenotype, was affected in N2 fixation. Nitrate had a severe effect on the ntrBC mutant and even derepression of its nitrogenase. Unusually the 'switching motility' was found to be upregulated in BntrBsp. Interestingly, for the first time, GlnY was found to be expressed (albeit at low level) in the ntrBC mutant along with down regulation of the other two PII proteins. Analyses of the expression of some nitrogen assimilatory genes revealed that their transcription was also affected by nitrogen.Thus it appears that NtrBC of Azoarcus strain BH72 has a significant contribution on the N-metabolism.