Structural organization of the glnBA region of the Azospirillum brasilense genome

The Azospirillum brasilense genomic region containing the glnBA genes was previously cloned in a broad-host range plasmid named pAB441. Previous results from our laboratory have shown that A. brasilense spontaneous mutants resistant to ethylenediamine carrying this plasmid had no nitrogenase activity. The 19 kb insert of this plasmid was fully sequenced and no other gene potentially involved with nitrogen fixation was identified, nor any gene potentially involved in the regulation of nif genes expression. Apart from glnBA, this region contains several genes involved with different functions: assisting protein folding and degradation, DNA organization, electron transport and energy conversion and conserved hypothetical proteins of unknown function. Since previous data on the literature showed that mutation of clpX gene of A. brasilense resulted in higher nitrogenase activity, we hypothesize that higher expression of the clpX gene from the plasmid pAB441 may be involved with Nif− phenotype of the A. brasilense mutant strains.