Regulation of NifA Synthesis and Activity in Azospirillum Brasilense Sp7

Abstract

Bacteria of the genus Azospirillum are Gram negative, curved rod shaped, aerobic chemoorganotrophs which can fix nitrogen under free-living conditions or in association with grasses (Elmerich et al. 1992). The organization and the regulation of the genes involved in nitrogen fixation and ammonia assimilation share common features with that of other members of the alpha subdivision of proteobacteria such as rhizobia and photosynthetic bacteria (Young 1992). The genetics is best documented in A. brasilense Sp7. The DNA region that contains the nitrogenase structural genes nifHDK, nifE, nifUS also carries homologues to fixABC of Rhizobium (Galimand et al. 1989). The g1nA gene is preceded by glnB as also found in Rhizobium and in Rhodobacter capsulatus (Colonna-Romano et al. 1987, Martin et al. 1987, Kranz et al. 1990). Nitrogenase activity is regulated as in photosynthetic bacteria through reversible ADP-ribosylation and the draTG genes coding for this process are located upstream of the nifHDK operon (Zhang et al. 1992).