Recent developments in the structural organization and regulation of nitrogen fixation genes in Herbaspirillum seropedicae

Herbaspirillum seropedicae is a nitrogen-fixing bacterium found in associat ion with economically important gramineae. Regulation of nitrogen fixation involves the transcriptional activator NifA protein. The regulation of NifA protein and its truncated mutant proteins is described and compared with t hat of other nitrogen fixation bacteria. Nitrogen fixation control in H. se ropedicae, of the P-subgroup of Proteobacteria, has regulatory features in common with Klebsiella pneumoniae, of the gamma -subgroup, at the level of nifA expression and with rhizobia and Azospirillum brasilense, of the alpha -subgroup, at the level of control of NifA by oxygen. (C) 2001 Elsevier Sc ience B.V. All rights reserved.