Open AccessPosttranslational regulation of nitrogenase activity in Azospirillum brasilense ntrBC mutants: ammonium and anaerobic switch-off occurs through independent signal transduction pathways
Author(s) -
Yaoping Zhang,
R. H. Burris,
Paul W. Ludden,
Gary P. Roberts
Publication year - 1994
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.176.18.5780-5787.1994
Subject(s) - nitrogenase , azospirillum brasilense , mutant , biology , glutamine synthetase , biochemistry , signal transduction , enzyme repression , microbiology and biotechnology , glutamine , gene expression , psychological repression , bacteria , gene , microbial inoculant , genetics , nitrogen fixation , amino acid
Nitrogenase activity is regulated by reversible ADP-ribosylation in response to NH4+ and anaerobic conditions in Azospirillum brasilense. The effect of mutations in ntrBC on this regulation was examined. While NH4+ addition to ntrBC mutants caused a partial loss of nitrogenase activity, the effect was substantially smaller than that seen in ntr+ strains. In contrast, nitrogenase activity in these mutants was normally regulated in response to anaerobic conditions. The analysis of mutants lacking both the ntrBC gene products and dinitrogenase reductase activating glycohydrolase (DRAG) suggested that the primary effect of the ntrBC mutations was to alter the regulation of DRAG activity. Although nif expression in the ntr mutants appeared normal, as judged by activity, glutamine synthetase activity was significantly lower in ntrBC mutants than in the wild type. We hypothesize that this lower glutamine synthetase activity may delay the transduction of the NH4+ signal necessary for the inactivation of DRAG, resulting in a reduced response of nitrogenase activity to NH4+. Finally, data presented here suggest that different environmental stimuli use independent signal pathways to affect this reversible ADP-ribosylation system.