Open AccessNifA is the master regulator of both nitrogenase systems in Rhodobacter capsulatus
Author(s) -
Demtröder Lisa,
Pfänder Yvonne,
Schäkermann Sina,
Bandow Julia Elisabeth,
Masepohl Bernd
Publication year - 2019
Publication title -
microbiologyopen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.881
H-Index - 36
ISSN - 2045-8827
DOI - 10.1002/mbo3.921
Subject(s) - nitrogenase , rpon , rhodobacter , azotobacter vinelandii , nitrogen fixation , biology , biochemistry , plasmid , sigma factor , cofactor , structural gene , gene , enzyme , promoter , genetics , mutant , bacteria , gene expression
Rhodobacter capsulatus fixes atmospheric nitrogen (N 2 ) by a molybdenum (Mo)‐nitrogenase and a Mo‐free iron (Fe)‐nitrogenase, whose production is induced or repressed by Mo, respectively. At low nanomolar Mo concentrations, both isoenzymes are synthesized and contribute to nitrogen fixation. Here we examined the regulatory interplay of the central transcriptional activators NifA and AnfA by proteome profiling. As expected from earlier studies, synthesis of the structural proteins of Mo‐nitrogenase (NifHDK) and Fe‐nitrogenase (AnfHDGK) required NifA and AnfA, respectively, both of which depend on the alternative sigma factor RpoN to activate expression of their target genes. Unexpectedly, NifA was found to be essential for the synthesis of Fe‐nitrogenase, electron supply to both nitrogenases, biosynthesis of their cofactors, and production of RpoN. Apparently, RpoN is the only NifA‐dependent factor required for target gene activation by AnfA, since plasmid‐borne rpoN restored anfH transcription in a NifA‐deficient strain. However, plasmid‐borne rpoN did not restore Fe‐nitrogenase activity in this strain. Taken together, NifA requirement for synthesis and activity of both nitrogenases suggests that Fe‐nitrogenase functions as a complementary nitrogenase rather than an alternative isoenzyme in R . capsulatus .