NifA is the master regulator of both nitrogenase systems in Rhodobacter capsulatus

InRhodobacter capsulatus, biological nitrogen fixation is catalyzed by the molybdenum nitrogenase and a Mo-free iron-only nitrogenase. Here, we show that NifA controls synthesis of both nitrogenases by controlling synthesis of the sigma factor RpoN. AbstractRhodobacter capsulatus fixes atmospheric nitrogen (N2) 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 acti vators 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 the ir 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‐bornerpoN restoredanfH transcription in a NifA ‐deficient strain. However, plasmid‐bornerpoN did not restore Fe ‐nitrogenase activity in this strain. Taken together, NifA requirement for synthesis and activity of both nitrogenases suggests that Fe...
Source: MicrobiologyOpen - Category: Microbiology Authors: Tags: ORIGINAL ARTICLE Source Type: research