title: Coordinated expression of fdxD and molybdenum nitrogenase genes promotes nitrogen fixation by Rhodobacter capsulatus in the presence of oxygen.
abstract: Rhodobacter capsulatus is able to grow with N2 as the sole nitrogen source using either a molybdenum-dependent or a molybdenum-free iron-only nitrogenase whose expression is strictly inhibited by ammonium. Disruption of the fdxD gene, which is located directly upstream of the Mo-nitrogenase genes, nifHDK, abolished diazotrophic growth via Mo-nitrogenase at oxygen concentrations still tolerated by the wild type, thus demonstrating the importance of FdxD under semiaerobic conditions. In contrast, FdxD was not beneficial for diazotrophic growth depending on Fe-nitrogenase. These findings suggest that the 2Fe2S ferredoxin FdxD specifically supports the Mo-nitrogenase system, probably by protecting Mo-nitrogenase against oxygen, as previously shown for its Azotobacter vinelandii counterpart, FeSII. Expression of fdxD occurred under nitrogen-fixing conditions, but not in the presence of ammonium. Expression of fdxD strictly required NifA1 and NifA2, the transcriptional activators of the Mo-nitrogenase genes, but not AnfA, the transcriptional activator of the Fe-nitrogenase genes. Expression of the fdxD and nifH genes, as well as the FdxD and NifH protein levels, increased with increasing molybdate concentrations. Molybdate induction of fdxD was independent of the molybdate-sensing regulators MopA and MopB, which repress anfA transcription at micromolar molybdate concentrations. In this report, we demonstrate the physiological relevance of an fesII-like gene, fdxD, and show that the cellular nitrogen and molybdenum statuses are integrated to control its expression.
authors.affiliation: Biologie der Mikroorganismen, Fakultät für Biologie und Biotechnologie, Ruhr-Universität Bochum, Bochum, Germany.
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Hoffmann
authors.forename: Alexandra
authors.initials: A
authors.lastname: Müller
authors.forename: Maria
authors.initials: M
authors.lastname: Fehringer
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Pfänder
authors.forename: Franz
authors.initials: F
authors.lastname: Narberhaus
authors.forename: Bernd
authors.initials: B
authors.lastname: Masepohl
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D026901:Membrane Transport Proteins / Q000378:metabolism; D008982:Molybdenum / Q000378:metabolism / Q000494:pharmacology; D009584:Nitrogen / Q000378:metabolism / Q000494:pharmacology; D009586:Nitrogen Fixation / Q000502:physiology*; D009591:Nitrogenase / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000494:pharmacology*; D016354:Rhodobacter capsulatus / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; C081166:mopA protein, Rhodobacter capsulatus; C081167:mopB protein, Rhodobacter capsulatus; D008982:Molybdenum; D009591:Nitrogenase; D009584:Nitrogen; D010100:Oxygen