Nitrogen and Molybdenum Control of Nitrogen Fixation in the Phototrophic Bacterium Rhodobacter capsulatus
The vast majority of the purple nonsulfur photosynthetic bacteria are diazotrophs, but the details of the complex regulation of the nitrogen fixation process are well understood only for a few species. Here we review what is known of the well-studied Rhodobacter capsulatus, which contains two different nitrogenases, a standard Mo-nitrogenase and an alternative Fe-nitrogenase, and which has overlapping transcriptional control mechanisms with regard to the presence of fixed nitrogen, oxygen, and molybdenum as well as the capability for the post-translational control of both nitrogenases in response to ammonium. R. capsulatus has two PII proteins, GlnB and GlnK, which play key roles in nitrogenase regulation at each of three different levels: activation of transcription of the nif-specific activator NifA, the post-translational control of NifA activity, and the regulation of nitrogenase activity through either ADP-ribosylation of NifH or an ADP-ribosylation-independent pathway. We also review recent work that has led to a detailed characterization of the molybdenum transport and regulatory system in R. capsulatus that ensures activity of the Mo-nitrogenase and repression of the Fe-nitrogenase, down to extremely low levels of molybdenum.
KeywordsNitrogen Fixation Rhodobacter Capsulatus Rhodopseudomonas Palustris MoFe Protein Purple Nonsulfur Bacterium
Research in the authors’ laboratories is supported by Deutsche Forschungsgemeinschaft (BM) and the Natural Sciences and Engineering Research Council of Canada Discovery Grants Program (PCH).
- Glazer AN, Kechris KJ (2009) Conserved amino acid sequence features in the α subunits of MoFe, VFe, and FeFe nitrogenases. PLoS ONE 4:e6136Google Scholar
- Gourley DG, Schüttelkopf AW, Anderson LA, Price NC, Boxer DH, Hunter WN (2001) Oxyanion binding alters conformation and quaternary structure of the C-terminal domain of the transcriptional regulator ModE. Implications for molybdate-dependent regulation, signaling, storage, and transport. J Biol Chem 276:20641–20647PubMedCrossRefGoogle Scholar
- Pau RN (2004) Molybdenum uptake and homeostasis. In: Klipp W, Masepohl B, Gallon JR, Newton WE (eds) Genetics and regulation of nitrogen fixation in free-living bacteria. Kluwer, Dordrecht pp. 225–256Google Scholar
- Pawlowski A, Riedel K-U, Klipp W, Dreiskemper P, Groß S, Bierhoff H, Drepper T, Masepohl B (2003) Yeast two-hybrid studies on interaction of proteins involved in regulation of nitrogen fixation in the phototrophic bacterium Rhodobacter capsulatus. J Bacteriol 185: 5240–5247PubMedCrossRefGoogle Scholar
- Schmehl M, Jahn A, Meyer zu Vilsendorf A, Hennecke S, Masepohl B, Schuppler M, Marxer M, Oelze J, Klipp W (1993) Identification of a new class of nitrogen fixation genes in Rhodobacter capsulatus: A putative membrane complex involved in electron transport to nitrogenase. Mol Gen Genet 241:602–615PubMedCrossRefGoogle Scholar
- Yakunin AF, Fedorov AS, Laurinavichene TV, Glaser VM, Egorov NS, Tsygankov A, Zinchenko VS, Hallenbeck PC (2001) Regulation of nitrogenase in the photosynthetic bacterium Rhodobacter sphaeroides containing draTG and nifHDK genes from Rhodobacter capsulatus. Can J Microbiol 47:206–212PubMedGoogle Scholar