Identification of two new genes involved in diazotrophic growth via the alternative Fe-only nitrogenase in the phototrophic purple bacterium Rhodobacter capsulatus.

Growth of Rhodobacter capsulatus with molecular dinitrogen as the sole N source via the alternative Fe-only nitrogenase requires all seven gene products of the anfHDGK-1-2-3 operon. In contrast to mutant strains carrying lesions in the structural genes of nitrogenase (anfH, anfD, anfG, and anfK), strains defective for either anf1, anf2, or anf3 are still able to reduce the artificial substrate acetylene, although with diminished activity. To obtain further information on the role of Anf1, we screened an R.

Yeast two-hybrid studies on interaction of proteins involved in regulation of nitrogen fixation in the phototrophic bacterium Rhodobacter capsulatus.

Rhodobacter capsulatus contains two PII-like proteins, GlnB and GlnK, which play central roles in controlling the synthesis and activity of nitrogenase in response to ammonium availability. Here we used the yeast two-hybrid system to probe interactions between these PII-like proteins and proteins known to be involved in regulating nitrogen fixation. Analysis of defined protein pairs demonstrated the following interactions: GlnB-NtrB, GlnB-NifA1, GlnB-NifA2, GlnB-DraT, GlnK-NifA1, GlnK-NifA2, and GlnK-DraT.

Role of GlnB and GlnK in ammonium control of both nitrogenase systems in the phototrophic bacterium Rhodobacter capsulatus.

In most bacteria, nitrogen metabolism is tightly regulated and P(II) proteins play a pivotal role in the regulatory processes. Rhodobacter capsulatus possesses two genes (glnB and glnK) encoding P(II)-like proteins. The glnB gene forms part of a glnB-glnA operon and the glnK gene is located immediately upstream of amtB, encoding a (methyl-) ammonium transporter.

The H-NS-like protein HvrA modulates expression of nitrogen fixation genes in the phototrophic purple bacterium Rhodobacter capsulatus by binding to selected nif promoters.

Genetic analyses based on chromosomal lac fusions to nitrogen fixation (nif) genes demonstrated that NifA-dependent transcriptional activation of expression of Rhodobacter capsulatus nifH and nifB1 was negatively modulated by HvrA, whereas regulation of rpoN, nifA1, and nifA2 was independent of HvrA. Expression of hvrA itself was not influenced by a mutation in ntrC, which is absolutely essential for N(2) fixation. Furthermore, HvrA accumulated to comparable levels in the presence and absence of ammonium, suggesting that the amount of HvrA in the cells does not differ under nitrogenase-repressing or -derepressing conditions.

The Hfq-like protein NrfA of the phototrophic purple bacterium Rhodobacter capsulatus controls nitrogen fixation via regulation of nifA and anfA expression.

The Rhodobacter capsulatus nrfA gene product exhibits extensive similarity to the nif (nitrogen fixation) regulatory factor NrfA of Azorhizobium caulinodans and the nucleoid-associated protein Hfq of Escherichia coli. Mutational analysis revealed that, in contrast to the situation in A. caulinodans, NrfA is not essential for diazotrophic growth of R.

Regulation of nitrogen fixation in the phototrophic purple bacterium Rhodobacter capsulatus.

In R. capsulatus synthesis and activity of the molybdenum and the alternative nitrogenase is controlled at three levels by the environmental factors ammonium, molybdenum, light, and oxygen. At the first level, transcription of the nifA1, nifA2, and anfA genes--which encode the transcriptional activators of all other nif and anf genes, respectively--is controlled by the Ntr system in dependence on ammonium availability.

Mutational analysis of the dimethylsulfoxide respiratory (dor) operon of Rhodobacter capsulatus.

Four genes, dorC, dorD, dorB and dorR of the DMSO respiratory gene cluster of Rhodobacter capsulatus have been identified and sequenced. dorC encodes a pentahaem c-type cytochrome of the NirT class and the derived DorC protein sequence shows highest similarity to TorC from the Escherichia coli trimethylamine-N-oxide (TMAO) respiratory system. Mutagenesis of dorC resulted in the loss of a 46 kDa haem-staining polypeptide from membranes of R.